High Alignment/Fabrication Tolerance Compact Multistage Trident-Type Silicon Nitride Edge Coupler

In this letter, we propose and demonstrate a compact multistage trident-shaped edge coupler with high misalignment and fabrication tolerance, comprising a central multistage tapered waveguide and two auxiliary waveguides on both sides, which achieves excellent compatibility with high-numerical-aperture (HNA) fibers. Simulation results reveal coupling efficiencies exceeding 94.7% and 93.1% for TE and TM polarizations, respectively, across the 1300∼ 1700 nm wavelength range, with a total device length of only 71.2μm. Furthermore, the device exhibits robust fabrication tolerance: under waveguide width deviations of -50 nm~150 nm, spacing deviations of ±500 nm, and sidewall angle variations of 10°, the coupling efficiency degradation remains below 5%. The 1dB alignment tolerance reaches ± 1.8μ m and ± 1.6 μm in both the y and z -directions. Experimental measurements demonstrate insertion losses of 0.96dB and 0.84dB for TE and TM modes, respectively.