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Fiber Optic Isolators

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Fiber Optic Isolators

Isolator TypeFiber Type
Polarization-Independent*SM Fiber
Polarization-DependentPM Fiber

*Units with PM Fiber use PANDA-type PM fiber with a core-cladding size of 7/125/400 µm. All other isolators have fiber with 250 µm outer coating.


  • Minimize Feedback into Optical Systems
  • Wavelength Ranges from 770 to 2010 nm
  • Polarization Independent and Dependent Versions
  • Available With or Without Connectors
  • Minimum 1 m Length of Fiber per side of each Isolator
Drawing of Forward Direction Through an Isolator
Drawing of Forward Direction Through an Isolator

Isolator Schematic - For more information on the properties and function of isolators, please see the Isolator Tutorial tab.

Fiber isolators protect laser sources from back reflections and signals that can cause instabilities and damage to fiber coupled laser sources. An isolator is an optical device that allows light propagating in the forward direction to be transmitted, while absorbing or displacing light propagating in the reverse direction (see schematic above). Fiber isolators are available in both polarization-dependent and polarization-independent models throughout the 770 to 2010 nm wavelength range. High power fiber isolators are built using a specialized fiber end face process to increase power handling capabilities. A minimum of 1 m of fiber is included on both sides of each fiber isolator.

If you do not see an isolator that suits your application, please see the Non-Stock Isolators tab or contact Tech Support.

When choosing an isolator, operating power and wavelength are the two most important factors. Isolators for use below 3 W and with wavelengths longer than 1250 nm use a Bismuth Iron Garnet (BIG) rotator. For shorter wavelengths and the same power levels, Terbium-Gallium Garnet (TGG) rotators are typically employed. These rotators have a much lower Verdet constant than BIG rotators and require the use of magnets that are orders of magnitude larger. High power isolators, which are designed for maxiumum powers of 50 W (depending on model), use non-absorptive crystal polarizers and crystal Faraday rotators. Unless otherwise noted, the specifications below are valid at room temperature (23 - 25 °C).

Item #WavelengthaMax
780 - 850 nm Polarization-Independent Fiber Isolators (2 W)
IO-F-780780 ± 10 nm2 W (CW)30 - 38 dB1.0 - 1.6 dB≤0.25 dB->50 dB780HP
IO-F-850850 ± 10 nm2 W (CW)30 - 38 dB1.0 - 1.6 dB≤0.25 dB->50 dB780HP
980 nm Polarization-Independent Fiber Isolators (2 W)
IO-F-980980 ± 10 nm2 W (CW)33 - 38 dB0.7 - 1.2 dB≤0.2 dB->50 dBHI1060
980 nm Polarization-Dependent Fiber Isolators (3 W)
IO-J-980980 ± 10 nm3 W (CW)30 - 38 dB0.8 - 1.6 dB->20 dB>50 dBPM 980/1064
1064 nm Polarization-Independent Fiber Isolators (250 mW - 50 W)
IO-H-10641064 +20/-4 nm250 mW≥33 dBc1.4 - 2.0 dB≤0.20 dB->55 dBHI1060
IO-F-10641064 ±10 nm3 W (CW)33 - 38 dB0.7 - 1.3 dB≤0.15 dB->50 dBHI1060
IO-K-10641064 ± 10 nm10 W (CW)30 - 36 dB0.8 - 1.5 dB≤0.25 dB->50 dBHI1060
IOK-1064-LMA25-CRED1064 ± 10 nm50 W (CW)>30 dB<0.45 dB≤0.2 dB->50 dBLMA25
1064 Polarization-Dependent Fiber Isolators (3 W)
IO-G-10641064 ± 5 nm≤300 mW (CW)≥35 dB≤1.8 dB-≥20 dB≥50 dBFujikura SM98-PS-U25A
IO-J-10641064 ± 10 nm3 W (CW)32 - 38 dB0.6 - 1.3 dB->20 dB>50 dBPM 980/1064
IOT-J-1064-95B1064 ± 4 nm3 W (CW)42 - 47 dB1.0 - 1.7 dB->20 dB>50 dBSM98-PS-U40A-H
1310 nm Polarization-Independent Fiber Isolators (300 mW)
IO-H-13101310 ± 15 nm300 mW35 - 40 dB0.3 - 0.7 dB≤0.1 dB->55 dBSMF-28e
1310 nm Polarization-Dependent Fiber Isolators (300 mW)
IO-G-13101310 ± 20 nm≤300 mW (CW)≥28 dB≤0.55 dB-≥20 dB>55 dBFujikura SM13-PS-U25A
1550 nm Polarization-Independent Fiber Isolators (300 mW - 5 W)
IO-H-15501550 ± 15 nm300 mW35 - 40 dB0.3 - 0.7 dB≤0.1 dB->55 dBSMF-28e
IO-F-15501550 ± 20 nm5 W (CW)32 - 38 dB0.4 - 1.0 dB≤0.2 dB->55 dBSMF-28e
IO-K-15501550 ± 20 nm10 W (CW)30 - 38 dB0.8 - 1.5 dB≤0.25 dB->55 dBSMF-28e
1550 nm Polarization-Dependent Fiber Isolators (300mW or 5 W)
IO-G-15501550 ± 20 nm≤300 mW (CW)≥28 dB≤0.55 dB->20 dB>55 dBFujikura SM15-PS-U25A
IO-J-15501550 ± 20 nm5 W (CW)32 - 38 dB0.4 - 1.0 dB->20 dB>55 dBPM 1500
2000 nm Polarization-Independent Fiber Isolators (3 - 10 W)
IO-F-20002000 ± 10 nm3 W (CW)≥25 dB0.8 - 1.2 dB≤0.2 dB->50 dBSM2000
IO-K-20002000 ± 10 nm10 W (CW)≥25 dB1.4 - 1.6 dB≤0.2 dB->50 dBSM2000
2000 nm Polarization-Dependent Fiber Isolators (3 - 10 W)
IO-J-20002000 ± 10 nm3 W (CW)≥25 dB0.8 - 1.2 dB->18 dB>50 dBPM15-U40Ad
IO-L-20002000 ± 10 nm10 W (CW)≥25 dB1.4 - 1.6 dB->18 dB>50 dBPM2000

