Quasimatched parametric interaction of optical waves with equal group velocities

A theoretical study is made of the parametric interaction of optical waves in nonlinear layer media. The mismatch between the group velocities of the interacting waves may be varied in such media and the phasematching condition can be satisfied by the quasimomentum of periodic modulation of the nonlinear coefficient. The tuning curves of the group-velocity matching are given for an LiNbO₃ crystal. Analytic solutions of nonlinear equations are obtained by a secondary simplification method and these solutions are compared with the results of numerical calculations.