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Single Mode Fiber


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Single Mode Fiber: 320 to 430 nm

Stock Patch Cables Available with This Fiber
SM300 Fiber
Item # PrefixConnectorsLength
P1-305A-FCFC/PC to FC/PC1 or 2 m
P3-305A-FCFC/APC to FC/APC1 m
P5-305A-PCAPCFC/PC to FC/APC1 m
P1-305AR-2AR-Coated (300 - 510 nm) FC/PC to Uncoated FC/PC2 m
P5-305AR-2AR-Coated (300 - 510 nm) FC/PC to Uncoated FC/APC2 m
P4-305AR-2AR-Coated (300 - 510 nm) FC/APC to Uncoated FC/PC2 m
P3-305AR-2AR-Coated (300 - 510 nm) FC/APC to Uncoated FC/APC2 m
P1-305P-FCFC/PC to FC/PC (Low Insertion Loss)1 or 2 m
P3-305P-FCFC/APC to FC/APC (Low Insertion Loss)1 or 2 m
P5-305P-PCAPC-1FC/PC to FC/APC (Low Insertion Loss)1 m

Custom cables are also available. Click here for details.

Features

  • Single Mode Transmission from 320 to 430 nm
  • Dual Acrylate Coating
  • Shipped from Stock
  • No Minimum Purchase Required

Thorlabs' SM300 fiber consists of an undoped, pure silica core surrounded by a depressed, fluorine-doped cladding. Since these fibers do not contain germania (GeO2), which causes electronic defects and color centers associated with the Ge-O bond, the primary cause of photodarkening is greatly reduced. As a result, power handling in the blue region is increased from several milliwats to several watts. The transmission-limiting effects caused by other nonlinearities (e.g., stimulated scattering) or even thermal damage are also increased over those of a conventional silica fiber doped with germanium. In the UV region, the SM300 will still exhibit some photodarkening, but will have superior performance compared to conventional fibers.

Item #Operating WavelengthMode Field DiameteraCladdingCoatingCut-Off Wavelength
SM300320 - 430 nm2.2 µm @ 350 nm125 ± 1 µm233 - 257 µm<310 nm
Item #Short-Term Bend RadiusLong-Term Bend RadiusAttenuation (Max.)Proof Test LevelNACore IndexbCladding Indexb
SM300≥10 mm≥30 mm<70 dB/km @ 350 nm
<100 dB/km @ 450 nm
1% (100 kpsi)0.12 - 0.14320 nm: 1.48770
375 nm: 1.47809
430 nm: 1.47214
320 nm: 1.48276
375 nm: 1.47315
430 nm: 1.46720
  • MFD is a nominal, calculated value, estimated at the operating wavelength(s) using a typical value of NA & cutoff wavelength. Please see the MFD Definition tab for details.
  • The indices provided are for an NA of 0.12.

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam size of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. For a Gaussian power distribution, the MFD is the diameter where the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Silica Optical Fiber Maximum Power Densities
TypeTheoretical Damage ThresholdPractical Safe Value
CW
(Average Power)
1 MW/cm2250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm21 GW/cm2

Unterminated (Bare) Fiber
Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. A free-space beam of light must be focused down to a spot of roughly 80% of this diameter to be coupled into the fiber with good efficiency. MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, 80% of the MFD is typically filled with light. This yields an effective diameter of Ø2.4 µm and an effective area of 4.52 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.22 µm2 = 4.52 µm2

This can be extrapolated to a damage threshold of 11.3 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

4.25 µm2 • 2.5 mW/µm2 = 11.3 mW

Terminated Fiber
Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
SM300 Support Documentation SM300 : Single Mode Optical Fiber, 320 - 430 nm, Ø125 µm Cladding

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Posted Comments:
Poster: jlow
Posted Date: 2014-08-07 10:17:45.0
Response from Jeremy at Thorlabs: The dispersion is estimated to be around 47ps/(nm*km) at 2000nm.
Poster: mchen
Posted Date: 2014-07-09 10:56:22.61
Hi, Can you please tell me what is the dispersion of SM2000 fiber? thanks, Mike
Poster: pbui
Posted Date: 2014-06-02 09:46:36.0
There are no data sheets for damage threshold available, but it's possible to apply industry-standard damage thresholds for UV Fused Silica substrates to silica-based fibers. The surface areas and beam diameters involved at the air to glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, and this results in very small damage thresholds. Assuming you're launching into bare fiber (no connectors), 250 kW/cm^2 is a practical value for Maximum Power Density for CW lasers, while for a 10 ns Pulsed (peak power) laser, the max may be around 1 GW/cm^2. We will contact you directly to find out more about your setup and to provide further details.
Poster: lokirune
Posted Date: 2014-05-21 14:45:27.98
HI. I was using the SM450 and 460HP, and it seems to burn easily. Is there any data sheet for damage threshold for those fiber? Also, I used it before and find that it much easier to burn with pulse laser. It there any specific reason for that?
Poster: jlow
Posted Date: 2013-12-17 08:50:38.0
Response from Jeremy at Thorlabs: The refractive index for the core and clad is around 1.4682 and 1.4615 respectively for SMF-28e+ at 1550nm.
Poster: helmofon
Posted Date: 2013-12-15 14:18:47.37
Dear Sir/Madam I will be very grateful for the information about refractive index of core and clad of SMF - 28 @1550nm. Thank You, Maciej
Poster: akselrod
Posted Date: 2013-03-12 18:02:09.78
I would like to know the dispersion of this fiber at around 400 nm. Can you pleas let me know this value? Thanks! Gleb
Poster: jlow
Posted Date: 2013-04-11 15:40:00.0
Response from Jeremy at Thorlabs: Based on the generally used formula for waveguide dispersion and chromatic dispersion, the estimated dispersion for SM300 is on the order of -23 ps/(km-nm) at 400nm. That value can change depending on the actual numerical aperture and the cut-off wavelength of each spool of fiber.
Poster: bdada
Posted Date: 2012-06-05 19:30:00.0
Response from Buki at Thorlabs to Alfred: Thank you for participating in our feedback forum. Below is the refractive index of 780HP at 780nm: Core = 1.4598 Clad = 1.4537 Please contact TechSupport@thorlabs.com if you have any questions.
Poster:
Posted Date: 2012-06-05 04:25:46.0
Dear Sir or Madame, I want to know the refractive index of 780HP, then I will determine how long the fiber I will order. Thank you in advance. Alfred
Poster: tcohen
Posted Date: 2012-03-01 14:33:00.0
Response from Tim at Thorlabs: Thank you for your feedback. The S405-HP has a core index of 1.46958 and clad index of 1.46428 measured at 405nm. The MFD @ 460nm is 3.2 +/- .5 um. Please use these as references but note that they are approximate and may vary from lot to lot.
Poster: marko.vranicar
Posted Date: 2012-02-29 19:04:22.0
Dear Sir Or Madame, Recently, we purchased the S405-HP fiber. We need to know the cladding and core refractive indices as well as the core radius at 473nm that I cannot find in specs. I thank you in advance for your answer and assistance. Best regards, Marko
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SM300 Support Documentation
SM300 Customer Inspired! Single Mode Optical Fiber, 320 - 430 nm, Ø125 µm Cladding
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Single Mode Fiber: 400 to 680 nm

