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Abstract
Negligible power is coupled between two highly mismatched guides of a coupler. A periodic refractive index perturbation can assist the coupling, giving rise to complete power swapping between the guides at resonance. The power-induced refractive index change detunes the resonance, preventing power swapping between the guides again. As the coupling produced by the periodic perturbation in a grating-assisted coupler is very weak, the nonlinear-induced mismatch at low powers can easily overcome the linear coupling, leading to switching and amplification at a very low power level.