High performance sinusoidal phase modulating interferometer based on fundamental frequency mixing PGC demodulation and balanced detection

Abstract

A PGC demodulation scheme combining fundamental frequency mixing and balanced detection is proposed to enhance the measurement performance of sinusoidal phase modulating interferometer (SPMI). First, two interferometric signals with identical optical paths are differentially amplified by the principle of balanced detection. As a result, a high signal-to-noise ratio measurement signal, without DC bias, is obtained. Next, the orthogonal interferometric signal pair is obtained using the fundamental frequency mixing method, which not only reduces the phase modulation depth but also increases the amplitude of the useful signal component. Then Lissajous ellipse fitting is used to realize the normalization of the orthogonal interferometric signal pair. Finally, the phase demodulation of the measurement signal is achieved by using differential cross-multiplication (DCM) or arctangent (Arctan) algorithms. A sinusoidal phase modulating polarization interferometer based on Michelson structure is built, and experimental tests on the proposed demodulation scheme are conducted. The experimental results of nano displacement measurement investigate the accuracy of the proposed method and system within a deviation of $\pm$1.5 nm. Vibration measurement experiments at various frequencies demonstrate the proposed scheme has superior measurement performance. Under comparable hardware conditions, the proposed scheme has the optimal performance in terms of total harmonic distortion (THD), signal-to-noise distortion ratio (SINAD) and dynamic range of the demodulation results. Compared with the conventional methods, for the Arctan and the DCM phase demodulation approaches, the proposed scheme achieves a reduction in THD by 19.63 and 15.75 dB, respectively. It also enhances the SINAD by 12.03 and 8.04 dB, and increases the dynamic range by 18.52 dB @ 55 Hz and 15.54 dB @ 55 Hz, respectively.