Patent ID: 7679413

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