Stock Patch Cables Available with These Fibers
SM400 Fiber
Item # PrefixConnectorsLength
P1-405B-FCFC/PC to FC/PC1, 2, or 5 m
P3-405B-FCFC/APC to FC/APC1, 2, or 5 m
P5-405B-PCAPCFC/PC to FC/APC1 m
P2-405B-PCSMAFC/PC to SMA1 m
P1-405AR-2AR-Coated (400 - 700 nm) FC/PC to Uncoated FC/PC2 m
P5-405AR-2AR-Coated (400 - 700 nm) FC/PC to Uncoated FC/APC2 m
P4-405AR-2AR-Coated (400 - 700 nm) FC/APC to Uncoated FC/PC2 m
P3-405AR-2AR-Coated (400 - 700 nm) FC/APC to Uncoated FC/APC2 m
P1-405P-FCFC/PC to FC/PC (Low Insertion Loss)1, 2, or 5 m
P3-405P-FCFC/APC to FC/APC (Low Insertion Loss)1, 2, or 5 m
P5-405P-PCAPC-1FC/PC to FC/APC (Low Insertion Loss)1 m
SM450 Fiber
Item # PrefixConnectorsLength
P1-460B-FCFC/PC to FC/PC1, 2, or 5 m
P3-460B-FCFC/APC to FC/APC1, 2, or 5 m
P5-460B-PCAPCFC/PC to FC/APC1 m
P2-460B-PCSMAFC/PC to SMA1 m
P1-460AR-2AR-Coated (400 - 700 nm) FC/PC to Uncoated FC/PC2 m
P5-460AR-2AR-Coated (400 - 700 nm) FC/PC to Uncoated FC/APC2 m
P4-460AR-2AR-Coated (400 - 700 nm) FC/APC to Uncoated FC/PC2 m
P3-460AR-2AR-Coated (400 - 700 nm) FC/APC to Uncoated FC/APC2 m
P1-460P-FCFC/PC to FC/PC (Low Insertion Loss)1, 2, or 5 m
P3-460P-FCFC/APC to FC/APC (Low Insertion Loss)1, 2, or 5 m
P5-460P-PCAPC-1FC/PC to FC/APC (Low Insertion Loss)1 m

Custom cables are also available. Click here for details.

Features

  • SM Fiber at 400 nm to 680 nm
  • Shipped from Stock
  • Acrylate Jacket
  • No Minimum Purchase Required
Item #Operating WavelengthMode Field DiameterCladdingCoatingCut-Off Wavelength
S405-XP400 - 680 nm3.3 ± 0.5 µm @ 405 nm
4.6 ± 0.5 µm @ 630 nm
125.0 ± 1.0 µm245.0 ± 15.0 µm380 ± 20 nm
SM400405 - 532 nm3.0 µm @ 480 nm125 ± 1 µm245 µm ± 5%<400 nm
SM450a488 / 514 nm3.3 µmb @ 488 nm
3.4 µmb @ 514 nm
125 ± 1 µm245 ± 15 µm400 ± 50 nm
460HP450 - 600 nm3.5 ± 0.5 µm @ 515 nm125 ± 1.5 µm245 ± 15 µm430 ± 20 nm
Item #Short-Term Bend RadiusLong-Term Bend RadiusAttenuation (Max.)NACore IndexCladding Index
S405-XP≥6 mm≥13 mm≤30.0 dB/km @ 630 nm
≤30.0 dB/km @ 488 nm
0.12CalldCalld
SM400≥10 mm≥30 mm≤50 dB/km @ 430 nm
≤30 dB/km @ 532 nm
0.12 - 0.14405 nm: 1.47453e
467 nm: 1.46929e
532 nm: 1.46565e
405 nm: 1.46959e
467 nm: 1.46435e
532 nm: 1.46071e
SM450≥5 mm≥25 mm<50 dB/km @ 488 nmc0.10 - 0.14488 nm: 1.46645f
514 nm: 1.46501f
488 nm: 1.46302f
514 nm: 1.46159f
460HP≥6 mm≥13 mm<30 dB/km @ 515 nm0.13CalldCalld
  • The wavelength range is the spectral region between the cutoff wavelength and the bend edge and represents the region where the fiber transmits the TEM00 mode with low attenuation. For this fiber, the bend edge wavelength is typically 200 nm longer than the cutoff wavelength.
  • MFD is a nominal, calculated value, estimated at the operating wavelength(s) using a typical value of NA & cutoff wavelength. Please see the MFD Definition tab for details.
  • Stated attenuation is a worst-case value, quoted for the shortest design wavelength.
  • Please contact our Technical Support Staff to learn more about the refractive index of this fiber, as we are not permitted to publish this information on our website.
  • The indices provided are for an NA of 0.12.
  • The indices provided are for an NA of 0.10.

