Highly Efficient Continuous‐Wave Mid‐Infrared Emission and Communication in Nanophotonic Lithium Niobate Waveguides

ABSTRACT Modal‐phase matching (MPM) in the waveguides has been employed for second‐harmonic generation and sum‐frequency generation. However, mid‐infrared (MIR) generation via difference frequency generation (DFG) based on MPM waveguides has not been experimentally demonstrated. Here, both the reverse‐polarization dual‐layer and proton‐exchanged lithium niobate waveguides with MPM are utilized to generate MIR light through the DFG process, yielding a maximum normalized conversion efficiency of 443.8% W − 1 cm − 2 at 2565.2 nm in the dual‐layer lithium niobate waveguide. In addition, tunable MIR light with a bandwidth of 112.6 nm is achieved by controlling the temperature of the waveguide. This waveguide exhibits strong potential for practical applications, as demonstrated by the successful realization of MIR communication via DFG using a modulated signal light. These results not only confirm the superiority of modal‐phase‐matched waveguide structures for MIR light generation but also offer a novel strategy for enabling on‐chip MIR optical communication.