Design and simulation of high modulation efficiency, low group velocity dispersion lithium niobate slow-wave electro-optic modulator based on a fishbone-like grating

• In this paper, we propose an on-chip slow-wave electro-optic modulator with improved modulation efficiency on lithium-niobate-on-insulator platform. • The slow-light effect is realized with flat optical operating bandwidth, near zero group velocity dispersion, and low loss. • A matched micro-structure electrode is designed to realize the low group velocity of the microwave modulation signal. Thin-film lithium niobate (LN) has emerged as an excellent platform for electro-optic modulators (EOMs) owing to its strong electro-optic (Pockels) effect. However, it remains an open challenge to achieve high modulation efficiency in chip-scale EOMs, primarily due to the limitation of light-matter interaction. Here, we propose an on-chip slow-wave LN EOM with a length of 3.4 mm with high modulation efficiency by using a fishbone-like grating. By assembling the fishbone-like grating, the Pockels effect is significantly enhanced as a result of the compression of the local density of states. Benefiting from this effect, the modulation efficiency of the modulator can be improved to 4.6 times of the original. In addition, a 3 mm matched micro-structure electrode is designed to realize the low group velocity of the microwave modulation signal. The simulation results show that the modulation efficiency of this slow-wave EOM is 1.42 V·cm. The slow-light effect is realized theoretically with a flat optical operating bandwidth of about 21 nm, group velocity dispersion < 2 ps 2 /mm, and low loss < 0.33 dB. Additionally, a 3 dB modulation bandwidth of 80 GHz is verified by simulation by virtue of the proposed micro-structure electrode.