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We introduce a new form of stable spatiotemporal self-trapped optical packets stemming from the interplay of local and nonlocal nonlinearities. Pulsed self-trapped light beams in media with both electronic and molecular nonlinear responses are addressed to prove that spatial and temporal effects can be decoupled, allowing for independent tuning. We numerically demonstrate that (3 + 1)D light bullets and antibullets, i.e., bright and dark temporal solitons embedded in stable (2 + 1)D nonlocal spatial solitons, can be generated in reorientational media under experimentally feasible conditions.

We investigate the intensity dependent spatial drift of two-color plasma based terahertz (THz) sources. A simple scheme that uses an off-axis parabolic mirror is presented to overcome this shifting. In addition, the THz energy and electric field measurements are related via the real time images of the THz spot size.

We report two-photon photocurrent in a GaAs/AlGaAs multiple quantum well laser at 1.55 microm. Using 1ps pulses, a purely quadratic photocurrent is observed. We measure the device efficiency, sensitivity, as well as the two-photon absorption coefficient. The results show that the device has potential for signal processing, autocorrelation and possibly two-photon source applications at sub-Watt power levels.

We demonstrate efficient self phase modulation, as well as negligible nonlinear absorption, in low loss (<0.06 dB/cm), high index silica glass-based waveguides. Using approximately 1 ps pulses near 1560 nm we achieve a 1.5pi nonlinear phase shift in an integrated 45 cm long spiral waveguide with <60 W of peak input power, corresponding to a large nonlinearity (gamma) of 220 W(-1)km(-1). Further, we observe negligible nonlinear absorption for input intensities > 25 GW/cm(2). The high nonlinearity and low linear and nonlinear losses of these waveguides make them promising for nonlinear all-optical signal processing applications.

We experimentally study the polarization dynamics (orientation and ellipticity) of near-infrared light transmitted through magneto-optical yttrium iron garnet isolator crystal pairs using a modified balanced detection scheme. When the pair separation is in the submillimeter range, we observed a proximity effect in which the saturation field is reduced by up to 20%. One-dimensional calculations suggest that the proximity effect originates from magnetostatic interactions between the dipole moments of the isolator crystals.

We investigate the effect of nonlinearity in a system described by an adiabatically evolving Hamiltonian. Experiments are conducted in a three-core waveguide structure that is adiabatically varying with distance, in analogy to the stimulated Raman adiabatic passage process in atomic physics. In the linear regime, the system exhibits an adiabatic power transfer between two waveguides which are not directly coupled, with negligible power recorded in the intermediate coupling waveguide. In the presence of nonlinearity the adiabatic light passage is found to critically depend on the excitation power. We show how this effect is related to the destruction of the dark state formed in this configuration.

We demonstrate a general linear pulse-shaping technique based on integrated III-V Bragg gratings (BGs). Such a technique allows for the synthesizing of complex waveforms with picosecond resolution using a compact single-waveguide design. This approach is experimentally demonstrated by fabricating and testing a series of integrated ultrafast optical pulse shapers based on BG geometries acting as time-domain code generators operating at 500 Gbits/s.

Discrete spatial solitons traveling along the interface between two dissimilar one-dimensional arrays of waveguides were observed for the first time. Two interface solitons were found theoretically, each one with a peak in a different boundary channel. One evolves into a soliton from a linear mode at an array separation larger than a critical separation where-as the second soliton always exhibits a power threshold. These solitons exhibited different power thresholds which depended on the characteristics of the two lattices. For excitation of single channels near and at the boundary, the evolution behavior with propagation distance indicates that the solitons peaked near and at the interface experience an attractive potential on one side of the boundary, and a repulsive one on the opposite side. The power dependence of the solitons at variable distance from the boundary was found to be quite different on opposite sides of the interface and showed evidence for soliton switching between channels with increasing input power.

We observe nonlinear pulse reshaping of femtosecond pulses in a waveguide array owing to coupling between waveguides. Amplified pulses from a mode-locked fiber laser are coupled to an AlGaAs core waveguide array structure. The observed power-dependent pulse reshaping agrees with theory, including shortening of the pulse in the central waveguide.

