光栅平动式光调制器结构参量的优化分析

Optimization and Analysis for Structural Parameters of Grating Moving Light Modulator

提出的光栅平动式光调制器是一种基于微机电系统(MEMS)工艺的光调制器,利用其表面具有的变形部分(可动光栅)提供衍射光栅,通过控制可动光栅的位移实现光调制器的两种工作状态,即亮态和暗态。根据衍射理论和傅里叶光学对光栅平动式光调制器工作状态的光学特性进行了详细的理论分析和仿真。重点讨论了可动光栅占空比、长度L1、垂直光栅周期方向上边框长度、光栅栅条宽度、整个器件的光栅周期数等对光调制器工作性能的影响。结果表明,可动光栅与反射镜的距离为入射波长的一半时,调制器工作在暗态;而当可动光栅向反射镜方向下移入射波长的1/4时,光调制器工作在亮态;要达到最佳的衬比度,需满足可动光栅的栅条宽度为光栅周期的一半,L1应该为光栅周期的整数倍;在不满足L1为光栅周期d的整数倍时,可动光栅在垂直于光栅周期方向上的边框越小越好;光栅栅条越宽、光栅周期数越多,衬比度越高。

The proposed grating moving light modulator is based on micro-electromechanical system, the diffraction grating is provided by the deformed part on its surface, movable grating, and the two working states, on and off, are realized by controlling the displacement of movable grating. Detailed theoretical analysis and simulation for the optical properties of grating moving light modulator at working state are carried out, and the effects of duty ratio, length, frame length perpendicular to the grating period direction, grating stake width and period number of the movable grating on the working performance of grating moving light modulator are discussed with emphasis. The result shows that, the modulator is off when the distance between the movable grating and the mirror is half of the wavelength of incident light, and when the above distance is shortened to a quarter of the wavelength, the modulator is on. For the optimal contrast, it requires that, the stake width is half of the grating period and the length of the movable grating is integral times of the grating period. When the latter condition is not fulfilled, a high contrast can be obtained with short frame, narrow stake and large period number.