Ultrahigh-efficiency slow-light modulator based on thin-film lithium niobate

Integrated high-bandwidth electro-optic modulators are the crucial cornerstones for next-generation communication and quantum information processing. Thin-film lithium niobate has emerged as a promising platform for developing such devices. Nevertheless, achieving miniaturized lithium niobate modulators that simultaneously offer large bandwidth and low loss remains a significant challenge for further on-chip applications. Here, we propose and simulate a high-efficiency slow-light modulator configuration consisting of a grating heterogeneously integrated on a lithium niobate waveguide. Leveraging the pronounced slow-light effect of high-order photonic modes, the designed electro-optic modulator achieves an ultra-high modulation efficiency of 0.67 V·cm with a group index as high as 9.58. Through elaborately optimizing the coupling tapers for the desired mode and designing the microstructured electrodes, the modulator transmittance is larger than 0.8 with a large operation bandwidth of 10 nm, and a 3 dB modulation bandwidth over 130 GHz is obtained. These exceptional performance metrics establish a solid foundation for developing advanced integrated photonic devices.