Ultracompact folded racetrack modulator based on lithium niobate on insulator platform

Currently, thin-film lithium niobate structures have been employed to develop high-speed electro-optic modulators. Although lithium niobate electro-optic modulation technology has matured significantly, its conventional devices remain constrained by centimeter-scale footprints, hindering high-density integration. In this work, we propose a lithium niobate racetrack modulator based on a folded waveguide and electrode, overcoming large size limitations through structural reconfiguration. Experimental results demonstrate a breakthrough modulation efficiency of 8 pm/V, an expanded electro-optic bandwidth of 30.5 GHz, and successful 112 Gbps (56 GBaud PAM-4) data transmission. Compared with the Mach-Zehnder modulators, although the modulation efficiency of this modulator has decreased, its area has been reduced by an order of magnitude. Compared to traditional racetrack modulators with equivalent lengths, this design achieves nearly doubled bandwidth and reduces the physical footprint by approximately one half while maintaining identical optical performance. The proposed modulator establishes a viable pathway toward ultra-compact, broadband modulators for next-generation optical interconnects systems.