| 摘要 |
PURPOSE:To calculate the distance to an object from the relation between a wavelength and phase delay, by respectively changing the wavelengths of two lights to hold respective phase delay quantities to definite values. CONSTITUTION:Lights (lambda1, lambda2) having wavelengths changed by acoustooptical modulators 2, 3 and divided into two by a half mirror 7 are selectively incident to an interference optical system through a shutter 9 and detected by detector 14 to be fed back to a voltage control oscillator 4 while the phase delays phi thereof are detected by a detector 15. At an angular velocity omega0, a light-velocity (c) and a light path length (d), the amplitudes of lights returned through reference and length measuring light paths are superposed to be detected by the detector 14. The phase of the output of said detector 14 is compared with that of the drive signal of a modulation signal source 13 by a comparator 15. When the light lambda1 is incident from a window (a) and the frequency of the oscillator 4 is changed to set phase delay to phi1-phi2=0, omega0(d2-d1)/c=2pi(d1-d2)/lambda1=2npi, d1-d2=n1lambda1 is formed. The window (a) is changed over to a window (b) to lock phase delay to d1-d2=n2lambda2. An absolute value (n1-n2)=1 is set and the frequencies f1, f2 of oscillators 4, 5 are counted by a counter 17 to accurately determine the lights lambda1, lambda2 and a length is measured according to d2-d1=c/(f1-f2).
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