Phase-modulated interferometer II

摘要

The invention relates to a phase-modulated interferometer with a novel drive and signal conditioning. The object, of achieving overlay signals which are capable of evaluation in the case of a phase-modulated interferometer without complicated driving of the phase modulator, is achieved according to the invention in that the known phase modulator (2) is fed with a sinusoidal drive signal having a modulation frequency ( omega 0) and an amplitude ( phi 0), a multiplicative mixing is carried out of the overlay signal, generated in the interferometer, from the measurement and reference arm by a sine-wave signal which is rigidly coupled in terms of phase and frequency with reference to the drive signal and has a specific mixing frequency ( omega M), and, in an electronic bandpass filter (9), at whose filter frequency ( omega F) the sum frequency and difference frequency of two harmonics of the modulation frequency ( omega 0) and of the mixing frequency ( omega M) assume equal values, a cosine signal is filtered out in a conventional way for evaluating the phase shift, if the amplitude ( phi 0) of the drive signal fulfils the condition for a suitable operating point of the phase modulator (2). The invention is applied in phase-modulated interferometers, in particular for precision length measuring devices having a preferably heterodyne evaluation method.