We experimentally study dispersive shock waves in nonlinear waveguide arrays. In contrast with gap solitons, the nonlinearity here pushes the propagation constant further into the transmission bands, facilitating Bloch mode coupling and energy transport. We directly observe this coupling, both within and between bands, by recording intensity in position space and power spectra in momentum space.

We consider dispersive optical shock waves in nonlocal nonlinear media. Experiments are performed using spatial beams in a thermal liquid cell, and results agree with a hydrodynamic theory of propagation.

The holographic reconstruction of optically-induced objects typically assumes that the object is axially thin. Here, we demonstrate a simple approach that works for axially thick objects which evolve dynamically. Results are verified by reconstructing linear scattering experiments in a self-defocusing photorefractive crystal.

We consider the propagation of a partially coherent spatial beam in both self-focusing and self-defocusing nonlinear media. Using a Gaussian-Schell model, we derive an equation governing the width of highly incoherent beams as they propagate in both types of media and confirm its validity by using numerical simulations. Experiments performed in a biased photorefractive crystal match the predicted scaling.

We examine an all-optical bump-on-tail instability by considering the nonlinear interaction of two partially incoherent spatial beams. Using a radiation transport approach, we develop plasmalike dispersion relations for perturbation modes and show that a positive gradient in the power spectrum can trigger instability. Theoretical considerations are confirmed by experiment and numerical simulation.

A novel all-solid Bragg fiber composed entirely of silica material is proposed in this paper. The core of this Bragg fiber is composed of conventional silica, and the cladding is formed by a set of alternating layers of up-doped and down-doped silica. This all-solid silica Bragg fiber is technically feasible and can simplify the fabrication technique. Dispersion properties of this silica Bragg fiber are investigated, and simulations show that zero dispersion wavelength lambda0 near 1.55 m with nonlinear coefficient gamma about 50 W-1km-1 can be obtained in silica Bragg fiber.

We study the over-focusing of spatial light beams due to self-focusing nonlinearity, in both local and nonlocal nonlinear media. Numerical simulation of both cases reveals a peaked profile, with a near-cusp at the center surrounded by exponentially-decaying tails, at a critical self-focusing power. The profile is a local effect, occurring as diffraction counteracts nonlinearity. Nonlocality, however, is needed to prevent modulation instability of the initial beam and to prevent catastrophic collapse in 2D. The peaked profile remains for weak nonlocality but disappears for wide nonlocal responses. Beyond the critical power for a peaked solution, or for longer propagation distances, competition between nonlinearity and diffraction causes oscillatory collapse-bounce behavior. The numerical results are confirmed by observing these dynamics in a self-focusing glass with a nonlocal, thermal response.

We demonstrate an all-optical bump-on-tail instability by considering the nonlinear interaction of two partially coherent spatial beams. For weak wave coupling, we observe momentum transfer with no variation in intensity. For strong wave coupling, modulations appear in intensity and evidence appears for wave (Langmuir) collapse at large scales. Borrowing plasma language, these limits represent regimes of weak and strong spatial optical turbulence. In both limits, the internal spectral energy redistribution is observed by recording and reconstructing a hologram of the evolving dynamics. The results are universal and can appear in any wave-kinetic system with short-wave-long-wave coupling.

We study the dynamics of phasons in a nonlinear photonic quasicrystal. The photonic quasicrystal is formed by optical induction, and its dynamics is initiated by allowing the light waves inducing the quasicrystal to nonlinearly interact with one another. We show quantitatively that, when phason strain is introduced in a controlled manner, it relaxes through the nonlinear interactions within the photonic quasicrystal. We establish experimentally that the relaxation rate of phason strain in the quasicrystal is substantially lower than the relaxation rate of phonon strain, as predicted for atomic quasicrystals. Finally, we monitor and identify individual 'atomic-scale' phason flips occurring in the photonic quasicrystal as its phason strain relaxes, as well as noise-induced phason fluctuations.

We report the experimental observation of temporal vector soliton propagation and collision in a linearly birefringent optical fiber. To the best of the authors' knowledge, this is both the first demonstration of temporal vector solitons with two mutually incoherent component fields, and of vector soliton collisions in a Kerr nonlinear medium. Collisions are characterized by an intensity redistribution between the two components, and the experimental results agree with numerical predictions of the coupled nonlinear Schrödinger equation.

