Transverse Localization Research Articles

Spatial acoustic emission localization method for damage to prestressed steel strands of girders using special-shaped waveguide rods

As an essential load-bearing member of post-tensioned prestressed girders, prestressed steel strands will inevitably reduce the safety and durability of the bridge if damaged. However, traditional damage localization methods for the steel strand require numerous acoustic emission (AE) sensors with a complex arrangement in the prestressed girder. This study proposes a spatial AE localization method using a dual-sensor array with the assistance of special-shaped waveguide rods. The spatial damage localization is achieved by combining the time difference of arrival (TDOA) of the AE wave with the propagation attenuation law. Transverse and longitudinal damage localization for prestressed steel strands are verified on a simplified platform containing different special-shaped waveguide rods. For transverse damage localization, the TDOA of the maximum AE amplitudes is superior to that of the first waves. For longitudinal damage localization, the relative localization accuracy reaches 94%. With this method, only two AE sensors are required to localize the three-dimensional damage to the prestressed steel strands in a girder.

Isotropic gap formation, localization, and waveguiding in mesoscale Yukawa-potential amorphous structures

Amorphous photonic structures are mesoscopic optical structures described by electrical permittivity distributions with underlying spatial randomness. They offer a unique platform for studying a broad set of electromagnetic phenomena, including transverse Anderson localization, enhanced wave transport, and suppressed diffusion in random media. Despite this, at a more practical level, there is insufficient work on both understanding the nature of optical transport and the conditions conducive to vector-wave localization in these planar structures, as well as their potential applications to photonic nanodevices. In this study, we fill this gap by investigating experimentally and theoretically the characteristics of optical transport in a class of amorphous photonic structures and by demonstrating their use to some basic waveguiding nanostructures. We demonstrate that these 2-D structures have unique isotropic and asymmetric band gaps for in-plane propagation, controlled from first principles by varying the scattering strength and whose properties are elucidated by establishing an analogy between photon and carrier transport in amorphous semiconductors. We further observe Urbach band tails in these random structures and uncover their relation to frequency- and disorder-dependent Anderson-like localized modes through the modified Ioffe-Regel criterion and their mean free path - localization length character. Finally, we illustrate that our amorphous structures can serve as a versatile platform in which photonic devices such as disorder-localized waveguides can be readily implemented.

Light wave propagation and diffraction inhibition in three-dimensional photonic quasicrystal lattices

We have investigated the linear propagation of light wave in three-dimensional photonic quasicrystal lattices by numerical simulation. The diffraction characteristics of the light waves in the longitudinal non-modulated, in-phase modulated and out-of-phase modulated quasicrystal lattices have been compared and discussed. We have demonstrated the diffraction inhibition of light wave in three-dimensional photonic quasicrystals. Linear transverse light localization has been realized in the longitudinal out-of-phase modulated three-dimensional quasicrystal lattices by adjusting the structural parameters appropriately. Furthermore, the results also show that the longitudinal out-of-phase modulated photonic quasicrystals are easier to produce diffraction inhibition than the longitudinal out-of-phase modulated periodic lattices under low transverse refractive index contrast. Distortionless dot image transmission has numerically demonstrated in out-of-phase modulated photonic quasicrystals array. It provides a new way for distortion-free image transmission, which has promising applications in optical information transmission and all-optical signal processing.

From topological phase to transverse Anderson localization in a two-dimensional quasiperiodic system

From topological phase to transverse Anderson localization in a two-dimensional quasiperiodic system

Lattice model for the quantum anomalous Hall effect in moiré graphene

Inspired by experiments on magic angle-twisted bilayer graphene, we present a lattice mean-field model for the quantum anomalous Hall effect in a moir\'e setting. Our hopping Hamiltonian provides a simple route to a moir\'e Chern insulator in commensurately twisted systems. We study our model in the ribbon geometry and demonstrate the presence of thick chiral edge states that have a transverse localization that scales with the moir\'e lattice spacing. We also study the electronic structure of a domain wall between opposite Chern insulators. Our model and results are relevant to experiments that will image or manipulate the moir\'e quantum anomalous Hall edge states.

