Graded-Index (GRIN) Multimode Fibers

  • Graded Refractive Index Profile Enables High Bandwidth
  • Ø50 µm Core and Ø62.5 µm Core Options
  • OM1, OM2, OM3, and OM4 Fibers Available

Graded-Index Multimode Fiber Cross Section

(Not to Scale)

Refractive Index Profile of Graded-Index Fiber

Acrylate Coating


Doped Core


Graded-Index Fiber, Ø50 µm Core


100-Meter Length of GIF625 Ø62.5 µm Core Fiber

Related Items

Please Wait
Stock Patch Cables Using This Fiber
Fiber Type Connectors Available Lengths Patch Cable Item #
GIF625 FC/PC 1, 2, 3, 5, 10, 20 m M31Lxx
GIF50C FC/PC 1, 2, 5 m M115Lxx
GIF50E FC/PC 1, 2, 5 m M116Lxx
GIF50E FC/PC to LC/PC 1, 2, 5 m M117Lxx
Optical Fiber Manufacturing
Custom Fiber Patch Cables


  • Ø50 µm Core / Ø125 µm Cladding and Ø62.5 µm Core / Ø125 µm Cladding Fibers Available
  • Three Bandwidth Options (OM2, OM3, or OM4) for Ø50 µm Core Fiber (See Specs Tab for More Information)
  • Ø62.5 µm Core Fiber Available Pre-Spooled in 100 m and 1000 m Lengths

Thorlabs' graded-index (GRIN) multimode fiber provides lower modal dispersion and less bend loss than traditional multimode step-index fiber, with a broad operating wavelength range from 800 - 1600 nm (see the Graphs tab for attenuation plots over this range). Because of the larger core size compared to single mode fiber, these fibers provide a higher transmission capacity and are used for short-range communication networks and high-speed transmission applications. The gradient of the refractive index between the core and cladding determines the available bandwidth at a given wavelength.

Our Ø50 μm core / Ø125 µm cladding graded-index fibers provide improved transmission rates and are available with three different bandwidths (OM2, OM3, or OM4). The fiber coating is a Ø242 μm mechanically strippable acrylate coating. These fibers are particularly well suited for use in telecom applications; the bandwidth is optimized for high-performance 850 nm laser systems, but can also be used with LEDs at 850 nm or 1300 nm at a reduced bandwidth (see the Specs tab for more information). 

Low-loss, high-bandwidth Ø62.5 μm core / Ø125 μm cladding graded-index fiber (OM1) uses a dual-layer acrylate coating that protects against water, temperature, and humidity extremes. GIF625 fiber is offered per meter or pre-spooled in lengths of 100 m or 1 km.

Item # GIF50C GIF50D GIF50E GIF625
Geometrical and Physical Specifications
Core Diameter 50.0 ± 2.5 µm 62.5 ± 2.5 µm
Cladding Diameter 125.0 ± 1.0 µm 125 ± 1 µm
Coating Diameter 242 ± 5 µm 245 ± 10 µm
Core Non-Circularity ≤5% ≤5%
Cladding Non-Circularity ≤1.0% ≤1%
Coating Non-Circularity - ≤5%
Core-Cladding Concentricitya ≤1.5 µm ≤1 µm
Coating-Cladding Concentricity <12 µm ≤8 µm
Core Doping Germanium Germanium
Coating Material Acrylate Acrylate
Proof Test ≥100 kpsi ≥100 kpsi
Core Index Proprietaryb Proprietaryb
Cladding Index Proprietaryb Proprietaryb
Operating Temperature -60 to 85 °C -60 to 85 °C
Optical Specifications
Operating Wavelength 800 - 1600 nm 800 - 1600 nm
Numerical Aperture 0.200 ± 0.015 0.275 ± 0.015
Optical Multimode (OM) Type OM2 OM3 OM4 OM1
Bandwidth High-Performance EMB (@ 850 nm)c 950 MHz•km 2000 MHz•km 4700 MHz•km -
Overfilled Modal Bandwidthd 700 MHz•km @ 850 nm
500 MHz•km @ 1300 nm
1500 MHz•km @ 850 nm
500 MHz•km @ 1300 nm
3500 MHz•km @ 850 nm
500 MHz•km @ 1300 nm
≥200 MHz•km @ 850 nm
≥500 MHz•km @ 1300 nm
Attenuation ≤2.3 dB/km @ 850 nm
≤0.6 dB/km @1300 nm
≤2.9 dB/km @ 850 nm
≤0.6 dB/km @ 1300 nm
Macrobend Attenuation - 100 Turns on a Ø75 mm Mandrel:
≤0.5 dB @ 850 nm and @ 1300 nm
Effective Group Index of Refraction 1.482 @ 850 nm
1.477 @ 1300 nm
1.496 @ 850 nm
1.491 @ 1300 nm
Zero Dispersion Wavelength 1295 nm (Min)
1315 nm (Max)
1320 nm (Min)
1365 nm (Max)
Zero Dispersion Slope ≤0.101 ps/(nm2•km) ≤0.11 ps/(nm2•km)
  • This is also known as the core-cladding offset.
  • We regret that we cannot provide this proprietary information.
  • For high-performance laser systems, ensured via minEMBc per TIA/EIA 455-220A and IEC 60793-1-49.
  • For LED sources overfilling the fiber. OFL BW, per TIA/EIA 455-220A and IEC 60793-1-41. For more information on overfilling, please see the Launch Conditions section of our Multimode Fiber Tutorial.

