Photon Localization Research Articles

Photon localization transition in a magnetorheological fluid

We investigate photon transport in magnetically tunable fluids, specifically magnetic nanofluids and magnetorheological fluids (MRFs). Our study focuses on the statistical analysis of light transport in these fluids, with a particular focus on earlier theoretical proposals related to the possibility of Anderson localization in these systems. We employ a well-known mesoscopic quantifier, the generalized conductance, to assess the domain of light transport in these systems. Magnetic nanofluids, which contain nanometer-sized magnetite particles, exhibit weak scattering with no substantial consequence on conductance, regardless of the applied magnetic field. In contrast, magnetorheological fluids, a bidispersion of micrometer-sized magnetizable spheres in a magnetic nanofluid, show a decrease in conductance to values below unity as the magnetic field strength increases. This decrease occurs at the magnetic-field-induced photonic bandgap in MRFs, which plays a crucial role in the localization process and is characterized by reduced transmitted intensity, altered speckle patterns, and significant changes in intensity statistics. Our findings also highlight the temporal evolution of field-induced speckles, where the initial high correlation decreases over time, and the correlation width widens indicating that the duration of sustained correlation enhances as the system reaches equilibrium. Consequently, the evolution of field-induced scatterers in MRFs significantly emulates light localization effects as the system attains equilibrium. This study concludes that our system is a prime candidate to observe possible strong localization in a magnetically tunable, dissipative complex system. Such systems hold potential applications in optical switching, adaptive optics, and smart materials design through controlled light manipulation using external magnetic fields.

Photonic crystal fibers based on Dirac point-guiding

—In this work photonic crystal fibers of different cross-sectional patterns are studied. Dirac points of these various lattices are explored, propagation diagrams showing positions of the Dirac spectrums are obtained, and their application in fiber guiding is discussed. A quasi-3D FDTD simulation method, which is simpler and more efficient than a commercial 3D FDTD simulation software, is developed for photonic crystal fiber. This method is then applied to the new photonic crystal fiber proposed in [Fiber guiding at the Dirac frequency beyond photonic bandgaps, Light Sci. & App. 4 (2015) e304.]. Dirac-point guidance, which is based on Dirac localization of photons, is verified for these fibers.

Preparation of Ag@Au core-shell nanoparticles embedded in TiO2 inverse opal for light harvesting and efficiency enhancement in quantum dot sensitized solar cells

In the fabrication of Quantum dot sensitized solar cells (QDSSCs), it is important to fabricate a photoanode with a high ability to trap photons as well as transfer photogenerated electrons. TiO2 inverse opal (TIO) photonic crystals with their organized porous structures, besides their chemical nature, have unique optical features such as the slow-photon effect, photon localization, and photonic bandgap (PBG). Herein, to improve the efficiency of QDSSCs, gold, silver, and silver/gold core-shell (Ag@Au) plasmonic nanoparticles (nps) are loaded on TIO. The plasmonic nanoparticle-decorated inverse opal improves the light scattering process and provides direct charge transfer tunnels, which can effectively prevent the recombination of electron-hole pairs. In this work, fabricated QDSSCs with TIO (double-layer)/ZnS/CdS/CdSe/ZnSe/ZnS photoanode, and a 6 μm total thickness of the TIO multilayer, has an open circuit voltage (Voc) of 0.745 V and short-circuit current density (JSC) of 16.22 mA/cm2. The obtained results are higher than the common anatase TiO2 (TiO2-A)/ rutile TiO2 (TiO2-R)/QD photoanode. Also, the TIO (double-layer)/Ag@Au/QDs photoanode exhibits JSC=20.3283 mA/cm2, Voc= 0.75 V, and a power conversion efficiency (PCE) of ƞ=10.79 %.

Photon routing in disordered chiral waveguide QED ladders: interplay between photonic localization and collective atomic effects.

In recent years, photon routing has garnered considerable research activity due to its key applications in quantum networking and optical communications. This paper studies the single photon routing scheme in many-emitter disordered chiral waveguide quantum electrodynamics (wQED) ladders. The wQED ladder consists of two one-dimensional lossless waveguides simultaneously and chirally coupled with a chain of dipole-dipole interacting two-level quantum emitters (QEs). In particular, we analyze how a departure from the periodic placement of the QEs due to temperature-induced position disorder can impact the routing probability. This involves analyzing how the interplay between the collective atomic effects originating from the dipole-dipole interaction and disorder in the atomic location leading to single-photon localization can change the routing probabilities. As for some key results, we find that the routing probability exhibits a considerable improvement (more than $90{\% }$ value) for periodic and disordered wQED ladders when considering lattices consisting of twenty QEs. This robustness of collective effects against spontaneous emission loss and weak disorders is further confirmed by examining the routing efficiency and localization length for up to twenty QE chains. These results may find applications in quantum networking and distributed quantum computing under the realistic conditions of imperfect emitter trappings.