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam size of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. For a Gaussian power distribution, the MFD is the diameter where the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Silica Optical Fiber Maximum Power Densities
TypeTheoretical Damage ThresholdPractical Safe Value
CW
(Average Power)
1 MW/cm2250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm21 GW/cm2

Unterminated (Bare) Fiber
Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. A free-space beam of light must be focused down to a spot of roughly 80% of this diameter to be coupled into the fiber with good efficiency. MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, 80% of the MFD is typically filled with light. This yields an effective diameter of Ø2.4 µm and an effective area of 4.52 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.22 µm2 = 4.52 µm2

This can be extrapolated to a damage threshold of 11.3 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

4.25 µm2 • 2.5 mW/µm2 = 11.3 mW

Terminated Fiber
Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
460HP Support Documentation 460HP : Single Mode Optical Fiber, 450 - 600 nm , Ø125 µm Cladding
S405-XP Support Documentation S405-XP : Single Mode Optical Fiber, 400-680 nm, Ø125 µm Cladding
SM400 Support Documentation SM400 : Single Mode Optical Fiber, 405 - 532 nm, Ø125 µm Cladding
SM450 Support Documentation SM450 : Single Mode Optical Fiber, 488 / 514 nm, Ø125 µm Cladding

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Posted Comments:
Poster: bdada
Posted Date: 2011-03-08 18:45:00.0
Response from Buki: Thank you for your feedback Michael. For the 460HP fiber, at 532nm, the cladding refractive index is about 1.461, and the core refractive index is about 1.467. For the S460-HP, at 633nm, the core refractive index is about 1.46873 and the cladding refractive index is about 1.46298.
Poster: michael.ireland
Posted Date: 2011-03-07 17:47:54.0
I need to know the cladding refractive index (at ~550nm or some nearby wavelength) for the 460HP and S460-HP fibers. This doesnt seem to be given in the spec sheets.
Poster: bdada
Posted Date: 2011-03-07 15:24:00.0
Response from Buki. For single mode fiber, a flat cleave would provide a good optical surface that makes it unnecessary for the end to be polished. We have two products for fiber cleaving: XL411 and S90W.
Poster: cmarkle
Posted Date: 2011-03-07 13:37:42.0
I recently bought some optical fiber (460hp) from you guys and was wondering how to polish the ends. My application does not require a connector but it seems the polishing kits do. Can you Help?
Poster: Adam
Posted Date: 2010-03-31 19:40:48.0
A response from Adam at Thorlabs to fahd: We have three methods for stripping this type of fiber. The first is using a mechanical stripper, which would not work for your application. The next two might: Method 2: Chemical Dip in solvent for a few minutes. Jackets will absorb the solvent and swell up. Grab fiber between thumb and index finger (with some tissue in between) and rub swollen portion off. Method 3: Hot Sulfuric Acid Hot sulfuric acid (T=150-180°C). Dip a few minutes or until all acrylate is dissolved. Rinse in clean water after excess acid is drained off. Then, rinse in acetone, then isopropyl alcohol and blow dry. I will email directly with more information about method 2.
Poster: fahd_ali2000
Posted Date: 2009-11-24 05:37:46.0
Hello, i have bought SMF-28-100. I have a problem of stripping this fiber. I want to strip from middle in 1 meter fiber but could not, it always break. its very rough from inside. dont know what to do. I appreciate if you can help me. thanks bye
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S405-XP Single Mode Optical Fiber, 400-680 nm, Ø125 µm Cladding
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SM400 Single Mode Optical Fiber, 405 - 532 nm, Ø125 µm Cladding
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460HP Single Mode Optical Fiber, 450 - 600 nm , Ø125 µm Cladding
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Single Mode Fiber: 600 to 860 nm

Stock Patch Cables Available with These Fibers
SM600 Fiber
Item # PrefixConnectorsLength
P1-630A-FCFC/PC to FC/PC1, 2, 5, or 10 m
P3-630A-FCFC/PC to FC/PC1, 2, or 5 m
P5-630A-PCAPCFC/PC to FC/APC1 m
P2-630-PCSMAFC/PC to SMA1 m
P1-630AR-2AR-Coated (600 - 800 nm) FC/PC to Uncoated FC/PC2 m
P5-630AR-2AR-Coated (600 - 800 nm) FC/PC to Uncoated FC/APC2 m
P4-630AR-2AR-Coated (600 - 800 nm) FC/APC to Uncoated FC/PC2 m
P3-630AR-2AR-Coated (600 - 800 nm) FC/APC to Uncoated FC/APC2 m
P1-630P-FCFC/PC to FC/PC (Low Insertion Loss)1, 2, or 5 m
P3-630P-FCFC/APC to FC/APC (Low Insertion Loss)1, 2, or 5 m
P5-630P-PCAPC-1FC/PC to FC/APC (Low Insertion Loss)1 m

Custom cables are also available. Click here for details.

Features

  • Shipped from Stock
  • No Minimums
  • True Single Mode Operation for HeNe and All Visible Laser Diodes
  • Acrylate Coating
  • Exceptional Core/Clad Concentricity
  • 630HP Offers Tight Second Mode Cutoff Tolerances
  • 630HP Offers a Tight Bend Radius for Applications in Miniaturized Fiber Optic Packages
Item #Operating WavelengthMode Field DiameterCladdingCoatingCut-Off Wavelengthd
SM600600 - 800 nma,b4.3 µm @ 633 nmc
4.6 µm @ 680 nmc
125 ± 1.0 µm245 µm ± 5%550 ± 50 nm
S630-HP630 - 860 nm4.2 ± 0.5 µm @ 630 nm125 ± 1.0 µm245 ± 15 µm590 ± 30 nm
630HP600 - 770 nm4.0 ± 0.5 µm @ 630 nm125 ± 1.5 µm245 ± 15 µm570 ± 30 nm
Item #Short-Term Bend RadiusLong-Term Bend RadiusMax AttenuationNACore IndexCladding Index
SM600≥5 mm≥25 mm<15 dB/kme0.10 - 0.14600 nm: 1.46147f
700 nm: 1.45872f
800 nm: 1.45675f
600 nm: 1.45804f
700 nm: 1.45530f
800 nm: 1.45332f
S630-HP≥6 mm≥13 mm≤10 dB/km @ 630 nm0.12CallgCallg
630HP≥6 mm≥13 mm<12 dB/km @ 630 nm0.13CallgCallg
  • The wavelength range is the spectral region between the cutoff wavelength and the bend edge and represents the region where the fiber transmits the TEM00 mode with low attenuation. For this fiber, the bend edge wavelength is typically 200 nm longer than the cutoff wavelength.
  • Wavelength range is illustrative and not guaranteed.
  • MFD is a nominal, calculated value, estimated at the operating wavelength(s) using a typical value of NA & cutoff wavelength. Please see the MFD Definition tab for details.
  • The wavelength at which the fiber only allows a single mode to propogate.
  • Attenuation is worst-case value, quoted for the shortest wavelength.
  • The indices provided are for an NA of 0.10.
  • Please contact our Technical Support Staff to learn more about the refractive index of this fiber, as we are not permitted to publish this information on our website.

