Self-compression of spatially limited laser pulses in a system of coupled light-guides

Abstract

The self-action features of wave packets propagating in a two-dimensional system of equidistantly arranged fibers are studied analytically and numerically on the basis of the discrete nonlinear Schrödinger equation. Self-consistent equations for the characteristic scales of a Gaussian wave packet are derived on the basis of the variational approach, which are proved numerically for powers P < 10Pcr exceeding slightly the critical one for self-focusing. At higher powers, the wave beams become filamented, and their amplitude is limited due to nonlinear breaking of the interaction between neighbor light-guides. This make impossible to collect a powerful wave beam into the single light-guide. The variational analysis show the possibility of adiabatic self-compression of soliton-like laser pulses in the process of their three-dimensional self-focusing to the central light-guide. However, the further increase of the field amplitude during self-compression leads to the longitudinal modulation instability development and formation of a set of light bullets in the central fiber. In the regime of hollow wave beams, filamentation instability becomes predominant. As a result, it becomes possible to form a set of light bullets in optical fibers located on the ring.

Stability of out-of-phase solitons and laser pulse self-compression in active multicore fibers

“…Figure 1 shows schematically an MCF fiber with N = 3. The analysis will be based on the standard theoretical model [7,8,13,16,17,27,37], in the framework of which it is assumed that the fundamental guided modes of the optical cores oriented parallel to the z-axis are weakly coupled. In this case, the propagation of laser pulses in the MCF can be described approximately as a superposition of fundamental modes localized in each core (1) where φ(x, y) is the structure of the lowest spatial mode in the core, E n is the envelope of the electric field strength in the n-th core, which slowly changes along the z-axis.…”

“…Again, it is possible to show the uniqueness of the functional F (13) turning to zero only for the ±-mode with κ m = π (that is, m = N ). For all other m = N , functional (13) can be set to zero for u n = u (m) n . This fact reflects the presence of filamentation instability at κ m = π.…”

“…As shown by theoretical and experimental studies [6][7][8][9][10][11][12], such systems have its own critical power/energy, at which self-focusing of the quasi-homogeneous distribution of the discrete wave field occurs, and the field disintegrates into a set of incoherent structures [13]. Despite that, a number of interesting results were obtained in this direction related to studying the possibilities of generating a supercontinuum [14,15], reducing the duration of laser pulses [13,[16][17][18][19][20][21][22][23], controlling the structure of the wave field [24][25][26][27][28], and producing light bullets [10-12, 29, 30]. The presence of discrete critical power/energy leads to the fact that the power/energy of the used laser radiation is also limited by the destruction threshold or self-focusing in a separate core.…”

Out-of-phase few-cycle solitons in multicore fibers

“…A number of interesting results have been obtained in such MCFs: supercontinuum generation [23][24][25], the laser pulse compression [24][25][26][27][28][29][30][31][32], nonlinear switching [33] and the light bullet formation [24][25][26][27][28][29][30][34][35][36][37]. However, most of them were obtained for in-phase field distributions, which are influenced by a discrete analogue of filamentation instability and stochasticity [38].…”

Multicore-fiber solitons and laser-pulse self-compression at light-bullet excitation in the central core of multicore fibers

“…Studies have shown that self-focusing of wide wave field distribution with a power exceeding a certain critical value [24] (which differs from the critical self-focusing power in a homogeneous non-linear medium) leads to decomposition of the wave field into a set of incoherent structures [4] in the process of propagation in a medium with a periodic set of weakly coupled optical fibers. For stable operation with more powerful wave beams, one can use multi-core optical fibers (MCF) with a small number of cores.…”