Research On Phase Shift Digital Holographic Measurement Technology Based On SLM

With the rapid development of micro-nano technology,micro-optical components such as MEMS components,micro-lens arrays,micro-sensors are widely used in various fields,so it is great significance to realize precise measurement of micro-structured structure.There are characteristics of the full-field,no contact and fast measurement in phase shift digital holographic technology.However,due to the traditional phase-shift method using mechanical movement,random and systematic errors will inevitably be introduced.When measuring micro-nano structures phase distortion is generated,which leads to problems such as low resolution and unsatisfactory image quality.Therefore,how to increase phase reconstruction accuracy of the phase shift digital holographic system has become the current main research direction.The Spatial Light Modulator(SLM)can be controlled in real time,and the light field can achieve pure phase modulation.The SLM and phase shift digital holograph were combined in this paper for further study.The main work is as follows:1.In order to solve the problem of random error and systematic error in traditional mechanical phase shift,SLM is applied to phase shift digital holography system.In this paper,the reflective phase type SLM is studied.A reflectivity-phase delay mathematical model is established,and the relationships between different polarization angles and SLM reflectivity and phase delay,respectively,are simulated and analyzed.The experimental system of optical power meter method is constructed,and It is verified that when the Angle between polarization Angle and liquid crystal optical axis of SLM is 0°,it can work in phase-only mode.In order to facilitate the calibration of the phase modulation curve of the SLM device under the optimal polarization condition,a gray-scale coding method is proposed based on the digital wavefront interferometry system,and the phase regulated by different gray-scale values of the device is obtained.2.In order to eliminate the edge effect and spatial inhomogeneity of SLM,a second phase calibration method is proposed.By means of two-dimensional image interpolation algorithm and gray-scale algorithm,distorted phase conjugated gray-scale image is designed to adjust the gray-scale value of each liquid crystal unit,so as to correct the whole distorted phase.The experimental results show that the phase modulation error between liquid crystals can be reduced by the second phase calibration method,the PV value of wavefront difference decreases from 0.182 ? to 0.088 ?,and the RMS value decreases from 0.039 ? to 0.022 ?,which the phase modulation accuracy of SLM is effectively improved.3.The Mach-Zehnder phase-shifting digital holography system based on SLM is constructed to measure the micro-lens array of phase objects and verify the effectiveness of SLM as a phase shifter.The relative error of the longitudinal vector height of the micro-lens array is reduced from 3.23% to 1.31%,when the second calibration SLM is applied to the phase-shifting digital holographic measurement system.The method proposed in this paper is applied to the phase measurement of micro-optical components,which reduces the influence of the distortion on the reconstructed phase and improves the measurement accuracy of the phase-shift digital holographic microscope system.