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基于严格耦合波理论建立了梯形介质膜光栅的衍射机理模型,利用该模型讨论了底角为70°的梯形介质膜光栅-1级的衍射行为。通过对梯形介质膜光栅的占空比、槽深和剩余厚度的优化,设计了应用于1053 nm和51.2°角度入射的梯形介质膜光栅。对于顶层为HfO2的介质膜光栅,当槽深为200 nm,剩余厚度为100 nm,占空比为0.35时,其衍射效率优于99.5%,而对于顶层为SiO2的梯形光栅,为获得99.5%的衍射效率,其槽深为800 nm,剩余厚度为320 nm。而且,获得同样的衍射效率,顶层为HfO2的梯形光栅具有更宽的光谱特性。数值计算表明,严格耦合波理论模型对梯形介质膜光栅衍射效率的计算具有很好的收敛性和稳定性。
The diffraction mechanism model of trapezoidal dielectric film grating is established based on the strictly coupled wave theory. The diffraction behavior of the trapezoidal dielectric film grating -1 order with the base angle of 70 ° is discussed. By optimizing the duty cycle, groove depth and residual thickness of the trapezoidal dielectric grating, trapezoidal dielectric grating is designed for the incident angles of 1053 nm and 51.2 °. For the dielectric film grating with HfO2 as the top layer, the diffraction efficiency is better than 99.5% when the groove depth is 200 nm, the residual thickness is 100 nm and the duty cycle is 0.35. For the trapezoidal grating with SiO2 as the top layer, 99.5% Of the diffraction efficiency, the groove depth of 800 nm, the remaining thickness of 320 nm. Moreover, to obtain the same diffraction efficiency, the trapezoidal grating with HfO2 top layer has broader spectral characteristics. Numerical calculations show that the rigorous coupled-wave theory model has good convergence and stability for the calculation of diffraction efficiency of trapezoidal dielectric grating.