Features

• Minimize Feedback into Optical Systems
• Operating Ranges of 1054 - 1074 nm or 1059 - 1069 nm
• At Least 0.8 m of SM Fiber on Both Sides
• Available with 2.0 mm Narrow Key FC/APC Connectors or Bare Ends
• Designed for CW Applications
• Each Unit is Individually Tested
• Fiber to Free-Space Option Available
• Custom Isolators Available (See Custom Isolators Tab)

Fiber isolators protect light sources from back reflections and signals that can cause intensity noise and optical damage. Optical isolators, also known as Faraday isolators, are magneto-optic devices that preferentially transmit light in the forward direction while absorbing or displacing light propagating in the reverse direction (see the schematic below). Please see the Isolator Tutorial tab for an explanation of the operating principles of a Faraday isolator.

Thorlabs' polarization-independent Nd:YAG isolators, sold on this page, are compatible with single mode (SM) fibers. In contrast, our polarization-dependent Nd:YAG isolators are designed to connect to polarization-maintaining (PM) fibers. Our high-power units are built using a specialized fiber end face process that increases the maximum power. A length of 0.8 m of fiber is built in to each side of the isolator, and an arrow on the body indicates the transmission direction. In addition, each unit is tested before shipment to ensure compliance with our specifications and a complete test report comes with every serialized part.

Thorlabs also manufactures free-space isolators and fiber isolators designed for the infrared range. Please use the Selection Guide table above for more information. If you do not see an isolator that suits your application, please refer to our Custom Isolators page for information on our build-to-order options, or contact Tech Support.

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 US 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 comparable stock unit, but with a 2- to 3-week lead time. 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. Below is a sample list of the services we can provide.

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.

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 770 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.

Please use the Non-Stock Isolator web form below to request a quotation for non-stock isolators.

Customer Information:

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Non-Stock Isolator Worksheet:

Please select your input type:   Free-Space Input   |   Fiber Input

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Free-Space Input Wavelength or Wavelength Range (nm): Power (W): Max 1/e2 Beam Diameter (mm): Isolation (dB): % Transmission: Notes: Required Fields Fiber Input Wavelength or Wavelength Range (nm): Power (W): Polarization Sensitivity: Dependent  |  Independent Isolation (dB): % Transmission: Fiber: Fiber Connector: FC/PC   |  FC/APC   |  Other Output: Fiber   |  Free-Space Notes: Required Fields