Research On System Of Simultaneous Phase-shifting Interference Based On NPBS

Phase-shifting interferometry is an ultra-high precision optical phase measurement technique.The traditional time-domain phase-shifting interferometer has been gradually replaced by a simultaneous phase-shifting interferometer because of its instability.simultaneous phase-shifting interferometer can capture multiple phase-shifting interferometric images instantaneously.Due to this real-time performance,its ability to resist environmental interference is greatly improved.However,acquiring multiple interferograms at a time will reduce the utilization of the camera’s field of view.The two step phase-shifting simultaneous interferometer only needs to record two interferograms,which increasing the utilization of the camera’s field of view.In this paper,a two step phase-shifting simultaneous interference system based on NPBS is proposed.The details are as follows:Firstly we study the Jones matrix of polarized light.The Jones matrix of polarizer and quarter-wave wave plate required for polarization phase-shifting is derived,and the principle of polarization phase-shifting interference is analyzed.Secondly,a two step phase-shifting simultaneous interference system using polarization phase-shifting technique is designed.The structure and principle of the system are introduced.The concrete design ideas are given from the four parts of interference,beam splitting,phase-shifting and image acquisition.The part of interference uses a Twyman-Green interference structure.Non-Polarizing beamsplitters is used to replace the two quarter-wave plates in the conventional simultaneous phase-shifting using Twyman-Green interference system.The Non-Polarizing beamsplitters is insensitive to polarization,and keeps the polarization of the object light and the reference light unchanged,so as to ensure the two orthogonal polarized lights needed by the polarization phase-shifting interference.The part of beam spilt adopts the combination of Non-Polarizing beamsplitters and reflecting mirror.The structure has the same splitting ratio,which is more cost-effective than the high-quality grating.According to the design of the structure,a corresponding experimental setup is set up.Two phase-shifting interferograms withπ/2 phase-shifting are acquired simultaneously.The Visibility of fringe pattern is good and there is an obvious phase shift.Finally,we study four kinds of phase extraction algorithms and two kinds of phase unwrapping algorithms,and the simulation and experiment are used to analyze and compare these algorithms.The system designed in this paper was used to test the surface of a plane by several times.The surface morphology was obtained after unwrapping the phase.The results show that the root mean square error of the repeated measurement is less than 0.015λ under laboratory conditions,which proves the system has good stability and feasibility.