针对平面波导系统中光能利用率低、光栅制备成本高且工艺复杂的问题, 设计大周期、高衍射效率的光栅结构, 从而提高系统光效、节约成本。首先, 提出以梯形光栅作为最初面型进行标量理论计算, 以梯形的角度、占空比、高度为变量, 得出光栅面型为直角三角形时, -1级有较高衍射效率。随后分析了设计的直角三角光栅和两种常见的线性光栅的衍射效率, 并且讨论了深度加工误差、入射光发散角对三种面型光栅衍射效率的影响。仿真结果显示：周期为3 μm的直角三角光栅, 入射光垂直入射时-1级衍射效率达81%, 与小周期倾斜光栅的衍射效率相差较小, 但考虑到深度加工误差和入射光的发散角度对三种面型光栅衍射效率的影响时, 直角三角光栅则具有明显优势。设计的直角三角光栅在具有较大周期时, 仍可实现较高衍射效率。

Aiming at the problems of low light energy efficiency, high fabrication cost and complicated process, a kind of grating structure with large period and high diffractive efficiency was designed to improve system light efficiency and save cost. Firstly, based on scalar theory, the trapezoidal grating was put forward as the initial surface shape. The angle, duty cycle and depth of the trapezoid grating were used as variables to analyze the diffraction efficiency. It is found that the right triangular grating presents the higher efficiency at -1st order. Then the diffraction efficiency of the designed right triangular grating and two common linear gratings were simulated as well as the effects of depth error and incident light divergence angle on the diffraction efficiency. Simulation results show that the diffraction efficiency at the -1st order of the right triangular grating with a period of 3 μm is 81% when the incident light is normal-incidence, which is slightly less than the diffraction efficiency of the small-period oblique grating. However, when considering the depth processing error and the divergence angle of the incident light, the right triangular grating presents the obvious advantage over the oblique grating. The right triangular grating designed could achieve higher diffraction efficiency with a large period.