Mid-infrared continua via spectral broadening and difference-frequency generation in a nanophotonic lithium niobate waveguide

Periodically poled thin film lithium niobate waveguides provide simultaneous access to efficient second- and third-order nonlinear processes, enabling broadband generation of coherent laser light. Here, we demonstrate the generation of a broadband mid-infrared continuum in a nanophotonic lithium niobate waveguide pumped by a telecom-wavelength femtosecond source. Specifically, our dual-stage design includes third-order nonlinear spectral broadening followed by a dedicated periodically poled waveguide section performing efficient broadband intrapulse difference-frequency generation. Driven by sub-100 fs pulses with an estimated on-chip pulse energy of around 200 pJ, the generated mid-infrared light covers wavelengths from 3200 to 4800 nm. Cascaded harmonic generation also extends the spectrum into the visible and ultraviolet domains, resulting in an overall spectral bandwidth ranging from 350 to 4800 nm.