Section-wise-exact coupled-mode theory of waveguide quasi-phase-matched second-harmonic generation

We derive exact mathematical expressions For both the amplitude and phase e volution of optical waves duct to linear and nonlinear interactions in a wa veguide device and propose a section-wise-exact coupled-mode theory analysi s for quasi-phase-matched second-harmonic generation in the waveguide, Sect ion-wise-exact coupled-mode theory is readily applicable to nonuniform quas i-phase-matched gratings and can be useful as a quantitative method in thei r analysis and design, Using the method, several numerical results are pres ented for second-harmonic generation in periodically poled LiNbO3 channel w aveguides, In addition, me introduce a split-step method which takes propag ation losses into account and which can include linear and two-photon absor ption and waveguide losses.