Optical Modes Research Articles

Production and reconstruction mechanism of consumption spaces in urban fringe areas under capital intervention: Evidence from Guangming town in Shenzhen

As the rapid urban expansion and the rise of consumer society, urban fringe areas have become an essential place for urban capital to intervene and achieve spatial regeneration, and it has triggered the consumerization and transformation of space. Taking Guangming Town in the urban fringe area of Shenzhen as an example, this paper reveals the process and dynamics of spatial consumerization transformation under the influence of capital intervention. It examines the intricate mechanisms of capital operation underlie the production of space, and endeavors to explore a novel model of rural spatial regeneration in China's urban fringe areas. This paper found that the production of space in Guangming Town under the capital intervention includes the material production and social relations production. With the reconstruction of spatial form and relationships, new local products, spatial configuration, social services and organizational relations are generated, forming a consumption space with heterogeneous landscape, market institutionalized management, commercialization and symbolization. The realization of the production of consumption space in urban fringe areas is based on the joint action of core elements such as land, capital and government, which provide the material foundation, operational power and coordination organization for space consumption. These promote capital to complete the triple cycle of “acquiring land - creating space scarcity - realizing space consumption”, and then realizing space reproduction and capital appreciation. In the Chinese context, the spatial transformation and production of urban fringe areas should not be regarded as a local practice of Western counter-urbanization or rural gentrification theory. Rather, it as a new spatial regeneration mode that harmonizes urban and rural production, lifestyles and development trajectories. This paper offers valuable practical insights and analytical perspectives for promoting integrated urban-rural development and fostering a new type of urbanization, thereby broadening the regional framework of rural development.

Photon-pair generation using inverse-designed thin-film lithium niobate mode converters

Spontaneous parametric down-conversion (SPDC) has become a key method for generating entangled photon pairs. Periodically poled thin-film lithium niobate (TFLN) waveguides induce strong SPDC but require complex fabrication processes. In this work, we experimentally demonstrate efficient SPDC and second harmonic generation using modal phase matching methods. This is achieved with inverse-designed optical mode converters and low-loss optical waveguides in a single nanofabrication process. Inverse design methods provide enhanced functionalities and compact footprints for the converter. Despite the extensive achievements in inverse-designed photonic integrated circuits, the potential of inverse-designed TFLN quantum photonic devices has been seldom explored. The device shows an on-chip conversion efficiency of 3.95% W−1 cm−2 in second harmonic generation measurements and a coincidence count rate up to 21.2 kHz in SPDC experiments. This work highlights the potential of the inverse-designed TFLN photonic devices and paves the way for their applications in on-chip nonlinear or quantum optics.

Tensile Control of Vibrational Strong Light‐Matter Coupling with Flexible Polyester Films

AbstractPolaritons are generated by strong interaction between photons and matter, with the hybridization fundamentally changing the energy landscape of the system. Future exploitation of polaritons will benefit from implementing low‐cost, flexible, and easily tuneable configurations, as electronics have before. Here, coherent coupling of the carbonyl stretch vibrations of polyester (poly(ethylene terephthalate), PET) films to the optical modes of a Fabry–Perot (FP) cavity is presented, in which the FP cavity is directly formed on flexible, free‐standing, and commercially available PET films. For 2‐µm thick PET films, the carbonyl stretch vibration of the PET overlaps with the half‐wavelength FP cavity mode, leading to the coupling of the two modes, a Rabi splitting above 160 cm−1, and associated anticrossing in angular dispersion measurements. The study demonstrates dynamic control of light‐matter interaction strength by modulating film thickness under tension, finding that a 25% tensile stretch can tune the light‐matter interaction from 20:80 mixing to near‐perfect 50:50 hybridization at normal incidence. These findings are discussed in the context of future foldable/twistable/wearable polaritonic devices.

Spatial Invariant Tensor Self-Representation Model for Hyperspectral Anomaly Detection.

With the development of hyperspectral imaging technology, the hyperspectral anomaly has attracted considerable attention due to its significant role in many applications. Hyperspectral images (HSIs) with two spatial dimensions and one spectral dimension are intrinsically three-order tensors. However, most of the existing anomaly detectors were designed after converting the 3-D HSI data into a matrix, which destroys the multidimension structure. To solve this problem, in this article, we propose a spatial invariant tensor self-representation (SITSR) hyperspectral anomaly detection algorithm, which is derived based on the tensor-tensor product (t-product) to preserve the multidimension structure and achieve a comprehensive description of the global correlation of HSIs. Specifically, we exploit the t-product to integrate spectral information and spatial information, and the background image of each band is represented as the sum of the t-product of all bands and their corresponding coefficients. Considering the directionality of the t-product, we utilize two tensor self-representation methods with different spatial modes to obtain a more balanced and informative model. To depict the global correlation of the background, we merge the unfolding matrices of two representative coefficients and constrain them to lie in a low-dimensional subspace. Moreover, the group sparsity of anomaly is characterized by l2.1.1 norm regularization to promote the separation of background and anomaly. Extensive experiments conducted on several real HSI datasets demonstrate the superiority of SITSR compared with state-of-the-art anomaly detectors.

