715 Polarizer

Conoptics said if a source laser is unpolarized or randomly polarized, conventional polarizers such as its model 720 cause a time-averaged 50-percent loss to the forward beam. The 721 avoids this loss by splitting the incident beam into two orthogonal linear components using double refraction in a birefringent crystal (calcite). A Faraday rotator and model 730 compensator are oriented so 45-degree rotations cancel in the forward direction. A second 721 recombines the beams that proceed from the assembly. The model 730 is required to properly orient the polarization of the separated beams with respect to the displacement plane of the output 721.

In the backward direction, the first 721 encountered performs in its normal beam splitting function, Conoptics said. The 45-degree rotations of the 730 and Faraday rotator add, thereby reversing, the polarization of the two beams as compared to that in the forward direction. The second 721 encountered further spreads the beams, rather than recombining them. Since the returned power is absorbed by aperture stops that are part of the assembly, strong reflections of high power sources for more than brief durations will result in heating. In special situations where persistent strong reflections cannot be avoided, a modification to the 721 which extracts rather than absorbs the backward flowing power is available.

In order to transmit in the forward direction and block in the backward direction, the length of the birefringent element in the model 721 must be sufficient to spatially resolve the two beams, the company said. Since the beams travel laterally separated in the rotator and compensator, the effective clear aperture of polarization insensitive assemblies incorporating 721s must be reduced to 1.75 mm and offset 1 mm from the mechanical centerline.

ConOptics Inc.    
19 Eagle Rd.
Danbury, CT 06810
(800) 748-3349