Wave propagation in nonlinear multilayer structures

We investigate the adequacy of the Kronig-Penney {δ}-function model in describing the electromagnetic wave propagation in periodic structures consisting of thin layers of materials with an intensity-dependent dielectric constant. We find that the model captures the most essential features of nonlinear response to radiation. Excellent agreement is found between the results from the {δ}-function model and the exact solutions of nonlinear wave equations. However, discrepancies do exist below the bottom of transmission bands due to the rigidness of the band edge in the {δ}-function model. Consequently, gap solitons cannot form in the {δ}-function model when the nonlinear Kerr coefficient is positive. {} 1996 The American Physical Society.