Phase-matched guided-wave optical bistability in x s2d optical resonators

Cascaded second-order nonlinear effects attract great interest because of their potential use in devices that require nonlinear (NL) phase shifts. – 9 It is only recently that the case of x s2d distributed couplers in the cascading regime has been considered. The nonlinear effect studied in Ref. 10 is second-harmonic generation, for which only the fundamental frequency field (at v) is incident upon x s2d prism or grating couplers. But the situation is different whether one deals with second-harmonic generation, i.e., sv, vd ! 2v, or with subharmonic generation i.e., 2v ! sv, vd, of light, as one may infer by considering the NL polarizations at frequencies 2v and v: