Difference-frequency generation in silicon nitride waveguides based on all-optical poling

Integrated photonics leverages strong field confinement and long interaction lengths for the observation of a wide variety of nonlinear phenomena on-chip. Among them, wavelength conversion is one of the key, actively studied fields. Frequency conversion through the second-order susceptibility ( χ (2) ) is prohibited in most of the integrated photonics platforms, such as silicon, since they possess a centrosymmetric structure. Nevertheless, second-order nonlinear processes, such as sum- and difference-frequency generation (DFG), are desirable in applications for frequency comb stabilization [1] and mid-infrared (mid-IR) spectroscopy [2] . To bring efficient three-wave frequency mixing processes on silicon photonics we must first induce an effective χ (2) and satisfy the phase-matching condition of the interacting waves. The former can be realized through symmetry breaking using resonant structures [3] and poling processes [4] . The latter is typically achieved by quasi-phase-matching (QPM).