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam size of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. For a Gaussian power distribution, the MFD is the diameter where the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Silica Optical Fiber Maximum Power Densities
TypeTheoretical Damage ThresholdPractical Safe Value
CW
(Average Power)
1 MW/cm2250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm21 GW/cm2

Unterminated (Bare) Fiber
Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. A free-space beam of light must be focused down to a spot of roughly 80% of this diameter to be coupled into the fiber with good efficiency. MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, 80% of the MFD is typically filled with light. This yields an effective diameter of Ø2.4 µm and an effective area of 4.52 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.22 µm2 = 4.52 µm2

This can be extrapolated to a damage threshold of 11.3 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

4.25 µm2 • 2.5 mW/µm2 = 11.3 mW

Terminated Fiber
Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
630HP Support Documentation 630HP : Single Mode Optical Fiber, 600 - 770 nm, Ø125 µm Cladding
S630-HP Support Documentation S630-HP : Single Mode Optical Fiber, 630 - 860 nm, Ø125 µm Cladding
SM600 Support Documentation SM600 : Single Mode Optical Fiber, 600 - 800 nm, Ø125 µm Cladding

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Posted Comments:
Poster: Thorlabs
Posted Date: 2010-12-07 15:53:01.0
Response from Javier at Thorlabs to Peter: We will gladly send you a quotation. we will contact you shortly to get your contact details.
Poster: taenzer
Posted Date: 2010-12-07 14:54:24.0
please send me offer for 2000 m of single mode fibre SM600 thanks Peter Taenzer, Germany
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SM600 Support Documentation
SM600 Single Mode Optical Fiber, 600 - 800 nm, Ø125 µm Cladding
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S630-HP Support Documentation
S630-HP Single Mode Optical Fiber, 630 - 860 nm, Ø125 µm Cladding
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630HP Support Documentation
630HP Single Mode Optical Fiber, 600 - 770 nm, Ø125 µm Cladding
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Single Mode Fiber: 780 to 970 nm

Stock Patch Cables Available with These Fibers
780HP Fiber
Item # PrefixConnectorsLength
P1-780A-FCFC/PC to FC/PC1, 2, or 5 m
P3-780A-FCFC/APC to FC/APC2 or 5 m
P5-780A-PCAPCFC/PC to FC/APC1 m
P2-780A-PCSMAFC/PC to SMA1 m
P1-780AR-2AR-Coated (780 - 970 nm) FC/PC to Uncoated FC/PC2 m
P5-780AR-2AR-Coated (780 - 970 nm) FC/PC to Uncoated FC/APC2 m
P4-780AR-2AR-Coated (780 - 970 nm) FC/APC to Uncoated FC/PC2 m
P3-780AR-2AR-Coated (780 - 970 nm) FC/APC to Uncoated FC/APC2 m
SM800-5.6-125 Fiber
Item # PrefixConnectorsLength
P1-830A-FCFC/PC to FC/PC1, 2, 5, or 10 m
P3-830A-FCFC/APC to FC/APC1, 2, or 5 m
P5-830A-PCAPCFC/PC to FC/APC1 m
P2-830A-PCSMAFC/PC to SMA1 m

Custom cables are also available. Click here for details.

Features

  • Shipped from Stock
  • No Minimums
  • Acrylate Jacket
  • Exceptional Uniformity
  • Exceptional Core/Clad Concentricity
  • 780HP Offers Tight Second Mode Cutoff Tolerances
  • 780HP Offers a Tight Bend Radius for Applications in Miniaturized
    Fiber Optic Packages
  • SM800G80 Offers Enhanced Bend-Insensitivity
Item #Operating WavelengthMode Field DiameterCladdingCoatingCut-Off Wavelength
780HP780 - 970 nm5.0 ± 0.5 µm
@ 850 nm
125 ± 1.5 µm245 ± 15 µm730 ± 30 nm
SM800-5.6-125830 nma5.6 µmb125 ± 1 µm245 µm ± 5%660 - 800 nm
SM800G80830 nma4.2 µm
@ 830 nm
80 ± 1 µm175 µm ± 5%600 - 800 nm
Item #Short-Term Bend RadiusLong-Term Bend RadiusAttenuation (Max)NACore IndexCladding Index
780HP≥6 mm≥13 mm<3.5 dB/km
@ 780 nm
0.13CalldCalld
SM800-5.6-125≥5 mm≥25 mm<5 dB/kmc0.10 - 0.14830 nm: 1.45625e830 nm: 1.45282e
SM800G80≥5 mm≥12 mm
(or 38 mm for 25 Year Life)
≤5 dB/kmc0.14 - 0.18830 nm: 1.45954f830 nm: 1.45282f
  • The wavelength range is the spectral region between the cutoff wavelength and the bend edge and represents the region where the fiber transmits the TEM00 mode with low attenuation. For this fiber, the bend edge wavelength is typically 200 nm longer than the cutoff wavelength.
  • MFD is a nominal, calculated value, estimated at the operating wavelength(s) using a typical value of NA & cutoff wavelength. Please see the MFD Definition tab for details.
  • Attenuation is a worse-case value, quoted for the shortest design wavelength.
  • Please contact our Technical Support Staff to learn more about the refractive index of this fiber, as we are not permitted to publish this information on our website.
  • The index provided is for an NA of 0.10.
  • The index provided is for an NA of 0.14.

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam size of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. For a Gaussian power distribution, the MFD is the diameter where the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Silica Optical Fiber Maximum Power Densities
TypeTheoretical Damage ThresholdPractical Safe Value
CW
(Average Power)
1 MW/cm2250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm21 GW/cm2

Unterminated (Bare) Fiber
Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. A free-space beam of light must be focused down to a spot of roughly 80% of this diameter to be coupled into the fiber with good efficiency. MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, 80% of the MFD is typically filled with light. This yields an effective diameter of Ø2.4 µm and an effective area of 4.52 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.22 µm2 = 4.52 µm2

This can be extrapolated to a damage threshold of 11.3 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

4.25 µm2 • 2.5 mW/µm2 = 11.3 mW

Terminated Fiber
Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
780HP Support Documentation 780HP : Single mode Optical Fiber, 780 - 970 nm, Ø125 µm Cladding
SM800-5.6-125 Support Documentation SM800-5.6-125 : Single Mode Optical Fiber, 830 nm, Ø125 µm Cladding
SM800G80 Support Documentation SM800G80 : Single Mode Optical Fiber, 830 nm, 0.14-0.18 NA, Ø80 µm Cladding

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Single Mode Fiber: 980 to 1600 nm

Stock Patch Cables Available with These Fibers
SM980-5.8-125 Fiber
Item # PrefixConnectorsLength
P1-980A-FCFC/PC to FC/PC1, 2, or 5 m
P3-980A-FCFC/APC to FC/APC1, 2, or 5 m
P5-980A-PCAPCFC/PC to FC/APC1 m
P2-980A-PCSMAFC/PC to SMA1 m
P1-980AR-2AR-Coated (970 - 1650 nm) FC/PC to Uncoated FC/PC2 m
P5-980AR-2AR-Coated (970 - 1650 nm) FC/PC to Uncoated FC/APC2 m
P4-980AR-2AR-Coated (970 - 1650 nm) FC/APC to Uncoated FC/PC2 m
P3-980AR-2AR-Coated (970 - 1650 nm) FC/APC to Uncoated FC/APC2 m

Custom cables are also available. Click here for details.