Laser-Induced Damage in Silica Optical Fibers

The following tutorial details damage mechanisms relevant to unterminated (bare) fiber, terminated optical fiber, and other fiber components from laser light sources. These mechanisms include damage that occurs at the air / glass interface (when free-space coupling or when using connectors) and in the optical fiber itself. A fiber component, such as a bare fiber, patch cable, or fused coupler, may have multiple potential avenues for damage (e.g., connectors, fiber end faces, and the device itself). The maximum power that a fiber can handle will always be limited by the lowest limit of any of these damage mechanisms.

While the damage threshold can be estimated using scaling relations and general rules, absolute damage thresholds in optical fibers are very application dependent and user specific. Users can use this guide to estimate a safe power level that minimizes the risk of damage. Following all appropriate preparation and handling guidelines, users should be able to operate a fiber component up to the specified maximum power level; if no maximum is specified for a component, users should abide by the "practical safe level" described below for safe operation of the component. Factors that can reduce power handling and cause damage to a fiber component include, but are not limited to, misalignment during fiber coupling, contamination of the fiber end face, or imperfections in the fiber itself. For further discussion about an optical fiber’s power handling abilities for a specific application, please contact Thorlabs’ Tech Support.

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

Damage at the Air / Glass Interface

There are several potential damage mechanisms that can occur at the air / glass interface. Light is incident on this interface when free-space coupling or when two fibers are mated using optical connectors. High-intensity light can damage the end face leading to reduced power handling and permanent damage to the fiber. For fibers terminated with optical connectors where the connectors are fixed to the fiber ends using epoxy, the heat generated by high-intensity light can burn the epoxy and leave residues on the fiber facet directly in the beam path.

Estimated Optical Power Densities on Air / Glass Interfacea
Type Theoretical Damage Thresholdb Practical Safe Levelc
(Average Power)
~1 MW/cm2 ~250 kW/cm2
10 ns Pulsed
(Peak Power)
~5 GW/cm2 ~1 GW/cm2
  • All values are specified for unterminated (bare), undoped silica fiber and apply for free space coupling into a clean fiber end face.
  • This is an estimated maximum power density that can be incident on a fiber end face without risking damage. Verification of the performance and reliability of fiber components in the system before operating at high power must be done by the user, as it is highly system dependent.
  • This is the estimated safe optical power density that can be incident on a fiber end face without damaging the fiber under most operating conditions.

Damage Mechanisms on the Bare Fiber End Face

Damage mechanisms on a fiber end face can be modeled similarly to bulk optics, and industry-standard damage thresholds for UV Fused Silica substrates can be applied to silica-based fiber. However, unlike bulk optics, the relevant surface areas and beam diameters involved at the air / glass interface of an optical fiber are very small, particularly for coupling into single mode (SM) fiber. therefore, for a given power density, the power incident on the fiber needs to be lower for a smaller beam diameter.

The table to the right lists two thresholds for optical power densities: a theoretical damage threshold and a "practical safe level". In general, the theoretical damage threshold represents the estimated maximum power density that can be incident on the fiber end face without risking damage with very good fiber end face and coupling conditions. The "practical safe level" power density represents minimal risk of fiber damage. Operating a fiber or component beyond the practical safe level is possible, but users must follow the appropriate handling instructions and verify performance at low powers prior to use.

Calculating the Effective Area for Single Mode Fibers
The effective area for single mode (SM) fiber is defined by the mode field diameter (MFD), which is the cross-sectional area through which light propagates in the fiber; this area includes the fiber core and also a portion of the cladding. To achieve good efficiency when coupling into a single mode fiber, the diameter of the input beam must match the MFD of the fiber.

As an example, SM400 single mode fiber has a mode field diameter (MFD) of ~Ø3 µm operating at 400 nm, while the MFD for SMF-28 Ultra single mode fiber operating at 1550 nm is Ø10.5 µm. The effective area for these fibers can be calculated as follows:

SM400 Fiber: Area = Pi x (MFD/2)2 = Pi x (1.5 µm)2 = 7.07 µm= 7.07 x 10-8 cm2

 SMF-28 Ultra Fiber: Area = Pi x (MFD/2)2 = Pi x (5.25 µm)2 = 86.6 µm= 8.66 x 10-7 cm2

To estimate the power level that a fiber facet can handle, the power density is multiplied by the effective area. Please note that this calculation assumes a uniform intensity profile, but most laser beams exhibit a Gaussian-like shape within single mode fiber, resulting in a higher power density at the center of the beam compared to the edges. Therefore, these calculations will slightly overestimate the power corresponding to the damage threshold or the practical safe level. Using the estimated power densities assuming a CW light source, we can determine the corresponding power levels as:

