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EOT 1030 - 1080nm Faraday Isolators
V. Tuning your Faraday Isolator
A. Adjusting Input Polarization
The transmission axis of the Input Polarizer is parallel to the scribe line found on the Input Polarizer Endplate. If the linear polarization of the laser source is geometrically known aligning the Input Polarization of the Faraday Isolator to that of the laser source is straightforward. Simply loosen the #4-40 socket head Baseplate Clamp Screw in the Baseplate until the magnet housing rotates freely. Continue to rotate the magnet Housing until the Input Polarizer transmission axis scribe line is aligned to that of your laser source. If the direction of any rejected polarizations at the input polarizer is important they can be determined by noting that the "dot" superimposed on one of the Endplate scribe lines is associated with the direction that a backward propagating beam will be directed. Re-tighten the Baseplate Clamp Screw.
If it is desired to critically adjust the input polarization for maximum transmission of the Faraday Isolator the power rejected by the Input PBSC in transmission can be minimized. This rejected beam can be accessed as per Section IV above. As always, use caution when allowing rejected beams to escape from the Polarizer Covers. Confirm the direction and safe termination of these beams at low power. Wear laser Safety Glasses or Goggles. Protect your colleagues by safely terminating beams and ensuring that they are wearing Safety Glasses/Goggles as appropriate. At the desired operating power level minimize the power in the rejected input polarization with a power meter or other suitable power indicator. When the power is minimized re-tighten the Baseplate Clamp Screw.
B. Coarse Wavelength Adjustment
If it becomes necessary to operate the Faraday Isolator at a wavelength other than the factory aligned wavelength it is possible to optimize the isolation of the device anywhere within the wavelength range of 1030 to 1080nm. This can be achieved quickly by simply aligning the polarization scribe line on the Output Polarizer with the appropriate wavelength indicator scribe line on the Polarizer Clamp Ring. The optimal operating wavelength corresponding to scribe lines labeled "A" and "B" is a function of the rotation sense of the device ordered (see Section III for definition). Use the table below to determine the optimal operating wavelength corresponding to each scribe line.
 To re-align the Output Polarizer Mount, loosen the three button head Polarizer Clamp Ring screws just enough to allow the Output Polarizer Mount to rotate easily. Once adjusted, re-tighten the Polarizer Clamp Ring screws by equal amounts.
C. Fine Wavelength Adjustment
The above procedure is convenient for a quick re-alignment of the operating wavelength. To achieve maximum isolation for a given wavelength the following procedure should be used.
With the source laser operating at an average power of 0.5W or less (attenuate the beam if necessary to achieve such a low power level) direct the source laser beam through the Faraday Isolator in the reverse direction -through the Output Polarizer first and then through the Input Polarizer. Use an IR viewer to view the transmitted radiation to ensure that it is directed onto a Power Meter. The Power Meter should be sensitive enough to detect power levels below 0.5µW. If necessary, loosen the Baseplate Clamp Screw to allow the Output Polarizer transmission axis to be rotated parallel to the source laser polarization axis -re-tighten this screw when complete.
Loosen the three button head Output Polarizer Clamp Ring screws just enough to that the Output Polarizer Mount can be rotated (the Output Polarizer is adjacent to the laser source at this point). Rotate the Output Polarizer Mount until a minimal reading is indicated on the Power Meter. Re-tighten the Output Polarizer Clamp Ring Screws. The minimal reading should be below 0.5µW. If not call EOT (see Section VI below). The Faraday Isolator is now optimized to operate at the new laser source operating wavelength. It may now be installed for operation in transmission with the laser source as per Section IV.
D. Changing the direction of Output Polarizer PBSC Rejected Beam Steering
Section A above described how to orient the Input Polarizer PBSC to steer rejected beams as desired. If the Output Polarizer rejected beam steering direction needs to be changed, loosen the three Output Polarizer Clamp Screws and rotate the Output Polarizer Mount by 180° before re-tightening the Screws. Depending upon the isolation requirements, follow either Procedure B (coarse adjustment) or Procedure C (fine adjustment) in order to fully optimize the isolation of the device with this Output Polarizer orientation.
E. Waveplate Option and Adjustment
As described in Section III above in the "Numbering Fields and Coordinate System" description it is possible to order a Faraday Isolator with a half-waveplate on the output. Should any of the above adjustments become necessary, or if the desired output polarization changes, the waveplate will need to be adjusted. To re-align the waveplate loosen the radially oriented set-screw in the output polarizer endplate and rotate the waveplate until the desired output polarization is achieved. Re-tighten the waveplate set-screw. Do not over-tighten.
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