Unsupervised full-color cellular image reconstruction through disordered optical fiber

Recent years have witnessed the tremendous development of fusing fiber-optic imaging with supervised deep learning to enable high-quality imaging of hard-to-reach areas. Nevertheless, the supervised deep learning method imposes strict constraints on fiber-optic imaging systems, where the input objects and the fiber outputs have to be collected in pairs. To unleash the full potential of fiber-optic imaging, unsupervised image reconstruction is in demand. Unfortunately, neither optical fiber bundles nor multimode fibers can achieve a point-to-point transmission of the object with a high sampling density, as is a prerequisite for unsupervised image reconstruction. The recently proposed disordered fibers offer a new solution based on the transverse Anderson localization. Here, we demonstrate unsupervised full-color imaging with a cellular resolution through a meter-long disordered fiber in both transmission and reflection modes. The unsupervised image reconstruction consists of two stages. In the first stage, we perform a pixel-wise standardization on the fiber outputs using the statistics of the objects. In the second stage, we recover the fine details of the reconstructions through a generative adversarial network. Unsupervised image reconstruction does not need paired images, enabling a much more flexible calibration under various conditions. Our new solution achieves full-color high-fidelity cell imaging within a working distance of at least 4 mm by only collecting the fiber outputs after an initial calibration. High imaging robustness is also demonstrated when the disordered fiber is bent with a central angle of 60°. Moreover, the cross-domain generality on unseen objects is shown to be enhanced with a diversified object set.

Tunable Dispersion and Supercontinuum Generation in Disordered Glass-Air Anderson Localization Fiber

In this paper, we discuss chromatic dispersion properties of transverse Anderson localization optical fiber (TALOF) and their implications on broad band supercontinuum (SC) generation. Our dispersion study reveals a clear correlation between the Anderson localization length and the dispersion properties of highly localized TALOF modes. We demonstrate that the zero dispersion wavelength can be tuned over more than 300 nm within the same fiber by selected excitation of specific modes. We exploit this unique TALOF property, which we validated with rigorous finite-element modeling, to generate multi octave spanning SC ranging from 460–1750 nm, highlighting the great potential of disordered Anderson localization fibers for nonlinear applications.

Strong localization and suppression of Anderson modes in an asymmetrical optical waveguide.

In this paper, transverse Anderson localization of light waves in a 3D random network is achieved inside an asymmetrical type optical waveguide, formed within a fused-silica fiber by capillary process. Scattering waveguide medium originates from naturally formed air inclusions and Ag nanoparticles in rhodamine dye doped-phenol solution. Multimode photon localization is controlled by changing the degree of the disorder in the optical waveguide to suppress unwanted extra modes and obtain only one targeted strongly localized single optical mode confinement at the desired emission wavelength of the dye molecules. Additionally, the fluorescence dynamics of the dye molecules coupled into the Anderson localized modes in the disordered optical media are analyzed through time resolved experiments based on a single photon counting technique. The radiative decay rate of the dye molecules is observed to be enhanced up to a factor of about 10.1 through coupling into the specific Anderson localized cavity within the optical waveguide, providing a milestone for investigation of transverse Anderson localization of light waves in 3D disordered media to manipulate light-matter interaction.

Evanescent field trapping and propulsion of Janus particles along optical nanofibers

Small composite objects, known as Janus particles, drive sustained scientific interest primarily targeted at biomedical applications, where such objects act as micro- or nanoscale actuators, carriers, or imaging agents. A major practical challenge is to develop effective methods for the manipulation of Janus particles. The available long-range methods mostly rely on chemical reactions or thermal gradients, therefore having limited precision and strong dependency on the content and properties of the carrier fluid. To tackle these limitations, we propose the manipulation of Janus particles (here, silica microspheres half-coated with gold) by optical forces in the evanescent field of an optical nanofiber. We find that Janus particles exhibit strong transverse localization on the nanofiber and much faster propulsion compared to all-dielectric particles of the same size. These results establish the effectiveness of near-field geometries for optical manipulation of composite particles, where new waveguide-based or plasmonic solutions could be envisaged.

Optimum Design of Glass–Air Disordered Optical Fiber with Two Different Element Sizes

This paper presents a detailed study investigating the effect of the material refractive index distribution at the local position of a glass–air disordered optical fiber (G-DOF) on its localized beam radius. It was found that the larger the proportion of the glass material, the smaller its localized beam radius, which means that the transverse Anderson localization (TAL) effect would be stronger. Accordingly, we propose a novel G-DOF with large-size glass elements doped in the fiber cross-section. The simulation results show that the doped large-size glass elements can reduce the localized beam radius in the doped region and has a very tiny effect on the undoped region, thus contributing to reducing the average localized beam radius of G-DOF.

Bloch Surface Waves in Open Fabry-Perot Microcavities.

