Design and simulation of a compact and ultra-wideband polarization beam splitter based on sub-wavelength grating multimode interference coupler

摘要

A compact and ultra-wideband multimode interferometer (MMI)-based polarization beam splitter (PBS) is designed in a silicon-on-insulator (SOI) platform. A sub-wavelength grating (SWG) structure is employed in the multimode region to reduce the overall length of the structure and also increase its operating bandwidth. Instead of using the beat-length difference to separate the transverse electric (TE) and transverse magnetic (TM) polarized waves, the TM waves are directly coupled to the output bar port through an interconnecting waveguide, while the TE polarized waves are transmitted to the cross port by the self-imaging process. This substantially reduces the length of the PBS and the overall footprint can be as small as 4.8 x 21 mu m(2). The proposed device exhibits the extinction ratio of more than 15 dB in a 250 nm wavelength range (1.38-1.63 mu m) and more than 12 dB in the 350 nm wavelength range (1.3-1.65 mu m) for the TE and TM polarizations, respectively. In addition, the insertion loss remains below 1.2 dB for both the TE and TM polarization in a broad wavelength range from 1.38 to 1.54 mu m. The proposed PBS can be fabricated by a single-step etching process on an SOI wafer. Moreover, our simulations show the robustness of the PBS performance to the fabrication errors'.