Multiwavelength interferometer detects amplitude modulation of electrical signal with difference in frequency of signal by detecting phase difference between difference frequency and modulation frequency signals

摘要

A photodetector (12) corrects optical interference signals obtained by recombination of light beam reflected from reflecting object and reference beam (6) into electrical signals. Signal processors (14,15,17,19,23) detect amplitude modulation of electrical signals with difference in frequency of signal by detecting phase difference between difference frequency signal ( DELTA f) and modulation frequency signal. The beam splitter or fiber coupler (5) splits output signal (4) of electro-optical crystal (2) by which laser signals with optical carrier frequencies (f1-f3) are modulated by modulation frequency signal (fmod1-fmod3) generated from respective oscillators (3a-3c), into measurement laser beam (7) for detecting position of reflection object (10) and reference beam (6). A frequency shifter (11) outputs difference frequency signal ( DELTA f) before irradiation of light onto the reflecting object. The recombiner (9) recombines the reference beam and light reflected from object into interference signals. The photodetector (12) converts the optical interference signal into electrical signals. The signal processors process the electrical signals by detecting phase difference between DELTA f-fmod1, DELTA f-fmod2 and DELTA f-fmod3 for detecting the position of reflected object.