Simulation of random fiber Bragg grating array in polarization-maintaining fiber based on photonic localization effect

Simulation of random fiber Bragg grating array in polarization-maintaining fiber based on photonic localization effect

Design of a Neural Network Model for Point-Defect Microcavities in Two-Dimensional Silicon-Based Dielectric Column Photonic Crystals

Currently, circuits are becoming more and more highly integrated, but current electronic chip technology has difficulty in meeting the requirements for increased data transmission speed and capacity because of its characteristics of increased energy loss due to interactions between electronic components. In contrast, photonic technology is a promising solution due to its characteristics of high speed, wide bandwidth, and low interaction. Photonic crystals are materials with an artificial periodic dielectric structure, with photonic bandgap and localization properties that are critical to their performance. Photonic crystals, which use photons as an information transfer medium, allow flexible control of photon propagation, just as electrons are controlled in semiconductors, and the study of multifunctional photonic crystals is important for the construction of integrated optical circuits. This paper proposes a neural network-based model to analyze and predict the optical properties of point defect microcavities in 2D silicon-based dielectric column photonic crystals. By modeling the complex relationship between the structural parameters of the photonic crystal and its optical response, a theoretical approach for the design of 2D silicon dielectric column photonic crystals can be provided.

Tunable wave localization at the Dirac frequency in a metallic photonic crystal cavity.

In this study, the two-dimensional (2D) triangular lattice metallic photonic crystals (PCs) in visible and infrared bands have been utilized to achieve light confinement at the Dirac frequency. Distinct from the traditional bandgap or total internal reflection cavity modes, the unique photonic localization mechanism leads to an unusual algebraic decay of state and a unique frequency located beyond any bandgaps. This investigation delves into the band structure analysis of 2D metallic PCs, specifically focusing on their distinctive features, such as photonic bandgaps and Dirac cones. The plane wave expansion (PWE) method, enhanced with a linearization technique, is employed for band structure calculations, considering both the frequency-dependent dielectric properties and the intrinsic lossy nature of metallic materials described by the Drude model. The study provides a comprehensive derivation of the PWE equations for metallic PCs and investigates their band characteristics under both TM and TE polarizations. Focusing on TM modes in triangular lattice metallic PCs, it reveals zero density of states (DOS) at K points of the Brillouin corner and the existence of Dirac cones with linearly dispersion and linearly vanishing DOS. The study extends to exploring localized modes at Dirac frequencies, employing a relativistic quantum mechanics approach analogous to graphene's charge carriers. Theoretical predictions are corroborated by numerical simulations, and the potential for tunable Dirac localized modes is highlighted. This research not only deepens the understanding of Dirac properties in graphene-like systems but also lays the groundwork for further exploration of the practical quasi-2D devices, which will provide assistance in the integration of micro- and nano- devices, especially in applications requiring long-range coupling, given the critical importance of optical cavities in contemporary optical technologies.

Photon scattering by an electric field in noncommutative spacetime

As is known, the existence of a small noncommutativity between coordinates would generate nonlocal self-interactions in the electromagnetic theory. To explore some consequences of this effect on the propagation of photons we consider Moyal space half-filled with a static and homogeneous electric field and analyze electromagnetic fluctuations on top of this step-like background. Both the localization of photons and the possibility of photon production by strong electric fields are addressed. Several aspects of the Klein paradox in this setup are discussed as well.

The Explicit Form of the Unitary Representation of the Poincaré Group for Vector-Valued Wave Functions (Massive and Massless), with Applications to Photon Localization and Position Operators

We geometrically derive the explicit form of the unitary representation of the Poincaré group for vector-valued wave functions and use it to apply speed-of-light boosts to a simple polarization basis to end up with a Hawton–Baylis photon position operator with commuting components. We give explicit formulas for other photon boost eigenmodes. We investigate the underlying affine connections on the light cone in momentum space and find that while the Pryce connection is metric semi-symmetric, the flat Hawton–Baylis connection is not semi-symmetric. Finally, we discuss the localizability of photon states on closed loops and show that photon states on the circle, both unnormalized improper states and finite-norm wave packet smeared-over washer-like regions are strictly localized not only with respect to Hawton–Baylis operators with commuting components but also with respect to the noncommutative Jauch–Piron–Amrein POV measure.

On-Chip Photonic Localization in Aharonov-Bohm Cages Composed of Microring Lattices.

