Realization of an ultra-short silicon polarization beam splitter with an asymmetrical bent directional coupler.

An ultra-short (~10 μm long) polarization beam splitter (PBS) based on an asymmetrical bent directional coupler (DC) is demonstrated experimentally by using silicon-on-insulator nanowires. The bent DC is designed to cross-couple TM polarized light completely while there is almost no coupling for TE polarization. Grating couplers are introduced at both ends of the PBS for efficient coupling to single-mode fibers. The measurement results show that the extinction ratios of the fabricated ultra-short PBS are higher than 10 dB for both polarizations in a broad wavelength range. It is also shown that the present PBS has a large fabrication tolerance.