Abstract

Recently, high-resolution distance measurement of pm order in the range of 1-100 m is required to evaluate large-scale constructions. We have developed an optical time-of-flight distance meter, using two waveguide-type modulators and a laser diode of a wavelength 1.3 pm. In this system, the laser beam is interferometrically modulated at 3.5-GHz frequency and demodulated at (3.5 GHz + 50 kHz). The light reflected by the target is detected with a good SNR, >40 dB. This system is evaluated at distances up to 250 m, using a 50-m traveling carriage and an interferometric fringe counting system. From the results, the linearity in phase measurement was ~5 μm in standard deviation, after compensating the systematic cyclic error from the reflection on the surfaces of optical fibers and a phase sensitive phase meter.

© 1991 Optical Society of America