Features

  • Shipped from Stock
  • No Minimums
  • HI106-100 and HI1060-J9 have 900 µm Hytrel Outer Jacket
  • SM980-5.8-125 has a MFD Matched to Other Fibers used in EDFA Pump Laser Pigtails
  • 980HP and 1060XP Offer a Tight Second Mode Cutoff Tolerance
  • SM980G80 Offers Enhanced Bend-Insensitivity
Item #Operating WavelengthaMode Field DiameterCladdingCoatingCut-Off Wavelength
SM980-5.8-125970 - 1650 nm5.8 µm @ 980 nmb
6.2 µm @ 1064 nmb
10.4 µm @ 1550 nmb
125 ± 1 µm245 µm ± 5%870 - 970 nm
SM980G80980 - 1650 nm4.5 µm @ 980 nm
7.5 µm @ 1550 nm
80 ± 1 µm175 µm ± 5%870 - 970 nm
HI1060-J9
980 - 1060 nm5.9 ± 0.3 µm @ 980 nm
6.2 ± 0.3 µm @ 1060 nm
125 ± 0.5 µm245 ± 10 µm920 ± 50 nm
1060XP980 - 1600 nm5.9 ± 0.5 µm @ 980 nm
6.2 ± 0.5 µm @ 1060 nm
9.5 ± 0.5 µm @ 1550 nm
125 ± 0.5 µm245 ± 10 µm920 ± 30 nm
980HP980 - 1600 nm4.2 ± 0.5 µm @ 980 nm
6.8 ± 0.5 µm @ 1550 nm
125 ± 1.5 µm245 ± 15 µm920 ± 30 nm
Item #Short-Term Bend RadiusLong-Term Bend RadiusAttenuation (Max)NACore IndexCladding Index
SM980-5.8-125≥5 mm≥25 mm<3 dB/kmc0.13 - 0.15970 nm: 1.45660d
1310 nm: 1.45259d
1650 nm: 1.44854d
970 nm: 1.48081d
1310 nm: 1.44680d
1650 nm: 1.44275d
SM980G80≥5 mm≥12 mm (or 38 mm for 25 Year Life)≤3 dB/km0.17 - 0.19980 nm: 1.46058e
1310 nm: 1.45670e
1650 nm: 1.45265e
980 nm: 1.45068e
1310 nm: 1.44680e
1650 nm: 1.44275e
HI1060-J9
2.1 dB/km @ 980 nm
1.5 dB/km @1060 nm
0.14ProprietaryfProprietaryf
1060XP≥6 mm≥13 mm≤2.1 dB/km @ 980 nm
≤1.5 dB/km @ 1060 nm
0.14CallgCallg
980HP≥6 mm≥13 mm≤3.5 dB/km @ 980 nm0.20CallgCallg
  • Wavelength range is illustrative and not guaranteed.
  • MFD is a nominal, calculated value, estimated at the operating wavelength(s) using a typical value of NA & cutoff wavelength. Please see the MFD Definition tab for details.
  • Attenuation is a worst-case value, quoted for the shortest design wavelength.
  • The indices provided are for an NA of 0.13.
  • The indices provided are for an NA of 0.14.
  • We regret that we cannot provide this proprietary information.
  • Please contact our Technical Support Staff to learn more about the refractive index of this fiber, as we are not permitted to publish this information on our website.

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam size of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. For a Gaussian power distribution, the MFD is the diameter where the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Silica Optical Fiber Maximum Power Densities
TypeTheoretical Damage ThresholdPractical Safe Value
CW
(Average Power)
1 MW/cm2250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm21 GW/cm2

Unterminated (Bare) Fiber
Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. A free-space beam of light must be focused down to a spot of roughly 80% of this diameter to be coupled into the fiber with good efficiency. MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, 80% of the MFD is typically filled with light. This yields an effective diameter of Ø2.4 µm and an effective area of 4.52 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.22 µm2 = 4.52 µm2

This can be extrapolated to a damage threshold of 11.3 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

4.25 µm2 • 2.5 mW/µm2 = 11.3 mW

Terminated Fiber
Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
1060XP Support Documentation 1060XP : Single Mode Optical Fiber, 980 - 1600 nm, X-High Performance, Ø125 µm Cladding
980HP Support Documentation 980HP : Single Mode Optical Fiber, 980 - 1600 nm, Ø125 µm Cladding
HI1060-100 Support Documentation HI1060-100 : 100 m of HI1060 with Ø900 µm Jacket, Ø125 µm Cladding
Part Number Product Description
HI1060-J9 Support Documentation HI1060-J9 : HI1060 with Ø900 µm Jacket, Ø125 µm Cladding
SM980-5.8-125 Support Documentation SM980-5.8-125 : Single Mode Optical Fiber, 970 - 1650 nm, Ø125 µm Cladding
SM980G80 Support Documentation SM980G80 : Single Mode Optical Fiber, 980 - 1650 nm, Ø80 µm Cladding

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HI1060-100 100 m of HI1060 with Ø900 µm Jacket, Ø125 µm Cladding
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Single Mode Fiber: 1260 to 1625 nm

Stock Patch Cables Available with These Fibers
SMF-28e+ Fiber
Item # PrefixConnectorsLength
P1-SMF28E-FCFC/PC to FC/PC1, 2, 5, or 10 m
P3-SMF28E-FCFC/APC to FC/APC1, 2, or 5 m
P5-SMF28E-FCFC/PC to FC/APC1, 2, or 5 m
P2-SMF28E-PCSMAFC/PC to SMA1 m
P1-SMF28EAR-2AR-Coated (1260 - 1620 nm) FC/PC to Uncoated FC/PC2 m
P5-SMF28EAR-2AR-Coated (1260 - 1620 nm) FC/PC to Uncoated FC/APC2 m
P4-SMF28EAR-2AR-Coated (1260 - 1620 nm) FC/APC to Uncoated FC/PC2 m
P3-SMF28EAR-2AR-Coated (1260 - 1620 nm) FC/APC to Uncoated FC/APC2 m
1550BHP Fiber
Item # PrefixConnectorsLength
P1-1550A-FCFC/PC to FC/PC1, 2, 5, or 10 m
P3-1550A-FCFC/APC to FC/APC1, 2, or 5 m

Custom cables are also available. Click here for details.

