| 摘要 |
PROBLEM TO BE SOLVED: To obtain a pure measuring signal at low cost by a constitution wherein an increment generator coupled with means for varying the difference of optical path length generates a reference signal for varying the frequencies of reference signal and interference signal independently from the variation rate of the difference of optical path length. SOLUTION: Light from a laser diode 22 is enlarged through a collimator 23 and arrives, as a parallel luminous flux, at a lattice generator comprising movable and fixed reference lattices 24a, 24b through a displacement unit. A produced bright/dark signal arrives at an amplifier reading photoelectric light receiving element 25. A reference signal generated in the amplifier of element 25 has same frequency as a measuring signal generated at the output of light receiving prestage amplifier in an avalanche photodiode 17 and superposed with noise. Both signals arrive at a demodulation and subsequent conversion unit 26 for two paths having phase shift of 90 deg.. Output signal from the unit 26 is converted through an A/D converter 27 and stored in a control evaluation unit 19. Signal from a displacement unit 18 is fed to the unit 19 and can be represented as a function of displaced place.
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