a For specified isolation, the IL specification is valid over double the wavelength range listed
b Polarization Extinction Ratio
c Specified at 1064 nm
d This fiber is not manufactured by Thorlabs

Optical Isolator Tutorial

An optical isolator is a passive magneto-optic device that only allows light to travel in one direction. Isolators are used to protect a source from back reflections or signals that may occur after the isolator. Back reflections can damage a laser source or cause it to mode hop, amplitude modulate, or frequency shift. In high-power applications, back reflections can cause instabilities and power spikes.

An isolator’s function is based on the Faraday Effect. In 1842, Michael Faraday discovered that the plane of polarized light rotates while transmitting through glass (or other materials) that is exposed to a magnetic field. The direction of rotation is dependent on the direction of the magnetic field and not on the direction of light propagation; thus, the rotation is non-reciprocal. The amount of rotation Q equals V x L x H, where V, L, and H are as defined below.

Faraday Effect in an Isolator Drawing
Figure 1

Faraday Rotation

Q = V x L x H

V: the Verdet Constant, a property of the optical material, in minutes/Oersted-cm.

L: the path length through the optical material in cm.

H: the magnetic field strength in Oersted.

An optical isolator consists of an input polarizer, a Faraday rotator with magnet, and an output polarizer. The input polarizer works as a filter to allow only linearly polarized light into the Faraday rotator. The Faraday element rotates the input light's polarization by 45°, after which it exits through another linear polarizer. The output light is now rotated by 45° with respect to the input signal. In the reverse direction, the Faraday rotator continues to rotate the light's polarization in the same direction that it did in the forward direction so that the polarization of the light is now rotated 90° with respect to the input signal. This light's polarization is now perpendicular to the transmission axis of the input polarizer, and as a result, the energy is either reflected or absorbed depending on the type of polarizer.

Drawing of Light Propagation Through an Isolator
Figure 2. A polarization-dependent isolator. Light propagating in the reverse direction is rejected by the input polarizer.

Polarization-Dependent Isolators

The Forward Mode
In this example, we will assume that the input polarizer's axis is vertical (0° in Figure 2). Laser light, either polarized or unpolarized, enters the input polarizer and becomes vertically polarized. The Faraday rotator will rotate the plane of polarization (POP) by 45° in the positive direction. Finally, the light exits through the output polarizer which has its axis at 45°. Therefore, the light leaves the isolator with a POP of 45°.

The Reverse Mode
Light traveling backwards through the isolator will first enter the output polarizer, which polarizes the light at 45° with respect to the input polarizer. It then passes through the Faraday rotator rod, and the POP is rotated another 45° in the positive direction. This results in a net rotation of 90° with respect to the input polarizer, and thus, the POP is now perpendicular to the transmission axis of the input polarizer. Hence, the light will either be reflected or absorbed.

Polarization-Independent Fiber Isolators

The Forward Mode
In a polarization independent fiber isolator, the incoming light is split into two branches by a birefringent crystal (see Figure 3). A Faraday rotator and a half-wave plate rotate the polarization of each branch before they encounter a second birefringent crystal aligned to recombine the two beams.

Light Propagation Through a Polarization-Independent IsolatorClick for Details
Figure 3. A polarization independent isolator. Light is deflected away from the input path and stopped by the housing.

