Metasurfaces provide a low weight, small footprint device for nonlinear optical generation with applications for infra-red detectors via second harmonic generation or for ghost imaging via entangled photon-pair generation. The advantage of metasurfaces includes, among other things, no phase-matching requirement, although enhancement of the resonance at the nonlinear wavelengths is crucial. Recent work has demonstrated that harmonic generation can be enhanced by orders of magnitude by using high quality factor resonances derived from Bound States in the Continuum (quasi-BICs). The enhancement of higher order nonlinear processes, such as the classical Sum Frequency Generation (SFG) and the quantum photon-pair generation, require enhancement at multiple frequencies though.
We present our recent work at creating metasurfaces that contain multiple reconfigurable quasi-BICs. We demonstrate that SFG can be enhanced by many orders of magnitude at both the signal and idler wavelengths and that these quasi-BICs, with a linewidth in the picometer range, have wavelengths that are reconfigurable over a broadband range. We then show that this means that photon-pairs can be generated over a broadband with picometer linewidths.