Nonlinear dynamics in multimode optical fibers

Abstract

We overview recent advances in the research on spatiotemporal beam shaping in nonlinear multimode optical fibers. An intense light beam coupled to a graded index (GRIN) highly multimode fiber undergoes a series of complex nonlinear processes when its power grows larger. Among them, the lowest threshold effect is the Kerr-induced beam self-cleaning, that redistributes most of the beam energy into a robust bell-shaped beam close to the fundamental mode. At higher powers a series of spectral sidebands is generated, thanks to the phase matching induced by the long period grating due to the periodic self-imaging of the beam and the Kerr effect. Subsequently a broadband and spectrally flat supercontinuum is generated, extending from the visible to the mid-infrared.

Refractive index profile tailoring of multimode optical fibers for the spatial and spectral shaping of parametric sidebands

“…The last few years witnessed a strong renewed interest in the research on controllable spatio-temporal beam shaping with multimode optical fibers. In particular, graded-index multimode fibers (GRIN MMFs), thanks to their reduced modal dispersion which permits relatively long interaction lengths among the guided modes, were found to host a rich variety of spatiotemporal dynamical effects [1][2][3]. Among these, we may cite multimode solitons [4], ultra-wideband spectral sideband series generation from either oscillating multimode solitons [1,5] or quasi continuous-wave (CW) pulses (also known as geometric parametric instability, GPI) [6][7][8][9], intermodal four-wave mixing (IMFWM) [10,11], beam self-cleaning in passive [7,8,12,13] and active MMFs [14], supercontinuum generation [15,16], spatio-temporal mode-locking [17,18], and wavefront shaping control of frequency conversion processes [19], to name a few.…”

Oscillating propagation and parametric instability of the partial Gaussian beam in graded-index multimode fibers

“…Multimode fibers (MMFs) have drawn renewed attention owing to their versatile platform to investigate the rich and complex phenomena in multimodal nonlinear environments such as spatiotemporal dynamics [1][2][3], spatial beam self-cleaning [4,5], rogue waves [6], supercontinuum generation [7,8], spatiotemporal mode-locking [9,10], multimode solitons [11][12][13], and geometric parametric instability (GPI) [14,15]. These studies are expected to enhance the bandwidth of telecom systems through spacedivision multiplexing as well as can offer a new route to mode-area scaling for high-power lasers in imaging systems [16][17][18], especially oriented toward the biomedical imaging domain [19][20][21][22].…”

Spatial beam self-cleaning in multimode lanthanum aluminum silicate glass fiber

“…Graded-index multimode optical fibers (GRIN MMFs) have been recently reconsidered, owing to their potential to implement complex nonlinear spatiotemporal phenomena, involving a rich variety of novel nonlinear processes [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Among others, we may list, for instance, Kerr-beam self-cleaning (which allows for brightness improvement of a multimode beam) [4], geometric parametric instability (GPI) [5][6], multimode solitons [7], intermodal four-wave mixing (IMFWM) [8][9][10], modulation instability [11], ultrabroadband dispersive radiation generation [12], second harmonic generation induced by an all-optical poling process [13][14], supercontinuum generation [15][16], spatio-temporal mode-locking [17][18], and control of nonlinear multimode propagation by means of wavefront shaping [19][20].…”