Three-dimensional trident edge coupler with ultralow loss and broad bandwidth for standard single-mode fiber

We present a three-dimensional trident edge coupler based on silicon nitride material specifically designed for standard single-mode fiber. The coupler demonstrates exceptional performance, achieving total coupling losses of 0.15 dB for the TE mode and 0.31 dB for the TM mode at a wavelength of 1550 nm and a 0.5 dB optical bandwidth exceeding 200 nm. The polarization-dependent loss remains below 0.18 dB across the wavelength range of 1450–1650 nm. Furthermore, the fiber alignment tolerances for 1 dB excess loss are ±1.9µm and ±2µm in the horizontal and vertical directions, respectively. The robustness of the design against fabrication imperfections is also evaluated, highlighting its practical applicability. This result provides a new ultralow-loss end-coupling solution for optoelectronic integrated chips.