利用有限元方法和时域有限差分方法,优化设计了一种结构紧凑的基于绝缘体上硅脊型纳米线光波导方向耦合器的TE/TM 偏振分束器。考虑到方向耦合器的波导间隙较小时制作工艺较为困难,且模式失配会引入一些损耗,因此波导间隙取约100 nm 较为合适。通过优化脊型纳米线光波导的几何尺寸(脊高和脊宽)、耦合区波导间隙,使得偏振分束器长度最短。数值计算结果表明经过优化的偏振分束器最短长度大约为17.3 μm,偏振分束器的消光比大于15 dB 时,波导宽度制作容差为－20～10 nm,带宽约为50 nm。

A compact TE/TM polarization beam splitter (PBS) based on a silicon-on-insulator (SOI) ridge nanowire directional coupler is designed and optimized by using a finite-element method (FEM) and a finite difference time domain (FDTD) method. Considering the fabrication precision and the mode mismatching loss in a directional coupler,a gap width about 100 nm is chosen. The ridge height,the ridge width and the gap of two parallel nanowires are optimized to have the shortest length for the polarization splitter. The numerical simulations show that the optimized PBS has a short length of about 17.3 μm,and the waveguide width has a fabrication tolerance of about－20-10 nm,and the bandwidth is about 50 nm when the extinction ratios for both polarizations are larger than 15 dB.