Nonlinear frequency conversion with quasi-phase-mismatch effect.

In conventional frequency conversion based on chi(2)-induced nonlinear optical effects, a number of phase-matching techniques have been deployed to resolve the phase mismatch between the interacting waves. In this work, we report that in the quasi-phase-matching scheme, the accumulation of the phase mismatch can induce a quasi-phase-mismatch effect. And on the contrary, instead of eliminating the phase mismatch, modulating the quasi-phase-mismatch effect can lead to bandwidth enhancement and multiple-wavelength conversion. Both of these are essential factors for applications in nonlinear frequency conversion. As examples, designs with reset-periodic and cascaded-periodic optical superlattices based on such modulation are presented.