Thanks to the increasing availability of technologies for thin film deposition, all-dielectric structures are becoming more and more attractive for integrated photonics. As light-matter interactions are involved, Bloch Surface Waves (BSWs) may represent a viable alternative to plasmonic platforms, allowing easy wavelength and polarization manipulation and reduced absorption losses. However, plasmon-based devices operating at an optical and near-infrared frequency have been demonstrated to reach extraordinary field confinement capabilities, with localized mode volumes of down to a few nanometers. Although such levels of energy localization are substantially unattainable with dielectrics, it is possible to operate subwavelength field confinement by employing high-refractive index materials with proper patterning such as, e.g., photonic crystals and metasurfaces. Here, we propose a computational study on the transverse localization of BSWs by means of quasi-flat Fabry-Perot microcavities, which have the advantage of being fully exposed toward the outer environment. These structures are constituted by defected periodic corrugations of a dielectric multilayer top surface. The dispersion and spatial distribution of BSWs' cavity mode are presented. In addition, the hybridization of BSWs with an A exciton in a 2D flake of tungsten disulfide (WS2) is also addressed. We show evidence of strong coupling involving not only propagating BSWs but also localized BSWs, namely, band-edge and cavity modes.

Linear and nonlinear optical properties surface plasmon polariton localization in plasmonic crystal metallic nanowires

Functionality and spatial concentration of light in periodic and disordered plasmonic crystal metallic nanowires are investigated under Kerr nonlinearity. The results show that nonlinear transverse localization of surface plasmon polaritons (SPP) in a periodic and disordered array of nanowires embedded in the Kerr medium changes with incident input wave amplitude (A). We study periodic and diagonal disordered nanowire arrays and study the propagation of SSPs under different inputs by solving nonlinear coupling relations. Finally, off-diagonal disordered nanowire arrays are studied. The results show that localization and effective beamwidth of the SPPs increases with an increase in their input amplitudes. Also, the SPPs become more localized with increase of diagonal (δr) and off-diagonal disorder (δd) into the nanowire arrays. Controlling SSPs' localization in the nanowire array using their input amplitude provides a high functional sub-wavelength device that can be utilized in future applications of nanophotonics functions.

Analysis of Localized Modes in Disordered Optical Waveguides Mediated by Transverse Anderson Localization

Disordered waveguides mediated by transverse Anderson localization (TAL) can be used as mode division multiplexing system. The whole cross-section of the disordered waveguides is covered by all localized modes, which function as independent space channels. The localized modes are independent of the boundary and external excitation. The numerical results reveal that the average width tends to be steady in one particular realization of the disordered waveguide with a sufficient number of localized modes. In this paper, we proposed that localization length can be measured by the average width of localized modes. Besides, we explore the impact of the disordered waveguide design parameters, such as refractive index contrast, fill-fraction, and feature size, on the average width of localized modes.

Transverse Anderson Localization Enhancement for Low-Filling-Rate Glass–Air Disordered Fibers by Optimizing the Diameter of Air Holes

We demonstrate a method to enhance the transverse Anderson localization (TAL) effect of the glass–air disordered optical fiber (G-DOF) by adjusting the number and diameter of air holes. This method does not need to enlarge the air-filling fraction of G-DOF, leading to the mitigation of fabrication complexity. By choosing the appropriate diameter and number of air holes, the average localized beam radius of G-DOF with the highest air-filling fraction of 30% can be successfully reduced by 18%. Moreover, the proposed method is always functional for the situations of the air-filling fraction lower than 50%. We also identify that, under the same air-filling fraction, a larger number of air holes in the G-DOF leads to the smaller standard deviation of the corresponding localized beam radius, indicating a stable fiber structure. The results will provide new guidance on the G-DOF design.

Modal analysis of transverse Anderson localization based on the imaginary distance BPM.

The transverse Anderson localization (TAL) can always be observed in one-dimensional (1D) disordered systems as long as the transverse dimension is significantly larger than the localization length. This paper presents a detailed modal analysis in one particular realization of the 1D disordered optical waveguides with wavelength-scale feature size based on the imaginary distance beam propagation method (BPM). The localized modes are independent of the physical properties of the external excitation. Additionally, we investigate how the boundaries of disordered waveguides affect the localized modes, which are only related to the design parameters such as feature size, refractive index contrast, and fill-fraction. Finally, we explore the impact of the design parameters on the average localized mode width in the 1D disordered waveguides.

