High-Efficiency Cladding-Free Thermo-Optic Modulators via 1T′-MoTe₂/Silicon Waveguides

Silicon-based optical modulators are crucial for advancing silicon photonics, particularly in optical communication and sensing applications. Thermo-optic (TO) modulation is a convenient and effective approach with a large phase modulation depth, which stands out among various techniques. However, conventional TO modulators face inherent trade-offs: metallic heaters require thick SiO₂ isolation layers that limit thermal efficiency, while graphene-based designs incur large optical losses from transfer process-induced interfacial defects and absorption, ultimately restricting scalability in photonic integrated circuits. Herein, we demonstrate a high-efficiency thermo-optic Mach-Zehnder modulator (TO-MZM) based on 1T'-MoTe₂/silicon hybrid waveguides at a 1550 nm telecommunication wavelength. Through direct in situ fabrication of the hybrid waveguide structures on large-scale 1T'-MoTe₂ films grown on silicon-on-insulator (SOI) substrates, our design eliminates the requirement for thick silicon dioxide cladding in conventional metal-heater architectures while simultaneously improving thermal transfer efficiency and maintaining CMOS process compatibility. The device achieves a heating efficiency of 82.73 K·μm³/mW and an optimized phase-tuning efficiency of 0.396 π·mW^-1 with low optical loss, surpassing the performance metrics of previously reported electrically controlled TO-MZMs. Furthermore, the device achieves 30° beam steering in a 16-channel optical phased array, highlighting its potential for wide field view and low-power applications in LiDAR systems. Our results offer a scalable, energy-efficient solution for next-generation optical modulators in advanced optoelectronic systems.