Optical EngineeringAbsolute distance measurement using wavelength-multiplexed phase-locked laser diode interferometry
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A new type of two-wavelength interferometer which applies a phase-lock technique is described. The wavelength tunability 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 ? is 15 mm and the measurement accuracy reaches ~?/400. The error sources in the system and the error analysis are also described.