Einrichtung zur Längenmessung

摘要

An optical interferometer with a measurement light path, a reference light path coupled to it and a laser diode light source is supplied by a d.c. source modulated by an a.c. signal. A first phase modulator receiving the modulation signal drives the sine input of an up/down counter via a low pass filter. A second phase modulator driving the cosine input via another low pass receives the interferometer photodetector output and a frequency multiplied modulation signal. The filter corner frequencies exceed the modulation signal frequency. The modulation signal amplitude is controlled to eliminate a difference between the modulator output signals. USE/ADVANTAGE - Evaluation of demodulation rotary field signal is improved and can be used with large optical path length difference changes.