ABSOLUTE DISTANCE MEASUREMENT USING WAVELENGTH-MULTIPLEXED PHASE-LOCKED LASER-DIODE INTERFEROMETRY

A new type of two-wavelength interferometer which applies a phase-lock technique is described. The wavelength tunability of a laser diode (L D) is used for phase modulation and phase control in this interferomet er. Since the two wavelengths are derived from a single LD in our syst em, the optical system is simple and there is no need to consider the fluctuation of relative wavelength between the two LD's in the convent ional two-wavelength interferometers. The equivalent wavelength Lambda is 15 mm and the measurement accuracy reaches <similar similar to Lam bda/400. The error sources in the system and the error analysis are al so described. (C) 1996 Society of Photo-Optical instrumentation Engine ers.