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

Abstract

The intensity dependence of stimulated four photon mixing (SFPM) spectra generated in 15 m of a 4-mode optical fiber by 25ps 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.

Spectral broadening of picosecond laser pulses in optical fibres

“…3b is taken below the onset of stimulated Raman scattering. The side lobes at 690 nm and 698 nm are due to phase-matched parametric four-photon interaction (stimulated parametric four-wave mixing i/ L + i/ L -* */ 3 -f v A [4,5,[10][11][12][13]; phase-matching is achieved by coupling of different modes in the low-order mode fibre [11,21]). …”

“…The nonlinearity length L nl is defined by k L AnL n] = 7I/L^II1 = 1 Kl> giving ^1 = 1/7I4 (13) For fibre lengths /> L nh nonlinear optical effects like self-phase modulation become important. In Fig.…”

“…If two pulses at WL and U>R are present the nondegenerate fourphoton interaction (II) w L + WR -* w 3 + w 4 is possible as well. If no signal at w 3 and u/4 is entered to the fibre, one speaks of stimulated four-photon mixing [4,5,13,[40][41][42][43], stimulated parametric four-photon interaction [44,45], stimulated four-wave parametric emission [46], or parametric four-photon generation (start from quantum noise and black-body radiation [37]). If a weak signal at either w 3 or w 4 is already present, one speaks of four-photon parametric amplification [4,5,10,47].…”

“…Optical fibres are most appropriate for spectral broadening by selfphase modulation because high intensities in a small spot are maintained over long distances [4][5][6][7][8]. In fibres the spectral broadening may be extended by cross-phase modulation [4,5], modulation instability [4,5,9], stimulated Raman scattering [4,5], stimulated four-photon mixing [4,5,[10][11][12][13] and parametric amplification [4,11,14]. Strongly broadened spectral pulses in monomode fibres [7,12,13,15,16] and multimode fibres [17,18] have been reported.…”

Supercontinuum generation in hydrogenated amorphous silicon waveguides at telecommunication wavelengths

“…In both studies, the waveguides were engineered to exhibit anomalous group velocity dispersion. Contrary to the normal dispersion regime where due to poor phase-matching the main nonlinear process is self phase modulation (SPM) [11,12], the anomalous dispersion regime allows in addition to SPM many other nonlinear effects such as, modulation instability, soliton shift, soliton fission and Cherenkov radiation [2]. The combination of some or all these effects allows maximum spectral broadening of the SC.…”