Exploring edge states in square–octagon moiré lattice

Moiré lattices, achieved by the superposition of two or more twisted identical periodic lattices, are of interest to various fields because they provide additional degrees of freedom. Here, we theoretically and experimentally study the edge states in a square–octagon moiré lattice. This moiré lattice is created by superimposing two identical square sublattices with an antiphase and a special twist angle. Five different edges, named type-I zigzag edge, type-II zigzag edge, type-I bearded edge, type-II bearded edge, and armchair edge, are explored. Through band structure analysis and numerical simulation of edge excitation, we find that all five edges support edge states. The topological property of the type-I edge states is verified by calculating the 2D polarization of the lattice. Furthermore, the edge mode distribution manifests that multiple bands support identical edge states at the armchair and type-II bearded edges. In the experiment, the moiré lattice is generated by the CW-laser-writing technique, thereby observing all the edge states with corresponding edge excitations. This study broadens the understanding of edge states in the coupled moiré photonic lattices and provides a new platform for exploring topological physics.

Oscillatory instability of magneto-convection during the melting of non-Newtonian ferromagnetic nano-enhanced phase change materials at low Rayleigh number

This work complements mechanism of the oscillatory instability of magneto-convection in the process of melting heat transfer controlled by magnetic field at low Rayleigh number (Ra), aiming to provide a theoretical basis for improving the stability of energy storage system and melting manufacturing process. A latent heat storage cavity unit exposed in uniform magnetic field is designed to reveal the magnetic-controlled heat transfer in solid–liquid phase change process. The volume average method is used to describe porous media composite nano-enhanced phase change materials in latent heat unit. Special attentions are paid to the key parameters of Magnetic number (Mn) and Ra, and coupling flow heat transfer mechanism of magnetic force and natural convection effect is numerically studied. The evolution stages of different flow patterns are divided according to the Kelvin force, vorticity, velocity, flow field and isotherm distributions of characteristic points. Main results show that the magnetic field-modulated phase change process at low Ra can be divided into three stages, of which the second stage is characterized by periodic oscillations. Increasing Mn at fixed Ra accelerates the second stage of oscillatory convection heat transfer coming earlier and promotes melting. When Mn increase to 5 × 106, the full melting time is reduced to the greatest extent, resulting in 11.6 % reduction in heat storage but 17.4 % increase in heat storage efficiency. Three mechanisms of magnetic forced convection coupled with natural convection are found during the increase of Ra: synergistic (Ra < 2 × 103), antagonistic (2 × 103≤ Ra < 1 × 104), and natural convection-dominated (Ra = 1 × 104). Finally, the mode distribution map of Ra-Mn regulation is obtained, in which the unstable transformation mechanism of steady-state, periodic oscillation and chaotic oscillation heat transfer in the melting process under the control of magnetic field is described.

Dual-input optoelectronic synaptic transistor based on amorphous ZnAlSnO for multi-target neuromorphic simulation

Optoelectronic synapses can perceive both optical and electrical signals, which are critical for the realization of neuromorphic computing. We have rationally designed an optoelectronic synaptic transistor based on amorphous ZnAlSnO for multi-target neuromorphic simulation and recognition. The dual-input models are well operated by applying light pulses on the channel and electric pulses on the gate, and the transformation from short-term potentiation (STP) to long-turn potentiation (LTP) is identified for tunable synaptic plasticity. In the electrical operation mode, a single-layer artificial neural network was established to recognize handwritten digits by LTP/LTD (long-turn depression) modulation, with a recognition accuracy of 89.2 % for the actual device. In the optical operation mode, the processes of repetitive learning, image recognition, and biased/correlated random-walk learning are simulated on the basis of frequency, quantity, and power of light, with an energy consumption per event as low as 4.3 pJ. This work will facilitate the development of future artificial synapses and highlights the potential of amorphous oxide semiconductors for next-generation computer hardware applications.

