Intensity effects on the stimulated four photon spectra generated by picosecond pulses in optical fibers

The intensity dependence of stimulated four photon mixing (SFPM) spectra generated in 15 m of a 4-mode optical fiber by 25- ps pulses has been investigated. Despite the shortness of pulses, the SFPM conversion was highly efficient due to the intrinsic phase matching condition. In addition to usual features of SFPM spectra generated by nanosecond pump pulses, picosecond SFPM spectra were broadened by self phase modulation (SPM) and cross phase modulation (XPM). At the highest pump powers, intensity saturated frequency continua, arising from the combined effects of SFPM, stimulated Raman scattering (SRS), SPM, and XPM were generated all over the visible spectrum.