Our Adjustable Narrowband Isolators can be tuned to maximize the peak isolation for any wavelength within a narrow spectral range (shaded in this graph). See the Wavelength Tuning tab for more details. Click to Enlarge
Custom Isolators Available (See Custom Isolators Tab)
Thorlabs is pleased to stock a variety of free-space optical isolators designed for use in the visible spectral range (395 - 690 nm). Optical isolators, also known as Faraday isolators, are magneto-optic devices that preferentially transmit light along a single direction, shielding upstream optics from back reflections. Back reflections can create a number of instabilities in light sources, including intensity noise, frequency shifts, mode hopping, and loss of mode lock. In addition, intense back-reflected light can permanently damage optics. Please see the Isolator Tutorial tab for an explanation of the operating principles of a Faraday isolator.
In the visible wavelength range, we offer three types of isolators. The first type, Fixed Narrowband Isolators, contains fixed, factory-aligned optics, for which peak isolation and peak transmission occurs at a pre-defined center wavelength. Any deviation from this wavelength will cause a dip in isolation and transmission. The second type, Adjustable Narrowband Isolators, offers the user the ability to adjust the alignment of the input and output polarizers, allowing tuning of the center wavelength within a 20 - 40 nm range, depending upon the exact isolator. The third type, Tandem Narrowband Isolators, consists of two Faraday rotators in series, boosting the isolation to at least 55 dB at the expense of lower transmission. Please see the Isolator Types tab for additional design details and representative graphs of the wavelength-dependent isolation.
Each isolator's housing is marked with an arrow that indicates the direction of forward propagation. In addition, all isolators have engravings that indicate the alignment of the input and output polarizers.
Thorlabs also manufactures isolators for fiber optic systems and wavelengths extending into the infrared (see the Selection Guide table to the right). If Thorlabs does not stock an isolator suited for your application, please refer to our Custom Isolators page for information on our build-to-order options, or contact Tech Support. Thorlabs' in-house manufacturing service has over 25 years of experience and can deliver a free-space isolator tuned to your center wavelength (from 244 - 2800 nm).
Shaded regions on a graph represent the center wavelength tuning range of the isolator. With these isolators, the isolation and transmission curves will shift as the center wavelength shifts. If the graph is not shaded, then the isolator is non-tunable. Please note that these curves were made from theoretical data and that isolation and transmission will vary from unit to unit.
Optimize Our Isolators to Provide the Same Peak Isolation Anywhere Within Their Tuning Range
Simple Tuning Procedure, Illustrated Below, Consists Primarily of Rotating the Output Polarizer
Slight Transmission Losses Occur Due to Polarizer Rotation
When the isolator is tuned away from its design wavelength, the maximum transmission falls because the output polarizer's transmission axis is not parallel to the polarization direction of the output light. Click to Enlarge
Our Adjustable Narrowband Isolators can be tuned to maximize the peak isolation for any wavelength within a narrow spectral range (shaded in this graph). Click to Enlarge
Light Not at the Design Wavelength is Partially Transmitted Click to Enlarge
Operating Principles of Optical Isolators Thorlabs' Adjustable Narrowband Isolators are designed to provide the same peak isolation anywhere within a 20 - 40 nm tuning range. They contain a Faraday rotator that has been factory tuned to rotate light of the design wavelength by 45°. Light propagating through the isolator in the backward direction is polarized at 45° by the output polarizer and is rotated by 45° by the Faraday rotator, giving a net polarization of 90° relative to the transmission axis of the input polarizer. Therefore, an isolator rejects backward propagating light. See the Isolator Tutorial tab for a schematic of the beam path.
The magnitude of the rotation caused by the Faraday rotator is wavelength dependent. This means that light with a different wavelength than the design wavelength will not be rotated at exactly 45°. For example, if 670 nm light is rotated by 45° (that is, 670 nm is the design wavelength), then 660 nm light is rotated by 46.5°. If 660 nm light is sent backward through an isolator designed for 670 nm without any tweaking, it will have a net polarization of 45° + 46.5° = 91.5° relative to the axis of the input polarizer. The polarization component of the light parallel to the input polarizer's axis will be transmitted, and the isolation will therefore be significantly reduced.
