4.45 µm light propagating in the forward direction is polarized at 0° by the input polarizer and rotated by 45.4° by the Faraday rotator, but the output polarizer is now at 44.6°. This adjustment increases the isolation back to the same value as at the design wavelength.Ĭonsequences of Wavelength Tuning ProcedureĪs a direct consequence of rotating the output polarizer, the maximum transmission in the forward direction decreases. In our example, the new polarizer angle is 90° - 45.4° = 44.6°. Since the net polarization needs to be 90° to obtain the maximum isolation, the output polarizer is rotated to compensate for the extra rotation being caused by the Faraday isolator. The polarization component of the light parallel to the input polarizer's axis will be transmitted, and the isolation will therefore be reduced. If 4.45 µm light is sent backward through an isolator designed for 4.5 µm without any tweaking, it will have a net polarization of 45° + 45.4° = 90.4° relative to the axis of the input polarizer. For example, if 4.5 µm light is rotated by 45° (that is, 4.5 µm is the design wavelength), then 4.45 µm light is rotated by 45.4°. This means that light with a different wavelength than the design wavelength will not be rotated at exactly 45°. The magnitude of the rotation caused by the Faraday rotator is wavelength dependent. See the Isolator Tutorial tab for a schematic of the beam path.

Therefore, an isolator rejects backward propagating light. 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. They contain a Faraday rotator that has been factory tuned to rotate light of the design wavelength by 45°. Thorlabs' Adjustable Narrowband Isolators are designed to provide the same peak isolation anywhere within a 50 - 100 nm tuning range. Operating Principles of Optical Isolators

Light at the Design Wavelength is Rejected We offer a selection of these products from stock and can provide custom Faraday rotators upon request.

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 nm to 4.55 µm. Our vertically integrated manufacturing structure allows us to offer Faraday rotators used in optical isolators. If Thorlabs does not stock an isolator suited for your application, please refer to the Custom Isolators tab for information on our built-to-order options, or contact Tech Support. Thorlabs also manufactures isolators for fiber optic systems and wavelengths extending down to the UV (see the Selection Guide table to the left). The isolators can be mounted in a variety of adapters compatible mounting options are listed with each product as well as at the bottom of the page. In addition, all isolators have engravings that indicate the alignment of the input and output polarizers. Please see the Isolator Types tab for additional design details and representative graphs of the wavelength-dependent isolation.Įach isolator's housing is marked with an arrow that indicates the direction of forward propagation. They also offer the user the ability to adjust the alignment of the output polarizer with respect to the input polarizer, allowing the peak of the isolation curve to lie anywhere within a 50 - 200 nm range see the tables below for details. These isolators are factory aligned to provide peak isolation at the specified center wavelength. Isolators can be mounted close to the breadboard surface. Please see the Isolator Tutorial tab for an explanation of the operating principles of a Faraday isolator. In addition, intense back-reflected light can permanently damage optics. Back reflections can create a number of instabilities in light sources, including intensity noise, frequency shifts, mode hopping, and loss of mode lock. 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. Thorlabs' Free-Space Adjustable Narrowband MIR Optical Isolators offer operating ranges that span 2.20 - 4.55 µm and are designed for use in the MIR spectral range.

Minimum Isolation of 30 dB or Higher at Center Wavelength.

Please Contact Tech Support or See Our Custom Isolators Page.

Customizable Wavelength, Aperture, Max Power, Housing, Polarizers, and.