Interference detecting system for use in interferometer

Abstract

Interference light occurring between a first laser light of a reference phase and a second laser light of a measuring phase is divided via a light divider into two interference light beams to be directed in two directions. One of the divided interference light beams is received by a polarizing light separator, which separates components of the first and second laser lights from the received interference light beam. First and second light detectors convert respective light energy of the separated components into corresponding electric signals. Adder adds together the converted electric signals. Third light detector converts light energy of the other divided interference light beam into an electric signal. Comparator compares the electric signal from the third light detector with the output of the adder as a reference value, to generate a detection output of a predetermined phase. In an alternative, the output from the adder is subtracted from the converted electric signal from the third light detector and a square root of a product between the electric signals output from the first and second light detector is evaluated, so that a signal, indicative of interference intensity of the interference light occurring between the first and second laser lights, is provided by dividing the output of the subtracter by the square root.