Compact polarization beam splitter based on subwavelength grating waveguide assisted directional coupler in ultra-thin silicon nitride platform

Abstract

We propose a compact PBS in the ultra-thin Si3N4 platform based on a subwavelength grating (SWG) waveguide-assisted three-waveguide directional coupler. Compared with the two-waveguide directional coupler (DC), it has a larger supermode effective refractive index difference, so it can significantly reduce the beat length of TE and TM polarization coupling. In addition, by replacing one of the dielectric waveguides with a subwavelength grating waveguide, the beat length of TE polarization coupling can be exactly twice that of TM polarization. The coupling region length of our proposed PBS is only 190 μm. In the bandwidth from 1480nm to 1600nm, the insertion loss of the PBS for TE and TM polarizations are both less than 0.41 dB, and the polarization extinction ratios are higher than 15 dB.