SM400 Fiber: 7.07 x 10-8 cm2 x 1 MW/cm2 = 7.1 x 10-8 MW = 71 mW (Theoretical Damage Threshold)
     7.07 x 10-8 cm2 x 250 kW/cm2 = 1.8 x 10-5 kW = 18 mW (Practical Safe Level)

SMF-28 Ultra Fiber: 8.66 x 10-7 cm2 x 1 MW/cm2 = 8.7 x 10-7 MW = 870 mW (Theoretical Damage Threshold)
           8.66 x 10-7 cm2 x 250 kW/cm2 = 2.1 x 10-4 kW = 210 mW (Practical Safe Level)

Effective Area of Multimode Fibers
The effective area of a multimode (MM) fiber is defined by the core diameter, which is typically far larger than the MFD of an SM fiber. For optimal coupling, Thorlabs recommends focusing a beam to a spot roughly 70 - 80% of the core diameter. The larger effective area of MM fibers lowers the power density on the fiber end face, allowing higher optical powers (typically on the order of kilowatts) to be coupled into multimode fiber without damage.

Damage Mechanisms Related to Ferrule / Connector Termination

Click to Enlarge
Plot showing approximate input power that can be incident on a single mode silica optical fiber with a termination. Each line shows the estimated power level due to a specific damage mechanism. The maximum power handling is limited by the lowest power level from all relevant damage mechanisms (indicated by a solid line).

Fibers terminated with optical connectors have additional power handling considerations. Fiber is typically terminated using epoxy to bond the fiber to a ceramic or steel ferrule. When light is coupled into the fiber through a connector, light that does not enter the core and propagate down the fiber is scattered into the outer layers of the fiber, into the ferrule, and the epoxy used to hold the fiber in the ferrule. If the light is intense enough, it can burn the epoxy, causing it to vaporize and deposit a residue on the face of the connector. This results in localized absorption sites on the fiber end face that reduce coupling efficiency and increase scattering, causing further damage.

For several reasons, epoxy-related damage is dependent on the wavelength. In general, light scatters more strongly at short wavelengths than at longer wavelengths. Misalignment when coupling is also more likely due to the small MFD of short-wavelength SM fiber that also produces more scattered light.

To minimize the risk of burning the epoxy, fiber connectors can be constructed to have an epoxy-free air gap between the optical fiber and ferrule near the fiber end face. Our high-power multimode fiber patch cables use connectors with this design feature.

Determining Power Handling with Multiple Damage Mechanisms

When fiber cables or components have multiple avenues for damage (e.g., fiber patch cables), the maximum power handling is always limited by the lowest damage threshold that is relevant to the fiber component. In general, this represents the highest input power that can be incident on the patch cable end face and not the coupled output power.

As an illustrative example, the graph to the right shows an estimate of the power handling limitations of a single mode fiber patch cable due to damage to the fiber end face and damage via an optical connector. The total input power handling of a terminated fiber at a given wavelength is limited by the lower of the two limitations at any given wavelength (indicated by the solid lines). A single mode fiber operating at around 488 nm is primarily limited by damage to the fiber end face (blue solid line), but fibers operating at 1550 nm are limited by damage to the optical connector (red solid line).

In the case of a multimode fiber, the effective mode area is defined by the core diameter, which is larger than the effective mode area for SM fiber. This results in a lower power density on the fiber end face and allows higher optical powers (on the order of kilowatts) to be coupled into the fiber without damage (not shown in graph). However, the damage limit of the ferrule / connector termination remains unchanged and as a result, the maximum power handling for a multimode fiber is limited by the ferrule and connector termination. 

Please note that these are rough 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, these applications typically require expert users and testing at lower powers first to minimize risk of damage. Even still, optical fiber components should be considered a consumable lab supply if used at high power levels.

Intrinsic Damage Threshold

In addition to damage mechanisms at the air / glass interface, optical fibers also display power handling limitations due to damage mechanisms within the optical fiber itself. These limitations will affect all fiber components as they are intrinsic to the 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 a localized area. The light escaping the fiber typically has a high power density, which burns the fiber coating 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 the risk of damage. Thorlabs manufactures and sells 0.22 NA double-clad multimode fiber, which boasts very high, megawatt range power handling.

A second damage mechanism, called photodarkening or solarization, can occur in fibers used with ultraviolet or short-wavelength visible light, particularly those with germanium-doped cores. Fibers used at these wavelengths will experience increased attenuation over time. The mechanism that causes photodarkening is largely unknown, but several fiber designs have been developed to mitigate it. For example, fibers with a very low hydroxyl ion (OH) content have been found to resist photodarkening and using other dopants, such as fluorine, can also reduce photodarkening.

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

Preparation and Handling of Optical Fibers

General Cleaning and Operation Guidelines
These general cleaning and operation guidelines are recommended for all fiber optic products. Users should still follow specific guidelines for an individual product as outlined in the support documentation or manual. Damage threshold calculations only apply when all appropriate cleaning and handling procedures are followed.

