Multiple control frequency phase modulator in phase modulated interferometer precision distance measuring system
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United States of America Patent
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Oct 17, 1995
Grant Date -
N/A
app pub date -
Feb 1, 1994
filing date -
Feb 23, 1993
priority date (Note) -
Expired
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Abstract
A phase-modulated interferometer has improved control and signal processing. Superimposition signals capable of evaluation in a phase-modulated interferometer without a complicated sawtooth control of the phase modulator are attained, in that two sinusoidal control signals which have modulation frequencies (.omega..sub.1, .omega..sub.2) and are rigidly coupled with respect to phase and frequency are applied to the known phase modulator and a cosine signal which is used in a conventional manner for evaluating the phase displacement is filtered of the superimposition signal generated in the interferometer by an electronic bandpass filter. At the filter frequency (.omega..sub.F) of the bandpass filter, an odd-number harmonic and an even-number harmonic of the two modulation frequencies (.omega..sub.1, .omega..sub.2) have the same frequency, when the amplitudes (.phi..sub.1, .phi..sub.2) of the control signals satisfy the condition for the suitable operating point of the phase modulator. The improvement has application to phase-modulated interferometers, in particular, for precision distance measuring devices, preferably by the heterodyne evaluating method.
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