Liquid Crystal Phased Array Modeling Analysis And Wave Control Algorithms

Optical phased array (OPA) is derived from microwave phased array radar, it is a new non-mechanical beam steering technology that makes possible high-resolution, high accuracy, random-access pointing. Liquid crystal optical phased arrays (LCOPA) produced by nematic liquid crystal material have advantages of low driving voltage, simple to fabricate, small size, light weight, low power consumption and low cost etc. By using the LCPA, laser radar can obtain fast, agile beam steering and spatial scanning capability. Because LCOPA has many unique characteristics which are different with microwave phased array, the beam pointing performances of the device are limit by the influence of some factors. Therefore, how to achieve high efficiency and high precise beam steering have been the key problems of LCOPA technology.In this thesis, the high efficiency, high precise beam steering control technology of liquid crystal phased array has been investigated. The work of the thesis is shown below:1. By using the optical Fresnel diffraction theory and the angular spectrum diffraction theory, the different beam propagation model are established, the sampling conditions of different models are derived.2. The principle of LCOPA phase modulation is analyzed, the periodic and aperiodic phase modulation models are established, and comparisons and analysis of the periodic and aperiodic phase modulation model are given.3. The physical model of the liquid crystal cell is established on the basis of its geometric structure. According computing the liquid crystal director field in liquid crystal cell with a finite difference combined with iteration method, the electro-optic curve for the liquid crystal cell that relates applied voltage to relative optical phase delay for impinging light is obtained. By using numerical modeling and far-field beam distribution simulation method, several typical factors affecting the steering performances of the LCOPA are investigated, and the dependence of the steering performances on the various physical parameters of a liquid crystal optical phased array (LCOPA) is given, the relationship between key performances of LCOPA with the influence factors are analyzed numerically.4. Aiming at the problem of the key performances of LCOPA device are limited by the influence factors, a closed-loop wave front control algorithm based on phase retrieval is proposed. The GS algorithm and the phase retrieval algorithm based on beam intensity measurements in three planes are improved, and a phase retrieval algorithm without the amplitude information of input plane is proposed, the phase retrieval accuracy and convergence of these algorithms is given. The iterative algorithms for wavefront control based on phase retrieval are proposed, including the constant step length method and the auto-adaptive step length control method, and the improvement of beam steering performance based on the two methods are compared and analyzed, the convergence speed of two methods are compared.