Ultra‐Broadband Continuous‐Wave Mid‐Infrared Wavelength Conversion in Germanium‐on‐Silicon Waveguides

The mid‐infrared (MIR) spectral region is pivotal for a wide range of applications, including molecular spectroscopy, free‐space communication, and hyperspectral imaging. Despite significant advancements in miniaturizing MIR sources over the past two decades, the development of fully integrated, widely tunable sources remains constrained by limitations in available gain materials, especially for the first atmospheric transparency window (3–5 µm). Nonlinear wavelength conversion in integrated photonic chips offers a promising approach to creating compact tunable MIR sources, serving as a competitive alternative to quantum cascade lasers, interband cascade lasers, and optical parametric oscillators. Here, ultra‐broadband MIR wavelength conversion in germanium‐on‐silicon (Ge‐on‐Si) waveguides is achieved for the first time using a continuous‐wave pump source. A maximum conversion efficiency of −27.71 dB is attained with a moderate pump power of 22.14 dBm. By incorporating higher‐order dispersion, an unprecedented conversion bandwidth of 1852 nm is experimentally demonstrated. This breakthrough highlights the potential of highly nonlinear Ge‐on‐Si platforms for developing widely tunable on‐chip MIR sources through efficient broadband frequency conversion.