Ultralow-loss polarization-insensitive silicon nitride-assisted double-etched silicon edge coupler with polarization splitting

High-performance silicon-based edge couplers for interfacing with standard single-mode fibers encounter significant challenges due to limitations imposed by the minimum fabrication width. Here, we propose a silicon nitride-assisted double-etched O-band silicon edge coupler with a minimum width of 180 nm. Notably, the polarization splitting function naturally integrates into this edge coupler. Through simulation, the proposed edge coupler, without a cantilever, demonstrates a minimum coupling loss of 0.53/0.82 dB with an average extinction ratio of 42/18 dB for TE/TM polarization. Additionally, this edge coupler exhibits weak polarization dependence with an average difference of only 0.24 dB in the O band. Leveraging a segmented taper shape design, the 0.5-dB bandwidth of coupling loss extends to approximately 100 nm for both TE and TM polarizations, despite the inclusion of two evanescent coupling parts.