Highly Efficient Intramodal and Intermodal Acousto-Optic Modulation on an Etchless Lithium Niobate Integrated Platform

Abstract

Harnessing light–sound interaction in photonic integrated circuits can enable many classical and quantum applications on a chip. With excellent piezoelectricity and broad transparency window, lithium niobate on insulator (LNOI) is an ideal platform for integrated acousto-optic devices. Here, by utilizing bound states in the continuum for ultralow-loss waveguiding, highly efficient intramodal and intermodal acousto-optic modulation is demonstrated on an etchless lithium niobate integrated platform in the telecommunication band. The maximal intramodal acousto-optic modulation efficiency is −13.17 dB, measured at microwave power of 14 dBm and drive frequency of 0.76 GHz, corresponding to a VπL of 1.133 V cm. The intermodal acousto-optic modulation is realized with TM00–TM10 mode conversion, achieving a single-sideband contrast of >20 dB over a broad optical bandwidth at drive frequency of ≈0.663 GHz, corresponding to a VπL of 1.993 V cm measured at ≈1551.6 nm. These devices establish a direct link between optical and microwave photons on LNOI platform, paving the way for many applications such as acoustic sensing, magnetic-free isolation, on-chip heterodyne detection, and programmable photonic routing.