Generating Fano resonances in the microwave domain using acousto-optic modulation on a polymer-loaded LNOI platform

Advances in microwave photonics call for the investigation of Fano resonances in the microwave domain for efficient signal generation and processing. While emerging integrated acousto-optic (AO) technology provides a promising approach for this purpose, Fano resonances in these systems have seldom been reported. Here, based on a polymer-loaded lithium niobate on insulator (LNOI) platform, we achieve efficient AO and electro-optic (EO) coupling in a well-designed photonic crystal nanobeam cavity (PCNBC), enabling Fano resonance in the microwave domain within a single AO modulator. The characteristics of the Fano resonance are strongly determined by the acoustic modes. By adjusting the gap between the PCNBC and the interdigital transducer, the Fano resonance can be periodically tuned for a given acoustic mode. Additionally, its dependence on radio-frequency power is demonstrated, achieving a high extinction ratio up to 44 dB at a low radio-frequency power of -25 dBm. This work provides an approach to achieve the Fano resonance in the microwave domain, promoting the development of the AO-based devices in microwave photonics.