Features

  • Shipped from Stock
  • No Minimums
  • Fibers have Acrylate Coatings
  • SMF-28-100, SMF-28-1000, SMF-28-J9, and CCC1310-J9 have
    Ø900 µm Hytrel Outer Jackets
  • Exceptional Core/Clad Concentricity Specifications
  • 1550BHP Offers Tight Second Mode Cut-off Tolerances
  • SM1250G80, CCC1310-J9, and SM1500G80 Offer Enhanced Bend-Insensitivity (See the Specs Tab for Information)
Item #Operating WavelengthMode Field DiameterCladdingCoatingCut-Off Wavelength
SMF-28-J91260 - 1625 nm9.2 ± 0.4 µm @ 1310 nm
10.4 ± 0.5 µm @ 1550 nm
125 ± 0.7 µm245 ± 5 µm<1260 nm
CCC1310-J91260 - 1625 nm8.6 ± 0.4 µm @ 1310 nm
9.7 ± 0.5 µm @ 1550 nm
125.0 ± 0.7 µm245 ± 5 µm≤1260 nm
1310BHP1300 - 1625 nm8.6 ± 0.5 µm @ 1310 nm
9.7 ± 0.5 µm @ 1550 nm
125 ± 1.0 µm245 ± 15 µm1260 ± 30 nm
SM1250G801310 nm
1550 nm
9.0 µm @ 1310 nm
10.5 µm @ 1550 nm
80 ± 1.0 µm175 µm ± 5%1150 - 1250 nm
1550BHP1460 - 1620 nm9.5 ± 0.5 µm @ 1550 nm125 ± 1.0 µm245 ± 15 µm1400 ± 50 nm
SM1500G801550 nm6.4 µm @ 1550 nm80 ± 1.0 µm175 µm ± 5%1350 - 1500 nm
Item #Short-Term Bend RadiusLong-Term Bend RadiusAttenuation (Max)NACore IndexCladding Index
SMF-28-J90.33 - 0.35 dB/km @ 1310 nm
0.19 - 0.20 dB/km @ 1550 nm
0.141550 nm: 1.46821550 nm: 1.4615
CCC1310-J90.33 - 0.35 dB/km @ 1310 nm
0.19 - 0.21 dB/km @ 1550
0.142 µm: 1.4436-
1310BHP≥6 mm≥13 mm0.5 dB/km @ 1310 nm & 1550 nm0.13CallaCalla
SM1250G80≥5 mm≥12 mm (or 38 mm for 25 Year Life)≤2 dB/km0.11 - 0.131310 nm: 1.45094b
1550 nm: 1.44813b
1310 nm: 1.44680b
1550 nm: 1.44399b
1550BHP≥6 mm≥13 mm0.5 dB/km @ 1550 nm0.13CallaCalla
SM1500G80≥5 mm≥12 mm (or 38 mm for 25 Year Life)≤2 dB/km0.19 - 0.211550 nm: 1.45636c1550 nm: 1.44399c
  • Please contact our Technical Support Staff to learn more about the refractive index of this fiber, as we are not permitted to publish this information on our website.
  • The indices provided are for an NA of 0.11.
  • The index provided is for an NA of 0.19.
CCC1310-J9 Macrobend Loss Specifications
Mandrel RadiusNumber of TurnsWavelengthInduced Attenuationa
5 mm11550 nm≤0.1 dB
7.5 mm11550 nm≤0.05 dB
10 mm11550 nm≤0.03 dB
15 mm101550 nm≤0.03 dB
5 mm11625 nm≤0.3 dB
  • The induced Attenuation due to a fiber wrapped around a mandrel of a specified diameter.

CCC1310-J9, SM1250G80, and SM1500G080 Bend Loss Information

The CCC1310-J9 fiber is designed to have similar characteristics to SMF-28e+, with the advantage of enhanced bend insensitivity. The table to the right shows complete macrobend loss specifications for CCC1310-J9 for different mandrel radii, and the table below shows a comparison between CCC1310-J9 and SMF-28e+.

The SM1250G80 and SM1500G80 offer a smaller cladding size (80 µm vs. 125 µm), which offers an even lower bend loss. When bent, an 80 µm fiber suffers approximately 40% lower stress than standard 125 µm cladding fibers.

Mandrel RadiusNumber of TurnsWavelengthSMF-28e+ Induced AttenuationCCC1310-J9 Induced Attenuation
0.5" (12.7 mm)101550 nm1.19 dB0.30 dB
0.5" (12.7 mm)101670 nm2.95 dB0.51 dB

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam size of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. For a Gaussian power distribution, the MFD is the diameter where the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Silica Optical Fiber Maximum Power Densities
TypeTheoretical Damage ThresholdPractical Safe Value
CW
(Average Power)
1 MW/cm2250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm21 GW/cm2

Unterminated (Bare) Fiber
Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. A free-space beam of light must be focused down to a spot of roughly 80% of this diameter to be coupled into the fiber with good efficiency. MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, 80% of the MFD is typically filled with light. This yields an effective diameter of Ø2.4 µm and an effective area of 4.52 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.22 µm2 = 4.52 µm2

This can be extrapolated to a damage threshold of 11.3 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

4.25 µm2 • 2.5 mW/µm2 = 11.3 mW

Terminated Fiber
Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
1310BHP Support Documentation 1310BHP : Select Cut-Off Single Mode Fiber, 1310 and 1550 nm, Ø125 µm Cladding
1550BHP Support Documentation 1550BHP : Single Mode Optical Fiber, 1460 - 1620 nm, Ø125 µm Cladding
CCC1310-J9 Support Documentation CCC1310-J9 : 1260 - 1625 nm Low Bend Loss Fiber with Ø900 µm Jacket, Ø125 µm Cladding
SM1250G80 Support Documentation SM1250G80 : Single Mode Fiber, 0.11-0.13 NA, 1310/1550 nm, Ø80 µm
Part Number Product Description
SM1500G80 Support Documentation SM1500G80 : Single Mode Optical Fiber, 0.19-0.21 NA, 1550 nm , Ø80 µm
SMF-28-100 Support Documentation SMF-28-100 : 100 m of SMF-28e+ with Ø900 µm Jacket, Ø125 µm Cladding
SMF-28-1000 Support Documentation SMF-28-1000 : 1000 m of SMF-28e+ with Ø900 µm Jacket, Ø125 µm Cladding
SMF-28-J9 Support Documentation SMF-28-J9 : SMF-28e+ with Ø900 µm Jacket, Ø125 µm Cladding