Since the net polarization needs to be 90° to obtain high isolation, the output polarizer is rotated to compensate for the extra rotation being caused by the Faraday isolator. In our example, the new polarizer angle is 90° - 46.5° = 43.5°. This adjustment increases the isolation back to the same value as at the design wavelength.
Consequences of Wavelength Tuning Procedure However, as a direct consequence of rotating the output polarizer, the maximum transmission in the forward direction decreases. 660 nm light propagating in the forward direction is polarized at 0° by the input polarizer and rotated by 46.5° by the Faraday rotator, but the output polarizer is now at 43.5°. The amount of the transmission decrease can be quantified using Malus' Law:
Malus' Law
Here, θ is the angle between the polarization direction of the light after the Faraday rotator and the transmission axis of the polarizer, I0 is the incident intensity, and I is the transmitted intensity. For small deviations from the center wavelength, the decrease in transmission is very slight, but for larger deviations, the decrease becomes noticeable. In our example (a 10 nm difference between the design wavelength and the usage wavelength), θ = 46.5° - 43.5° = 3.0°, so I = 0.997 I0. This case is shown in the graphs above.
In applications, the decrease in transmission caused by the tuning procedure is usually less important than the significantly enhanced isolation gained by tuning. For example, if the 670 nm isolator shown in the graphs above were used at 650 nm without tuning, the transmission would be 88.7% (instead of 88.0%), but the isolation would be only 25 dB (instead of 40 dB). This case is also shown in the graphs above.
Thorlabs' isolator housings make it easy to rotate the output polarizer without disturbing the rest of the isolator. Our custom isolator manufacturing service (see the Non-Stock Isolators tab) can also provide an isolator specifically designed for a particular center wavelength, which can eliminate or strongly mitigate the transmission losses that occur at the edges of the tuning range. These custom isolators are provided at the same cost as their equivalent stock counterparts. For more information, please contact Technical Support.
Illustrated Tuning Procedure
To optimize the isolation curve for a specific wavelength within the tuning range, the alignment of the output polarizer may be tweaked following the simple procedure outlined below. Only a minor adjustment is necessary to cover a range of several nanometers. The procedure differs slightly for different isolator packages, but the principle remains the same across our entire isolator family, and complete model-specific tuning instructions ship with each isolator.
Step 1: Orient the isolator in the backward direction with respect to the beam (i.e., with the arrow pointing antiparallel to the beam propagation direction). A power meter with high sensitivity at low power levels should be placed after the isolator.
Use the included 5/64" hex key to loosen the isolator from its saddle.
Step 2: Grip the isolator by the sides and gently bring it out of its saddle. It is only necessary to bring it out far enough to expose the 8-32 setscrew at the top, as shown in the photo to the left.
Step 3: Use the included 5/64" hex key to tighten the isolator back into its saddle with the 8-32 setscrew exposed.
The isolator is mechanically stable in this position as long as the isolator has not been brought forward too much. (The amount shown in the image to the left is safe by several millimeters.) It should therefore not be necessary to reinsert the isolator at the end of the tuning procedure.
Step 5: Rotate the output polarizer to minimize the power on the power meter. Tighten the 8-32 setscrew once optimization is achieved.
As long as the isolator was not brought forward too much at the end of Step 2, the isolator will be mechanically stable in this position. Attempting to reinsert the isolator at this point may cause misalignment.
Fixed Narrowband Isolator
The isolator is set for 45° of rotation at the design wavelength. The polarizers are non-adjustable and are set to provide maximum isolation at the design wavelength. As the wavelength changes the isolation will drop; the graph shows a representative profile.
Fixed Rotator Element, Fixed Polarizers
Polarization Dependent
Smallest and Least Expensive Isolator Type
No Tuning
Adjustable Narrowband Isolator
The isolator is set for 45° of rotation at the design wavelength. If the usage wavelength changes, the Faraday rotation will change, thereby decreasing the isolation. To regain maximum isolation, the output polarizer can be rotated to "re-center" the Gaussian isolation curve. This rotation causes transmission losses in the forward direction that increase as the difference between the usage wavelength and the design wavelength grows.
