Phase-Shifted Quadrature-Phase demodulation based on a Multi-Longitudinal mode laser Self-Mixing sensor for displacement measurement

Abstract

We present a novel method by a multi-longitudinal mode laser with a waveplate to generate two orthogonally polarized signals with stable and adjustable phase differences. The phase difference is observed from the output of the Wollaston prism, and is determined by the angle between the optical axes of the Wollaston prism and the waveplate. A phase-shifted quadrature-phase demodulation algorithm is proposed to construct a signal with a 90° phase-shift between one of the two polarized signals. This outcome allows us with low requirements on optical component adjustment accuracy and optical element manufacturing accuracy and also simplifies the processing of phase demodulation for displacement measurement under very weak optical feedback level. Experimental results show that the error is less than 38 nm when the displacement is 10.00 μm. Given its simplicity and efficiency, the proposed system has guiding significance for the design of the self-mixing interferometers and the high-precision online measurement.