Dispersion and nonlinearities associated with supercontinuum generation in microstructure fibers.

摘要

Air-silica microstructure fibers are of great interest due their enhanced effective nonlinearity as a result of the reduced confined mode. In addition, the fiber waveguide geometry allows anomalous dispersion and a zero group-velocity dispersion point in the near infrared. These properties augment the effect of fiber nonlinearities including self-phase modulation and stimulated Raman scattering for the injection of high power pulses centered near the zero group-velocity dispersion wavelength. One significant result of pulse propagation in microstructure fibers is supercontinuum generation due the simultaneous action and combination of these nonlinear effects. Important applications for supercontinuum generation include ultrashort pulse generation and extending the Ti:sapphire laser frequency comb for optical frequency metrology. However, to fully utilize the supercontinuum it is important to know the dominant nonlinear effects that produce the extreme spectral broadening. To assess these component effects, an exhaustive study of the initial stages of supercontinuum generation was performed for varying pump wavelength, initial pulse chirp and initial peak power. From this work we observe Raman soliton generation, which was verified by numerically solving the nonlinear Schrödinger equation. As the peak power is increased the interaction of self-phase modulation and stimulated Raman scattering leads to supercontinuum generation. Furthermore, we investigate the extension of the Ti:sapphire laser frequency comb in the supercontinuum by mixing it with spectral components produced by a synchronously-pumped optical parametric oscillator. This study tests the integrity of the supercontinuum frequency comb near the Ti:sapphire pump wavelength and at the signal wavelength of 1450 nm.