Femtosecond soliton generation in air-silica microstructure fibers

We investigate femtosecond pulse propagation in air-silica microstructure fiber (ASMF), reporting the generation of femtosecond Raman soliton pulses tunable over 200 nm in the near infrared. For sufficiently broad spectral content, SRS transfers energy from the higher frequency spectral components to lower frequencies, resulting in a continuous self-frequency shift to longer wavelengths. Furthermore, numerical solutions to the nonlinear Schrodinger equation (NLSE), using the measured intensity and phase of the injected pulse as initial condition for the split-step Fourier method (SSFM), predict accurately the observed spectra and the presence of the Raman soliton.