Phase-modulated interferometer III

摘要

The invention relates to a phase-modulated interferometer for evaluating phase shifts on the basis of variations in optical wavelengths in the measuring arm of the interferometer. The object of realising a phase-modulated interferometer which generates the sin-cos signals which are usual in length measuring systems and makes them available as conventional interface, is achieved according to the invention in conjunction with sinusoidal driving of the phase modulator (11) by admixing with the split superimposed signal from the reference arm (12) and the measuring arm (13) in a separate and mutually parallel fashion in each case sinusoidal signals of the form sin [(2n-1) omega t] and cos (2m omega t) which are coupled to the drive signal of the phase modulator in a phase-locked and frequency-locked manner. After filtering by means of two low-pass filters (51, 52), the conventional quadrature signals are available at an interface (5). The invention is preferably used for precision length measuring systems based on a heterodyne evaluation.