Precision vibration measurement using differential phase-modulated homodyne interferometry

A novel precision vibration measurement using differential phase-modulated homodyne interferometry is pre-sented. The orthogonal linearly polarized phase-modulated single frequency laser source is constructed by using a distributed feedback (DFB) fiber laser and a fiber-coupled electro-optic phase modulator (EOM). An auxiliary monitoring signal is used to differentially compensate the optical path drift and common-mode noise of the fiber. By pre-scanning the wavelength of DFB laser to introduce enough phase changes, ellipse fitting can be real-ized without moving the object more than half a wavelength. Therefore, the periodic nonlinearity of the phase generated carrier (PGC) demodulation is compensated. Experimental setup was built and the real-time signal processing was realized based on field programmable gate array (FPGA). The experiments of pulse vibration, si-nusoidal vibration and comparison with commercial laser vibrometer were performed to verify the feasibility of the proposed method. The experimental results show that the average deviation of vibration amplitude is about 0.97 nm in the frequency range of 0.5 kHz to 10.0 kHz, which indicates that the proposed method has significant application for precision vibration measurement.