  1. All light sources should be turned off prior to installing or integrating optical fibers (terminated or bare). This ensures that focused beams of light are not incident on fragile parts of the connector or fiber, which can possibly cause damage.

  2. The power-handling capability of an optical fiber is directly linked to the quality of the fiber/connector end face. Always inspect the fiber end prior to connecting the fiber to an optical system. The fiber end face should be clean and clear of dirt and other contaminants that can cause scattering of coupled light. Bare fiber should be cleaved prior to use and users should inspect the fiber end to ensure a good quality cleave is achieved.

  3. If an optical fiber is to be spliced into the optical system, users should first verify that the splice is of good quality at a low optical power prior to high-power use. Poor splice quality may increase light scattering at the splice interface, which can be a source of fiber damage.

  4. Users should use low power when aligning the system and optimizing coupling; this minimizes exposure of other parts of the fiber (other than the core) to light. Damage from scattered light can occur if a high power beam is focused on the cladding, coating, or connector.

Tips for Using Fiber at Higher Optical Power
Optical fibers and fiber components should generally be operated within safe power level limits, but under ideal conditions (very good optical alignment and very clean optical end faces), the power handling of a fiber component may be increased. Users must verify the performance and stability of a fiber component within their system prior to increasing input or output power and follow all necessary safety and operation instructions. The tips below are useful suggestions when considering increasing optical power in an optical fiber or component.

  1. Splicing a fiber component into a system using a fiber splicer can increase power handling as it minimizes possibility of air/fiber interface damage. Users should follow all appropriate guidelines to prepare and make a high-quality fiber splice. Poor splices can lead to scattering or regions of highly localized heat at the splice interface that can damage the fiber.

  2. After connecting the fiber or component, the system should be tested and aligned using a light source at low power. The system power can be ramped up slowly to the desired output power while periodically verifying all components are properly aligned and that coupling efficiency is not changing with respect to optical launch power.

  3. Bend losses that result from sharply bending a fiber can cause light to leak from the fiber in the stressed area. When operating at high power, the localized heating that can occur when a large amount of light escapes a small localized area (the stressed region) can damage the fiber. Avoid disturbing or accidently bending fibers during operation to minimize bend losses.

  4. Users should always choose the appropriate optical fiber for a given application. For example, large-mode-area fibers are a good alternative to standard single mode fibers in high-power applications as they provide good beam quality with a larger MFD, decreasing the power density on the air/fiber interface.

  5. Step-index silica single mode fibers are normally not used for ultraviolet light or high-peak-power pulsed applications due to the high spatial power densities associated with these applications.

