Visible and Near-Infrared Thin-Film Lithium Niobate Modulators with Thermo-Optic Bias

High Resolution Image Download MS PowerPoint Slide Integrated photonics at submicrometer wavelengths holds the potential to enable scalable microsystems for quantum technologies, metrology, biophotonics, sensing, and displays, but on-chip modulation in this range remains challenging due to the limited availability of integration-ready materials that combine optical transparency with fast electro-optical (EO) modulation. Thin-film lithium niobate (TFLN) offers strong EO properties and a broad transparency window, and recent advances are rapidly expanding the functionality and performance of integrated TFLN platforms. At sub-μm wavelengths, however, the EO response is suppressed at low frequencies by rapid dielectric relaxation, hindering stable EO biasing and bias-sensitive operation. Here, we report sub-μm-wavelength TFLN Mach–Zehnder modulators (MZMs) that decouple bias control from radio frequency EO modulation by integrating thermo-optic (TO) phase shifters: the TO section provides stable bias tuning, while the EO section is reserved for high-frequency operation. Devices targeting wavelength bands from blue to 940 nm are fabricated in a single wafer-scale TFLN process, providing a foundry-compatible approach for bias-stable modulation across this spectral range. A blue-green MZM achieves an EO V π L of 0.91 V·cm at 488 nm, a TO P π of 40.4 mW at the same wavelength, and an EO bandwidth of >26.5 GHz at 461 nm, while a near-infrared MZM achieves an EO V π L of 2.81 V·cm, a TO P π of 150.3 mW, and an EO bandwidth of >26.5 GHz at 940 nm. We characterize the dielectric-relaxation time constants of the EO sections across all three designs and find values in the range of 0.9–6 μs. We further demonstrate bias stability exceeding 1 h at 461 nm and high-extinction-ratio pulse generation sustained for over 1.5 h at 875 nm, highlighting thermal biasing as a practical and scalable solution for bias-stable, high-speed TFLN modulators across the visible and submicrometer near-infrared spectrum.