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Single Mode Fiber: 1.7 to 2.1 µm

Stock Patch Cables Available with These Fibers
SM2000 Fiber
Item # PrefixConnectorsLength
P1-2000-FCFC/PC to FC/PC1 or 2 m
P3-2000-FCFC/APC to FC/APC2 m
P5-2000-PCAPCFC/PC to FC/APC1 m
P2-2000-PCSMAFC/PC to SMA1 m
P1-2000AR-2AR-Coated (1700 - 2100 nm) FC/PC to Uncoated FC/PC2 m
P5-2000AR-2AR-Coated (1700 - 2100 nm) FC/PC to Uncoated FC/APC2 m
P4-2000AR-2AR-Coated (1700 - 2100 nm) FC/APC to Uncoated FC/PC2 m
P3-2000AR-2AR-Coated (1700 - 2100 nm) FC/APC to Uncoated FC/APC2 m

Custom cables are also available. Click here for details.

Features

  • Shipped from Stock
  • No Minimums
  • Ge-Doped Silica Core, Pure Silica Cladding, and a UV Cured Acrylate Coating
  • Large Core for Coupling 2 µm Light
  • NA Compatible with Corning's SMF-28 Fiber
  • Exceptional Core/Clad Concentricity Specifications
  • Low Bend Losses (See Specs Tab)
Item #Operating
Wavelength
NAMFDCore
Diameter
Cladding
Diameter
Cladding
Noncircularity
Core/Cladding
Concentricity Error
BufferCore Index
Cladding
Index
SM20001700 - 2100 nm0.1113 µm11 ± 1 µm125 ± 1.0 µm≤2%≤0.8 µm245 ± 10 µm2 µm: 1.44362 µm: 1.4381
SM2000 and SMF28 Bend losses
Click to Enlarge

Using a 1996 nm source and a Ø30 mm mandrel, the bend losses (dB) of the SM2000 and SMF28 fibers were measured for each turn of the fiber around the mandrel. Based on the measurement, the loss/turn of the SM2000 fiber is ~0.08 dB. For the SMF28 fiber, the loss/turn is ~3 dB. The SM2000 fiber is much less sensitive to bending than SMF-28e fiber.
SM2000 Power
Click to Enlarge

Power as a function of distance measurements were obtained by starting with 150 m of SM2000 fiber and measuring power output after a series of cut backs. For this measurement 1996 nm input light was used.

Definition of the Mode Field Diameter

The mode field diameter (MFD) is one measure of the beam size of light propagating in a single mode fiber. It is a function of wavelength, core radius, and the refractive indices of the core and cladding. While much of the light in an optical fiber is trapped within the fiber core, a small fraction propagates in the cladding. For a Gaussian power distribution, the MFD is the diameter where the optical power is reduced to 1/e2 from its peak level.

Measurement of MFD
The measurement of MFD is accomplished by the Variable Aperture Method in the Far Field (VAMFF). An aperture is placed in the far field of the fiber output, and the intensity is measured. As successively smaller apertures are placed in the beam, the intensity levels are measured for each aperture; the data can then be plotted as power vs. the sine of the aperture half-angle (or the numerical aperture).

The MFD is then determined using Petermann's second definition, which is a mathematical model that does not assume a specific shape of power distribution. The MFD in the near field can be determined from this far-field measurement using the Hankel Transform.

Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Undamaged Fiber End
Power Handling Limitations Imposed by Optical Fiber
Click to Enlarge
Damaged Fiber End

Laser Induced Damage in Optical Fibers

The following tutorial details damage mechanisms in unterminated (bare) and terminated optical fibers, including damage mechanisms at both the air-to-glass interface and within the glass of the optical fiber. Please note that while general rules and scaling relations can be defined, absolute damage thresholds in optical fibers are extremely application dependent and user specific. This tutorial should only be used as a guide to estimate the damage threshold of an optical fiber in a given application. Additionally, all calculations below only apply if all cleaning and use recommendations listed in the last section of this tutorial have been followed. For further discussion about an optical fiber’s power handling abilities within a specific application, contact Thorlabs’ Tech Support.

Damage at the Free Space-to-Fiber Interface

There are several potential damage mechanisms that can occur at the free space-to-fiber interface when coupling light into a fiber. These come into play whether the fiber is used bare or terminated in a connector.

Silica Optical Fiber Maximum Power Densities
TypeTheoretical Damage ThresholdPractical Safe Value
CW
(Average Power)
1 MW/cm2250 kW/cm2
10 ns Pulsed
(Peak Power)
5 GW/cm21 GW/cm2

Unterminated (Bare) Fiber
Damage mechanisms in bare optical fiber can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber (refer to the table to the right). The surface areas and beam diameters involved at the air-to-glass interface are extremely small compared to bulk optics, especially with single mode (SM) fiber, resulting in very small damage thresholds.

The effective area for SM fiber is defined by the mode field diameter (MFD), which is the effective cross-sectional area through which light propagates in the fiber. A free-space beam of light must be focused down to a spot of roughly 80% of this diameter to be coupled into the fiber with good efficiency. MFD increases roughly linearly with wavelength, which yields a roughly quadratic increase in damage threshold with wavelength. Additionally, a beam coupled into SM fiber typically has a Gaussian-like profile, resulting in a higher power density at the center of the beam compared with the edges, so a safety margin must be built into the calculated damage threshold value if the calculations assume a uniform density.

Multimode (MM) fiber’s effective area is defined by the core diameter, which is typically far larger than the MFD in SM fiber. Kilowatts of power can be typically coupled into multimode fiber without damage, due to the larger core size and the resulting reduced power density.

It is typically uncommon to use single mode fibers for pulsed applications with high per-pulse powers because the beam needs to be focused down to a very small area for coupling, resulting in a very high power density. It is also uncommon to use SM fiber with ultraviolet light because the MFD becomes extremely small; thus, power handling becomes very low, and coupling becomes very difficult.

