Efficient Silicon Nitride Coupler for Intrinsic Silicon Nitride Single-photon Emitters

Efficient coupling remains a critical challenge in quantum photonics, primarily due to the size mismatch and material incompatibility between quantum emitters and photonic integrated circuits.[1] To overcome these limitations, we utilize inverse design methodologies to develop a topology-optimized silicon nitride (Si₃N₄) coupler. This structure functions as a photonic–plasmonic hybrid cavity, designed to maximize both the emitted power and photon extraction efficiency from intrinsic silicon nitride single-photon emitters (SPEs), while maintaining fabrication feasibility.[2] Our approach employs topology optimization (TO) supported by a commercial finite-difference time-domain solver (Tidy3D).[3] The simulation model incorporates a Si₃N₄ nanopillar as the excitation source within the design region, which is directly connected to an output waveguide. The Si₃N₄ nanopillar enables the site-controlled generation of silicon nitride SPEs,[4] while a gold nanodisk placed atop the pillar introduces plasmonic enhancement. Together, these elements form a hybrid photonic–plasmonic cavity. The resulting optimized structure improves mode overlap and directional emission, leading to a significant enhancement in both photon extraction and waveguide coupling efficiency. The proposed coupler design supports the development of scalable and high-performance quantum photonic systems by addressing key integration challenges of single-photon sources. Moreover, our work underscores the potential of topology optimization in creating highly efficient photonic components, thereby facilitating the realization of robust and practical quantum technologies, including quantum communication and quantum sensing. A manuscript detailing this work is in preparation and will be submitted for publication.