Fixed Rotator Element, Adjustable Polarizers
Polarization Dependent
General-Purpose Isolator
Adjustable Broadband Isolator
The isolator is set for 45° of rotation at the design wavelength. There is a tuning ring on the isolator that adjusts the amount of Faraday rotator material that is inserted into the internal magnet. As your usage wavelength changes, the Faraday rotation will change, thereby decreasing the isolation. To regain maximum isolation, the tuning ring is adjusted to produce the 45° of rotation necessary for maximum isolation.
Adjustable Rotator Element, Fixed Polarizers
Polarization Dependent
Simple Tuning Procedure
Broader Tuning Range than Adjustable Narrowband Isolators
Fixed Broadband Isolator
A 45° Faraday rotator is coupled with a 45° crystal quartz rotator to produce a combined 90° rotation on the output. The wavelength dependences of the two rotator materials work together to produce a flat-top isolation profile. The isolator does not require any tuning or adjustment for operation within the designated design bandwidth.
Fixed Rotator Element, Fixed Polarizers
Polarization Dependent
Largest Isolation Bandwidth
No Tuning Required
Tandem Isolators
Tandem isolators consist of two Faraday rotators in series, which share one central polarizer. Since the two rotators cancel each other, the net rotation at the output is 0°. Our tandem designs yield narrowband isolators that may be fixed or adjustable.
Up to 60 dB Isolation
Polarization Dependent
Highest Isolation
Fixed or Adjustable
Polarizer Types, Sizes, and Power Limits
Thorlabs designs and manufactures several types of polarizers that are used across our family of optical isolators. Their design characteristics are detailed below. The suffix of the part number of a given isolator identifies the type of polarizer that isolator contains.
Polarizer Comparison
Type
Schematic (Click to Enlarge)
Maximum Power Density
Description
Very Low Power (VLP)
25 W/cm2 (CW)
Our Very Low Power Absorptive Film Polarizers are the most compact option.
Polarizing Beamsplitter (PBS)
50 W/cm2 (CW)
Polarizing Beamsplitter Cubes are commonly used in low-power applications and feature an escape window useful for monitoring or injection locking.
Low Power (LP)
250 W/cm2 (CW) 25 MW/cm2 (Pulsed)
Our Low Power Polarizers are Glan-type, crystal polarizers, providing high transmission and power densities at the expense of a larger package than VLP and PBS polarizers.
Medium Power (MP)
100 W/cm2 (CW) 50 MW/cm2 (Pulsed)
Medium Power Polarizers are Glan-type, crystal polarizers, capable of handling higher powers. The rejected beam is internally scattered, which reduces the maximum power density, but also eliminates a stray beam from the setup.
High Power (HP)
500 W/cm2 (CW) 150 MW/cm2 (Pulsed)
High Power Polarizers are Glan-type, crystal polarizers, similar in size and transmission to LP polarizers, but capable of handling higher powers. They feature an escape window suited for injection locking.
Very High Power (VHP)
20 kW/cm2 (CW) 2 GW/cm2 (Pulsed)
Our Very High Power Polarizers are based on Brewster windows and feature the highest power handling possible. These polarizers have larger packages than HP-based designs, but are also more economical.
Optical Isolator Tutorial
Function 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 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.
The Forward Mode Laser light, whether or not polarized, enters the input polarizer and becomes linearly polarized, say in the vertical plane (0°). It then enters the Faraday rotator rod, which rotates the plane of polarization (POP) by 45°. Finally, the light exits through the output polarizer whose axis is 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.
General Information
Damage Threshold Our isolators typically have higher transmittance and isolation compared to all other isolators on the market. Furthermore, because of certain proprietary features (covered by 25 years of experience and 5 U.S. patents), Thorlabs' isolators are smaller and have higher performance than any units of equivalent aperture available anywhere. 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.
Magnet 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.
Temperature 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.
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
Example: 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, Thorlabs has made a commitment to ship our most popular free-space and fiber isolator models from stock. We currently offer same-day shipping on more than 90 isolator models. In addition to these stock models, non-stock isolators with differing aperture sizes, wavelength ranges, package sizes, and polarizers are available. These generally have the same price as a similar stock unit. If you would like a quote on a non-stock isolator, please fill out the form below and a member of our staff will be in contact with you.
