Robust self-trapping of vortex beams in a saturable optical medium

We report the first observation of robust self-trapping of vortex beams propagating in a uniform condensed medium featuring local saturable self-focusing nonlinearity. Optical vortices with topological charge m=1, that remain self-trapped over ~ 5 Rayleigh lengths, are excited in carbon disulfide using a helical light beam at 532 nm and intensities from 8 to 10 GW/cm^2. At larger intensities, the vortex beams lose their stability, spontaneously breaking into two fragments. Numerical simulations based on the nonlinear Schr\"odinger equation including the three-photon absorption and nonpolynomial saturation of the refractive nonlinearity demonstrate close agreement with the experimental findings.Comment: 27 pages, 7 figures,to be published in Phys. Rev. A (2016

Generation of multiple ultrashort solitons in a third-order nonlinear composite medium with self-focusing and self-defocusing nonlinearities

Theoretical consideration of the propagation of femtosecond-Gaussian pulses in a 1D composite medium, consisting of alternating self-focusing (SF) and self-defocusing (SDF) waveguide segments with normal group-velocity dispersion predicts the generation of trains of bright solitons when an optical pulse first propagates in the SF segment, followed by the SDF one. The multiple temporal compression (MTC) process, based on this setting, offers a method for controllable generation of multiple ultrashort temporal solitons. Numerical solutions of the generalized nonlinear Schr\"{o}dinger equation modeling this system demonstrate that the intrapulse Raman scattering plays a major role in the temporal and spectral dynamics. Collisions between ultrashort solitons with different central wavelengths are addressed too. The paper provides, for the first time, a procedure for producing controllable trains of ultrashort temporal solitons by incident optical pulses propagating in a composite medium.Comment: To be published in Phys. Rev.

Observation of Replica Symmetry Breaking in the 1D Anderson Localization Regime in an Erbium-Doped Random Fiber Laser

The analogue of the paramagnetic to spin-glass phase transition in disordered magnetic systems, leading to the phenomenon of replica symmetry breaking, has been recently demonstrated in a two-dimensional random laser consisting of an organic-based amorphous solid-state thin film. We report here the first demonstration of replica symmetry breaking in a one-dimensional photonic system consisting of an erbium-doped random fiber laser operating in the continuous-wave regime based on a unique random fiber grating system, which plays the role of the random scatterers and operates in the Anderson localization regime. The clear transition from a photonic paramagnetic to a photonic spin glass phase, characterized by the probability distribution function of the Parisi overlap, was verified and characterized. In this unique system, the radiation field interacts only with the gain medium, and the fiber grating, which provides the disordered feedback mechanism, does not interfere with the pump

Optical limiting behavior of bismuth oxide-based glass in the visible range

The authors report experimental results on the optical limiting behavior of a bismuth oxide-based glass by exciting the samples with nanosecond laser pulses at 532 and 598 nm. The results show that two-photon and free-carrier absorption processes contribute for the nonlinear absorption. Values for β, the two-photon absorption coefficient, and σe, the absorption cross section due to free carriers, were determined. The values for β and σe are dependent on the amount of bismuth oxide in the glass composition

Generation of robust temporal soliton trains by the multiple-temporal-compression (MTC) method

We report results of systematic numerical analysis for multiple soliton generation by means of the recently reported multiple temporal compression (MTC) method, and compare its efficiency with conventional methods based on the use of photonic crystal fibers (PCFs) and fused silica waveguides (FSWs). The results show that the MTC method is more efficient to control the soliton fission, giving rise to a larger number of fundamental solitons with high powers, that remain nearly constant over long propagation distances. The high efficiency of the MTC method is demonstrated, in particular, in terms of multiple soliton collisions and the Newton's-cradle phenomenology.Comment: To be published in Optics Communications (Special Issue - Solitons and coherent structures in optics: 50th anniversary of the prediction of optical solitons in fiber