Ultracompact Silicon-Based Polarization Beam Splitter Using Subwavelength Gratings

An ultracompact polarization beam splitter based on silicon nitride-on-silicon platform is proposed and analyzed, where the two polarized modes are guided in two separated layers independently, almost no affecting each other. By using subwavelength grating structure in bottom silicon layer, the injected TE mode undergoes a strong coupling from input port to adjacent waveguide and then outputs from a bending waveguide. As to the injected TM mode, it is directly transmitted along the above silicon nitride layer. Moreover, the adjacent waveguide in bottom layer is cut by a right angle at one corner to further enhance the device performance. Results show that a coupling length of only 2.7 μm is achieved with an insertion loss of 0.22 dB (0.2 dB), an extinction ratio of 27.05 dB (25.73 dB), and a reflection loss of -26.94 dB (-37.79 dB) for TE (TM) mode at 1.55 μm. In addition, fabrication tolerances and field evolution are also presented.