Posted Comments:
Norbert Linz  (posted 2024-03-08 13:50:29.553)
Can you please give me somer information regarding the pitch length for GIF625 when using 515 nm wavelength?
cdolbashian  (posted 2024-03-15 04:57:18.0)
Thank you for reaching out to us with this inquiry. Unfortunately we have limited data from the vendor, and it is only regarding the design wavelength of ~1300nm. I have contacted you directly to share this information with you.
taywin witee  (posted 2023-10-05 19:57:22.54)
้Hi Sir / Madam i will order GIF50E but i have some detail from you. i want to know GIF50E have some material coating Cladding and Germanium- Doped Core or not? from the picture i think its have Acrylate Coating outside so please you give me more detail or clear its for me thanks taywin w
jpolaris  (posted 2023-10-05 01:15:27.0)
Thank you for contacting Thorlabs. Yes, the core of GIF50E is Germanium-doped and the coating is acrylate. I have reached out to you directly to discuss this fiber in more detail.
Jingwen Deng  (posted 2023-06-21 22:37:52.847)
Hi, I am interested in trying GRIN optical fiber for 660 - 750 nm wavelength transmission. I was wondering if you guys know the transmittance in this wavelength range. Thanks! Best, Jingwen
jpolaris  (posted 2023-06-26 01:59:30.0)
Thank you for contacting Thorlabs. Additional specifications and data can be requested by contacting I have reached out to you directly with some relevant data.
Radu Stancu  (posted 2023-01-18 14:14:46.993)
Hi! Could you please let me know what is the gradient constant for the GIF625 fibre? Many thanks!
jgreschler  (posted 2023-01-20 01:41:08.0)
Thank you for reaching out to Thorlabs. Additional specs and data can be requested by emailing I have reached out to you directly to provide the data.
peter li  (posted 2022-11-20 01:27:34.233)
what is dispersion v.s wavelength of GIF50E fiber?
jgreschler  (posted 2022-11-22 08:16:09.0)
Thank you for reaching out to Thorlabs. Additional specs and data can be requested by contacting I have reached out to you directly to provide the requested graph.
peter li  (posted 2022-11-20 01:26:23.477)
what is dispersion v.s wavelength of GIF625 fiber?
jgreschler  (posted 2022-11-22 08:16:10.0)
Thank you for reaching out to Thorlabs. Additional specs and data can be requested by contacting I have reached out to you directly to provide the requested graph.
peter li  (posted 2022-11-19 23:12:12.26)
If I use a spherical lens to couple this fiber,I based on this formula:f = D( πω/4λ),In order to couple light of wavelength λ、 beam of 1/e2 diameter D mode field diameter ω, choose a lens with a focal length f=7.5cm. is this way possible to succesful couple? I want the coupling at lest 45%。 any suggestion?thanks!
jgreschler  (posted 2022-11-22 08:16:11.0)
Thank you for reaching out to Thorlabs. Spot size, and therefore coupling efficiency, rely on more factors than provided. General advice to attain good coupling efficiency is to use a small focal length aspheric lens, or an equivalent achromat if you are coupling broadband light. I have reached out to you directly to discuss your specific application further.
Xu Jinggang  (posted 2022-09-07 18:47:09.35)
For GIF625, could you provide the length of the pitch.I want to buy the full multiples of the pitch.
jgreschler  (posted 2022-09-13 09:18:28.0)
Thank you for reaching out to Thorlabs. The full pitch length of GIF625 at 1550 is approximately 1,052um.
Chao Xu  (posted 2022-05-02 20:50:33.41)
For GIF625, could you provide the formula coefficients of gradient constant and central refractive index? I mean the coefficients like K0,K1,K2, B, C. Thank you.
jgreschler  (posted 2022-05-05 03:42:49.0)
Thank you for reaching out to Thorlabs. Additional data and specifications can be requested by emailing I have contacted you directly to discuss your request.
Pablo Fernández  (posted 2021-11-04 11:06:00.703)
I am interested in seeing a plot conveying information on modal dispersion of GRIN-fiber. For example differential mode delay or range of light speed between main modes. (I am particularly interested on the relative delay between modes to see if I could use this over a single-mode fiber)
jgreschler  (posted 2022-01-06 11:08:48.0)
Thank you for reaching out to Thorlabs. Additional data can be requested by contacting Tech Support. I have reached out to you directly to discuss this further.
cook0302  (posted 2019-03-07 22:42:13.927)
Hello I recently purchased some GIF625 and am trying to figure out the length to use to produce a 0.23 pitch lens. Are you able to advise on this at all? I am working around 1550nm. Regards, Peter Cook
nbayconich  (posted 2019-03-15 08:39:21.0)
Thank you for contacting Thorlabs. The estimated length need of GIF625 is about 263um to create a 0.23 pitch lens at 1550nm.
etienne.genier  (posted 2019-01-24 12:42:51.68)
Hello, would it be possible to have the refractive index profile and the gradient constant for the GIF50C and GIF625.
YLohia  (posted 2019-01-29 10:32:50.0)
Hello, I will reach out to you directly with the profile for GIF625. Unfortunately, we do not have this information for the GIF50C at the moment.
nawid17  (posted 2018-11-07 14:20:25.063)
Hello ! Would it be possible to have any kind of information (such as a profile) for the refractive index concerning gradient index fibers please ?
YLohia  (posted 2018-11-07 10:29:33.0)
Hello, please see my last response to your question. I will reach out to you directly with the data for GIF625 again.
nawid17  (posted 2018-10-17 14:00:41.423)
Hello ! Would it be possible to have the refractive index for the GIF50C; GIF50D and GIF50E profile please ?
YLohia  (posted 2018-10-17 10:21:55.0)
Hello, thank you for contacting Thorlabs. Unfortunately, the refractive index profiles for these three fibers is proprietary. That being said, we are still able to supply this information for the GIF625 if you are interested in that. We apologize for any inconvenience caused by this.
xavier.attendu  (posted 2017-12-18 18:06:59.153)
Hello. It would be very helpful to have the refractive index profile. Also, do you have any information regarding calculating the refractive index variation at different wavelengths (Sellmeier coefficients for example). Thanks in advance.
nbayconich  (posted 2017-12-20 01:23:15.0)
Thank you for contacting Thorlabs. We do not have the Sellmeier coefficients for this graded index fiber but I can provide the refractive index profile for you. I will reach out to you directly with more information.
alexandreabid  (posted 2017-11-03 17:07:30.057)
Hi I would need some infos on the GIF625 Grin lens. Could you send me the gradient constant as weel as the refractive index at 830nm? I would also need the refractive index of your SM800 fiber. Thanks for your help.
nbayconich  (posted 2017-12-15 04:58:31.0)
Thank you for contacting Thorlabs. We do not have the gradient constant for the GIF625 but we can provide the refractive index profile for you. I will reach out to you directly with more information regarding the refractive index of GIF625 and SM800.
ee14d209  (posted 2017-10-29 01:49:23.64)
Dear, May I know the dispersion value for GIF625 fiber at 1550nm. What does minimum zero dispersion value mean?
tfrisch  (posted 2017-12-14 09:07:04.0)
Hello, thank you for contacting Thorlabs. The material dispersion is about 21.5 ps/(nm km), and the Pulse Dispersion is about 0.78 ns/km at 1550nm. The actual value of the zero dispersion wavelength can change from one production lot to another, but it will be between 1320nm and 1365nm. I will reach out to you directly to discuss this in greater detail.
chiwon.lee  (posted 2017-06-19 10:05:10.95)
Hi, I'm wondering how much power can be handled with the GIF50C and GIF625 fiber. For example, my application needs to handle the laser pulse energy of 20 microjoule (peak power 10^8 W) with minimum modal dispersion, and I think this graded index fiber might be an safer option in terms of damage than single mode fiber. Thanks.
tfrisch  (posted 2017-07-07 04:44:00.0)
Hello, thank you for contacting Thorlabs. It looks like you are using a fs source, and while we don't have any formal damage threshold testing, I can reach out to you to discuss this application. In general, a larger core fiber will have a higher damage threshold, but keep in mind GIF fibers are multimode, so even though they have less modal dispersion than a step index multimode fiber, it will still be greater than a single mode fiber which only supports one mode.
