Energy localization in photonic crystals of a purely nonlinear origin

We investigate electromagnetic localization in a nonlinear photonic crystal, i.e., a structure with a stop band in its nonlinear spectral response. Taking a one-dimensional model of degenerate two-wave interaction we introduce the concept of parametric nonlinear-gap solitons, that is, strongly localized two-color locked envelopes arising from interplay of two nonlinear effects, which propagate slowly. We discuss the observable signature of these novel localized structures.     

Raman-induced localization in Kerr waveguide arrays

We show that during the spatiotemporal compression in a periodic Kerr waveguide array, stimulated Raman scattering can effectively balance the effects of self-phase modulation, diffraction, and group-velocity dispersion, eliminating collapse and breakup over a wide range of input powers and leading to stable propagation in a single site.     

Nonlinearity and disorder in fiber arrays

We experimentally investigate light propagation in a disordered two-dimensional array of mutually coupled optical fibers. In the linear case light either spreads in a diffusive manner or localizes at a few sites. For high excitation power diffusive spreading is arrested by the focusing nonlinearity, i.e., forming a discrete soliton. By contrast, fields, which are localized in the linear regime, can experience both spreading and contraction caused by the nonlinearity.     

Dispersive shock waves in nonlinear arrays

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.     

Self-organized coherence in fiber laser arrays

We report the production of stable, coherent, and same-phase states in arrays of fiber lasers. Provided that proper interactions between the lasers are present, arrays will spontaneously self-organize into stable coherent same-phase states. There is no need for active control. Power scaling, power spectra, spatial interference fringes, and temporal data all support this conclusion.     

ps级脉冲光纤放大器和压缩器

 对掺镱双包层脉冲光纤放大器进行实验研究。当用入纤功率为1.9 W的半导体激光器激光泵浦0.5 m长的双包层掺镱光纤时,把平均功率为7 mW、重复频率25.4 MHz的激光放大到505 mW,相应的单脉冲能量为19.8 nJ,经过光栅对压缩后,得到2.7 ps的脉冲激光。     

ps级脉冲光纤放大器和压缩器

对掺镱双包层脉冲光纤放大器进行实验研究。当用入纤功率为1.9 W的半导体激光器激光泵浦0.5 m长的双包层掺镱光纤时,把平均功率为7 mW、重复频率25.4 MHz的激光放大到505 mW,相应的单脉冲能量为19.8 nJ,经过光栅对压缩后,得到2.7 ps的脉冲激光。     

All-optical switching in quadratically nonlinear waveguide arrays

We demonstrate a scheme for efficient switching and routing of low-power signals in waveguide arrays with second-order nonlinearity. With control beams the signal can be switched to different output positions and can be simultaneously converted to another wavelength with low cross talk.     

Discrete X-wave formation in nonlinear waveguide arrays

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.     

Tamm oscillations in semi-infinite nonlinear waveguide arrays

We demonstrate the existence of nonlinear Tamm oscillations at the interface between a substrate and a one-dimensional waveguide array with either cubic or saturable, self-focusing or self-defocusing nonlinearity. Light is trapped in the vicinity of the array boundary due to the interplay between the repulsive edge potential and Bragg reflection inside the array. In the special case when this potential is linear these oscillations reduce themselves to surface Bloch oscillations.     

Discrete vector solitons in Kerr nonlinear waveguide arrays

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.     

Beam interaction in one-dimensional inhomogeneous Kerr nonlinear arrays

The interactions between two parallel and co-polarized beams in weakly coupled cubic focusing nonlinear waveguide arrays with transverse inhomogeneous modulation of the refractive index were investigated by means of beam propagation method. Results show that the in-phase beams attract each other and coalesce when the inhomogeneous parameter is smaller than a critical value. For the out-of-phase beams, oscillations exist at low power level, and the larger inhomogeneous parameter, the larger period and amplitude of oscillation. At a high power level, solitonlike propagation of weak coupling occurs. The inhomogeneity of waveguide arrays provide a flexible way to control the interactions of beams, and may find potential applications in all-optical systems.     

Anderson localization in nonlocal nonlinear media

We theoretically and numerically investigate the effect of focusing and defocusing nonlinearities on Anderson localization in highly nonlocal media. A perturbative approach is developed to solve the nonlocal nonlinear Schr?dinger equation in the presence of a random potential, showing that nonlocality stabilizes Anderson states.     

Energy localization in general relativity: A new hypothesis

A new hypothesis for energy localization in general relativity is introduced which is based upon the fact that the energy-momentum conservation laws are devoid of content in vacuum. The vanishing of pseudotensor components forms the basis of coordinate conditions consistent with the above. The implication is that energy is localized where the energy-momentum tensor is nonvanishing. As a consequence, gravitational waves are not carriers of energy in vacuum. A detailed analysis of a Feynman detector interacting with a plane gravitational wave is consistent with the hypothesis. The fact that there has never been a confirmed direct energy transfer to a detector via gravitational radiation is also consistent with the hypothesis.     

Observation of dynamic localization in periodically curved waveguide arrays

We report on a direct experimental observation of dynamic localization (DL) of light in sinusoidally-curved lithium-niobate waveguide arrays which provides the optical analog of DL for electrons in periodic potentials subjected to ac electric fields as originally proposed by Dunlap and Kenkre [Phys. Rev. B 34, 3625 (1986)10.1103/PhysRevB.34.3625]. The theoretical condition for DL in a sinusoidal field is experimentally demonstrated.     

Interrogation of fiber grating sensor arrays with a wavelength-swept fiber laser

We demonstrate a novel application of a wavelength-swept fiber laser to fiber Bragg grating sensor-array interrogation. The laser provides high signal powers of >3 mW with <0.1-nm spectral resolution over a 28-nm wavelength span. Using time-interval counting, we demonstrate static-dynamic strain measurements with a resolution of 0.47mu? rms at a sampling rate of 250 Hz.     

Slow-light optical bullets in arrays of nonlinear Bragg-grating waveguides

We demonstrate that propagation direction and velocity of optical pulses can be controlled independently in the structures with multiscale modulation of the refractive index in transverse and longitudinal directions. We reveal that, in arrays of waveguides with phase-shifted Bragg gratings, the refraction angle does not depend on the speed of light, allowing for efficient spatial steering of slow light. In this system, both spatial diffraction and temporal dispersion can be designed independently, and we identify the possibility for self-collimation of slow light when spatial diffraction is suppressed for certain propagation directions. We also show that broadening of pulses in space and time can be eliminated in nonlinear media, supporting the formation of slow-light optical bullets that remain localized irrespective of propagation direction.     

Control of lasing filament arrays in nonlinear liquid media

Multiple filamentation in a high concentration solution of coumarin 153 in ethanol is studied. It is shown that the output filament pattern may be controlled by placing diffractive elements (circular aperture, edge) in the input beam path. These filaments are formed in highly reproducible arrays along diffraction maxima corresponding to the element used. Experimental results are supported by numerical simulations. They confirm that diffraction-induced intensity gradients swamp modulational instability on the wavefront, forcing filaments to form along diffraction maxima. The effect of two-photon absorption by coumarin molecules on filament patterns is also investigated over a range of dye concentrations. Control results are finally exploited in the production of arrays of localized lasing filaments, which should open novel applications. The resultant lasing sources are mutually coherent and highly repeatable from shot-to-shot, as is shown by their far-field interference patterns. PACS 42.65.Tg; 52.38.Hb; 42.68.Ay