High extinction ratio and broadband polarization beam splitter based on bricked subwavelength gratings on SOI platform

Abstract

A compact asymmetrical directional coupler (ADC) based on coupling between a conventional subwavelength grating (SWG) and a bricked subwavelength grating (BSWG) is proposed to realize broadband polarization beam splitter (PBS) with high extinction ratio (ER) on silicon-on-insulator (SOI) platform. Apart from conventional SWG structural parameters (duty cycle and period), the BSWG is utilized to provide a new design space to control TE and TM modal effective index for accurate phase match. Accordingly, as to the TM mode, it is possible to satisfy phase-matching condition and then can be coupled more efficiently with higher ER by introducing the BSWG. Meanwhile, there is a significant phase mismatch for the TE mode. In this way, the proposed PBS that separates TE and TM mode to the through and cross ports can be realized. Simulation results show that the proposed PBS with a compact coupling length of 8.4 μm can achieve a high ER of 35.06 dB and an insertion loss of 0.25 dB for the TM mode at 1.55 μm, while the ER is 18.92 dB and insertion loss is 0.01 dB for the TE mode. Moreover, the operating bandwidth is up to 300 nm (1400∼1700 nm) for the TE mode and 155 nm (1487∼1642 nm) for the TM mode when the ER is >15 dB.