Observation of the critical regime near Anderson localization of light

The transition from diffusive transport to localization of waves should occur for any type of classical or quantum wave in any media as long as the wavelength becomes comparable to the transport mean free path l*. The signatures of localization and those of absorption, or bound states, can, however, be similar, such that an unequivocal proof of the existence of wave localization in disordered bulk materials is still lacking. Here we present time resolved measurements of light transport through strongly scattering samples with kl* values as low as 2.5. In transmission, we observe deviations from diffusion which cannot be explained by absorption, sample geometry, or reduction in transport velocity. Furthermore, the deviations from classical diffusion increase strongly with decreasing l* as expected for a phase transition. This constitutes an experimental realization of the critical regime in the approach to Anderson localization.     

Observation of the breakup of a prechirped N-soliton in an optical fiber

We present what is believed to be the first experimental evidence showing the breakup of a chirped N-soliton pulse into an ordered train of fundamental solitons, as predicted by theory. We also present numerical experiments that confirm this phenomenon. Implications for optical communications systems that use chirped pulses are discussed.     

Observation of the gradual transition from one-dimensional to two-dimensional Anderson localization

We study the gradual transition from one-dimensional (1D) to two-dimensional (2D) Anderson localization upon transformation of the dimensionality of disordered waveguide arrays. An effective transition from a 1D to a 2D system is achieved by increasing the number of rows forming the arrays. We observe that, for a given disorder level, Anderson localization becomes weaker with increasing numbers of rows-hence the effective dimension.     

Observation of inhomogeneous spectral broadening of stimulated brillouin scattering in an optical fiber

We report experimental results which show that the stimulated Brillouin scattering (SBS) spectrum in an optical fiber is inhomogeneous, exhibiting spectral broadening and hole burning under cw monochromatic laser excitation. This phenomenon arises from the waveguide interaction of the pump and Stokes signals and is a fundamental property of SBS in waveguiding systems due to their ability to confine a fan of radiation wave vector directions.     

Observation of twin-beam-type quantum correlation in optical fiber

We report generation of pulsed twin beams of light through optical parametric amplification in a fiber Sagnac loop. By pumping the Sagnac loop with picosecond pulses at a wavelength near the zero-dispersion wavelength of the fiber, we achieve phase-matched nondegenerate four-wave mixing with gain. For a gain of 2.2, the intensity noises of the amplified signal and the generated idler (conjugate) pulses are found to be correlated by 5.0 dB, and the subtracted noise drops below the shot-noise limit by 1.1 dB (2.6 dB when corrected for losses). We have investigated the gain dependence of the quantum-noise reduction as well as of the intensity noises of the amplified signal and idler pulses. As the gain increases, we observe the onset of excess noise on the idler pulses.     

Role of optical nonlinearity on transverse localization of light in a disordered one-dimensional optical waveguide lattice

We report a detailed numerical investigation on transverse localization of light in a 1D disordered lattice consisting of a large array of coupled waveguides in the presence of nonlinearity in the medium. Our study reveals that the presence of a focusing type of nonlinearity favors faster localization of light while a defocusing type of nonlinearity degrades the quality of localization. It is shown that presence of either of these could over-shadow localization of light unless the strength of disorder is sufficiently strong. Influence of the input beam width on propagation of light in such a disordered nonlinear medium has also been discussed. The present study should be useful in potential applications, in which one could exploit dominance of focusing nonlinearity on transverse localization of light in a disordered medium.     

Boundary-induced Anderson localization in photonic lattices

We analyze numerically localization of light in linear square waveguide arrays restricted in one dimension (“ribbons”), whose boundaries are disordered in propagation constant and/or coupling. We find that the disordered boundary induces a localization tendency in the bulk even for relatively wide ribbons.     

Quantum correlations in two-particle Anderson localization

We predict quantum correlations between noninteracting particles evolving simultaneously in a disordered medium. While the particle density follows the single-particle dynamics and exhibits Anderson localization, the two-particle correlation develops unique features that depend on the quantum statistics of the particles and their initial separation. On short time scales, the localization of one particle becomes dependent on whether or not the other particle is localized. On long time scales, the localized particles show oscillatory correlations within the localization length. These effects can be observed in Anderson localization of nonclassical light and ultracold atoms.     

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.     

基于光纤光栅技术的船体横扭角测量方法研究

简要介绍了常见的船体横扭角测量方法,与传统的船体横扭角测量方法相比,光栅技术具有精度高、体积小、测量通道多等优势。建立了从应变量到横扭角的转换模型,设计并完成了与测量船现有变形测量系统的对比测量试验。试验结果表明:在较短测量时段内光栅测量数据与现有船载变形测量系统的测量数据吻合度高,误差在5″范围内,满足船体变形测量的要求;在长时间测量过程中,外界振动干扰对测量结果影响显著。     

Suppression of Anderson localization in disordered metamaterials

We study wave propagation in mixed, 1D disordered stacks of alternating right- and left-handed layers and reveal that the introduction of metamaterials substantially suppresses Anderson localization. At long wavelengths, the localization length in mixed stacks is orders of magnitude larger than for normal structures, proportional to the sixth power of the wavelength, in contrast to the usual quadratic wavelength dependence of normal systems. Suppression of localization is also exemplified in long-wavelength resonances which largely disappear when left-handed materials are introduced.     

Anderson localization and wave absorption

Experimental signatures of classical wave localization in the absence and in the presence of attenuation are analyzed. The different regimes of the attenuation, reflection, and transmission coefficients for the diffusive and localized regimes are discussed. Apparent contradictory results presented previously by John and Anderson on the renormalization of absorption by localization are reconciled and shown to apply to different situations.     

Emergence of Anderson localization in plasmonic waveguides

The propagation of surface plasmon polaritons in dielectric loaded waveguides with randomly placed scatterers is studied using both numerical simulations and a simplified transfer matrix framework. Despite the importance of losses in this system, we find fingerprints of the localized behavior of one-dimensional disordered systems. Furthermore, losses amplify the impact of the necklace states on the transport properties for systems not much larger than the localization length. The system presented here also offers the possibility to use localization effects for engineering purposes by means of deliberately introduced disorder.     

Energy transfer and Anderson localization

The temporal decay characteristics of the donor fluorescence for inhomogeneously broadened optical lines is shown to be a direct determination of excitation localization, in the Anderson sense.     

Observation of orbital angular momentum transfer between acoustic and optical vortices in optical fiber

Acousto-optic interaction in optical fiber is examined from the perspective of copropagating optical and acoustic vortex modes. Calculation of the acousto-optic coupling coefficient between different optical modes leads to independent conservation of spin and orbital angular momentum of the interacting photons and phonons. We show that the orbital angular momentum of the acoustic vortex can be transferred to a circularly polarized fundamental optical mode to form a stable optical vortex in the fiber carrying orbital angular momentum. The technique provides a useful way of generating stable optical vortices in the fiber medium.