Measurement of absolute displacement based on dual-path submicron-aperture fiber point-diffraction interferometer

The measurement of three-dimensional absolute displacement within large range can be achieved with submicron-aperture fiber point-diffraction interferometer (SFPDI), in which the numerical iterative algorithm for displacement reconstruction and point-diffraction wavefront determine the achievable measurement accuracy, reliability and efficiency of the system. To avoid the poor measurement accuracy in the lateral direction parallel to the fringe direction in the SFPDI with only one fiber pair, a dual-path SFPDI (DP-SFPDI) based on modified fast searching particle swarm optimization (PSO) algorithm is proposed to realize the rapid and accurate measurement of three-dimensional absolute displacement. Based on the DP-SFPDI with two submicron-aperture fiber pairs and modified PSO method, the measurement reliability, efficiency and accuracy in all the three dimensions of the system are significantly improved, making it more feasible for practical application. The effect of point-diffraction wavefront error on the measurement is analyzed. Both the numerical simulation and comparison experiments have been carried out to demonstrate the accuracy and feasibility of the proposed DP-SFPDI system, high measurement accuracy, convergence rate and efficiency have been realized with the proposed method.