Patent ID: 6181420
Filing Date: 2001-01-30
Classification: G01B,G03F

Abstract:
A phase measurement system for minimizing cyclic errors in a relative phase between exit reference and measurement beams emerging from an interferometer, the phase measurement system comprising:a first optical processing channel comprising a first polarizer and a first detector, wherein during operation a first portion of the exit reference and measurement beams pass through the first polarizer to produce a first mixed beam and wherein the first detector measures an intensity of the first mixed beam;a second optical processing channel comprising a quarter wave retarder, a second polarizer, and a second detector, wherein during operation a second portion of the exit reference and measurement beams passes through the retarder and then the second polarizer to produce a second mixed beam and wherein the second detector measures an intensity of the second mixed beam; anda signal processor which during operation receives signals from the first and second detectors indicative of the intensities of the first and second mixed beams and processes the signals to determine, and minimize cyclic errors in, the relative phase between the exit reference and measurement beams, wherein the signal processor comprises a first phase interpolator which during operation receives the first signal and determines a phase of the first signal and a second phase interpolator which during operation receives the second signal and determines a phase of the second signal.