Patent ID: 7982513

Claim:
A method for tracking the position of a moving interferometer reflector, comprising the steps: (a) generating, using a detector, a master varying signal and a first subordinate varying signal from beams of radiation passed through an interferometer, the phase of the first subordinate varying signal being shifted from that of the master varying signal by a fraction of a cycle; (b) generating at least a second subordinate varying signal from the master and first subordinate varying signals, the second subordinate varying signal being out of phase with the master and first subordinate varying signals, the angular shift between each varying signal and the varying signals of closest phase relationship having a value of substantially 180° divided by the total number of the varying signals; (c) generating a master square-wave signal from the master varying signal such that the transition points of the master square-wave signal correspond to the zero crossing points of the master varying signal, and generating at least first and second subordinate square-wave signals from the first and second subordinate varying signals, respectively, such that the transition points of each of the subordinate square-wave signals correspond substantially to the zero crossing points of the subordinate varying signal from which it is generated; (d) correcting each of the square-wave signals as necessary to impart thereto the same, selected duty cycle character; (e) comparing each of the subordinate square-wave signals with the master square-wave signal, each as so corrected in said step (d), and generating a square-wave signal that is indicative of the phase relationship therebetween, the indicative signal being employed to adjust dynamically the phase relationship of each subordinate square-wave signal as necessary to conform the angular shift between it and the square-wave signals of closest phase relationship to a value of 180° divided by the total number of the square-wave signals, to thereby produce a phase relationship between the master square-wave signal and each subordinate square-wave signal; and (f) utilizing the transition points of the corrected master square-wave signal and each corrected subordinate square-wave signal, as adjusted in said step (e), to generate corresponding pulse trains indicative of the position of the interferometer reflector.