We demonstrate what we believe to be the first experimental observation of self-trapping and self-deflection of a planar optical beam by the photorefractive effect in a semiconductor. The semiconductor material is indium phosphide doped with iron. We show that the observed focusing and defocusing effects follow the component of the two-wave-mixing space charge field that is in phase with the intensity pattern, whereas the spatial beam deflection effects follow the 90 degrees -shifted component.

We investigate contradirectional two-wave mixing with partially coherent waves in photorefractive crystals in the nondepleted pump regime. Equations governing the propagation of the self-coherence function and the mutual-coherence function of the signal wave and the pump wave are derived and simulated numerically. Numerical solutions of these equations are in excellent agreement with the experimental measurements.

We demonstrate experimentally a new degenerate four-wave mixing (DFWM) geometry in waveguides that permits the simultaneous determination of the nonlinear refractive index, the absorption, and the response time of the thin-film materials. The geometry consists of two guided pumps in a planar waveguide with an unguided probe. We achieve nonlinear characterization by measuring only the DFWM signal and the guided pump power at the waveguide output. The technique has been tested on a polymeric film (di-alkylaminonitro- stilbene).

We experimentally demonstrate for the first time to our knowledge continuous-wave operation of saturablegain degenerate four-wave mixing by using a Nd:YVO(4) amplifier pumped by a cw Ti:sapphire laser. Such an amplifier exhibits continuous-wave two-pass gains as high as 200, and four-wave mixing reflectivities as high as 30% are obtained. A theoretical analysis is developed in the steady-state regime to explain the experimental results.

We demonstrate that a dielectric medium with purely quadratic nonlinearity [the so-called chi((2)) material] can display self-focusing phenomena through a new type of modulational instability of the interacting fundamental and second-harmonic field components and therefore can support propagation of (two-wave) optical solitons. We prove the existence of a family of such solitons, which are found numerically and, in some particular cases, also analytically. The two-wave solitons are stable in the whole parameter region in which they exist.

Using degenerate four-wave mixing in an Fe:LiNbO(3) 0.04-wt.% crystal and an external-reflection near-field optical microscope, we have achieved phase conjugation of light emitted by a fiber tip. We observe that the phase-conjugated light at a wavelength of 633 nm can reach a power of ~0.1 nW and produce a 180-nm-wide spot image in the near-field microscope. This is the first direct demonstration, to our knowledge, of the phase conjugation of near-field components of optical fields.

We present and experimentally demonstrate a new method for enhancing the signal-to-background ratio of two-wave mixing in photorefractive crystals. The method uses a mutually incoherent third beam to suppress the fanning in a dark ring-shaped region in which the amplified signal is located. A 20-fold improvement of the signal-to-background ratio is measured in BaTiO(3) at lambda = 514 nm. The extension of this principle to wide-field-of-view heterodyne detection is discussed.

We explore theoretically and experimentally how application of an electric field to a photorefractive crystal affects the recording and the readout of holograms. We consider, for the first time to our knowledge, the effects of fringe bending caused by nonlinear two-wave mixing on the change in Bragg condition and diffraction efficiency as a function of the applied electric field. Practical performance limitations for holographic data storage and image amplification are discussed.

A transient model of degenerate four-wave mixing in saturable amplifiers is developed for calculation of the phase-conjugate reflectivity in the weak-probe-beam limit. Our model takes into account the laser amplification of all the interacting beams together with the wave-mixing process between the two counterpropagating pump waves. Experimental investigations are made in a flash-lamp-pumped Nd:YAG amplifier with nanosecond pulses at 1.06 microm. A reflectivity of 22% is achieved when all the waves interfere within the laser medium.

We demonstrate that picosecond mode-locked laser-based degenerate four-wave mixing can be detected with good signal-to-noise ratios in an optically thin flame and that detailed turbulence statistics can be acquired by use of this technique. A regeneratively mode-locked Ti:sapphire laser was tuned to the 4(2)S((1/2))-4(2)P degrees ((1/2)) transition in atomic potassium (which was doped into the flame) at 769.9 nm. Using the all-forward degenerate four-wave mixing geometry, we achieved signal-to-noise ratios of 70:1 without the use of a spatial filter. A sensitivity curve and a method for acquiring turbulence statistics are presented.