Method of high-precision spatial distance measurement based on optical-carried microwave interference

High-precision spatial ranging plays a significant role in both scientific research and industrial practice. However, it is difficult for existing equipment to achieve high speed, high precision, and long distance simultaneously. Inspired by the concept of optical carrier-based microwave interferometry (OCMI), this paper reports a method of high-precision spatial distance measurement. A microwave-modulated broadband optical signal is sent to the interferometer whose measuring arm is an optical echo receiving system in free space. By scanning the microwave frequency, the measured distance can be resolved from the interferogram. Since the processing of the interference spectrum is performed in the microwave domain, this method is insensitive to the types of optical waveguides and states of optical polarizations. The experimental results show that the root mean square error (RMSE) of ten repeated measurements at 0.5 m is 0.016 µm, the RMSE is 0.023 µm within a 1 m distance, which can effectively represent the length measuring capability of the proposed system.