PROPAGATION OF BROAD-BAND OPTICAL PULSES IN DISPERSIONLESS MEDIA

In the present paper, the regimes of propagation of laser pulses in isotropic dispersionless (beta approximate to 0) media, such as hollow microstructured optical fibers (photonic crystal fibers), are presented. The nonlinear amplitude equation (NAE) is used to describe the evolution of such pulses, which differs from the nonlinear Schrodinger equation by two additional nonparaxial terms. Linear and nonlinear regimes of propagation are considered. In the linear regime, when only diffraction effects dominate the evolution of the laser pulse, its shape is preserved, but the position of the pulse shifts with the distance. This is due to the influence of the nonparaxial term in NAE. In the nonlinear propagation regime, the obtained solution of the NAE describes a dark soliton. It is formed as a result of the balance between the effects of diffraction and the nonlinearity of the medium.