We study experimentally and numerically the nonlinear scattering of wave packets by local multisite guiding centers embedded in a continuous dielectric medium as a function of the input power and angle of incidence. The extent of trapping into the linear modes of different sites is manipulated as a function of both the input power and the angle of incidence, demonstrating power-controlled switching of nonlinear trapping by local photonic potentials.

Quantum random walks are the quantum counterpart of classical random walks, and were recently studied in the context of quantum computation. Physical implementations of quantum walks have only been made in very small scale systems severely limited by decoherence. Here we show that the propagation of photons in waveguide lattices, which have been studied extensively in recent years, are essentially an implementation of quantum walks. Since waveguide lattices are easily constructed at large scales and display negligible decoherence, they can serve as an ideal and versatile experimental playground for the study of quantum walks and quantum algorithms. We experimentally observe quantum walks in large systems ( approximately 100 sites) and confirm quantum walks effects which were studied theoretically, including ballistic propagation, disorder, and boundary related effects.

We experimentally investigate the evolution of linear and nonlinear waves in a realization of the Anderson model using disordered one-dimensional waveguide lattices. Two types of localized eigenmodes, flat-phased and staggered, are directly measured. Nonlinear perturbations enhance localization in one type and induce delocalization in the other. In a complementary approach, we study the evolution on short time scales of delta-like wave packets in the presence of disorder. A transition from ballistic wave packet expansion to exponential (Anderson) localization is observed. We also find an intermediate regime in which the ballistic and localized components coexist while diffusive dynamics is absent. Evidence is found for a faster transition into localization under nonlinear conditions.

We have investigated both theoretically and experimentally the power threshold of discrete Kerr surface solitons at the interface between a discrete one-dimensional (1D) (waveguide array) and a continuous 1D (slab waveguide) AlGaAs medium. Decreasing power thresholds were predicted and measured for soliton trapping at sites with increasing distance from the boundary. The thresholds approached asymptotically the power required for a discrete soliton of equivalent width in an infinite lattice. The minimum threshold coincided with a minimum in the interchannel coupling strength.

We demonstrate the generation muJ-level, single-cycle terahertz pulses by optical rectification from a large-aperture ZnTe single crystal wafer. Energies up to 1.5 muJ per pulse and a spectral range extending to 3 THz were obtained using a 100 Hz Ti:sapphire laser source and a 75-mmdiameter, 0.5-mm-thick, (110) ZnTe crystal, corresponding to an average power of 150 muW and an energy conversion efficiency of 3.1 x 10(-5). We also demonstrate real-time imaging of the focused terahertz beam using a pyroelectric infrared camera.

We experimentally study the nonlinear scattering by local photonic structures embedded in continuous Kerr media and demonstrate nonlinear trapping in guiding structures and resonant transmission in antiguiding structures. An intuitive physical picture is presented and verified in simulations.

We demonstrate a technique for a single shot mapping of nonlinear phase shift profiles in spatial solitons that are formed during short pulse propagation through one-dimensional slab AlGaAs waveguides, in the presence of a focusing Kerr nonlinearity. The technique uses a single beam and relies on the introduction of a lithographically etched reflective planar mirror surface positioned in proximity to the beam's input position. Using this setup we demonstrate nonlinearity-induced sharp lateral phase variations for certain initial conditions, and creation of higher spatial harmonics when the beam is in close proximity to the mirror.

We have studied theoretically and experimentally the properties of optical surface modes at the hetero-interface between two meta-materials. These meta-materials consisted of two 1D AlGaAs waveguide arrays with different band structures.

We present experimental evidence for the spontaneous formation of discrete X waves in AlGaAs waveguide arrays. This new family of optical waves has been excited, for the first time, by using the interplay between discrete diffraction and normal temporal dispersion, in the presence of Kerr nonlinearity. Our experimental results are in good agreement with theoretical predictions.

