G. F. Nalesso

Conversion efficiency for second-harmonic generation in photonic crystals

We derive an analytical expression for the conversion efficiency of second-harmonic generation (SHG) in a photonic crystal. The results obtained for the undepleted-pump limit allow us to describe the role played by the feedback and dispersion introduced by the photonic crystal and hence to optimize the SHG process.

Synthesis of picosecond pulses by spectral compression and shaping of femtosecond pulses in engineered quadratic nonlinear media

Narrow-bandwidth picosecond pulses of predetermined spectral and temporal shapes are generated with high efficiency by frequency conversion of femtosecond pulses in lithium tantalate crystals with engineered quasi-phase-matching structures. We give examples of the synthesis of Gaussian and super-Gaussian picosecond pulses and also of a pair of synchronized phase-coherent picosecond pulses with a predetermined carrier-frequency difference.

Graphene sustained nonlinear modes in dielectric waveguides.

We discuss the existence of nonlinear modes sustained by graphene layers in dielectric waveguides. Taking advantage of the almost two dimensional nature of graphene, we introduce the nonlinear effect as a parameter in the continuity equations. We then apply our modeling to a simple slab waveguide to enlighten how graphene can be used to induce huge nonlinear phase shifts at easily accessible power levels.

Higher-order effects in bandwidth-limited soliton propagation in optical fibers.

By means of numerical studies and soliton perturbation theory we examine the effects of higher-order linear and nonlinear terms in bandwidth-limited amplified soliton propagation. We show that these effects are responsible for strong reductions of soliton-soliton interaction in such systems.

Dynamics of induced modulational instability in waveguides with saturable nonlinearity

We study the dynamics of the induced modulational instability in waveguides with saturable, third order, nonlinearity. The theoretical and numerical analysis reveal interesting features which could be exploited for all optical switching and processing.

Fast beam propagation method for the analysis of second-order nonlinear phenomena

We adopt an implicit scheme to solve both the dispersive/diffractive and the nonlinear step in the beam propagation method (BPM) code. Unlike the Runge-Kutta implementation used in the nonlinear part of the propagation, the totally implicit scheme is considerably fast. Transparent boundary conditions can be also applied to effectively treat radiation problems. To validate the method, numerical examples are given and results compared with analytical solutions.

Parametric gain in fiber systems with periodic dispersion management

We study the problem of optical noise growth, driven by modulation instability in fiber systems with dispersion management. We point out the role of dispersion-map asymmetry in sidebands generation nearby a pumping continuous wave, presenting a closed-form approximated theory to characterize the spectral distribution of noise. We propose some design guidelines for low-noise multi-wavelength optical systems, through an accurate prediction of noise growth in each channel, including the effects of map asymmetry and third-order dispersion.

Noise evolution and soliton internal modes in dispersion-managed fiber systems.

We perform a linear stability analysis of the Ablowitz-Biondini equations to explain the dynamic evolution of the noise squeezing, caused by the interplay among optical solitons and noise components, of initially uncorrelated statistics in fiber systems with dispersion management.

Two-dimensional variational analysis of self-trapped solutions in planar waveguides

Abstract A two-dimensional analysis of nonlinear planar waveguides is presented. In the framework of a variational approach the fundamental symmetric self-trapped solutions as well as their stability properties are determined.

Multiple-scale coupled-mode theory for second-harmonic generation in one-dimensional periodic structures

Using the multiple-scale approach, we derive an analytical expression for the conversion efficiency of second-harmonic generation (SHG) in a one-dimensional photonic crystal. The results, obtained in the undepleted pump limit for the continuous-wave case, allow us to describe the role played by the feedback and the dispersion introduced by the periodic structure and hence to optimize the SHG process. Numerical simulations are then used to explore the pulsed pump case, proving that the obtained results retain their validity up to a pump field bandwidth of less than approximately 12% of the stack transmission bandwidth. Shorter pulses experience both a reduced conversion efficiency and shape distortions.