hamiltonpo  (posted 2017-06-01 12:43:00.217)
Hello, could you please provide the refractive index profile of the GIF625? Thank you, Pearce.
nbayconich  (posted 2017-06-14 09:42:41.0)
Thank you for contacting Thorlabs. I will reach out to you directly with more information about the GIF625 index profile.
honza.stopka  (posted 2016-06-30 05:13:54.037)
Hello, could you please provide details on the refractive index profile of GIF625-10? I am using this fiber for my research for Master thesis. Thank you, Jan.
nburgwin  (posted 2014-10-28 12:19:52.493)
Can you provide any details on the refractive index profile of the GIF50C? This will be used for a research project. Thanks, Nick.
jlow  (posted 2014-10-30 01:59:56.0)
Response from Jeremy at Thorlabs: The index profile is considered proprietary information. I will contact you directly to discuss about this.
dbs660  (posted 2014-10-22 11:01:03.993)
Dear sir, Could you provide me with the refractive index profile parameters of the GIF625 fiber? thanks in advance, Dirk
jlow  (posted 2014-10-22 02:00:46.0)
Response from Jeremy at Thorlab: We will contact you directly to provide this information.
user  (posted 2014-07-09 05:07:46.677)
Hello, I am using the fiber GIF50C. I would be pleased, if you could offer me the refractive index profile/gradient constant or alternatively the pitchlength at 1550 nm? Thanks and regards, Yahua
jlow  (posted 2014-08-07 09:08:22.0)
Response from Jeremy at Thorlabs: We are not able to provide the refractive index profile for the GIF50C.
ghohert  (posted 2014-03-31 13:47:34.757)
Hi, I could use the refractive index profiles for GIF625 fiber. Thanks in advance.
pbui  (posted 2014-04-02 04:13:33.0)
We will contact you directly to provide the typical refractive index profile.
christoph.otte  (posted 2013-08-27 14:42:53.097)
Hello, i'm using the fiber GIF50C and GIF625. I would be pleased, if you could offer me the refractive index profile/gradient constant or alternatively the pitchlength at 1300 nm? Thanks a lot! regards, Christoph
pbui  (posted 2013-08-29 14:23:00.0)
Response from Phong at Thorlabs: We will contact you directly to provide these graphs.
bpursley  (posted 2013-03-06 15:12:40.1)
I currently have some gif625 and would like to use it at a wavelength of 2um if possible. Do you have attenuation data beyond 1600nm? Thanks
jlow  (posted 2013-03-08 17:03:00.0)
Response from Jeremy at Thorlabs: We do not have any test data at this moment for the attenuation of this fiber at 2µm. We have a theoretical estimate that the attenuation would be around 0.7 dB/km at 2µm.
tcohen  (posted 2012-11-07 17:53:54.617)
Response from Tim at Thorlabs: Thank you for your feedback. We currently have limited data in the visible for these fibers. To access this data and receive updates while we look to extend our curves, please contact us at
user  (posted 2012-11-07 10:45:20.557)
Can you add data for the attenuation across the visible, I have a number of wavelengths I'd like to transmit and can accept larger losses, but what to know approximately what to expect.
jlow  (posted 2012-07-31 16:55:00.0)
A response from Jeremy at Thorlabs: The typical pitch for the GIF625 fiber is around 0.986mm. The typical cladding/core(center) refractive index are about 1.45641/1.48585 (both at 656.20nm).
xie  (posted 2012-07-31 12:08:06.0)
Hi, I would like to know the pitch length (p) of GIF625 and the refractive index profiles of it. Thank you.
tcohen  (posted 2012-06-21 15:29:00.0)
Response from Tim at Thorlabs: Thank you for your interest in our graded index fibers! We are looking into the pitch for these fibers and have contacted you for more information on your application.
edouard.schmidtlin  (posted 2012-06-18 17:25:07.0)
Question about the grin media: What is the pitch, or the NR2 Zemax coeffifient?
tcohen  (posted 2012-05-17 11:42:00.0)
Response from Tim at Thorlabs: Thank you for your feedback! We have moved the effective group index of refraction into the main presentation and I have contacted you with data on the index profile.
jy_park  (posted 2012-05-16 02:01:20.0)
Hi, recently I bought a spool of GIF625 & GIF50C for my experiment, but I can't find any information of index profiles. Please offer this data. Thanks:)
jjurado  (posted 2011-09-05 21:27:00.0)
Response from Javier at Thorlabs to dirk.lorenser: We will send you the refractive index profiles for the GIF625 and GIF50C fibers shortly.
dirk.lorenser  (posted 2011-09-01 22:15:52.0)
Hi I have GIF50C as well as GIF625 in our lab and I would like to know the refractive index profiles. I also need to know the diameter of the inner cladding (normally this is visible in refractive index profiles). Thanks.
jjurado  (posted 2011-07-06 09:41:00.0)
Response from Javier at Thorlabs to avle: Thank you very much for contacting us! I will send you plots of the refractive index for these fibers shortly.
avle  (posted 2011-07-05 19:17:53.0)
Hi there, Do you have the refractive index profiles available for GIF 50 and GIF 625 optical fibers? Thanks!
jjurado  (posted 2011-02-11 11:09:00.0)
Response from Javier at Thorlabs to last poster: Thank you very much for your feedback. The GIF50 and GIF625 fibers are doped with germanium in the core. This dopant raises the refractive index of the glass, which inherently slows down the speed of light traveling through the fiber. Also, trace amounts of phosphorous dopant are used to facilitate the deposition process in manufacturing.
user  (posted 2011-02-08 10:44:47.0)
Might be useful to spec the doping material used in this fiber.
klee  (posted 2009-12-07 18:40:50.0)
A response from Ken at Thorlabs to rajesh: The index profile was measured at 546nm. Unfortunately, the manufacturer cannot measure if at 488nm.
rajesh  (posted 2009-12-02 07:55:02.0)
The refractive index profiles are extremely useful. I have a couple of more questions regarding the refractive index profile of GIF625. Could you also mention the wavelength of light used for the measurement of the profile. I am interested to use the fibre at a wavelength of 488nm or close to 488nm. Could you kindly provide the index profiles at or close to 488nm. Regards, Rajesh
Tyler  (posted 2009-01-26 08:20:29.0)
A response from Tyler at Thorlabs to shalin: I forwarded your request to the technical support department last week. At which time, they informed me that your request was approved and that they would be contacting you for shipping information. I hope that these fiber samples help you in your research and if we can be of further assistance, please let us know.
shalin  (posted 2009-01-21 04:11:50.0)
Hello, I am from National University of Singapore. Could you please provide us a small length of GIF50 and GIF625 as a sample? Thanks, Shalin (Graduate Student, Optical Bioimaging Lab).
chenav  (posted 2008-12-16 12:55:34.0)
Hello, We are looking to purchase a spool of multi-mode, graded-index fiber for working at 532nm. We are especially interested in fibers with an allowed bending radius as low as possible. Please recommend which of your products would be best fit and add details on their bending radii. Regards, Chen Avinadav Rafael Ltd.
Laurie  (posted 2008-09-17 14:07:23.0)
Response from Laurie at Thorlabs to hclee2: Thank you for our interest in our graded-index fiber. Someone from our technical support staff with be contacting you shortly with the requested information. In addition, we will add to the web information concerning the index of refraction as a function of radial distance in the very near future.
hclee2  (posted 2008-09-15 10:29:48.0)
Hi, I am interesting if you could provide the approximate refractive index distribution between n1, ng and n2 versus cross section distance. This informaion would be helpful for running this GIF in the simulation model to determine the appropriate length. Therefore, if there is any advanced infomation, please email to me. Thanks
Laurie  (posted 2008-07-09 08:55:22.0)
Response from Laurie at Thorlabs to wblee21: The GIF625HT will not work for the 200 - 800 nm wavelength range, but we have a new fiber that will be available soon (HPSC10) that covers the wavelength range from 280 to 750 nm. Unlike the GIF625HT, this new fiber will be a step-index fiber instead of a graded-index fiber.
wblee21  (posted 2008-07-09 03:20:49.0)
Can I use this GIF625HT for 200nm - 800nm also even if you mention this product operating wavelength 800-1350nm

