Ultra-broadband near- to mid-infrared electro-optic modulator on thin-film lithium niobate

The escalating capacity limitations of conventional near-infrared telecommunication bands have spurred urgent investigations into full-spectrum optical communication systems spanning from the near-infrared to mid-infrared regimes. This has motivated the development of optical components combining broadband bandwidth with high-speed operation. Thin-film lithium niobate (TFLN) modulators, while exhibiting state-of-the-art performance in voltage-length product, optical loss, and electro-optic (EO) bandwidth at telecommunication wavelengths, face challenges in achieving broad operational bandwidth due to waveguide dispersion and velocity mismatch at longer wavelengths. Here, we present a Mach-Zehnder EO modulator comprising two adiabatic power splitters and a high-bandwidth phase shifter, achieving an unprecedented 800-nm operational bandwidth that covers the full optical fibre communication spectrum and extends into the 2-µm mid-infrared band. The fabricated modulator demonstrates > 67 GHz EO bandwidth in both O/C-bands and 48 GHz (detector-limited) in the 2-µm band. This device enables single-lane transmission exceeding 100 Gbaud across O-, C-, and 2-µm bands. Notably, we achieve 100 Gbaud OOK and 65 Gbaud PAM-4 transmission in the 2-µm band - the highest rates reported for this spectral region. This breakthrough establishes TFLN as a compelling platform for multispectral photonics, bridging conventional telecom infrastructure with emerging 2-µm technologies for next-generation full-spectrum optical communications.