The Reverse Mode
Back-reflected light will encounter the second birefringent crystal and be split into two beams with their polarizations aligned with the forward mode light. The half wave plate is a non-reciprocal rotator, so it will cancel out the rotation introduced by the faraday rotator for the reverse mode light. When the light encounters the input birefringent beam displacer, it will be deflected away from the collimating lens and into the walls of the isolator housing, preventing the reverse mode from entering the input fiber.

General Information

Damage Threshold
With 25 years of experience and 5 U.S. patents, our isolators typically have higher transmission and isolation than other isolators, and are smaller than other units of equivalent aperture. For visible to YAG laser Isolators, Thorlabs' Faraday Rotator crystal of choice is TGG (terbium-gallium-garnet), which is unsurpassed in terms of optical quality, Verdet constant, and resistance to high laser power. Thorlabs' TGG Isolator rods have been damage tested to 22.5 J/cm2 at 1064 nm in 15 ns pulses (1.5 GW/cm2), and to 20 kW/cm2 CW. However, Thorlabs does not bear responsibility for laser power damage that is attributed to hot spots in the beam.

The magnet is a major factor in determining the size and performance of an isolator. The ultimate size of the magnet is not simply determined by magnetic field strength but is also influenced by the mechanical design. Many Thorlabs magnets are not simple one piece magnets but are complex assemblies. Thorlabs' modeling systems allow optimization of the many parameters that affect size, optical path length, total rotation, and field uniformity. Thorlabs' US Patent 4,856,878 describes one such design that is used in several of the larger aperture isolators for YAG lasers. Thorlabs emphasizes that a powerful magnetic field exists around these Isolators, and thus, steel or magnetic objects should not be brought closer than 5 cm.

The magnets and the Faraday rotator materials both exhibit a temperature dependence. Both the magnetic field strength and the Verdet Constant decrease with increased temperature. For operation greater than ±10 °C beyond room temperature, please contact Technical Support.

Dispersion Measurement of Isolator IS-5-780-HP
Figure 4

Pulse Dispersion

Pulse broadening occurs anytime a pulse propagates through a material with an index of refraction greater than 1. This dispersion increases inversely with the pulse width and therefore can become significant in ultrafast lasers.

τ: Pulse Width Before Isolator

τ(z): Pulse Width After Isolator

t = 197 fs results in t(z) = 306 fs (pictured to the right)
t = 120 fs results in t(z) = 186 fs

OEM and Non-standard Isolators

In an effort to provide the best possible service to our customers we have made a commitment to ship our most popular free-space isolator and fiber isolator models from stock. Currently we offer more than 50 isolators models with same day shipping. We also offer isolators with different apertures, wavelengths, package sizes, and polarizers. These non-stock units are usually priced the same as a similar stock units with only a 2 to 3 week lead time.

Thorlabs has many years of experience working with OEM customers and we are able to tailor an isolator to meet specific design requirements that challenge other manufacturers. In addition to customizing our isolators, we also offer various application services.  Below is a sample list of the services we can offer.

OEM Application Services

  • Direct Integration to Laser Head Assemblies
  • Combination Isolator and Fiber Coupling Units
  • Minimum Footprint Packages
  • Filter Integration
  • Feedback Monitoring
  • Private Labeling

Free-Space Isolators

We are able to provide a wide range of flexibility in manufacturing non-stock free-space isolators. Almost any combination of specifications from our standard product line can be made to suit our customers needs. The table below shows the range of specification we can cover.

Wavelength RangeFrom 248 nm to 10 µm
Apertures Sizes Up to Ø15 mm
Polarization DependanceDependent or Independent
Max PowerUp to 2 GW/cm2

We also can offer narrow and broadband performance options. Our housing size is very dependent on the desired power and aperture size desired, so please include a note in the quote form below if you have special requirements.

Fiber Isolators

The fiber isolator market is a rapidly changing field. Thorlabs is uniquely positioned to draw on experience in classical optics, fiber coupling, and isolators to bring a total solution to the fiber-isolator market.

We are able to provide the flexible designs covering a wide range of specifications. We are focusing our design efforts in increasing the maximum power of our fiber isolators in the 1064 nm range. We are also able to offer models with integrated ASE filters and taps. The table below highlights the parameter ranges we are able to offer.

Wavelength RangeFrom 780 nm to 1580 nm
Polarization DependanceDependent or Independent
Max Power10 W
Max Power for 1030 to 1080 nm30 W

The fiber used is often the limiting factor in determining the maximum power the isolator can handle. For the OEM, research, and Government markets we have experience working with standard single mode, multimode, polarization maintaining fibers (PM); single, double and triple clad fibers; as well as speciality fibers like: 10 to 30 µm LMA fibers and PM LMA fibers.

Company Information

In an effort to provide the best possible service to our customers, we have made a commitment to ship our most popular free-space and fiber isolator models from stock. There are now more than 50 isolator models available with same day shipping.

