Panagiotis Papagiannis

Propagation of chirped solitary pulses in optical transmission lines: perturbed variational approach

Abstract The evolution of a dressed solitary pulse subjected to filtered amplification is examined. The model equation used is complex cubic Ginzburg–Landau equation (CCGLE). A system of ordinary differential equations is derived on the basis of an extended-perturbed variational method. These equations are solved numerically for a set of initial conditions in the vicinity of the fixed point (corresponding to the exact solution of CCGLE) of the dissipative system these equations model. The stability and degree of stationarity (in propagation distance) of pulses with initial (launching) parameters falling in the vicinity of the fixed point are examined in the context of this method. A fully numerical simulation of the CCGLE finally tests the results of this investigation. Detailed comparisons reveal a wide class of initial pulse profiles, which are characterized by adequate stationarity and long propagation, distances before they disintegrate. In the anomalous dispersion regime there is an adequate quantitative agreement while in the normal dispersion regime the predictability of the method is impressive. Limitations of the proposed method are also discussed.

Dissipative soliton acceleration in nonlinear optical lattices.

An effective mechanism for dissipative soliton acceleration in nonlinear optical lattices under the presence of linear gain and nonlinear loss is presented. The key idea for soliton acceleration consists of the dynamical reduction of the amplitude of the effective potential experienced by the soliton so that its kinetic energy eventually increases. This is possible through the dependence of the effective potential amplitude on the soliton mass, which can be varied due to the presence of gain and loss mechanisms. In contrast to the case where either the linear or the nonlinear refractive index is spatially modulated, we show that when both indices are modulated with the same period we can have soliton acceleration and mass increasing as well as stable soliton propagation with constant non-oscillating velocity. The acceleration mechanism is shown to be very robust for a wide range of configurations.

Continuous-wave-controlled nonlinear x-wave generation.

We demonstrate that the interaction between a two-dimensional localized wave packet and a continuous-wave background can lead to efficient x-wave generation in nonlinear bidispersive optical systems. This x-wave generation process was found to depend on both the relative phase and amplitude of the background with respect to the superimposed wave packet. Pertinent configurations that lead to such generation are considered.

Propagation of Pereira–Stenflo type pulses in a dispersion varying link: variational approach

Abstract The evolution during propagation of a Pereira–Stenflo type (bright and chirped) solitary pulse subjected to dispersion modulation in a communication line with Er 3+ -doped fiber amplifiers is investigated on the basis of a variational effective particle model. The model leads to an extended phase plane representation of the dynamics of the pulse and yields the evolution equations for the pulse width and chirp. The associated Poincare surfaces of section provide a useful qualitative and quantitative designing tool for a soliton-based optical link with weak to mildly strong dispersion modulation. The investigation relates the general properties of the evolution to the modulation strength and its spatial periodicity. Both the sinusoidal and the step-wise dispersion modulation schemes are considered. For the sinusoidal, both weak and relatively strong dispersion modulation, it was found that for long periodicity of the modulation (as compared with the periodicity which characterizes the non-modulated breathing of the pulse), chaotic regions on the Poincare surfaces of section are either absent or limited and the pulse preserves its form for adequately long distances for a wide range of choices of its initial parameter values. On the contrary, the higher the modulation strength and/or frequency are the wider the chaotic region gets. For the case of the step-wise dispersion modulation the chaotic behavior sets in for lower values of the frequency of the dispersion modulation, thus, rending the regions for choosing the initial pulse parameters, which are associated with non-destructive propagation of the pulse, narrower.

Spatiotemporal interaction of optical beams in bidispersive media

The interaction of optical beams in bidispersive nonlinear media with self-focusing nonlinearity is numerically investigated. Under proper conditions, the interaction of spatially separated beams can lead to the creation of two prominent filaments along the other spatial or temporal dimension and, thus, to an effective spatiospatial or spatiotemporal exchange. This X-wave generation-based effect could potentially be exploited in optical realizations of spatial or spatiotemporal filtering.

Simulation and properties of highly nonlinear multilayer optical structures using the transmission line method

In this work we numerically investigate and analyse the properties of an optical structure comprised of successive thin film layers that can possess high values of nonlinear susceptibility, affecting the refractive index and/or the absorption coefficient. By applying the Transmission Line Method (TLM), properly modified to resolve the inclusion of third order nonlinearity, the spectral reflectivity and transmission of such a device are presented. Specifically, the method is applied for the case of conceptual design of a Distributed Bragg Reflector (DBR). Optical bistability can be observed, which translates not only to a change in the value of reflectivity, as the input power increases, but also to a shift of the Bragg wavelength.

Beam steering via peak power decay in nonlinear waveguide arrays

We report the experimental observation and theoretical analysis of a novel beam-steering effect in periodic waveguide arrays that arises from the interplay between discrete diffraction, Kerr nonlinearity and any mechanism that effectively weakens the nonlinear part of the beam. In this regime the propagation direction shows increased sensitivity to the input angle and for a certain angular range around normal incidence a nonlinear beam may be guided to a direction opposite to that initially inserted. For continuous wave beams the role of this mechanism is played by absorption of any kind, such as three photon absorption, two photon absorption or even linear absorption. For pulsed beams we show that the same dynamics can arise due to strong normal temporal dispersion, while absorption is not necessary and can be a further enhancing

Application of the transmission line method for the study of highly nonlinear multilayer optical structures

Abstract. In this work, we numerically investigate and analyze the properties of an optical structure composed of successive thin film layers that can possess high values of nonlinear susceptibility, affecting the refractive index and/or the absorption coefficient. By applying the transmission line method properly modified to resolve the inclusion of third-order nonlinearity, the spectral reflectivity and transmission of such a device are presented. Specifically, the method is applied to a conceptual design of a distributed Bragg reflector. Optical bistability can be observed, which translates not only to a change in the value of reflectivity as the input power increases, but also to a shift of the Bragg wavelength.

Gain-controlled Soliton Routing in Dissipative Optical Lattices

We investigate dynamical soliton trapping in optical lattices under the presence of gain and loss mechanisms. It is shown that depending on soliton initial power and velocity dynamical gain-controlled routing can take place.

Complex Soliton Dynamics in Lattices with Longitudinal Modulation

Soliton dynamics in longitudinally modulated optical lattices depend on both their initial power and momentum. New features are revealed such as enhanced beam mobility, dynamical switching and routing, extended and quasiperiodic trapping.