Optomechanical Integrated Circuits for Efficient Microwave-to-Optical Transduction

Abstract

Microwave-to-optical transduction is crucial for long-distance data transmission in both clas-sical and quantum networks. In classical applications, microwave-to-optical transduction can be achieved through electro-optics effect. In quantum applications, cavity-optomechanical systems with microwave phononic mode are uniquely suitable for this task. However, a scalable platform to achieve efficient microwave-to-optical transduction is still elusive. This work presents three novel approaches to address these limitations. First, a wafer-scale boron-doped gallium phosphide (BGaP) material platform is utilized to demonstrate scalable optomechanical devices. The BGaP optical resonators exhibit intrinsic quality factors exceeding 25,000 at visible and 200,000 at telecom wavelengths. It further demonstrates a low acoustic propagation loss and an integrated acousto-optic frequency shifter (AOFS) using a zinc oxide (ZnO) hybrid integration. These results show BGaP material as a promising platform for scalable optomechanical technologies. Second, we develop a BGaP-based optomechanical integrated circuit (OMIC) featuring the first ring-type optomechanical cavity—an optomechanical ring resonator (OMR)—in which phononic and photonic modes co-circulate and interact. The hybrid platform, which combines suspended BGaP for waveguiding and ZnO for phonon generation, achieved an intermodal conversion efficiency of ηi = 2.1% at a low acoustic pump power of 1.6 mW. This enables an efficient microwave-to-optical transduction for quantum information and microwave photonics applications. Finally, we introduce a non-suspended OMIC using silicon-on-sapphire (SOS), compatible with state-of-the-art superconducting qubits. By leveraging the triple co-resonance modes, we report a phonon pump-enhanced coupling rate Gb = 3.6 GHz/mW−1/2 at a low microwave drive power PMW = 3.6 mW. This is the first OMIC demonstration on a non-suspended material platform with a GHz pump-enhanced coupling rate, and we project a two-order magnitude improvement of coupling rate by optimizing the design, which paves the way for an ultra-efficient microwave- to-optical conversion for quantum interconnect. We conclude by discussing the outlook and the challenges of OMIC and propose possible ways to improve the OMIC performance for quantum transduction.