Thorlabs offers multimode bare optical fiber with silica, zirconium fluoride (ZrF4), or indium fluoride (InF3) cores. The table below details all of Thorlabs' multimode bare optical fiber offerings. Attenuation plots can be found by clicking the graph icons in the column to the right.

Index Profile NA Fiber Type Item # Core Size Wavelength Range Attenuation
(Click for Graph)
Step Index 0.100 Enhanced Coating
View These Fibers
FG010LDA Ø10 µm 400 to 550 nm and 700 to 1000 nm
FG025LJA Ø25 µm 400 to 550 nm and 700 to 1400 nm
FG105LVA Ø105 µm 400 to 2100 nm
(Low OH)
0.22 Standard Glass-Clad Silica
View These Fibers
FG050UGA Ø50 µm 250 to 1200 nm
(High OH)
FG105UCA Ø105 µm
FG200UEA Ø200 µm
FG400UEA Ø400 µm
FG600UEA Ø600 µm
FG1000UEA Ø1000 µm
FG050LGA Ø50 µm 400 to 2400 nm
(Low OH)
FG105LCA Ø105 µm
FG200LEA Ø200 µm
FG400LEA Ø400 µm
FG600LEA Ø600 µm
FG1000LEA Ø1000 µm
Polyimide Coating
View These Fibers
FG200UEP Ø200 µm 250 to 1200 nm
(High OH)
FG400UEP Ø400 µm
FG200LEP Ø200 µm 400 to 2400 nm
(Low OH)
FG400LEP Ø400 µm
Solarization Resistant for UV Use
View These Fibers
FG105ACA Ø105 µm 180 to 1200 nm
Acrylate Coating
for Ease of Handling
FG200AEA Ø200 µm
FG300AEA Ø300 µm
FG400AEA Ø400 µm
FG600AEA Ø600 µm
UM22-100 Ø100 µm 180 to 850 nm
Polyimide Coating
for Use up to 300 °C
UM22-200 Ø200 µm
UM22-300 Ø300 µm
UM22-400 Ø400 µm
UM22-600 Ø600 µm
High Power Double TECS /
Fluorine-Doped Silica Cladding,
View These Fibers
FG200UCC Ø200 µm 250 to 1200 nm
(High OH)
FG273UEC Ø273 µm
FG365UEC Ø365 µm
FG550UEC Ø550 µm
FG910UEC Ø910 µm
FG200LCC Ø200 µm 400 to 2200 nm
(Low OH)
FG273LEC Ø273 µm
FG365LEC Ø365 µm
FG550LEC Ø550 µm
FG910LEC Ø910 µm
0.39 High Power TECS Cladding
View These Fibers
FT200UMT Ø200 µm 300 to 1200 nm
(High OH)
FT300UMT Ø300 µm
FT400UMT Ø400 µm
FT600UMT Ø600 µm
FT800UMT Ø800 µm
FT1000UMT Ø1000 µm
FT1500UMT Ø1500 µm
FT200EMT Ø200 µm 400 to 2200 nm
(Low OH)
FT300EMT Ø300 µm
FT400EMT Ø400 µm
FT600EMT Ø600 µm
FT800EMT Ø800 µm
FT1000EMT Ø1000 µm
FT1500EMT Ø1500 µm
0.50 Hard Polymer Cladding
View These Fibers
FP200URT Ø200 µm 300 to 1200 nm
(High OH)
FP400URT Ø400 µm
FP600URT Ø600 µm
Ø1000 µm
FP1500URT Ø1500 µm
FP200ERT Ø200 µm 400 to 2200 nm
(Low OH)
FP400ERT Ø400 µm
FP600ERT Ø600 µm
FP1000ERT Ø1000 µm
FP1500ERT Ø1500 µm
0.20 Zirconium Fluoride (ZrF4) Core for Mid-IR
View These Fibers
Various Sizes Between
Ø100 µm and Ø600 µm
285 nm to 4.5 µm
0.26 Indium Fluoride (InF3) Core for Mid-IR
View These Fibers
Ø100 µm 310 nm to 5.5 µm
Graded Index 0.20 Graded Index for Low Bend Loss
View These Fibers
GIF50C Ø50 µm 800 to 1600 nm
0.275 GIF625 Ø62.5 µm 800 to 1600 nm
Back to Top

