Boost In Second Harmonic Generation Via Quasi-Bound States In The Continuum in a Gain-Loss Assisted Core-Shelled Nanowire

Engineering photonic resonators for high-efficiency performance has recently become an avenue for extensive research and development. In this direction, we present that optical Bound states in the continuum can enhance nonlinear response in cavities with spatial variation of gain-loss. We report an enhancement of 3 orders of magnitude in the SHG efficiency in a specially designed AlGaAs nanowire. The formation of high-Q modes via avoided resonance crossing at both the fundamental and second harmonic wavelengths boosts the second harmonic generation (SHG).