倒梯形双层金属光栅式偏振分束器

为获得高衍射效率、高消光比、宽带宽及大角度容差的光栅结构，提出了一种在近红外波长区域工作的倒梯形双层金属光栅结构的偏振分束器。该结构引入了一层高折射率介质层，并且将光栅区的光刻胶斜切成倒梯形结构，新的设计增大了光栅的透射效率和消光比。使用严格耦合波分析方法，模拟和优化了偏振分束器的结构参数。结果表明，横磁波及横电波在1 290~1 840 nm波长范围内的透射效率和反射效率分别超过97%和95%。透射和反射的最大消光比分别为33 dB和53 dB。在波长为1 550 nm，入射角为-40~40时，光栅的透射和反射消光比都大于22 dB，达到了高性能偏振分束器的要求。相较于双层金属矩形光栅，所提出的倒梯形双层金属结构表现出更高的透射性与反射性，同时具有更好的设计灵活性。

Polarization beam splitter with inverted trapezoidal double-layer metal grating

In order to obtain high diffraction efficiency, high extinction ratio, wide spectrum, and large angle tolerance grating structure, a polarizing beam splitter with inverted trapezoidal double layer metal grating structure working in the near-infrared wavelength region was proposed. The PBS structure included a high refractive index dielectric layer and cut the photoresist of the grating region into an inverted trapezoidal structure, which increased the transmission efficiency and extinction ratio of the grating. Rigorous coupled-wave analysis method was used to simulate and optimize the polarization beam splitter parameters. The results show that more than 97% transmission efficiency of the transverse magnetic wave and over 95% reflection efficiency of the transverse electric wave can be achieved in the wavelength range from 1 290 to 1 840 nm. The corresponding maximum extinction ratios for the transmittance and reflectance are 33 dB and 53 dB, respectively. The proposed grating has an extinction ratios over 22 dB in the 1 550 nm wavelength and a large angle from -40 to 40, which meets the requirements for the high-performance polarizing beam splitters. Compared with the commonly used double layer metal rectangular gratings, the proposed inverted trapezoidal double layer structure exhibits higher transmittance and reflectance, which has greater design flexibility.