Nanometer-resolution displacement measurement system based on weak feedback effect of dual-frequency laser

A novel nanometer-resolution displacement measurement system based on weak feedback effect of Zeeman-birefringence dual-frequency laser has been demonstrated. An experimental setup based on an optical feedback dual-frequency laser is developed to realize displacement division and direction discrimination utilizing phase delay between the optical feedback fringes of the two orthogonally polarized lights. The sub-division circuits of fringes are mainly composed of Field Programmable Gate Array (FPGA) and Micro Controller Unit (MCU), can realize 400 subdivisions for each fringe. The FPGA is used to realize the division of integral number fringes, and the MCU is used to realize the “division” of the fractional number fringes through program of look-up table. The total measured displacement is the value sum of both the integral part and the fractional part. A comparison experiment with the HP5529A interferometer was carried out resulting in a linearity of about 5×10−6, and a concise theoretical model is given to explain the experimental results. The proposed system has a theoretical resolution as high as 0.791 nm, as well as a function of direction discrimination. Thereby, it can meet some demands of high-precision displacement measurements.