We study experimentally the interactions between normal solitons and tilted beams in glass waveguide arrays. We find that as a tilted beam, traversing away from a normally propagating soliton, coincides with the self-defocusing regime of the array, it can be refocused and routed back into any of the intermediate sites due to the interaction, as a function of the initial phase difference. Numerically, distinct parameter regimes exhibiting this behavior of the interaction are identified.

We report the experimental realization of an ultrafast all-optical temporal differentiator. Differentiation is obtained via all-fiber filtering based on a simple diffraction grating-assisted mode coupler (uniform long-period fiber grating) that performs full energy conversion at the optical carrier frequency. Due to its high bandwidth, this device allows processing of arbitrary optical signals with sub-picosecond temporal features (down to 180-fs with the specific realizations reported here). Functionality of this device was tested by differentiating a 700-fs Gaussian optical pulse generated from a fiber laser (@ 1535nm). The derivative of this pulse is an odd-symmetry Hermite-Gaussian waveform, consisting of two linked 500-fs-long, pi-phase-shifted temporal lobes. This waveform is noteworthy for its application in advanced ultrahigh-speed optical communication systems.

We report the first observation of enhanced third-order nonlinear effects in AlGaAs nanowires. AlGaAs nanowaveguides with widths varying from 100 to 600nm were fabricated and characterized. Nonlinear phase shifts of approximately pi were experimentally observed at 1.55mum with peak powers of 30-40W in 600mum long, 550nm wide guides.

We demonstrate that optical solitons can exist in dispersion-inverted highly-nonlinear AlGaAs nanowires. This is accomplished by strongly reversing the dispersion of these nano-structures to anomalous over a broad frequency range. These self-localized waves are possible at very low power levels and can form in millimeter long nanowire structures. The intensity and spectral evolution of solitons propagating in such AlGaAs nanowaveguides is investigated in the presence of loss, multiphoton absorption and higher-order dispersion.

We report the first observation of discrete optical surface solitons at the interface between a nonlinear self-focusing waveguide lattice and a continuous medium. The effect of power on the localization process of these optical self-trapped states at the edge of an AlGaAs waveguide array is investigated in detail. Our experimental results are in good agreement with theoretical predictions.

We have observed the incoherent interaction between a highly confined (blocker) soliton and wide, moving signal beams of a different wavelength in a one-dimensional discrete Kerr medium. Digital switching of the blocker solitons to successive adjacent channels was measured with increasing signal power via both one and two cascaded interactions in an AlGaAs waveguide array, operations equivalent to a reconfigurable three-output router.

A simplified near-field scanning optical microscope is employed to image the propagation of short laser pulses in planar silica waveguides, in the anomalous dispersion regime, under varying conditions of input beam power and width. Our results show a complex evolution of the transverse intensity profiles of the beam when there is a pronounced difference between the input diffraction and dispersion lengths. Numerical simulations confirm that these complex spatial dynamics are intimately related to the temporal and spectral evolution of the pulse.

We investigate experimentally and numerically the interaction of a highly localized, single-channel discrete soliton (blocker) with a wide, tilted beam in a one-dimensional AlGaAs array. In agreement with theory the blocker is observed to discretely shift its position by multiple channels, depending on the intensity and relative phase of the tilted beam.

The interaction between parallel beams in one-dimensional discrete Kerr systems has been investigated using arrays of coupled channel waveguides. The experiments were performed in AlGaAs waveguides at 1550 nm which corresponds to photon energies just below one half the semiconductor's bandgap. The input intensity and relative input phase between the input beams was varied and the output intensity patterns were recorded. Observed was behavior ranging from a linear response, to soliton interactions between moderately and then strongly localized spatial solitons. Finally the influence of multiphoton absorption and asymmetric beam inputs on these interactions was investigated at very high intensities.

We experimentally study polarization dependent linear and nonlinear dynamics in waveguide arrays. We found that in certain arrays, the band structure and the modal shapes of the array modes are markedly different for the two polarizations, in a manner that cannot be simply explained using the effective index approximation. Specifically, one of the gaps was found to be missing for the TM polarization. In the nonlinear regime, we observe mixed-polarization nonlinear localizations in high bands, such as Band-2 Floquet-Bloch vector solitons. The band structure anomaly enabled the excitation of a multiband moving breather.

