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FiberBench Polarization Modules
Beam Displacer Module
Variable Optical Attenuator Constructed Within a FiberBench System (See Applications Tab)
Thorlabs offers several polarization modules that can be used with our FiberBenches. Each module has two dowel pins on its base that precisely align it on a FiberBench. The Rotating Linear Polarizer Modules are made from nanoparticle film polarizers held in FBR Rotation Mounts that allow the user to easily adjust the State of Polarization (SOP) and are ideal for use in the 500 nm - 5.0 µm wavelength range. The Linear Polarization Reference Module is ideal for use in PM fiber alignment, polarimetry, and extinction ratio measurements. The left-/right-handed Beam Displacer Modules consist of an AR-coated Calcite crystal on a static mounting base. They are designed to displace the horizontal polarization for a variety of wavelength ranges. For more information or custom requests, please contact Tech Support.
Rotating Linear Polarizer Modules
Linear Polarization Reference Module
Calcite Beam Displacer Modules
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Variable Optical Attenuator
Variable Optical Attenuator Application
A continuously variable attenuator can be assembled using the FiberBench components listed in the table to the right. Since a variety of AR coatings and connectors are available, we recommend selecting individual components suited to your application.
The FiberPort collimates the beam from a SM or PM fiber, and the collimated beam then goes through a calcite beam displacer (walk-off polarizer) where it is split into its respective horizontal (P) and vertical (S) components. The orientation of the wave plate controls how much energy is in the beam. It can be rotated to give the desired attenuation - zero, partial, or full. The signal then enters a reversed beam displacer where it will be recombined or further separated. The only energy that will couple back into the output fiber is the signal on the central axis. The central beam will then be focused into the output fiber by the output FiberPort.
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The half-wave plate is rotated so that there is only one output beam; this also means that the input and output polarizations are the same.
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The half-wave plate is rotated so that there are three output beams. Its orientation will control how much energy is in each beam. The only energy that will couple into the fiber is the energy in the central beam. The attenuation range is 1 to 40 dB with any value in-between.
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The half-wave plate is rotated so that there are two output beams, which will be displaced to the left and to the right of the center. In this position, there will be minimal coupling efficiency, resulting in a maximum attenuation of 40 dB.
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A polarization splitter can be assembled using the components listed in the table below. Since a variety of AR coatings, connectors, and configurations are available, we recommend selecting individual components suited to your application.
The offset (pickoff) mirror is positioned such that it will intersect the displaced beam from the preceding calcite beam displacer (walk-off polarizer) and reflect it by 90°. This combination simplifies the alignment of complex systems by decoupling the reflected beam from the transmitted beam, thus allowing for the independent adjustment of the reflected beam path. Alignment is critical when aligning systems with a walk-off/pickoff combination as clipping can occur if the beam is too large or not centered.
Thorlabs' FiberBench Rotating Linear Polarizer Modules utilize a thin layer of sodium-silicate polarizer mounted in FBR Rotation Mounts. These modules absorb light that is not aligned to the transmission axis of the polarizer and are designed for the 500 - 720 nm, 650 - 2000 nm, or 1.5 - 5.0 µm wavelength range. These polarizers provide an excellent extinction ratio of >10,000:1 over most of their specified wavelength range (see Specs tab for details).
The mount for these polarizers features a rotating cell with a knurled edge and a 360° laser-engraved scale marked at 2° increments for precise, repeatable positioning and fine angular adjustment. A convenient top-located setscrew (0.050" hex) secures the rotational position of the stage. The transmission axis is marked by the engraved line on the front of the polarizer cells. The FBR mount can be coupled with an FBA post-mountable adapter for use in other applications.
The mount is SM05 threaded and the removable polarizer cell is held in the mount with an SM05 retaining ring for holding Ø1/2" optics (SM05RR). The polarizer cells in these modules are also compatible with other Ø1/2" optic mounts. When replacing a polarizer in the mount, be sure to align the engraving on the polarizer with the 0° engraving on the scale. Please note that the thin film in these polarizers is very delicate and should not be touched.
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Four Available Orientations (Fourth orientation not shown)
The Linear Polarization Reference Module consists of a Linear Polarizer held in a capture cage. The polarizer is set in the silver wheel on the front of the module, seen on the left, and can be rotated by adjusting the setscrew using a 0.035" hex key.
To use the module, place the front of the module into the cage facing your source with the 1 located at the top. Rotate the front wheel so that it matches the polarization of your source, and tighten the setscrew using a 0.035" hex key, located on the face to the left of the 2. This corresponds to a 0° rotation with respect to the input polarization. From here, the module can be easily positioned to the 2, 3, or 4 settings, which correspond to a 90°, 45°, and 135° clockwise shift of the input polarization, respectively. Position 4 is achieved by flipping the module; the wheel on this side of the housing does not rotate the polarizer but can be adjusted for use as a reference.
Please note that this linear polarization reference module does not incorporate a quarter-wave plate. However, other wavelengths and units with an integrated quarter-wave plate (to function as a manual polarimeter) are available by request. Please contact Tech Support for details.
Each Beam Displacer Module consists of an AR-coated Calcite crystal mounted on a static base so that it can be inserted at the correct height into a FiberBench setup. It is primarily designed to displace the horizontal polarization state by 1 mm. The beam displacing polarizers listed below are designed for use in different wavelength ranges (Visible, NIR, YAG, or IR), offering both left- and right-handed orientations.