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 tenability of a laser diode (LD) is used for phase modulation and phase control in this interferometer. Since the two wavelengths are derived from a single LD in our system, the optical system is simple and there is no need to consider the fluctuation of relative wavelength between the two LD's in the conventional two-wavelength interferometers. The equivalent wavelength Λ is 15 mm and the measurement accuracy reaches-Λ/400. The error sources in the system and the error analysis are also described