提出了一种基于硅基槽波导的级联多模干涉(MMI)耦合器型偏振分束器,由锥形及矩形结构MMI耦合器构成.级联结构使器件长度无需为两偏振模自镜像长度的公倍数,不仅能有效减小器件尺寸,而且提高设计灵活性.同时,利用槽波导的高双折射特性及MMI耦合器的锥形结构,可进一步缩短器件尺寸.分析结果表明,所提器件能够有效实现偏振束分离,两级MMI工作区总长度仅为42 μm,准TE与准TM模的偏振消光比分别为29.8和31.4 dB,1.55 μm波长下的插入损耗分别为0.395和0.699 dB,偏振消光比大于20 dB时光带宽为43 nm,覆盖整个C波段.最后,详细分析了器件关键参数的制造误差对器件性能的影响.

A compact polarization splitter (PS) based on tapered cascaded multimode interference (MMI) couplers in slot waveguide structures was proposed and characterized. By utilizing two cascaded MMI couplers, the two orthogonal polarizations, quasi-TE mode and quasi-TM mode, are efficiently separated without the necessary that the total length of the MMI must be common multiple of the self-imaging lengths of the two polarizations. This greatly reduces the length of the PS and improves the design flexibility. Meanwhile, the high birefringence of slot waveguides and the tapered MMI structure can further shorten the device length. Results show that a PS with a length of 42 μm in the MMI sections can be achieved, where the polarization extinction ratios (ERs) for the quasi-TE and quasi-TM modes are 29.8 and 31.4 dB, respectively. Optical bandwidth of 43 nm is obtained for keeping the ER over 20 dB. Moreover, fabrication tolerances to the structural parameters were investigated, and field evolution along the propagation distance through the PS was also demonstrated.