Patent ID: 7705994

Claim:
A displacement measuring plane minor interferometer adapted to receive as spatially separate inputs therein first and second beams, f 1 and f 2 respectively, the first beam differing in wavelength from the second beam, the interferometer comprising: a polarizing beam splitter sub-assembly constructed from a first optically transparent solid material, receiving beams f 1 and f 2 as spatially separate inputs therein, wherein beams f 1 and f 2 are not combined while traversing the polarizing beam splitter sub-assembly, a beam combiner sub-assembly comprising a second optically transparent solid material, the beam combiner sub-assembly receiving beams f 1 and f 2 as spatially separate inputs therein from the polarizing beam splitter sub-assembly, and combining beams f 1 and f 2 , and first and second plane minors, f 1 being reflected from the first minor and f 2 being reflected from the second minor; wherein the polarization states of f 1 and f 2 are mutually orthogonal upon entry into the polarizing beam splitter sub-assembly and wherein f 1 and f 2 traverse first and second optical paths, with substantially equal first and second optical path lengths, wherein the first optical path length is the sum of the optical path length traversed by f 1 through the first material of the polarizing beam splitter sub-assembly and the optical path length traversed by f 1 through the second material of the beam combiner sub-assembly, and wherein the second optical path length is the sum of the optical path length traversed by f 2 through the first material of the polarizing beam splitter sub-assembly and the optical path length traversed by f 2 through the second material of the beam combiner sub-assembly.