3D Heterogeneous Integration of Silicon Nitride and Aluminum Nitride on Sapphire toward Ultra-wideband Photonics Integrated Circuits

Extending two-dimensional photonic integrated circuits (PICs) to three-dimensional (3D) configurations promises great potential for scaling up integration, enhancing functionality, and improving performance of PICs. Silicon-based 3D PICs have made substantial progress due to CMOS compatibility. However, the narrow bandgap of silicon (1.1 eV) limits their use in short-wavelength applications, such as chemical and biological sensing, underwater optical communications, and optical atomic clocks. In this work, we developed a 3D photonics platform by heterogeneously integrating silicon nitride (SiN) and aluminum nitride (AlN) PICs on sapphire (Al$_2$O$_3$). The broadband transparency of these materials allow our platform to operate over a multi-octave wavelength ranging from ultraviolet to infrared. Leveraging this platform, we demonstrated efficient optical nonlinearity in an AlN microcavity, low-loss and tunable SiN waveguide-based optical components, and optical linking between AlN and SiN PICs layers in the visible and near-infrared spectrum, hinting at potential applications in integrated quantum systems. Our work presents an ultra-wideband 3D PICs platform, providing new opportunities for broadband and short-wavelength applications of PICs.