Grazing-Angle Fiber-to-Waveguide Coupler

The silicon photonics market has grown rapidly over recent decades due to the demand for high bandwidth and high data-transfer capabilities. Silicon photonics leverage well-developed semiconductor fabrication technologies to combine various photonic functionalities on the same chip. Complicated silicon photonic integrated circuits require a mass-producible packaging strategy with broadband, high coupling efficiency, and fiber-array fiber-to-chip couplers, which is a big challenge. In this paper, we propose a new approach to fiber-array fiber-to-chip couplers which have a complementary metal-oxide semiconductor-compatible silicon structure. An ultra-high numerical aperture fiber is polished at a grazing angle and positioned on a taper-in silicon waveguide. Our simulation results demonstrate a coupling efficiency of more than 90% over hundreds of nanometers and broad alignment tolerance ranges, supporting the use of a fiber array for the packaging. We anticipate that the proposed approach will be able to be used in commercialized systems and other photonic integrated circuit platforms, including those made from lithium niobate and silicon nitride.