Research On Wavefront Measurement System Of Large Deflection Angle Liquid Crystal Grating

The working principle of optical phased array technology is through altering the voltage which loads in different phased unit to change the phase、intensity and other optical properties of light waves that through different phased unit, under the electro-optic effect of electro-optic materials, in order to achieve independent control of each unit of light. It is widely used in the realization of laser beam deflection.This paper describes the liquid crystal grating phased array is optical phased array that its electro-optic material is liquid crystal molecule.Under the action of electric field,the liquid crystal molecules’permutation direction changes, and the refractive index of them is different, which leads to a certain angle of deflection in the direction of light beam passing through it. In order to achieve a better realization of the angle of the liquid crystal grating deflection, it is needed to understand the situation of its wavefront distortion.In this paper, the development of liquid crystal grating phased array and wavefront measurement technology is summarized, and the properties and working principle of liquid crystal grating are analyzed.To analyze the effect of different types of phase profile error on the performance of liquid crystal grating and the diffraction characteristics of liquid crystal grating.The intensity and phase distribution of the diffracted light field in different conditions are simulated by using MATLAB simulation technique, providing scientific basis for the correct placement of the liquid crystal grating in the following experiments.Through the analysis of selected appropriate wavefront testing method is single diffraction order inversion method to measure liquid crystal grating phase profile, measurement system measured near-field+1 order diffraction wavefront and taking single diffraction order inversion method to show at the liquid crystal grating wavefront phase, then feedback the situation to the controller.Wave device controller is applied to the voltage of liquid crystal grating, in its phase of feedback, according to the phase voltage measured is known to change the relationship between the applied voltage data,in order to readjust the direction of beam deflection.So the continuous beam deflection angle feedback repeated until a satisfactory.To study the optical path structure of liquid crystal grating wavefront measurement system. We are using the quadrilateral radial shearing interferometry to measure diffraction wavefront,the method has the advantages of shearing interferometry, that does not require the introduction of reference wave. The diffraction of the light beam through the liquid crystal grating is divided into two beams after the beam splitting prism:reflected light and transmitted light,then expanding and Shrinking the beam,at the end of the beam splitting prism, a large and small two spot overlap to generate the interference fringe pattern.The diffraction wavefront can be reconstructed by the fringe pattern.Through the optical design software to simulate the structure of the optical path, in order to obtain the accurate measurement of diffraction wavefront,the spacing of each component in line satisfy the requirements of the 4f system.Establishment of a Keplerian telescope system structure for shrinking and expanding beam and its optical simulation, and analyze the influence of parameters of the lens on the Telescope Aberrations of the system and beam splitter prism deflection of the beam changes.The interference fringes of the incident wave spectrum and several different carrier frequencies when the simulation is carried out.The simulation results have guiding significance for building and debugging of the measurement system.The liquid crystal grating wavefront measurement system is set up, and the actual large deflection angle liquid crystal grating is measured. Firstly, the shearing interferometer is calibrated, and the static phase distribution of liquid crystal grating and the phase profile of liquid crystal grating are measured.