Thorlabs has many years of experience working with OEM, government, and research customers, allowing us to tailor to specific design requirements that best other manufacturers. In addition to customizing our isolators (see the OEM Application Services list to the right), we also offer various application services.
Parameter
Range
Wavelength Range
From 244 - 2800 nma
Aperture Sizes
Up to Ø15 mm
Polarization Dependence
Dependent or Independent
Max Power
Up to 2 GW/cm²
Isolation
Up to 60 dB (Tandem Units)
Rotator material, for use in the 244 to 5000 nm range, available separately.
Free-Space Isolators
We are able to provide a wide range of flexibility in manufacturing non-stock, free-space isolators. Almost any selection of specifications from our standard product line can be combined to suit a particular need. The table to the right shows the range of specifications that we can meet.
We offer isolators suitable for both narrowband and broadband applications. The size of the housing is very dependent on the desired max power and aperture size, so please include a note in the quote form below if you have special requirements.
We can also offer our Faraday rotator material for use at wavelengths from 244 to 5000 nm.
Parameter
Range
Wavelength Range
From 633 - 2050 nma
Polarization Dependence
Dependent or Independent
Max Power (Fiber to Free-Space)
30 W
Max Power (Fiber to Fiber)
20 W
For wavelengths down into the visible, we recommend using our free-space isolators in conjunction with our modular FiberBench accessories. Please contact Technical Support for more information.
Fiber Isolators
Thorlabs is uniquely positioned to draw on experience in classical optics, fiber coupling, and isolators to provide flexible designs for a wide range of fiber optic specifications. Current design efforts are focused on increasing the maximum power of our fiber isolators at and near the 1064 nm wavelength. We offer models with integrated ASE filters and taps. The table to the right highlights the range of specifications that we can meet.
The fiber used is often the limiting factor in determining the maximum power the isolator can handle. We have experience working with single mode (SM) and polarization-maintaining fibers (PM); single-, double- and triple-clad fibers; and specialty fibers like 10-to-30 µm LMA fibers and PM LMA fibers.
In the spectral region below 633 nm, we recommend mounting one of our free-space isolators in a FiberBench system. A FiberBench system consists of pre-designed modules that make it easy to use free-space optical elements with a fiber optic system while maintaining excellent coupling efficiency. We are also in the process of extending our fiber isolator capabilities down into the visible region. For more information, please contact Technical Support.
Contact Information
Please contact us for more information at (973) 300-3000 or by using the form below.
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Posted Comments:
Poster: tcohen
Posted Date: 2012-08-20 16:05:00.0
Response from Tim at Thorlabs: We do not display any contact information that is left when writing your feedback. This comes to us in a private message. Only comments left in the main box will be displayed publicly. If you would like us to remove your feedback entirely, please let us know at techsupport@thorlabs.com and we will take down your post at your request.
Poster: a.j.h.meskers
Posted Date: 2012-08-20 10:27:42.0
Dear Sir/Madam,
Could you please remove my contact information from the message below?
Kind regards,
Arjan Meskers
Poster: tholste
Posted Date: 2012-07-30 13:12:00.0
A response from Tor at Thorlabs to Arjan: Thank you very much for contacting us. We are happy to provide the rotator for many of our free-space isolators. We will be sending you a quotation shortly.
Poster: a.j.h.meskers
Posted Date: 2012-07-30 07:35:43.0
Dear Sir/Madam, I"m currently looking for a Faraday rotator without an input polarizer -I"m looking for only a Faraday rotator. Do you also make these available? If yes, what will one cost? I"m currently using a few IO-3D-633-VLP"s.
Poster: tcohen
Posted Date: 2012-04-20 14:04:00.0
Response from Tim at Thorlabs: The SM1B2 has a setscrew which secures the isolator in place. This adapter can be threaded onto an LMR1 as you mentioned. Alternatively, the adapter could be inserted into an SM30 lens tube and held in with two retaining rings, which may be more secure when shipping the assembled setup over long distances.
Poster:
Posted Date: 2012-04-19 15:10:24.0
SM1B2 doesnt have any locking feature, trying to secure it into a LMR1, please consider customers who have to ship thier assembled system to remote locations.