Flatband localization endowed with robustness holds great promise for disorder-immune light transport, particularly in the advancement of optical communication and signal processing. However, effectively harnessing these principles for practical applications in nanophotonic devices remains a significant challenge. Herein, we delve into the investigation of on-chip photonic localization in AB cages composed of indirectly coupled microring lattices. By strategically vertically shifting the auxiliary rings, we successfully introduce a magnetic flux of π into the microring lattice, thereby facilitating versatile control over the localization and delocalization of light. Remarkably, the compact edge modes of this structure exhibit intriguing topological properties, rendering them strongly robust against disorders, regardless of the size of the system. Our findings open up new avenues for exploring the interaction between flatbands and topological photonics on integrated platforms.

Enhancing frequency stability and mode control in a Brillouin random fiber laser with a strongly scattering disordered grating

Random fiber lasers (RFLs) with disordered scattering feedback media provide a range of functionalities and properties. The primary drawback with weak Rayleigh scattering (RS)-based RFLs is their large frequency drift and mode hopping, which are caused by the random walk of photons at different round trips. Here, we present a technique to control the mode propagation of RFLs by using a narrow gain bandwidth from stimulated Brillouin scattering and photon localization from a strongly scattering disordered grating. Multiple scattering of light within the disordered grating leads to photon localization and narrow reflection peaks, which suppresses frequency drift and reduces the number of modes. The compact Brillouin random fiber laser (BRFL) with a 200 m strongly scattering disordered grating enables single-mode lasing with an ultra-narrow linewidth of ∼650 Hz. The results of the real-time spectral evolution obtained by the heterodyne method demonstrate long-term stability of the lasing frequency, confirming the capability of the strongly scattering disordered grating to control mode propagation of the BRFL. The BRFL exhibits an ultra-high frequency stability of 0.48 MHz and mode-hop-free operation up to 120 s. This work provides a perspective on the development of RFLs with high coherence and stability.

Improved N2 photo-fixation performance of nanocrystalline TiO2 films by photon localization effects and Fe doping

The development of clean and sustainable nitrogen-fixing methods has always attracted significant attention for decades.

Flat-band localization and interaction-induced delocalization of photons

Lattices with dispersionless, or flat, energy bands have attracted substantial interest in part due to the strong dependence of particle dynamics on interactions. Using superconducting circuits, we experimentally study the dynamics of one and two particles in a single plaquette of a lattice whose band structure consists entirely of flat bands. We first observe strictly localized dynamics of a single particle, the hallmark of all-bands-flat physics. Upon initializing two particles on the same site, we see an interaction-enabled delocalized walk across the plaquette. We further find localization in Fock space for two particles initialized on opposite sides of the plaquette. These results mark the first experimental observation of a quantum walk that becomes delocalized due to interactions and establishes a key building block in superconducting circuits for studying flat-band dynamics with strong interactions.

Machine Learning Designed and Experimentally Confirmed Enhanced Reflectance in Aperiodic Multilayer Structures

AbstractMachine learning (ML) methods have gained widespread attention in optimizing nanostructures for target transport properties and discovering unexpected physics. Here, an ML method is developed to discover and experimentally confirm binary CeO2‐MgO aperiodic multilayers (AMLs) for thermal barrier coatings with significantly enhanced reflectance. The effect of varying AML design parameters like total thickness, average period, and randomness in layer thicknesses, on the spectral and total reflectance is demonstrated. Introducing aperiodicity in layer thicknesses is shown to lead to a broadband increase in spectral reflectance due to photon localization. Since the number of possible AML structures increases exponentially with total thickness, a Genetic Algorithm optimizer is developed to efficiently discover AMLs with enhanced reflectance, for total thicknesses of 5–50 µm. Surprisingly, all the optimized structures show an odd number of layers with a CeO2 layer at both ends, deviating from the traditional way of designing binary superlattices with paired layers. The optimized AML and a reference periodic superlattice of 5 µm thickness are fabricated by Pulsed Laser Deposition and characterized by optical reflectance measurements. The fabricated AML, despite considerable fabrication uncertainty, still enhances the reflectance to 48% from 40% of the reference superlattice, validating the effectiveness of our ML‐based optimization process.

