High fabrication tolerance and broadband silicon polarization beam splitter by point-symmetric cascaded fast quasiadiabatic couplers

We propose a high fabrication tolerance and broadband silicon polarization beam splitter (PBS) by cascading point-symmetric 3-dB couplers designed using fast quasiadiabatic dynamics (FAQUAD). The FAQUAD strategy only requires access to a single control parameter, and it can shorten the conventional adiabatic designs, maintaining the broadband characteristic and robustness to fabrication errors. The 3-dB FAQUAD coupler for the TM₀ mode is made invisible to the TE₀ mode due to a large difference in their adiabaticity parameters. Moreover, the system of cascaded point-symmetric devices further enhances the bandwidth and fabrication tolerance of the FAQUAD PBS. The total length of the FAQUAD PBS is 89.4 µm. We find that the FAQUAD PBS exhibits > 10 dB extinction ratio (ER) for the input TM₀ mode and the input TE₀ mode over a bandwidth of 240 nm and 260 nm, with excess losses below 0.4 dB and 0.021 dB, respectively. The PBS also exhibits excellent fabrication tolerance, showing an ER > 24 dB and an excess loss < 0.19 dB for the TM₀ mode, and an ER > 16.8 dB and an excess loss < 0.024 dB for the TE₀ mode for waveguide width deviation from −100 nm to 100 nm. For silicon thickness variation from 210 nm to 230 nm, an ER > 15.3 dB and excess loss < 0.2 dB for the TM₀ mode, and an ER > 15.9 dB and excess loss < 0.015 dB for the TE₀ mode are observed.