Poster: Thorlabs
Posted Date: 2010-10-21 00:32:43.0
Response from Javier at Thorlabs to Stefania: The IO-2D-633-VLP will still work at 660 nm; however, the amount of isolation will decrease by about 14 dB. We can offer an isolator aligned at 660 nm. I will contact you directly with more details.
Poster: sdante
Posted Date: 2010-10-20 11:06:33.0
Hi, Im using a laser diode ML101J27 and Id like to use an optical isolator to prevent backwards reflections and stabilize the optical cavity. Ive seen that IO-2D-633-VLP can work till 663 nm (spectra you supplied) and I would like to know if it is possible to correctly work at 660 nm with this device.
Thank you very much for your help,
Stefania
Poster: Thorlabs
Posted Date: 2010-08-25 11:55:56.0
Response frm Javier at Thorlabs to jht: Thank you for your feedback. We are currently working on updating all of the power specifications for the freespace isolators. There will be other changes to the webpage, as well. For the IO-5-1064-VHP, the power handling spec will be centered at around 15 kW/cm^2.
Poster: Thorlabs
Posted Date: 2010-08-25 11:26:49.0
Response from Javier at Thorlabs to lawrence.berg: Thank you for your feedback. You are correct, power specs are given for operation in blocking mode. If the polarized input is well aligned with the polarizers, you should be able to to slightly exceed the power specifications. We would recommend attenuating the beam, aligning the polarization input, and slowly increasing the power.
Poster: lawrence.berg
Posted Date: 2010-08-25 09:04:38.0
Maximum power rating of 25W/cm2 for the absorptive polarizer. Is this assuming the input beam is crossed relative to the input polarizer, so that the input polarizer is absorbing (nearly) everything? The high peak power rating makes me thinks so. If I am aligned with the input polarizer, can I exceed this number slightly?
Poster: jht
Posted Date: 2010-08-24 19:19:36.0
The units of your maximum intensity ratings are incorrect. The additional product information shows, for instance, that the maximum intensity is 680 kW/cm^2, whereas on this page it shows with "W/cm^2" as the unit. Could you check all the high power isolators listed? It would be helpful to see the correct ratings on the summary page.
Poster: Tyler
Posted Date: 2009-01-26 08:31:49.0
A response from Tyler to melsscal: I forwarded your request to the technical support department so that they can create a quote for you custom Faraday Isolator. However, they will first contact you for addition information such as aperture size, power requirements, body type, etc. Our optical isolator division can easily customize an optical isolator for almost any visible or IR wavelength and is adept at fulfilling custom requests with short lead times.
Poster: melsscal
Posted Date: 2009-01-21 02:46:50.0
We are looking for a faradya Isoloator at 493nm .Can you make one & quote for same ?
A.K.Bose
Poster: Tyler
Posted Date: 2008-08-05 11:16:51.0
A response from Tyler at Thorlabs to Viswa: A quote is being generated and will be sent to you shortly. Thank you for your interest in our optical isolators. If we can offer any further assistance, please let us know.
Poster: vnv
Posted Date: 2008-08-04 18:43:44.0
Hi, I am looking for an Optical Isolator with the following specification. I can send you a schematic of the pulse format of the laser as an attachment with an email.
Faraday Isolator 1:
Wavelength of operation = 1064 nm
Laser charecteristic (this is rather a complex laser) = It is a modelocked laser with ~1 nS
pulses, the laser works in 200 uSec bursts at 10% duty cycle and within these 200 uSec
bursts we generate modelocked pulses that are 1 nS. The max power (avg.) of the laser is 25
Watts
Faraday Isolator 2:
Wavelength of operation = 1319 nm Laser charecteristic: It is a modelocked laser with ~1 nS
pulses, the laser works in 200 uSec bursts at 10% duty cycle and within these 200 uSec
bursts we generate modelocked pulses that are 1 nS. The max power (avg.) of the laser is 20
Watts.
I am looking at your 5 mm and 8 mm isolators. Please advice with model #s and a quote.
Many thanks.
- With best regards,
Viswa
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Visible Free-Space Isolators