Block paralleled BPM simulation of an optical waveguide with cross-sectional random refractive index distribution

Image transport mediated by transverse Anderson localization requires an optical waveguide to have high contrasted indices and subwavelength feature size in random distribution. Super-fine mesh therefore needs to be adopted in numerical solution techniques. Existing numerical simulation approaches such as the conventional beam propagation method (BPM), however, shows low efficiency and is often unstable with fine mesh and high contrasted random index distribution. In this work, we propose a block algorithm based on a 3D finite-difference full-vector BPM, which is appealing as a reliable tool in numerical simulation of optical waveguides with random refractive index distribution.

Investigation of the disordered optical fiber with wavelength-scale feature size mediated by transverse Anderson localization.

A narrow beam propagating through the disordered optical fiber first undergoes diffusive broadening, until its width becomes comparable to the localization length. The study of numerical algorithms and statistical methods in the simulation analysis process of disordered optical fibers demonstrates that the influence of polarization characteristics and transverse grids on calculation errors is critical for statistical numerical simulation in disordered systems. We performed a detailed numerical analysis of the effect of different design parameters in disordered fibers on the localization effect-that is, the localization length, including the refractive index contrast, feature size, and fill-fraction. The results show that the optimal fill-fraction is 50%, and that higher refractive index contrast and larger feature size relative to the wavelength both result in a smaller effective beam width. Finally, numerical evidence is also provided that optical images can be transported via transverse Anderson localization.

Supercontinuum generation and IR image transportation using soft glass optical fibers: a review [Invited

Soft glass optical fibers, especially highly nonlinear optical fibers, have expanded their application fields. We have been engaged in soft glass optical fibers, such fluoride, tellurite and chalcogenide glass, for optical signal processing, lightwave generation and waveguide applications. Furthermore, we have challenged the research on novel waveguides, for example, transverse Anderson localization of mid-infrared light using transversely disordered optical fiber. Here we report our achievements on SC generation and novel waveguides research using the soft glass highly nonlinear optical fibers.

The C2 domains of dysferlin: roles in membrane localization, Ca2+ signalling and sarcolemmal repair.

Dysferlin is an integral membrane protein of the transverse tubules of skeletal muscle that is mutated or absent in limb girdle muscular dystrophy 2B and Miyoshi myopathy. Here we examine the role of dysferlin's seven C2 domains, C2A through C2G, in membrane repair and Ca2+ release, as well as in targeting dysferlin to the transverse tubules of skeletal muscle. We report that deletion of either domain C2A or C2B inhibits membrane repair completely, whereas deletion of C2C, C2D, C2E, C2F or C2G causes partial loss of membrane repair that is exacerbated in the absence of extracellular Ca2+ . Deletion of C2C, C2D, C2E, C2F or C2G also causes significant changes in Ca2+ release, measured as the amplitude of the Ca2+ transient before or after hypo-osmotic shock and the appearance of Ca2+ waves. Most deletants accumulate in endoplasmic reticulum. Only the C2A domain can be deleted without affecting dysferlin trafficking to transverse tubules, but Dysf-ΔC2A fails to support normal Ca2+ signalling after hypo-osmotic shock. Our data suggest that (i) every C2 domain contributes to repair; (ii) all C2 domains except C2B regulate Ca2+ signalling; (iii) transverse tubule localization is insufficient for normal Ca2+ signalling; and (iv) Ca2+ dependence of repair is mediated by C2C through C2G. Thus, dysferlin's C2 domains have distinct functions in Ca2+ signalling and sarcolemmal membrane repair and may play distinct roles in skeletal muscle. KEY POINTS: Dysferlin, a transmembrane protein containing seven C2 domains, C2A through C2G, concentrates in transverse tubules of skeletal muscle, where it stabilizes voltage-induced Ca2+ transients and participates in sarcolemmal membrane repair. Each of dysferlin's C2 domains except C2B regulate Ca2+ signalling. Localization of dysferlin variants to the transverse tubules is not sufficient to support normal Ca2+ signalling or membrane repair. Each of dysferlin's C2 domains contributes to sarcolemmal membrane repair. The Ca2+ dependence of membrane repair is mediated by C2C through C2G. Dysferlin's C2 domains therefore have distinct functions in Ca2+ signalling and sarcolemmal membrane repair.

Transverse Anderson localization of mid-infrared light in a chalcogenide transversely disordered optical fiber.

We successfully fabricate a transversely disordered optical fiber made of AsSe2 and As2S5 glasses for high-resolution mid-infrared image transport. By using the fabricated fiber, we experimentally observe transverse Anderson localization of mid-infrared light at the wavelength of 3 µm. Moreover, we numerically evaluate the localization in the fiber by using a cross-sectional image of the fiber.