We report an experimental study of discrete gap solitons in binary arrays of optical waveguides. We observe self-focusing indicating soliton generation when the inclination angle of an input beam is slightly above the Bragg angle and show that the propagation direction of the emerging gap soliton is influenced by the effect of interband momentum exchange.

We report our investigation of Kerr nonlinear beam interactions in discrete systems. The influence of power and the relative phase between two Gaussian shaped beams was investigated in detail by performing numerical simulations of the discrete nonlinear Schrödinger equation and comparing the results with experiments done in AlGaAs waveguide arrays. Good agreement between theory and experiment was obtained.

We report the first experimental observation of modulation instability in a discrete optical nonlinear array.

Bright and dark spatial gap solitons are demonstrated in waveguide arrays. These gap solitons travel across the array at zero transverse velocity, in complete analogy with stationary (immobile) temporal gap solitons. Furthermore, the launching configuration for observing these stationary gap solitons is shown to be the analog of an "ideal experiment" for observing stationary temporal gap solitons, never observed so far. A clear distinction is established between the family of Floquet-Bloch solitons in general and discrete solitons in particular, and the limiting case of gap solitons.

We investigate the propagation of short, intense laser pulses in arrays of coupled silica waveguides, in the anomalous dispersion regime. The nonlinearity induces trapping of the pulse in a single waveguide, over a wide range of input parameters. A sharp transition is observed for single waveguide excitation, from strong diffraction at low powers to strong localization at high powers.

We report the first experimental observation of discrete vector solitons in AlGaAs nonlinear waveguide arrays. These self-trapped states are possible through the coexistence of two orthogonally polarized fields and are stable in spite of the presence of four-wave mixing effects. We demonstrate that at sufficiently high power levels the two polarizations lock into a highly localized vector discrete soliton that would have been otherwise impossible in the absence of either one of these two components.

Multiphoton fluorescence is used for the direct observation of a new class of breathers in waveguide arrays, which are a coherent superposition of Floquet-Bloch solitons of different bands. These Floquet-Bloch breathers oscillate along their spatial propagation axis, and possess several novel properties. Some behavior of these breathers is readily understood intuitively in terms of the band structure of the waveguide array and the properties of discrete solitons.

We investigated the interaction of discrete solitons with defect states fabricated in arrays of coupled waveguides. We achieved attractive and repulsive defects by decreasing and increasing, respectively, the spacing of one pair of waveguides in an otherwise uniform array. Linear and nonlinear propagation in the same samples show distinctly different properties. The role of the Peierls-Nabarro potential in the interaction of the soliton with the defect is discussed.

Band-gap structure of periodic waveguide arrays is investigated in the linear and the nonlinear regimes. Excitation of array modes belonging to high bands is demonstrated. Floquet-Bloch solitons are demonstrated experimentally and shown to be a generalization of discrete solitons.

We observed simultaneous focusing in both space and time for light pulses propagating in a planar waveguide. In particular, 60 fs pulses with a width of 170 microm were injected into a planar glass waveguide in the anomalous dispersion regime. Output pulses as short as 30 fs and as narrow as 20 microm were measured. The results suggest that multiphoton absorption and intrapulse stimulated Raman scattering arrest the spatiotemporal contraction. The results were compared to the pulse evolution in zero and normal dispersion regimes and were shown to be significantly different. All of the experimental results were reproduced by a numerical model.

We show that two regimes of diffraction exist in arrays of waveguides, depending upon the input conditions. At higher powers, normal diffraction leads to self-focusing and to the formation of bright solitons through the nonlinear Kerr effect. By slightly changing the input conditions, light experiences anomalous diffraction and is nonlinearly defocused. For the first time, self-focusing and self-defocusing have been achieved for the same medium, structure, and wavelength.

By using the diffraction properties of waveguide arrays, we propose a scheme to produce structures with designed diffraction. We fabricated arrays with reduced, canceled, and even reversed diffraction. Results of experiments with such waveguides are presented and compared with the predictions made by coupled-mode theory.