Compact and Efficient Acousto-Optic Modulation with Integrated Bragg Grating on a Suspended AlN Platform

Abstract

Acousto-optic (AO) modulation presents significant potential for applications in integrated microwave and optical signal processing. However, conventional AO devices struggle to achieve high modulation efficiency within an ultracompact footprint due to the limited interaction length. In this work, we demonstrate cavity-enhanced intramodal and intermodal AO modulators based on a Bragg grating Fabry–Perot (FP) resonator fabricated on suspended aluminum nitride (AlN) waveguide. The incorporation of FP resonator achieves a remarkable 10 dB enhancement in modulation efficiency within an ultracompact 450 × 70 μm2 footprint. The optimized device exhibits a high intramodal modulation efficiency of −22.5 dB and a narrow 3 dB RF bandwidth of 6.8 MHz at frequency of 2.43 GHz with RF drive power of 16 dBm. Moreover, the intermodal modulator efficiently scatters pump waves from TE00 mode to the TE10 anti-Stokes sideband, achieving a single-sideband contrast exceeding 15 dB. These results provide a novel strategy for enhancing modulation performance and show strong potential for on-chip acousto-optic frequency shifters and narrow-bandwidth microwave photonic filters.