Soliton induced supercontinuum generation in photonic crystal fiber

Soliton induced supercontinuum (SC) generation using an index-guiding triangular photonic crystal fiber (PCF) is experimentally studied by pumping with 140-fs pulses at several wavelengths in the positive slope anomalous dispersion region. The focused beam incident upon the PCF core is first confirmed by in situ observation based on the reflection method to make sure accurate input coupling conditions. The influence of pumping wavelength on the spectral profile of SC is examined as a function of input peak power P-0. Processes initiating SC generation are governed by the fission of higher-order solitons, which lead to the soliton self-frequency shift (SSFS) by intrapulse Raman scattering associated with blue-shifted Cherenkov type phase matched radiation. The fission of higher-order solitons is clearly observed in the input P-0 dependent spectrum and a plot of the square root of frequency shift versus input P-0. Further increase of input P-0 leads to a new SSFS accompanied by an additional blue-shifted peak located at shorter wavelength than that of the previous one. These processes continue to develop successive blue-shifted and SSFS peaks as increasing the input P-0, which determine the spectral width of SC. Spectral profile of SC is also dominated by these initial and growth processes. SC spectra obtained in the vicinity of zero dispersion wavelength shows smooth but relatively narrow, while SC generation at deep anomalous dispersion site exhibits broad bandwidth at relatively low P-0. The input P-0 required for approaching a saturated SC which is almost the same feature within the tuning pump wavelengths is decreased as increasing the degree of anomalous dispersion.