Nonlinear localization of chirped femtosecond pulse in layered photonic structure

Photonic crystals may be thought as important optical systems for which a nonlinear localization of laser energy is predicted theoretically. Such induced light structures are strongly localized in space (their sizes may be small), time-periodic, and rather stable (at least, long-lived). If a laser energy localization takes place due to spatial soliton appearance in certain elements of photonic crystal then its lifetime can be unbounded. Using this phenomenon, it is possible to design various types of all-optical switching devices in which light acts as a controlling factor and manipulating factor towards itself. Obviously, nonlinear localization of light energy depends on a local light intensity in photonic crystal elements with Kerr nonlinearity, therefore the standard averaging method cannot be applied for an investigation of its occurring. In this case, an analysis of nonlinear effects in photonic crystal is beyond the coupled mode theory approximation and needs more complicated approaches. Below we present computer simulation results for the laser energy nonlinear localization due to soliton appearance at interaction of an incident chirped femtosecond pulse with a layered photonic crystal. This interaction is described by the nonlinear Schrödinger equation. Because we consider the chirped pulse, therefore a nonlinear localization of laser energy can occur for both signs of a medium response. We investigate a soliton formation and its time evolution in dependence on the pulse carrier frequency position with respect to a photonic band gap. We claim essential influence of the incident pulse chirp on laser energy nonlinear localization.