A compact high extinction ratio polarization beam splitter based on an asymmetric directional coupler was proposed and theoretically investigated. The asymmetric directional coupler consists of a silicon wire waveguide and a 1D periodic silicon rods waveguide, which results in an ultracompact polarization splitting length. By using the plane wave expansion method, a minimum coupling length of 3.43 mu m was obtained, and the length was then confirmed by finite-difference time-domain simulation. Moreover, for 1550 nm wavelength, high extinction ratios of about 28 and 18 dB were also observed for TE and TM polarizations, respectively. The ultrahigh extinction ratio for TE polarization is mainly arising from the appearance of TM bandgap in the periodic rods waveguide. In addition, for both polarizations, the extinction ratios are all above 10 dB covering a 180 nm bandwidth, and it was also demonstrated that the device has a high transmission for TM polarization. (C) 2015 Optical Society of America
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