Light-matter interactions inside turbid medium can be controlled by tailoring the spatial distribution of energy density throughout the system. Wavefront shaping allows selective coupling of incident light to different transmission eigenchannels, producing dramatically different spatial intensity profiles. In contrast to the density of transmission eigenvalues that is dictated by the universal bimodal distribution, the spatial structures of the eigenchannels are not universal and depend on the confinement geometry of the system. Here, we develop and verify a model for the transmission eigenchannel with the corresponding eigenvalue close to unity. By projecting the original problem of two-dimensional diffusion in a homogeneous scattering medium onto a one-dimensional inhomogeneous diffusion, we obtain an analytical expression relating the intensity profile to the shape of the confining waveguide. Inverting this relationship enables the inverse design of the waveguide shape to achieve the desired energy distribution for the perfectly transmitting eigenchannel. Our approach also allows to predict the intensity profile of such channel in a disordered slab with open boundaries, pointing to the possibility of controllable delivery of light to different depths with local illumination.PACS numbers: 42.25. Dd,42.25.Hz, Interference of scattered waves in random media gives rise to well-known phenomena such as enhanced backscattering, Anderson localization and universal conductance fluctuation. These phenomena are general and occur not only for electromagnetic waves, but also for acoustic, electronic and other kinds of waves [1, 2]. Recently, there has been a growing interest in another interference effect -formation of perfectly transmitting channels [3, 4], which can greatly enhance the total transmission through opaque media [5][6][7][8]. In addition, the perfectly transmitting channels have energy density buildup deep inside the medium [7,[9][10][11], opening the possibility of enhancing linear and non-linear light-matter interactions inside turbid media. Recent advances of optical wavefront shaping techniques [12][13][14][15][16] enabled direct coupling of incident light to perfectly transmitting channels [11], making the depth profile of energy density dramatically different from the typical decay in a diffusive medium. To unlock the full potential of this approach for tailoring light-matter interactions in turbid media, it becomes imperative to understand what determines the spatial structure of the perfectly transmitting channels.Recently two theoretical models have been put forward to describe the spatial profile of the perfectly transmitting channels in lossless diffusive media. Davy et al [9] applied the supersymmetry theory to wave propagation in a quasi-one-dimensional random system and related the intensity profile to the return probability (RP) of diffusive waves. Ojambati et all [10,17] proposed that the perfectly transmitting channel in a disordered slab is related to the fundamental mode (FM) of the onedi...
We introduce a class of critical states which are embedded in the continuum (CSC) of a one-dimensional optical waveguide array with one non-Hermitian defect. These states are on the verge of being fractal and have real propagation constants. They emerge at a phase transition which is driven by the imaginary refractive index of the defective waveguide and it is accompanied by a mode segregation which reveals analogies with the Dicke super-radiance. Below this point the states are extended while above it they evolve to exponentially localized modes. An addition of a background gain or loss can turn these localized states into bound states in the continuum.
Within the range of validity of the stationary diffusion equation, an ideal diffusive-light invisibility cloak can make an arbitrary macroscopic object hidden inside of the cloak indistinguishable from the surroundings for all colors, polarizations, and directions of incident visible light. However, the diffusion equation for light is an approximation which becomes exact only in the limit of small coherence length. Thus, one expects that the cloak can be revealed by illumination with coherent light. The experiments presented here show that the cloaks are robust in the limit of large coherence length but can be revealed by analysis of the speckle patterns under illumination with partially coherent light. Experiments on cylindrical core-shell cloaks and corresponding theory are in good agreement.
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We demonstrate a possibility of using geometry to deterministically control nonlocal correlation of waves undergoing mesoscopic transport through a disordered waveguide. In case of nondissipative medium, we find an explicit relationship between correlation and the shape of the system. Inverting this relationship, we realize inverse design: we obtain specific waveguide shape that leads to a predetermined nonlocal correlation. The proposed technique offers an approach to coherent control of wave propagation in random media that is complementary to wave-front shaping.
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