Ultracompact and broadband polarization beam splitter utilizing the evanescent coupling between a hybrid plasmonic waveguide and a silicon nanowire.

An ultracompact polarization beam splitter (PBS) is proposed based on an asymmetrical directional coupler consisting of a silicon hybrid plasmonic waveguide (HPW) and a silicon nanowire. The widths of the two coupling waveguides are chosen so that the phase-matching condition is satisfied for TE polarization only while the phase mismatch is significant for TM polarization. A sharply bent silicon HPW is connected at the thru port to play the role of polarizer by utilizing its polarization-dependent loss. With the present principle, the designed PBS has a footprint as small as only ~1.9 μm × 3.7 μm, which is the shortest PBS reported until now, even when large waveguide dimensions (e.g., the waveguide widths w(1,2) = ~300 nm and the gap width w(gap) = ~200 nm) are chosen to simplify the fabrication process. The numerical simulations show that the designed PBS has a very broad band (~120 nm) with an extinction ratio >12 dB and a large fabrication tolerance to allow a waveguide width variation of ± 30 nm.