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提出了一种基于块状亚波长光栅的偏振不敏感宽光谱高反镜的设计方法。亚波长光栅的反射性能由光栅的结构参数即周期和占空比决定,优化周期和占空比值将使亚波长光栅在更宽的光谱范围内具有更高的反射率。采用严格耦合波分析法计算不同周期下光栅的反射率,再构造一个集合包含所有反射率超过99%的光栅周期值,运用迭代优化算法,减小集合的数据规模,从而快速确定最优的光栅周期值和它对应的占空比值。仿真结果显示,使用标准的绝缘体上硅(SOI)晶片制作的二维块状亚波长光栅反射镜将在182nm的光谱范围内保持超过99%的反射率,同时光栅的反射特性与垂直入射光的偏振态无关,但是当入射角大于7°时在1439~1621nm的波长范围内光栅的反射率将无法始终保持在99%以上。因此,可以将二维块状亚波长光栅应用在垂直腔面激光器上,用于激光多普勒测速或者构建光缓存的二维网络。最后,通过数值仿真证实,在二维块状亚波长光栅反射镜的制作过程中,允许周期值和占空比值存在一定的误差。
A design method of polarization-insensitive wide-spectrum high-reflex mirror based on block sub-wavelength grating is proposed. The sub-wavelength grating’s reflectivity is determined by the grating’s structural parameters, ie period and duty cycle. Optimizing the period and duty cycle values will result in sub-wavelength gratings with higher reflectivity over a wider spectral range. A rigorous coupled-wave analysis method was used to calculate the reflectivity of the grating at different periods. A set was constructed that included all the grating periods with reflectivity over 99%. Using an iterative optimization algorithm, the data size of the set was reduced to quickly determine the optimal grating The period value and its corresponding duty cycle value. Simulation results show that two-dimensional bulk subwavelength grating mirrors made using standard silicon on insulator (SOI) wafers will retain over 99% reflectivity over a spectral range of 182 nm, with the reflection characteristics of the gratings being similar to those of vertically incident light independent of the polarization state, but when the incident angle is greater than 7 ° in the wavelength range of 1439 ~ 1621nm grating reflectivity will not remain above 99%. Thus, the two-dimensional sub-wavelength grating block can be applied in the vertical cavity surface laser for laser Doppler speed or two-dimensional network to build optical buffer. Finally, it is confirmed by numerical simulation that there is a certain error in the values of the period value and the duty cycle in the fabrication of two-dimensional bulk subwavelength grating mirrors.