Integration of Zero Crossing Method in a Nonuniform Sampling System Using Optical Feedback Interferometry

In this article, a zero-crossing (ZC)-based method is proposed to improve the displacement sensing performance of nonuniform sampling (NUS) theory-based use of optical feedback interferometry (OFI) under a moderate optical feedback regime. The incorporation of ZCs as phase quantization levels (PQLs) allows doubling the samples for subsequent interpolation, without using any dithering scheme. When compared to the simple dither-free NUS method, the proposed method yields an overall improvement in the rms error over a wide range of target motion amplitudes and frequencies, with maximum improvement at low amplitudes. Experimentally, an improvement of up to 87% is obtained in precision when compared to a simple NUS system for an OFI sensor with a laser wavelength of 785 nm.