High-Efficiency and Ultra-Compact Thin-Film Lithium Niobate Phase Modulator Based on a Dual-Noncentered Waveguides Recycling Structure

Wideband electro-optic phase modulator (PM) serves as a pivotal component in modern photonic systems, enabling critical applications ranging from high-speed optical communication and broadband optical frequency comb (OFC) generation to high-resolution microwave photonic radar imaging. In this work, we propose a high-efficiency and ultra-compact thin-film lithium niobate (TFLN) PM based on a dual-noncentered waveguides recycling structure. In the proposed electro-optic PM, two specially-designed noncentered waveguides are placed within a shared modulation region of the capacitively-loaded travelling wave electrodes (CL-TWEs). By passing the optical signal through the modulation region twice via a loop-back waveguide and optical crossing, the interaction between the optical mode and electrical field is enhanced, thereby significantly boosting the modulation efficiency. The chip is designed, fabricated and evaluated. The experimental results demonstrate that the proposed TFLN PM achieves a low voltage-length product (V_π·L) of 3.5 V·cm at 11.6 GHz, a low-V_π bandwidth of 6.2 GHz, a high working frequency up to 46.6 GHz, and an ultra-compact footprint of 0.4×5.5 mm². By leveraging the fabricated TFLN-PM, tunable OFCs with comb spacings of 9 GHz, 11 GHz and 14 GHz are experimentally generated. The proposed TFLN PM delivers high modulation efficiency, wide operational bandwidth and an ultra-compact footprint, making it a promising candidate for next-generation optical communication and signal processing systems.