Design of a compact polarization beam splitter for silicon-based cross-slot waveguides

In this paper, a compact polarization beam splitter (PBS) for cross-slot waveguides is numerically proposed and designed. The device is based on the mode-coupling theory with an asymmetric directional coupler (DC) system, in which the input quasi-TM mode is fully coupled into the cross port and the quasi-TE mode remains transmitting in the through port. With properly chosen structural parameters, a compact PBS with a length of 13.2 mu m, including the coupling and S-bend sections, is realized. This is much shorter than PBSs using the symmetric DC system. The numerical results show that the optimized extinction ratios (ERs) are 25.5 and 23.6 dB for the quasi-TE and quasi-TM modes, respectively. Moreover, the ERs are higher than 15 dB for both polarizations over the wavelength range from 1.5 to 1.6 mu m, indicating a broad operating bandwidth.