We cover recent work on photo-induced second order nonlinearities in silicon nitride microresonators. We show that, like in waveguides, all-optical poling occurs in resonators via the photogalvanic process, resulting in high efficiencies owing to resonant enhancement but without sacrificing versatility and tunability. We also show that, owing to the large efficiency, cascaded nonlinear effects occur in normal dispersion microresonators once second and third order nonlinearities are combined, expanding the scope and potential of silicon nitride nonlinear photonics.
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