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嵌入式镀膜光栅是将平行四边形的介质膜层,以亚波长量级的周期嵌入波导中.针对该光栅在不同偏振态、不同角度入射下的各级衍射效率问题,本文基于严格耦合波分析理论,对该光栅进行建模与数值分析.结果表明,在TE模入射时,该光栅的一级衍射效率可随膜厚在[0,37%]内变化,其余非零级次的衍射效率低于2%.衍射特性可以满足平视器成像的效率递增要求,同时可以减少能量的损失与杂散成像光线.当入射光束的角度在纵向[45°,70°]、横向[-15°,15°]内变化时,一级衍射效率的变化平稳,可以保持平视器不同视场的成像能量均匀.针对入射光偏振态、光栅材料、嵌入膜层倾角、光栅周期对衍射特性的影响,给出了相应的数值分析,可为波导全息平视器中衍射元件的制作提供理论指导.
In the embedded coating grating, the parallelogram dielectric layers are embedded in the waveguides with sub-wavelength order.In this paper, based on the strict coupling wave theory , The grating is modeled and numerically analyzed.The results show that the first-order diffraction efficiency of the grating can change with the film thickness within [0, 37%] when the TE mode is incident, and the diffraction efficiency of the remaining non-zero order is low At 2%. The diffractive properties satisfy the progressive increase in efficiency of the frontal viewfinder imaging while reducing the energy loss and stray imaging light. When the angle of the incident light beam is in the longitudinal direction [45 °, 70 °], transverse direction [-15 °, 15 °], the first-order diffraction efficiency changes smoothly, and the imaging energy in different field of view of the front-viewers can be kept uniform. According to the influence of the polarization state of the incident light, the grating material, the inclination of the embedded layer and the grating period on the diffraction properties, The corresponding numerical analysis can provide theoretical guidance for the fabrication of diffraction elements in waveguide holographic head-up.