Light trajectory in Bessel-Gauss vortex beams.

We investigate the early stage of propagation of Bessel-Gauss vortex beams where a transition regime shows a progressive lateral expansion of the main intensity ring before reaching a diffraction-free regime. The eikonal equation is used to characterize the beam structure. The beam is featured by a family of hyperboloids with variable waists, generating a tapered tubular caustic. Our analytical results are in excellent agreement with numerical and experimental results. We show the transition regime can be well eliminated by using hollow input beams.

Experimental chaotic map generated by picosecond laser pulse-seeded electro-optic nonlinear delay dynamics.

We describe experimental studies of the dynamical behavior of a recently proposed electro-optic discrete time nonlinear delay oscillator. With appropriate choice of the oscillator loop parameters and external forcing of the dynamics using a pulsed laser source, the system allows for the physical realization of a high dimensional mathematical nonlinear mapping. The dynamical features observed with this new class of discrete time delay oscillator differ significantly from those observed with similar continuous time nonlinear delay feedback oscillators and reveal the intrinsic discrete time nature of the dynamics. We also discuss specific applications to chaos communications using regularly clocked binary data.

From flow to map in an experimental high-dimensional electro-optic nonlinear delay oscillator.

An optoelectronic nonlinear delay oscillator seeded by a pulsed laser source is used to experimentally demonstrate a new transition scenario for the general class of delay differential dynamics, from continuous to discrete time behavior. This transition scenario differs from the singular limit map, or adiabatic approximation model that is usually considered. The transition from the map to the flow is observed when increasing the pulse repetition rate. The mechanism of this transition opens the way to new interpretations of the general properties of delay differential dynamics, which are universal features of many other scientific domains. We anticipate that the nonlinear delay oscillator architecture presented here will have significant applications in chaotic communication systems.

Optical pulse generation using soliton-assisted time-lens compression.

A simple, stable, and tunable optical pulse source emitting 3.2 ps pulses at a 10 GHz repetition rate is presented. The pulses are obtained through soliton-assisted time-lens compression in a standard single mode fiber, and are fully characterized by wavelength-conversion frequency-resolved optical gating. The use of nonlinear effects relaxes the constraint of the high driving voltage on the phase modulator usually required in this type of source.

Reduction of phase jitter in dispersion-managed systems by in-line filtering.

The influence of in-line filters on the phase jitter of chirped optical pulses propagating in arbitrary dispersion-managed systems is studied with a semianalytic moment method. Because of its stabilizing effect on the amplitude, filtering reduces the nonlinear phase jitter that accumulates through self-phase modulation. As in the case of constant-dispersion soliton links, we observe that the phase variance grows only linearly with distance in the presence of filtering. Phase jitter reduction is observed and accurately predicted by the moment method in two dispersion-managed systems with different levels of nonlinearity and filter strength.

Milliwatt-peak-power pulse characterization at 1.55 microm by wavelength-conversion frequency-resolved optical gating.

A novel wavelength-conversion configuration based on four-wave mixing in an optical fiber has been used to generate a frequency-resolved optical gating (FROG) trace identical to that obtained from second-harmonic generation (SHG). The use of an optical fiber waveguide permits enhanced measurement sensitivity compared with that of conventional SHG-FROG and has been used for complete characterization of 1-mW peak-power picosecond pulses at 1.55 microm from an unamplified semiconductor laser diode gain switched at 10 GHz.