Abstract

The interplay of the Kerr-induced nonlinear refractive index changes and dispersion in nonlinear Fiber Bragg Gratings (FBGs) leads to a plethora of nonlinear phenomena, the most striking of which is perhaps the formation and propagation of gap solitons [1]. Whilst a considerable amount of theoretical work has been performed in this area [1,2,3,4] experimental observations of nonlinear grating behaviour are limited, principally by the difficulty in getting sufficiently high power densities within the core of a FBG in a suitable spectral and temporal range. In order to reduce the nonlinear threshold for gap soliton formation one can use the somewhat weaker dispersive properties of FBGs outside of the band gap and indeed recent experiments have yielded the first strong evidence of Bragg grating gap soliton formation by this means [5,6]. However, the strongest and most manifestly nonlinear effects are predicted to occur at wavelengths within the band gap, close to the Bragg wavelength of the grating structure and it is therefore essential to make measurements within this regime. In this paper we report what we believe to be the first clear experimental observation of nonlinearity within the band gap of an FBG, namely nonlinear self-switching and, at higher intensities, multiple gap soliton formation.

© 1997 Optical Society of America