Spontaneous generation of spectral incoherent solitons through supercontinuum generation

Summary form only given. The usual physical picture of supercontinuum SC generation changes profoundly when high power long pulses are injected into a photonic crystal fiber (PCF) which exhibits two zero dispersion wavelengths (ZDWs). Besides the thermalized central part of the incoherent SC spectrum, the analysis reveals that the Raman effect is responsible for the generation of spectral incoherent solitons (SIS) [1] in the low-frequency edge of the spectrum [2,3]. We recall that, contrary to conventional solitons, SISs do not exhibit a localization in the spatio-temporal domain, but exclusively in the frequency domain [1]. In the experiment we made use of a commercial high-power pump delivering 660-ps pulses at 1064 nm. We report in Fig. 1(a) the evolution of the spectrum of the PCF manufactured by IRCICA. We performed simulations with different models: (i) the generalized nonlinear Schrödinger equation (GNLSE) which is in good agreement with the experimental results, (ii) a reduced nonlinear Schrödinger equation (RNLSE) which solely accounts for the Raman effect, and (iii) the weak Langmuir turbulence kinetic equation (KE) [1]. Here, the seed of the SIS is provided by the modulation instability (MI) band at -65THz. The experimental behavior of SISs in the low-frequency edge of the SC spectrum is in qualitative agreement with the corresponding simulations of the RNLSE (see Fig. 1(a-b)).