Broadband TM-mode-pass polarizer and polarization beam splitter using asymmetrical directional couplers based on silicon subwavelength grating

In this paper, an on-chip polarizer passing the transverse-magnetic mode and a polarization beam splitter are proposed. The polarizer achieves an extinction ratio exceeding 20 dB within a spectral range from 1500 nm to 1610 nm, and has a value of 24dB at 1550 nm with a coupling efficiency of 84%. By employing a specific wavelength of 1570 nm, the polarizer behaves as the polarization beam splitter with extinction ratio for the transverse-electric mode and the transverse-magnetic mode of 29dB and 24 dB, respectively. In addition, the coupling efficiency of 95.98% and 78.18% for above two polarizations, demonstrate that our approach has a potential to efficiently control coupling splitting ratio via silicon subwavelength grating.