Abstract
Interplay between dispersion and nonlinearity in optical fibers is a fundamental research topic of nonlinear fiber optics. Here we numerically and experimentally investigate an incoherent continuous-wave (CW) optical field propagating in the fiber with normal dispersion, and introduce a distinctive spectral evolution that differs from the previous reports with coherent mode-locked fiber lasers and partially coherent Raman fiber lasers [Nat. Photonics 9, 608 (2015).]. We further reveal that the underlying physical mechanism is attributed to a novel interplay between group-velocity dispersion (GVD), self-phase modulation (SPM) and inverse four-wave mixing (IFWM), in which SPM and GVD are responsible for the first spectral broadening, while the following spectral recompression is due to the GVD-assisted IFWM, and the eventual stationary spectrum is owing to the dominant contribution of GVD effect. We believe this work can not only expand the light propagation in the fiber to a more general case and help advance the physical understanding of light propagation with different statistical properties, but also benefit the applications in sensing, telecommunications and fiber lasers.
Highlights
Dispersion and nonlinearity play important roles in fiber-based devices and systems
The optical waves propagating in the fiber are affected by dispersion and nonlinear effects simultaneously, and the interplay between dispersion and different nonlinear effects leads to a multitude of interesting phenomena in nonlinear fiber optics, such as the conservative optical solitons which are enabled by the exact balance between dispersion and Kerr nonlinearity [5], and supercontinuum generation whose
Focusing on the spectral evolutions, the interplay between groupvelocity dispersion (GVD) and self-phase modulation (SPM) effects leads to a monotonic but gradually saturated spectral broadening in the normal dispersion regime [2, 21], while soliton fission, dispersive wave, Raman solitons, and nonlinear interactions among them are responsible for the supercontinuum generation in the anomalous dispersion regime [22]
Summary
Dispersion and nonlinearity play important roles in fiber-based devices and systems. For example, dispersion-induced pulse broadening limits the capacity of fiber-optic communication systems [1]. Nonlinear Kerr effects such as self-phase modulation (SPM) and four-wave mixing (FWM) may contribute to the spectral broadening of optical waves [2], which is undesirable for some applications, e.g., narrow-linewidth fiber lasers [3], but benefits the novel light sources such as supercontinuum generation [4]. Focusing on the spectral evolutions, the interplay between groupvelocity dispersion (GVD) and SPM effects leads to a monotonic but gradually saturated spectral broadening in the normal dispersion regime [2, 21], while soliton fission, dispersive wave, Raman solitons, and nonlinear interactions among them are responsible for the supercontinuum generation in the anomalous dispersion regime [22]. K. Turitsyn et al investigated the partially coherent Raman fiber lasers propagating in the fiber, and demonstrated a new nonlinear effect called inverse four-wave mixing (IFWM) [32], which may occur in the normal dispersion regime and cause the spectral compression of incident light. The incoherent waves (such as thermal light sources and free-running lasers) propagating in the fiber and the underlying dynamics, which are both scientifically important and of great interest, have been relatively unexplored
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