Metadisorder for designer light in random systems

Large-scale fabrication of an ultrathin broadband absorber using quasi-random dielectric Mie resonators

Ultrathin broadband absorber maintaining a near-uniform low reflectivity over a broadband wavelength is essential for many optical applications, such as light harvesting and nanoscale imaging. Recently, there has been considerable interest in employing arrays of high-index dielectric Mie resonators on surfaces to trap light and reduce the reflectivity. For such Mie-resonant metasurfaces, however, antireflection properties featuring both a flat low reflectance curve and a wide bandwidth are hard to be satisfied simultaneously, and an efficient large-scale nanofabrication technique rarely exists. Here, we present a high-throughput laser interference induced quasi-random patterning (LIIQP) technique to fabricate quasi-random Mie resonators in large scale. Mie resonators with feature sizes down to sub-100 nm have been fabricated using a 1064 nm laser source. Each Mie resonator concentrates light at its shape-dependent resonant frequency, and all such resonators are arranged quasi-randomly to provide both rich (with broadband Fourier components) and strong (with large intensities) Fourier spectra. Specifically, a near-uniform broadband reflectivity over 400-1100 nm spectrum region has been confined below 3% by fabricating a large-scale ultrathin (around 400 nm) absorber. Our concept and high-throughput fabrication technique allows the rapid production of quasi-random dielectric Mie-resonant metasurfaces in a controllable way, which can be used in various promising applications including thin-film solar cells, display, and imaging.

Cloaking the underlying long-range order of randomly perturbed lattices

Random, uncorrelated displacements of particles on a lattice preserve the hyperuniformity of the original lattice, that is, normalized density fluctuations vanish in the limit of infinite wavelengths. In addition to a diffuse contribution, the scattering intensity from the the resulting point pattern typically inherits the Bragg peaks (long-range order) of the original lattice. Here we demonstrate how these Bragg peaks can be hidden in the effective diffraction pattern of independent and identically distributed perturbations. All Bragg peaks vanish if and only if the sum of all probability densities of the positions of the shifted lattice points is a constant at all positions. The underlying long-range order is then "cloaked" in the sense that it cannot be reconstructed from the pair correlation function alone. On the one hand, density fluctuations increase monotonically with the strength of perturbations a, as measured by the hyperuniformity order metric Λ[over ¯]. On the other hand, the disappearance and reemergence of long-range order, depending on whether the system is cloaked as the perturbation strength increases, is manifestly captured by the τ order metric. Therefore, while the perturbation strength a may seem to be a natural choice for an order metric of perturbed lattices, the τ order metric is a superior choice. It is noteworthy that cloaked perturbed lattices allow one to easily simulate very large samples (with at least 10^{6} particles) of disordered hyperuniform point patterns without Bragg peaks.

Disorder induced rotational-symmetry breaking to control directionality of whispering gallery modes in circularly symmetric nanowire assembly

Effect of disorder on the emission directionality of a whispering gallery mode resonator comprising of circularly symmetric nanowire array is investigated using finite-difference time-domain analysis technique. In spite of rotational symmetry breaking, whispering gallery mode-like isotropic emission characteristics are retained by the nanowire array up to a certain degree of spatial disorder. For higher degrees of randomness, Anderson localized resonant modes are obtained with unidirectional emission characteristics, though the beam direction remains unpredictable because of the underlying random-scattering process. This shortcoming is overcome by designing a system of correlated disorder where nanowire spacing is varied gradually along the preferred axis of unidirectionality. This system, in spite of its high degree of disorder, can effectively support high-Q whispering gallery modes with tunable unidirectional emission characteristics.

Hyperuniformity in amorphous speckle patterns

Hyperuniform structures possess the ability to confine and drive light, although their fabrication is extremely challenging. Here we demonstrate that speckle patterns obtained by a superposition of randomly arranged sources of Bessel beams can be used to generate hyperunifrom scalar fields. By exploiting laser light tailored with a spatial filter, we experimentally produce (without requiring any computational power) a speckle pattern possessing maxima at locations corresponding to a hyperuniform distribution. By properly filtering out intensity fluctuation from the same speckle pattern, it is possible to retrieve an intensity profile satisfying the hyperuniformity requirements. Our findings are supported by extensive numerical simulations.

Bohmian Photonics for Independent Control of the Phase and Amplitude of Waves

The de Broglie-Bohm theory is one of the nonstandard interpretations of quantum phenomena that focuses on reintroducing definite positions of particles, in contrast to the indeterminism of the Copenhagen interpretation. In spite of intense debate on its measurement and nonlocality, the de Broglie-Bohm theory based on the reformulation of the Schrödinger equation allows for the description of quantum phenomena as deterministic trajectories embodied in the modified Hamilton-Jacobi mechanics. Here, we apply the Bohmian reformulation to Maxwell's equations to achieve the independent manipulation of optical phase evolution and energy confinement. After establishing the deterministic design method based on the Bohmian approach, we investigate the condition of optical materials enabling scattering-free light with bounded or random phase evolutions. We also demonstrate a unique form of optical confinement and annihilation that preserves the phase information of incident light. Our separate tailoring of wave information extends the notion and range of artificial materials.

Target decoupling in coupled systems resistant to random perturbation

To suppress unwanted crosstalks between nearby optical elements, the decoupling technique for integrated systems has been desired for the target control of light flows. Although cloaking methods have enabled complete decoupling of optical elements by manipulating electromagnetic waves microscopically, it is difficult to be applied rigorously to control each unit element in coupled systems due to severe restrictions on material parameters for cloaking. Here we develop the macroscopic approach to design crosstalk-free regions in coupled optical systems. By inversely designing the eigenstate which encompasses target elements, the stable decoupling of the elements from the coupled system is achieved, being completely independent from the random alteration of the decoupled region, and at the same time, allowing coherent and scattering-free wave transport with desired spatial profiles. We also demonstrate the decoupling in disordered systems, overcoming the transport blockade from Anderson localization. Our results provide an attractive solution for "target hiding" of elements inside coupled systems.

Acceleration toward polarization singularity inspired by relativistic E×B drift

The relativistic trajectory of a charged particle driven by the Lorentz force is different from the classical one, by velocity-dependent relativistic acceleration term. Here we show that the evolution of optical polarization states near the polarization singularity can be described in analogy to the relativistic dynamics of charged particles. A phase transition in parity-time symmetric potentials is then interpreted in terms of the competition between electric and magnetic 'pseudo'-fields applied to polarization states. Based on this Lorentz pseudo-force representation, we reveal that zero Lorentz pseudo-force is the origin of recently reported strong polarization convergence to the singular state at the exceptional point. We also demonstrate the deterministic design of achiral and directional eigenstates at the exceptional point, allowing an anomalous linear polarizer which operates orthogonal to forward and backward waves. Our results linking parity-time symmetry and relativistic electrodynamics show that previous PT-symmetric potentials for the polarization singularity with a chiral eigenstate are the subset of optical potentials for the E×B "polarization" drift.