Abstract
Optical attenuators allow the power in an optical beam to be varied without undesirable variation in the spatial, temporal, spectral, or polarization state of the beam.1-4 This paper describes an attenuator using a standard field effect twisted nematic liquid crystal cell in a geometry using only planar transmissive optical elements. The liquid crystal cell (Fig. 1) is sandwiched between two slabs of crystalline calcite, each cut with its optic axis at 41.9° to the entrance surface normal. As a result, the input beam splits into an ordinary beam which propagates straight along the surface normal and an extraordinary beam which propagates at 6.23° to the normal. The two beams emerge from the slab both parallel to the normal but displaced from each other and then pass through the liquid crystal cell which does not deflect either beam but rather modifies their polarizations. When the voltage on the cell is zero, the polarization of each beam is rotated by 90° as it passes through the liquid crystal cell. When these beams traverse the second calcite slab (which has the same optic axis orientation as the first slab), they follow the paths Indicated by the dotted lines because of this polarization rotation and recombine at the output of the slab.
© 1982 Optical Society of America
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