Low-loss, large-bandwidth multi-tip edge coupler for heterogeneous chip integration with large-mode-field-diameter

To address the challenge of high coupling losses in integrating wide-waveguide, large mode-field-diameter (MFD) laser gain chips with silicon-based photonic chips, this paper proposes a four-segment multi-tip edge coupler (FS-MTEC) based on a Si₃N₄-on-insulator (SINOI) platform. By utilizing a multi-tip array structure at the coupling end to tailor the mode field distribution, the device achieves 95% mode overlap efficiency with laser gain chips featuring an elliptical spot MFD of 50 µm × 2.5 µm. The transition section adopts a three-segment tapered waveguide composite structure that suppresses modal perturbations and diffraction effects within a compact length of 650 µm. Three-dimensional finite-difference time-domain (3D-FDTD) simulations demonstrate that the optimized FS-MTEC achieves TE- and TM-mode coupling efficiencies as high as 88% and 92% respectively at 1550 nm wavelength, corresponding to coupling losses of merely 0.56 dB and 0.40 dB. This coupling performance rivals that of edge couplers specifically designed for single-mode or small MFD laser chips. The device exhibits ultrabroadband operation from the long-wave part of the O-band to L-band with <1 dB coupling loss, while maintaining a horizontal misalignment tolerance of ±8.5 µm for ≤1 dB excess loss. Moreover, we conducted manufacturing tolerance and Monte Carlo analyses on the FS-MTEC, demonstrating the strong robustness of this device. This work provides what we believe to be a new edge-coupling strategy for heterogeneous chip integration of wide-waveguide, large-MFD laser chips with silicon-based photonic chips.