Nonlinear Spectral Broadening in Solid-Core Bragg Fibers

We present results of a detailed theoretical study of nonlinear pulse propagation through solid-core photonic bandgap Bragg fibers. Pulse propagation is modeled using the extended nonlinear Schrodinger equation, which is numerically solved by using the split-step Fourier method. The influence of the fiber structure and various parameters of the input pulse on the spectrum of the output pulse are studied, with an aim to achieve Bragg fiber designs that have the potential for nonlinear applications such as continuum pulse generation. It is found that third-order dispersion is dominant in limiting the spectral width of the output pulse. Generation of dispersive waves is also observed at a wavelength close to the center frequency of the pulse, although it does not contribute to the broadening of the frequency spectrum. Simulations show the existence of an optimal length of the Bragg fiber beyond which spectral broadening reaches saturation.