Ultrashort and ultrabroadband silicon polarization beam splitter based on a bent directional coupler

A novel ultra-short polarization beam splitter (PBS) based on a bent directional coupler is proposed. The bent directional coupler has two bent optical waveguides with different core widths, which is designed to have phase-matching for TM polarization while there is a significant phase-mismatch for TE polarization. Therefore, the TM polarized light can be coupled from the narrow input waveguide to the adjacent wide waveguide while the TE polarization goes through the coupling region without significant coupling. An ultra-short (<10 mu m-long) PBS is designed based on silicon-on-insulator nanowires and the length of the bent coupling region is as small as 4.5 mu m when choosing the gap width as 200nm (large enough to simplify the fabrication). The numerical simulations show that the present PBS has a good fabrication tolerance for the variation of the waveguide width (more than +/- 60nm) and a very broad band (200nm) for an extinction ratio of > 10dB.