On-chip silicon dual-mode multiplexer via a subwavelength grating-based directional coupler and a mode blocker

An on-chip silicon dual-mode multiplexer (MUX) is proposed via a subwavelength grating (SWG)-based directional coupler and a mode blocker. The proposed mode MUX is optimized by utilizing the three-dimensional full-vectorial finite-difference time-domain-based band structure and propagation calculations. The simulated results indicate that an ultralow mode cross talk of $ - {40}\,\,{\rm dB}$-40dB at the operating wavelength of 1550 nm can be achieved by introducing a ${{\rm TE}_0}$TE₀ mode blocker. Benefiting from the triple SWG coupler, the mode-coupling strength can be significantly enhanced inside the proposed mode MUX, which can achieve a compact coupling length of 8.75 µm, a low insertion loss of 0.39 dB at 1550 nm, an ultrabroad bandwidth of 310 nm for the mode CT $ \lt - {15.0}\,\,{\rm dB}$<-15.0dB, and insensitivity to fabrication errors.