Please contact us at 973-300-3000 for more information. If you would like a quote a non-stock isolator, please fill out the form below and a member of our staff will be in contact with you. We are ready to assist you in selecting a product for you application.

Non-Stock Isolator Worksheet:
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Fiber Connector: FC/PC   |  FC/APC   |  Other
Output: Fiber   |  Free-Space

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Posted Comments:
Poster: dominic.siriani
Posted Date: 2012-03-26 17:17:45.0
Could you please provide the total packaged weight of the 1064nm isolator IO-F-1064?
Poster: bdada
Posted Date: 2011-08-22 16:06:00.0
Response from Buki at Thorlabs: The fiber in the IOK-1064-LMA25-CRED fiber isolator is a Nufern fiber, FUD-3440 fiber MM-GDF-25/250-11FA. It is a 25/250 fiber with 0.11NA. The output beam is collimated and is 0.9 – 1.1mm diameter at ~2cm from the output end of the isolator box.
Poster: alex.v.andrianov
Posted Date: 2011-08-22 12:18:13.0
Could you please provide more detailed information on the LMA fiber in the isolator IOK-1064-LMA25-CRED (core NA, clad diameter, or refernce to the manufacturers datasheet)? Also I would like to know the output beam diameter.
Poster: bdada
Posted Date: 2011-07-26 18:28:00.0
Response from Buki at Thorlabs: The PI (polarization independent) isolators use a birefringent polarizing element, Faraday rotator, 1/2 wave retarder. The polarization is split into the component S and P components which propagate through and are recombined. Because of the Faraday rotating element the returned energy takes a different beam path and will not couple back into the fiber. Any input polarization state can be put into the isolator with no effect on performance.
Poster: bmills
Posted Date: 2011-07-26 16:40:49.0
How do polarization insensitive isolators work? Do they need a pure linear polarization on the input or can they handle some circularity?
Poster: jjurado
Posted Date: 2011-07-18 15:36:00.0
Response from Javier at Thorlabs to seydi: The wavelength-dependent change in isolation varies from model to model. If the isolator is the low power IO-H-1064 type made with a BIG film rotator, then the transmission at 1030nm will be low in the 50% range. If the isolator is a higher power handling type such as the IO-F, IO-J, IO-L, IO-K type then the rotator is TGG and the transmission will be excellent. The calculated Isolation value in either case will be in the mid 20dB range ~23-26dB. I will contact you directly for further assistance.
Poster: seydi
Posted Date: 2011-07-18 10:53:30.0
Im using 1064nm low power isolator, but I want to learn the isolation value and effects on spectrum at 1030nm. Is it possible to inform me about this issue as soon as possible? Thanks..
Poster: jjurado
Posted Date: 2011-03-17 11:13:00.0
Response from Javier at Thorlabs to last poster: Thank you for contacting us. The specifications for our fiber-coupled isolators are rated at 23-25°C. Please contact us at if you have any further questions.
Posted Date: 2011-03-17 08:50:49.0
At what temperature, are the specifications rated?
Poster: Thorlabs
Posted Date: 2010-08-17 17:43:33.0
Response from Javier at Thorlabs to last poster: Thank you for your feedback. The typical fiber lengths range from 1.5 m to 2.0 m. We will update this information on the web.
Posted Date: 2010-08-17 01:42:04.0
Do you have any reason to hide fiber length for your inline isolators? typically 1m, right?
Poster: jens
Posted Date: 2009-06-11 08:46:52.0
A reply from Jens at Thorlabs: Mike, this is indeed confusing. The data sheet for the PM980 should have been included. I will have the correct data sheet send to you.
Poster: jens
Posted Date: 2009-05-13 18:44:55.0
A response from Jens at Thorlabs: Yes, the connector style is indeed FC/APC, the FC is often skipped in the description. I tried to find the drop down menu you mentioned but could only think of the shortcuts which come up when typing in a search. Is that where you were missing the part? I just tried and the item shows up here, so not sure if you were referring to another place on the web page. Thanks a lot.
Poster: bmcpherson
Posted Date: 2009-05-13 18:36:06.0
IO-H-1550APC was not listed in the drop down menu. Is the APC connector an FC/APC style connector? Thanks
Poster: Laurie
Posted Date: 2008-10-17 08:57:05.0
Response from Laurie at Thorlabs to hiepvv: Thank you for your interest in our isolators. I will forward your request to our sales department. Someone should be contacting you shortly to provide the requested quotation.
Poster: hiepvv
Posted Date: 2008-10-17 01:50:58.0
Dear Sir. I would like to purchase the optical isolator 1550nm.(Type:IO-H-1550 Qty:2pcs) Could you please send me the official quotaion. Thank and best regards Vo Van Hiep
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