High-speed integrated lithium niobate low-index rib loaded waveguide modulator without direct lithium niobate etching

Integrated thin film lithium niobate (TFLN) modulators are emerging as an appealing choice for fiber-optic communications, data centers, and microwave photonics due to their high modulation speed and low driving voltage. The key step in fabricating integrated TFLN modulators is the high-quality etching of TFLN, which typically requires long-term fabrication process iteration and specialized equipment. Here we present an integrated TFLN modulator by incorporating low-index rib loaded waveguides onto TFLN without direct etching of TFLN. Based on our systematic investigation into the theory and design methodology of this design, we experimentally demonstrated a 1.3 cm-long Mach-Zender modulator, featuring a 3-dB bandwidth of 59 GHz and a half-wave voltage of 1.96 V. Our design significantly simplifies the fabrication process of integrated TFLN modulators and in turn opens up new avenues for the mass production of high-performance TFLN modulators at low cost.