Fabrication‐Tolerant GaAs/SiN Coupling Above the Loss Threshold for Quantum Photonic Applications

ABSTRACT Quantum photonic integrated circuits (QPICs) are a promising platform for scalable quantum technologies. A major outstanding challenge is the efficient interconnection of diverse quantum photonic components, where optical losses must remain below the ∼10% threshold required for advanced quantum applications. In this paper, the optical coupling between GaAs single‐photon sources and a low‐loss SiN interposer is investigated, where reliable high‐efficiency transitions have not yet been achieved. To address this, a fully numerical framework is introduced for the optimization of waveguide mode couplers that directly incorporates experimentally characterized fabrication variations critically impacting performance, including waveguide misalignment, width deviation, and sidewall roughness. Using this approach, low‐loss GaAs/SiN transitions are designed and experimentally demonstrated with reproducible coupling efficiencies of –0.43 dB ± 0.14 dB. These results establish a viable path toward low‐loss heterogeneous QPICs tailored to advanced quantum applications.