Optomechanically Induced Benjamin–Feir Instability

AbstractBenjamin–Feir instability, which is originally discovered in hydrodynamics and plasma physics, has become a central process of nonlinear physics over the past decades. On‐chip solid‐state devices with controllable Benjamin–Feir instability can exhibit a rich set of spatio‐temporal dynamics that are inherently sensitive to their initial distribution, which are vital for force sensors and information processing. By exploiting the nonlinear photonic evolution and localization in a micro‐fabricated optomechanical chain, the direct signal of optomechanically induced Benjamin–Feir instability is identified within the reach of current experimental techniques. A spatio‐temporal dynamical theory of optomechanically induced Benjamin–Feir instability is represented, which provides a quantitative interpretation of the exponential growth characteristics. Numerical calculations of the spatio‐temporal dynamics in the optomechanical chain are in excellent agreement with this theory. Optomechanically induced Benjamin–Feir instability may entail a wide range of intriguing phenomena and find applications in on‐chip manipulations of light propagation and precision measurements due to their exponential growth characteristics.

Valley Polarized Edge States beyond Inversion Symmetry Breaking

AbstractValley‐contrast physics has gained considerable attention, particularly for realizing photonic topological insulators (PTIs) that support reflection‐free valley‐polarized edge modes (VPEMs) in the absence of inter‐valley scattering. It is an open question whether similar robust states can exist in the absence of topological valley phase, i.e., nonvanishing Berry curvature at the valleys. It is shown that a C6υ‐symmetric triangular photonic crystal (PhC) inherently exhibits uniform distribution of spatially varying phase vortices, which support a local (limited) version of valley Hall effect (LVHE), where the valley polarization is location defined as opposed to being fixed throughout the bulk. Then it is demonstrated that defect regions with sublattice asymmetry in otherwise a symmetric PhC lead to wave localization and splitting of photons according to their valley index, thus enabling VPEMs along a line defect waveguide. The device is fabricated on a silicon‐on‐insulator (SOI) slab, and it is characterized at near‐infrared frequencies showing robust transmission through sharp bends comparable to valley PTIs. The results present a new perspective to creating valley edge states and outline a new waveguiding mechanism applicable to electromagnetics as well as plasmonics, mechanics, and acoustics.

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.

Electrically switchable and tunable infrared light modulator based on functional graphene metasurface.

Graphene is emerging as an ideal material for new-generation optoelectronic devices. In this paper, a novel graphene metasurface-based electrically switchable and tunable infrared light modulator has been proposed and theoretically studied. The functional modulator comprises a monolayer graphene sheet sandwiched in a Fabry-Perot (FP) like nanostructure consisting of a metal reflector, a dielectric spacer, and an ellipse patterned anisotropy antenna layer. As a result of the photon localization effect of the guided-mode resonance (GMR) in the FP structure, the graphene electroabsorption can be significantly enhanced to enable a high-performance light modulator. By fine-tuning the Fermi energy (E f) of graphene via controlling its bias-gate voltage, the proposed modulator can switch between a perfect absorber and a reflective polarization converter of high conversion efficiency (i.e., >90%) at 1550nm. The conversion mechanism and the geometric dependences of the infrared light modulator have been investigated. We further demonstrated the tunability of the highly-efficient polarization converter over a broad spectrum by adjusting the real dispersion of E f. Our design concept provides an effective strategy for customizing novel optoelectronic devices by combining an electrically-tunable 2D material with a functional metasurface.

Validation of classical modeling of single-photon pulse propagation

"It is well-known to those who know it" that single-photon interference experiments can be modeled classically [S. Barnett, arXiv:2207.14632 (2022)]. When a single-photon light pulse was split by a biprism good agreement with a classical fit was obtained and the photon was counted only once, consistent with a probabilistic interpr.etation [V. Jacques et al, Eur. Phys. J. D 35, 561 (2002)]. A justification for this "well know result of Quantum Optics" is implicit in [M. Hawton, Phys. Rev A 104, 052211 (2021)] where a real covariant field describing a single photon is first quantized. Here the theoretical basis of this result is reviewed and the theory is extended to multiphoton states and QED Fock space. The crucial role of the CPT theorem in coupling to charged matter and resolution of the photon localization problem is discussed.

Theory and modeling of light-matter interactions in chemistry: current and future.

Light-matter interaction not only plays an instrumental role in characterizing materials' properties via various spectroscopic techniques but also provides a general strategy to manipulate material properties via the design of novel nanostructures. This perspective summarizes recent theoretical advances in modeling light-matter interactions in chemistry, mainly focusing on plasmon and polariton chemistry. The former utilizes the highly localized photon, plasmonic hot electrons, and local heat to drive chemical reactions. In contrast, polariton chemistry modifies the potential energy curvatures of bare electronic systems, and hence their chemistry, via forming light-matter hybrid states, so-called polaritons. The perspective starts with the basic background of light-matter interactions, molecular quantum electrodynamics theory, and the challenges of modeling light-matter interactions in chemistry. Then, the recent advances in modeling plasmon and polariton chemistry are described, and future directions toward multiscale simulations of light-matter interaction-mediated chemistry are discussed.