Implementation of real-time displacement precision measurement technology for the sinusoidal phase-shifting laser self-mixing interferometer

An advanced sinusoidal phase-shifting technique and a time-domain phase demodulation method were used to improve the measurement accuracy and realize the real-time measurement speed of the laser self-mixing interferometer in a large range of displacement. An electro-optic crystal modulator (EOM) was used to realize the sinusoidal phase-shifting on the laser beam in the external cavity. The interference signal was demodulated using a time-domain phase demodulation method. The speed requirement could be met by combining the two together in a wide range of displacement measurement processes together with the real-time measurement requirement as an interferometer at the same time. It was experimentally verified that the displacement measurement precision of a sinusoidal phase-shifting laser self-mixing interferometer could reach less than 0.5 μm in the hundred mm large-scale displacement measuring process. In addition, the factors affecting the interferometer’s measurement speed in the real-time displacement measurement process is analyzed and the maximum speed of our system was obtained as well. Keywords: self-mixing interference; phase modulation; time-domain phase demodulation