1,721,024 research outputs found
A thermodynamic study of low-power modal multiplexed systems
No full textModal multiplexing is a part of the more general space-division multiplexing (SDM) technique, aimed to solve the
capacity crunch issue adding a further multiplexing layer using multimode fibers. SDM system designers often
assume that groups of degenerate modes do not exchange power, and that the linear random-mode coupling
(RMC), caused by fiber imperfections, induces power exchange among quasi-degenerate modes only.
In our experimental and theoretical study, me show that RMC produces asymmetric power flow among modal
groups, promoting the lower-order mode groups at the expense of the higher-order groups. The study, completed
by a thermodynamic interpretation, is aimed to improve the design of SDM systems against RMC
Optical solitons in multimode fibers: recent advances
No full textOptical solitons in multimode fibers were predicted 40 years ago and extensively investigated theoretically. Transmission experiments in nonlinear multimode fibers have gained renewed interest, motivated by their potential to extend the capacity of long-distance transmission systems; only in the last few years, new experiments have revealed unexpected properties of optical solitons propagating in graded-index and step-index multimode fibers, partially re-writing the existing theory. Here we provide an overview of the recent experimental, numerical, and theoretical studies that revealed those new properties. It will be shown that multimode fiber solitons form with specific pulse width and energy dependent on the wavelength, and that they naturally evolve toward fundamentalmode Raman solitons. New soliton fission mechanisms, governed by the modal dispersion, will be explained. Possible applications in space-division multiplexed systems will be discussed. A recent thermodynamic approach to soliton condensation will be described. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved
Femtosecond extreme nonlinear optics with multimode fibers
No full textWe overview the nonlinear spatiotemporal propagation dynamics of femtosecond laser pulses in multimode optical fibers. Whenever the pulse peak power approaches the fiber breakdown threshold, several exotic nonlinear effects are observed
On spatial beam self-cleaning from the perspective of optical wave thermalization in multimode graded-index fibers
Full text linkThe input power-induced transformation of the transverse intensity profile at the output of graded-index multimode optical fibers from speckles into a bell-shaped beam sitting on a low intensity background is known as spatial beam self-cleaning. Its remarkable properties are the output beam brightness improvement and robustness to fiber bending and squeezing. These properties permit to overcome the limitations of multimode fibers in terms of low output beam quality, which is very promising for a host of technological applications. In this review, we outline recent progress in the understanding of spatial beam self-cleaning, which can be seen as a state of thermal equilibrium in the complex process of modal four-wave mixing. In other words, the associated nonlinear redistribution of the mode powers which ultimately favors the fundamental mode of the fiber can be described in the framework of statistical mechanics applied to the gas of photons populating the fiber modes. This description has been corroborated by a series of experiments by different groups. However, some open issues still remain, and we offer a perspective for future studies in this emerging and controversial field of research
Characterization of the modal distribution from linear and nonlinear mode coupling in multimode fibers
No full textWe introduce a new modal decomposition method which permits to analyse, with unprecedented accuracy, the mode power distribution from long spans of multimode optical fibers. We show that a Bose-Einstein distribution permits to describe the steady-state distribution both in the linear and in the nonlinear regime, up to soliton generation. The distribution results from the interplay of strong linear disorder caused by fiber imperfections, and nonlinear four-wave mixing
Spatiotemporal soliton attractor in multimode graded-index fibers
Full text linkThere is recently a considerable interest in nonlinear optical effects in multimode fibers (MMFs). Here we present the experimental evidence, supported by numerical simulations, that an initially excited multimode femtosecond soliton initially composed by few low-order transverse modes of a graded-index (GRIN) MMF irreversibly decays into a singlemode soliton carried by the fundamental mode of the MMF. Once formed, the singlemode soliton propagates stably over fiber lengths of up to 1 km, which corresponds to a record transmission distance, in a MMF, of 4600 modal dispersion distances, and 5600 chromatic dispersion lengths. This effect is of particular importance for technological applications, since it reveals that nonlinearity can counteract the effects of modal dispersion and random mode coupling, and enables a stable transport of high-spatial-quality beams over long distances by means of large area (when compared to singlemode fibers) MMFs. As a side aspect, our results invalidate theoretical predictions based on variational approaches, since the beam shape substantially evolves along the fiber, in such a way that the initial beam profile is not maintained [1] - [3]
Multiphoton-absorption-excited up-conversion luminescence in optical fibers
Full text linkWe experimentally demonstrate a previously unforeseen nonlinear effect in optical fibers: up-conversion luminescence generation excited by multiphoton absorption of femtosecond infrared pulses. We directly estimate the average number of photons involved in the up-conversion process, by varying the wavelength of the pump source. We highlight the role of nonbridging oxygen hole centers and oxygen-deficient center defects and directly compare the intensity of side-scattered luminescence with numerical simulations of pulse propagation
Multimode soliton collisions in graded-index optical fibers
Full text linkIn this work, we unveil the unique complex dynamics of multimode soliton
interactions in graded-index optical fibers through simulations and
experiments. By generating two multimode solitons from the fission of an input
femtosecond pulse, we examine the evolution of their Raman-induced red-shift
when the input pulse energy grows larger. Remarkably, we find that the output
red-shift of the trailing multimode soliton may be reduced, so that it
accelerates until it collides with the leading multimode soliton. As a result
of the inelastic collision, a significant energy transfer occurs between the
two multimode solitons: the trailing soliton captures energy from the leading
soliton, which ultimately enhances its red-shift, thus increasing temporal
separation between the two multimode solitons
Pure quartic three-dimensional spatiotemporal Kerr solitons in graded-index media
No full textWe analyze the formation of three-dimensional spatiotemporal solitons in waveguides with a parabolic
refractive index profile and pure quartic chromatic dispersion.We show, by applying both variational approaches
and full three-dimensional numerical simulations, that fourth-order dispersion has a positive impact on soliton
stabilization against spatiotemporal wave collapse. Specifically, pure quartic spatiotemporal solitons remain
stable within a significantly larger energy range with respect to their second-order dispersion counterpart
High-order dissipative solitons in Kerr resonators with parabolic potentials
No full textWe study the formation of high-order dissipative solitons in externally-driven Kerr resonators in the presence of radially symmetric parabolic potentials. To do so, we apply bifurcation analysis to purely dispersive and dispersive/diffractive cavities
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