Ultrahigh-extinction-ratio and broadband all-silicon TM-pass polarizer by employing multimode anti-symmetric apodized Bragg grating

Abstract

On-chip polarizers are the essential components for polarization management in integrated systems. Hence, polarizers with broad operation bandwidth (BW), low insert loss (IL), and high polarization extinction ratio (PER) are highly desired. A broadband and ultra-high ER all-silicon transverse-magnetic-pass polarizer is presented and experimentally demonstrated on the 220 nm silicon-on-insulator platform. The proposed device consists of a TE1 mode filter and a multimode anti-symmetric apodized Bragg grating (MASABG). The MASABG works as a Bragg reflector to convert forward TE0 to backward TE1 mode, and then the reflected TE1 gradually evolves into the TE0 mode in the mode filter and finally leaks out. The device exhibits efficient polarization selectivity, facilitated by fully etched rectangular holes inside the waveguide to introduce strong periodic perturbations in the MASABG. Simulation results predict that the designed polarizer achieves ultra-high PER ∼60 dB with low IL < 0.2 dB at around 1550 nm, and the calculated BWs for PER >30 and >40 dB are estimated to be 275 and 268 nm, respectively. More importantly, the reflection of the eliminated TE polarization is suppressed to below −12 dB. For the fabricated polarizer, the measured BWs for PER >30 and >40 dB are about 260 and 150 nm, respectively, and the measured IL is <0.9 dB in a wide wavelength range of 1410–1700 nm.