Abstract

Velocity and displacement measurements play an important role not only in the process of industrial production and metrology on the ground but also in satellite gravity measurement in space. A high-precision all-fiber heterodyne velocity and displacement interferometer based on digital phase-locked loop (DPLL) Doppler tracking is proposed in this paper. The target velocity is measured by tracking the heterodyne frequency changes of the beat-note signal, and the displacement is obtained by the integrated phase of the Doppler frequency change. A dual-signal differential optical-path scheme combined with DPLL signal tracking technology enables high-precision and high-linearity measurement of velocity and displacement simultaneously. For integration and compactness, the interferometer uses all-fiber optics that are packaged in a small box with dimensions of ${150} \times {150} \times {70}\;{{\rm mm}^3}$, except for an externally fiber-connected collimator as the sensor head. The experimental results show a velocity sensitivity below ${30}\;{{\rm pm/s/Hz}^{1/2}}$ in the 0.03–2 Hz band and a displacement sensitivity below ${10}\;{{\rm pm/Hz}^{1/2}}$ above 0.4 Hz.

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