Pumping wavelength dependence of super continuum generation in photonic crystal fibers

Generation of wide super continua several hundred nanometers wide is possible by pumping in the normal dispersion regime as the nonlinear effects broaden the spectra beyond the zero-dispersion wavelength. When pumping far away from the zero-dispersion wavelength, only self phase modulation (SPM) and Raman scattering contributes to the broadening leading to smooth stable spectra of limited width. Pumping closer to the zero-dispersion wavelength forms very broad spectra, but they are far more sensitive to fluctuations in pumping power and coupling efficiency between fiber and laser. The flattest and broadest spectra are achieved by pumping just below zero-dispersion wavelength and increase in power leads to flatter and broader spectrum. Furthermore, pumping close to the zero-dispersion wavelength enables generation of spectral components at shorter wavelengths below 750 nm through a four-wave mixing process.