Optimizing Sawtooth Electrodes for Ultra-high-speed Electro-optic Modulators

Electro-optic (EO) modulators with ultra-high speed and low driving voltage are essential for high-performance optical computing, optical communication, and broadband microwave photonic links. In this work, we have proposed an electrode optimization method for periodic structures, based on the RGLC transmission line model and exemplified by sawtooth traveling-wave electrodes (STWEs). We have established analytical expressions for characteristic parameters including the resistance, inductance, capacitance, as well as the slot depth and width of STWEs for the first time, achieving synchronous optimization of microwave loss minimization and velocity matching. Validated through simulations on thin-film lithium niobate modulators, the approach achieves an ultra-high EO bandwidth of up to 290 GHz and a low voltage-length product of 2.5 V·cm. The optimized STWEs feature a minimum linewidth of 5 μm and a metal thickness as thin as 500 nm, which are compatible with deep ultraviolet lithography and suitable for large-scale, low-cost fabrication. This work would pave the way for developing scalable ultra-high-speed EO modulator arrays.