Alejandro B. Aceves

Bragg solitons in nonlinear PT -symmetric periodic potentials

It is shown that slow Bragg soliton solutions are possible in nonlinear complex parity-time (PT ) symmetric periodic structures. Analysis indicates that the PT -symmetric component of the periodic optical refractive index can modify the grating band structure and hence the effective coupling between the forward and backward waves. Starting from a classical modified massive Thirring model, solitary wave solutions are obtained in closed form. The basic properties of these slow solitary waves and their dependence on their respective PT -symmetric gain/loss profile are then explored via numerical simulations.

Tuning of surface plasmon polaritons beat length in graphene directional couplers

We investigate the tuning of the coupling of surface plasmon polaritons between two spatially separated graphene layers. We demonstrate that by slightly changing the chemical potential, a graphene coupler can switch from the bar to the cross state; as a consequence, the coupling coefficient in such structures can be easily controlled by means of an applied electrical signal.

Nonlinear control of soliton pulse delay with asymmetric dual-core photonic crystal fibers

Dual-core photonic crystal fiber nonlinear couplers permit the achievement of distortion-free power-controlled delay of picosecond pulses. The stable control of pulse time delay is achievable by means of resonance soliton solutions.

Polychromatic filament in quadratic media: spatial and spectral shaping of light in crystals

We demonstrate that monochromatic infrared laser pulses can generate polychromatic light in noncentrosymmetric crystals simultaneously covering the ultraviolet, visible, and infrared domains. The spatial shape of the beam and its energy can influence this multicolor frequency conversion, unveiling complex and interesting dynamics. We performed our experiments in a bulk crystal of periodically poled lithium niobate, working close to the optimal condition for second-harmonic generation. We used an input laser beam wide enough that, at very low intensities, the diffraction leaves its diameter unchanged along the propagation in the crystal. At high intensities instead, as we show in this work, such a spatially wide laser beam can be reshaped into a beam of much smaller diameter and guiding multispectral components. We also show how this outcome may permit exploitation of other parameters, like the crystal temperature, for tuning the spectrum of the generated multicolor light.

Widely varying giant Goos–Hänchen shifts from Airy beams at nonlinear interfaces

We present a numerical study of the giant Goos-Hänchen shifts (GHSs) obtained from an Airy beam impinging on a nonlinear interface. To avoid any angular restriction associated with the paraxial approximation, the analysis is based on the nonlinear Helmholtz equation. We report the existence of nonstandard nonlinear GHSs displaying an extreme sensitivity to the input intensity and the existence of multiple critical values. These intermittent and oscillatory regimes can be explained in terms of competition between critical coupling to a surface mode and soliton emission from the refracted beam component and how this interplay varies with localization of the initial Airy beam.

Optical UV filament and vortex dynamics

The propagation of high intensity nanosecond UV pulses in air is investigated theoretically and numerically. The stability of localized fundamental and vortex stationary solutions, obtained via Newton?s iterations, are analyzed. Numerical propagation results are provided to corroborate the predicted instabilities of the filament and vortex beams.

Model of the Self-Q-Switching Instability of Passively Phased Fiber Laser Arrays

We present a simple model for self-pulsation instability in passively phased high power optical fiber amplifier arrays with external feedback. Its key features are, first, the feedback levels sensitivity, and thus that of the cavity Q-value, to small phase changes of the array fields, and, second, the effect of refractive index nonlinearity in the amplifiers. The models prediction of an instability threshold for arrays of at least two amplifiers is confirmed by a linearized stability analysis of a system in ring-cavity geometry, and the magnitudes of predicted power levels are well within the domain of recent experiments.

On the asymptotic evolution of finite energy Airy wave functions.

In general, there is an inverse relation between the degree of localization of a wave function of a certain class and its transform representation dictated by the scaling property of the Fourier transform. We report that in the case of finite energy Airy wave packets a simultaneous increase in their localization in the direct and transform domains can be obtained as the apodization parameter is varied. One consequence of this is that the far-field diffraction rate of a finite energy Airy beam decreases as the beam localization at the launch plane increases. We analyze the asymptotic properties of finite energy Airy wave functions using the stationary phase method. We obtain one dominant contribution to the long-term evolution that admits a Gaussian-like approximation, which displays the expected reduction of its broadening rate as the input localization is increased.

Efficiency of dispersive wave generation in dual concentric core microstructured fiber

We describe the generation of powerful dispersive waves that are observed when pumping a dual concentric core microstructured fiber by means of a sub-nanosecond laser emitting at the wavelength of~1064 nm. The presence of three zeros in the dispersion curve, their spectral separation from the pump wavelength, and the complex dynamics of solitons originated by the pump pulse break-up, all contribute to boost the amplitude of the dispersive wave on the long-wavelength side of the pump. The measured conversion efficiency towards the dispersive wave at 1548 nm is as high as 50%. Our experimental analysis of the output spectra is completed by the acquisition of the time delays of the different spectral components. Numerical simulations and an analytical perturbative analysis identify the central wavelength of the red-shifted pump solitons and the dispersion profile of the fiber as the key parameters for determining the efficiency of the dispersive wave generation process.

On the co-existence of IR and UV optical filaments

In this work we first present analytical results showing the co-existence of intense infra-red, ultra-violet stationary filaments. Their existence is reminiscent of the universal scaling properties of the Townes soliton. We study different configurations and their propagation properties in a simplified time-independent model.