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Thin-film lithium niobate (TFLN) has gained significant attention as a platform for photonic integrated circuits (PICs) due to its exceptional properties, including high nonlinear coefficients and a strong electro-optic response. However, efficient coupling between TFLN chips and optical fibers remains a challenge, with current edge coupler designs often facing issues related to fabrication complexity and alignment precision. In this paper, we propose a high-efficiency, fabrication-friendly, and alignment-tolerant bident edge coupler based on TFLN to overcome these limitations. The design comprises three distinct regions: the facet coupling region, the beam combining region, and the adiabatic taper region. It achieves a measured coupling efficiency of better than -1.52 dB per facet at 1550 nm, with an average efficiency ranging from -1.85 to -1.6 dB across the C-band, and a mode field diameter of approximately 4 μm. Notably, the coupler offers a large alignment tolerance of ±1 μm. This design simplifies the fabrication process, requiring only a single overlay step. The proposed coupler offers a practical solution for optical interface packaging in TFLN devices, enabling high performance with low process complexity.
Liu et al. (Wed,) studied this question.