High-efficiency fiber-to-chip interface for aluminum nitride quantum photonics

Integrated nonlinear photonic circuits received rapid development in recent years, providing all-optical functionalities enabled by cavity-enhanced photon-photon interaction for classical and quantum applications. A high-efficiency fiber-to-chip interface is key to these integrated photonic circuits for quantum information tasks, as photon-loss is a major source that weakens quantum protocols. Here, overcoming material and fabrication limitation of thin-film aluminum nitride by adopting a stepwise waveguiding scheme, we demonstrate low-loss adiabatic fiber-optic couplers in aluminum nitride films with a substantial thickness (similar to 600 nm) for optimized nonlinear photon interaction. For telecom (1550 nm) and near-visible (780 nm) transverse magnetic-polarized light, the measured insertion loss of the fiber-optic coupler is -0.97 dB and -2.6 dB, respectively. Our results will facilitate the use of aluminum nitride integrated photonic circuits as efficient quantum resources for generation of entangled photons and squeezed light on microchips. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement