Ultra-broadband and high extinction ratio silicon TM-pass polarizer based on grating-assisted antisymmetric multimode waveguide

We propose an all-silicon TM-pass polarizer using a grating-assisted antisymmetric multimode waveguide (GAMW). The GAMW design facilitates the conversion of the undesired TE0 0 mode into the back-reflected TE1 1 mode, enabling efficient transmission of the desired TM0 0 mode with low insertion loss (IL) and high extinction ratio (ER). Furthermore, by cascading multiple GAMW structures, the device can filter TE0 0 mode over a broader spectral range effectively. The simulation results indicate that the single-GAMW-based polarizer achieves IL < 0.17 dB and ER > 40 dB in the wavelength range from 1480 nm to 1620 nm. When cascaded, the device expands the bandwidth to 275 nm (1435 nm-1710 nm), maintaining IL < 1 dB and ER > 40 dB simultaneously. The bandwidth can be further improved by cascading more GAMW structures working at different central Bragg wavelength. Limited by the measuring equipment, the measured wavelength range is between [1470 nm, 1630 nm]. The results of experiment demonstrate that the fabricated single-GAMW-based polarizer achieves IL < 0.65 dB and ER > 28.4 dB in 144 nm bandwidth ranging from 1470 nm to 1614 nm. For the cascaded-GAMW-based polarizer, IL < 0.83 dB and ER > 28.8 dB is achieved throughout the entire measuring wavelength range.