Gigahertz thermoelastic acousto-optic modulation in lithium niobate integrated photonic device.

Tailoring the interaction between acoustic waves and optical waves in integrated photonic circuits has emerged as a promising avenue for quantum optics and high-speed information processing. Among various approaches, on-chip acousto-optic modulation (AOM) has been extensively explored in the past decade and successfully demonstrated across many integrated photonics platforms. In this paper, we design and fabricate metallic gratings with periods varying from 0.4 μm to 3 μm deposited on a half-etched thin film lithium niobate (TFLN) device cladded by 1-μm thick silica. By illuminating the metallic grating with an intensity-modulated pump beam, we can generate thermoelastically driven SAWs with frequencies up to 6.58 GHz, and a linewidth of 1.8 MHz at a center frequency of 1.41 GHz. This thermoelastic approach eliminates reliance on a piezoelectric material response, offering broader compatibility for integrated photonics applications.