Ø50 µm Core / Ø125 µm Cladding Fiber

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
GIF50C Support Documentation
GIF50CGraded-Index Multimode Fiber, Ø50 µm Core / Ø125 µm Cladding, OM2 , 0.200 NA
Per Meter
Volume Pricing
GIF50D Support Documentation
GIF50DGraded-Index Multimode Fiber, Ø50 µm Core / Ø125 µm Cladding, OM3, 0.200 NA
Per Meter
Volume Pricing
GIF50E Support Documentation
GIF50EGraded-Index Multimode Fiber, Ø50 µm Core / Ø125 µm Cladding, OM4, 0.200 NA
Per Meter
Volume Pricing

* Orders for in-stock bare fiber placed by 3:00 PM ET are eligible for same-day shipment.

Back to Top

Ø62.5 µm Core / Ø125 µm Cladding Fiber

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
GIF625 Support Documentation
GIF625Graded-Index Multimode Fiber, Ø62.5 µm Core / Ø125 µm Cladding, OM1, 0.275 NA
Per Meter
Volume Pricing
GIF625-100 Support Documentation
GIF625-100Graded-Index Multimode Fiber, Ø62.5 µm Core / Ø125 µm Cladding, OM1, 0.275 NA, 100 Meters
GIF625-1000 Support Documentation
GIF625-1000Graded-Index Multimode Fiber, Ø62.5 µm Core / Ø125 µm Cladding, OM1, 0.275 NA, 1000 Meters

* Orders for in-stock bare fiber placed by 3:00 PM ET are eligible for same-day shipment.