Example Calculation
For SM400 single mode fiber operating at 400 nm with CW light, the mode field diameter (MFD) is approximately Ø3 µm. For good coupling efficiency, 80% of the MFD is typically filled with light. This yields an effective diameter of Ø2.4 µm and an effective area of 4.52 µm2:

Area = πr2 = π(MFD/2)2 = π • 1.22 µm2 = 4.52 µm2

This can be extrapolated to a damage threshold of 11.3 mW. We recommend using the "practical value" maximum power density from the table above to account for a Gaussian power distribution, possible coupling misalignment, and contaminants or imperfections on the fiber end face:

250 kW/cm2 = 2.5 mW/µm2

4.25 µm2 • 2.5 mW/µm2 = 11.3 mW

Terminated Fiber
Optical fiber that is terminated in a connector has additional power handling considerations. Fiber is typically terminated by being epoxied into a ceramic or steel ferrule, which forms the interfacing surface of the connector. When light is coupled into the fiber, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, inside the ferrule.

The scattered light propagates into the epoxy that holds the fiber in the ferrule. If the light is intense enough, it can melt the epoxy, causing it to run onto the face of the connector and into the beam path. The epoxy can be burned off, leaving residue on the end of the fiber, which reduces coupling efficiency and increases scattering, causing further damage. The lack of epoxy between the fiber and ferrule can also cause the fiber to be decentered, which reduces the coupling efficiency and further increases scattering and damage.

The power handling of terminated optical fiber scales with wavelength for two reasons. First, the higher per photon energy of short-wavelength light leads to a greater likelihood of scattering, which increases the optical power incident on the epoxy near the end of the connector. Second, shorter-wavelength light is inherently more difficult to couple into SM fiber due to the smaller MFD, as discussed above. The greater likelihood of light not entering the fiber’s core again increases the chance of damaging scattering effects. This second effect is not as common with MM fibers because their larger core sizes allow easier coupling in general, including with short-wavelength light.

Fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. This design feature, commonly used with multimode fiber, allows some of the connector-related damage mechanisms to be avoided. Our high-power multimode fiber patch cables use connectors with this design feature.

Combined Damage Thresholds
As a general guideline, for short-wavelength light at around 400 nm, scattering within connectors typically limits the power handling of optical fiber to about 300 mW. Note that this limit is higher than the limit set by the optical power density at the fiber tip. However, power handing limitations due to connector effects do not diminish as rapidly with wavelength when compared to power density effects. Thus, a terminated fiber’s power handling is "connector-limited" at wavelengths above approximately 600 nm and is "fiber-limited" at lower wavelengths.

The graph to the right shows the power handling limitations imposed by the fiber itself and a surrounding connector. The total power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at that wavelength. The fiber-limited (blue) line is for SM fibers. An equivalent line for multimode fiber would be far above the SM line on the Y-axis. For terminated multimode fibers, the connector-limited (red) line always determines the damage threshold.

Please note that the values in this graph are rough guidelines detailing estimates of power levels where damage is very unlikely with proper handling and alignment procedures. It is worth noting that optical fibers are frequently used at power levels above those described here. However, damage is likely in these applications. The optical fiber should be considered a consumable lab supply if used at power levels above those recommended by Thorlabs.

Damage Within Optical Fibers

In addition to damage mechanisms at the air-to-glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. Two categories of damage within the fiber are damage from bend losses and damage from photodarkening.

Bend Losses
Bend losses occur when a fiber is bent to a point where light traveling in the core is incident on the core/cladding interface at an angle higher than the critical angle, making total internal reflection impossible.Under these circumstances, light escapes the fiber, often in one localized area. The light escaping the fiber typically has a high power density, which can cause burns to the fiber as well as any surrounding furcation tubing.

A special category of optical fiber, called double-clad fiber, can reduce the risk of bend-loss damage by allowing the fiber’s cladding (2nd layer) to also function as a waveguide in addition to the core. By making the critical angle of the cladding/coating interface higher than the critical angle of the core/clad interface, light that escapes the core is loosely confined within the cladding. It will then leak out over a distance of centimeters or meters instead of at one localized spot within the fiber, minimizing damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

Photodarkening
A second damage mechanism within optical fiber, called photodarkening or solarization, typically occurs over time in fibers used with ultraviolet or short-wavelength visible light. The pure silica core of standard multimode optical fiber can transmit ultraviolet light, but the attenuation at these short wavelengths increases with the time exposed to the light. The mechanism that causes photodarkening is largely unknown, but several strategies have been developed to combat it. Fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening. Other dopants, including fluorine, can also reduce photodarkening.

Germanium-doped silica, which is commonly used for the core of single mode fiber for red or IR wavelengths, can experience photodarkening with blue visible light. Thus, pure silica core single mode fibers are typically used with short wavelength visible light. Single mode fibers are typically not used with UV light due to the small MFD at these wavelengths, which makes coupling extremely difficult.

Even with the above strategies in place, all fibers eventually experience photodarkening when used with UV light, and thus, fibers used with these wavelengths should be considered consumables.

Tips for Maximizing an Optical Fiber's Power Handling Capability

With a clear understanding of the power-limiting mechanisms of an optical fiber, strategies can be implemented to increase a fiber’s power handling capability and reduce the risk of damage in a given application. All of the calculations above only apply if the following strategies are implemented.

One of the most important aspects of a fiber’s power-handling capability is the quality of the end face. The end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Additionally, if working with bare fiber, the end of the fiber should have a good quality cleave, and any splices should be of good quality to prevent scattering at interfaces.

The alignment process for coupling light into optical fiber is also important to avoid damage to the fiber. During alignment, before optimum coupling is achieved, light may be easily focused onto parts of the fiber other than the core. If a high power beam is focused on the cladding or other parts of the fiber, scattering can occur, causing damage.

Additionally, terminated fibers should not be plugged in or unplugged while the light source is on, again so that focused beams of light are not incident on fragile parts of the connector, possibly causing damage.

Bend losses, discussed above, can cause localized burning in an optical fiber when a large amount of light escapes the fiber in a small area. Fibers carrying large amounts of light should be secured to a steady surface along their entire length to avoid being disturbed or bent.

Additionally, choosing an appropriate optical fiber for a given application can help to avoid damage. Large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications. They provide good beam quality with a larger MFD, thereby decreasing power densities. Standard single mode fibers are also not generally used for ultraviolet applications or high-peak-power pulsed applications due to the high spatial power densities these applications present.

Click the Support Documentation icon document icon or Part Number below to view the available support documentation
Part Number Product Description
SM2000 Support Documentation SM2000 : Single Mode Optical Fiber, 1.7-2.1 µm, Ø125 µm Cladding

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