Analysis of the Sapphire Fiber Fabry-Perot Interferometer Fringe Visibility under Different Excitation Conditions

In this paper, a theoretical analysis of how the excitation conditions affect the sapphire fiber Fabry-Perot interferometer (SFPI) visibility was performed. The conditions were considered, in which an SFPI was excited by a single-mode fiber (SMF), a multimode fiber (MMF), and a fiber collimator. The finite difference method (FDM) was used to realize the numerical solution of the modal electric fields, and then, the modal excited distributions in the sapphire fiber and the SFPI visibility were calculated. The results showed that different numbers of modes were excited in sapphire fibers under different excitation conditions and finally affected the fringe visibility of the SFPI. The fiber collimator excited the fewest modes and the visibility remained at the highest level. Finally, an experiment was performed, and the experimental results agreed well with the theoretical results.

Stability of Intensity Imbalance between Left‐ and Right‐Circulation Modes in GaN Hexagonal Microdisk

The mechanisms underlying the stability of the intensity imbalance between the left‐ and right‐circulating lasing modes in a GaN hexagonal microdisk resonator are investigated. Finite‐difference time‐domain simulations reveal that the imbalance is determined by the position of the point light source (seed light for lasing) inside the resonator. The coupling mechanism between the resonance modes and light from the source is clarified using numerical calculations. In addition, it is confirmed that light is highly coupled with one of the circulation modes when the source is placed off the bilateral symmetry axis of the mode near the side of the resonator, without any influence of the polarization of the source. The results indicate that the imbalance of the lasing modes observed in the experiments is determined by the position of the seed light near the side of the resonator, which must be spontaneous emission from impurities or defects, such as donor–acceptor pairs, donor‐bounded excitons, basal plane stacking faults, or the transition of free electrons in the conduction band to acceptor levels et al.

Orthogonal multi-peak solitons from the coupled fractional nonlinear Schrödinger equation

In this paper, we investigate the dynamics and stability of multi-peak solitons from the coupled nonlinear Schrödinger equation with the fractional dimension based on Lévy random flights. By implementing linear stability analysis and direct simulations, we demonstrate regions where the single and multi-peak modes are stable. Analysis of perturbed coupled solitons confirms the stability of higher-order modes compared to lower-order modes under the same configurations. The stability diagrams show that the force coupling, Lévy index, power, and the nonlinear intensity significantly influence the stability of high-order modes. Our findings indicate that stability is favored in self-defocusing systems with high Lévy indices under weak coupling conditions, with higher-order states exhibiting smaller stability regions.

Localized and extended collective optical phonon modes in regular and random arrays of contacting nanoparticles: Escape from phonon confinement

Localized and extended collective optical phonon modes in regular and random arrays of contacting nanoparticles: Escape from phonon confinement

Matter Is the Representation of Space-Time

The continuous flowing spacetime forms a spacetime group _G_, one of its fundamental groups is the Poincare group _PO(1,3)_, and the matter and interaction fields are representations of its intrinsic spacetime group. As a kind of quantized space-time unit, space-time group elements generate both space-time manifolds and matter. Matter and fields are aggregates of the quantum space-time within them and determine their type: the Lorentz group _SO(1,3)_ represents a rotating spacetime corresponding to visible matter and the translation group _P1,3_ represents a translational spacetime corresponding to dark matter and dark energy. The aggregation mode of space-time degrees of freedom in matter reveals that charge conjugation symmetry is the inverse symmetry of internal time of charged particles, and the external parity breaking of neutrinos is also due to their internal spatial aggregation mode.

Multi-Source Dataset Assessment and Variation Characteristics of Snow Depth in Eurasia from 1980 to 2018

Snow is an indicator of climate change. Its variation can affect surface energy, water balance, and atmospheric circulation, providing important feedback on climate change. There is a lack of assessment of the spatial characteristics of multi-source snow data in Eurasia, and these data exhibit high spatial variability and other differences. Therefore, using data obtained from the Global Historical Climatology Network Daily (GHCND) from 1980 to 2018, snow depth information from ERA5, MERRA2, and GlobSnow is assessed in this study. The spatiotemporal variation characteristics and the primary spatial modes of seasonal variations in snow depth are analyzed. The results show that the snow depth, according to GlobSnow data, is closer to that of the measured site data, while the ERA5_Land and MERRA2 data are overestimated. The annual variations in snow depth are consistent with seasonal variations in winter and spring, with an increasing trend in the mountains of Central Asia and Siberia and a decreasing trend in most of the rest of Eurasia. The dominant patterns of snow depth in late autumn, winter, and spring are all north–south dipole patterns, and there is overall consistency in summer.

Splitting of Optical Spatial Modes via Stern‐Gerlach Effect

AbstractStern‐Gerlach (SG) effect, initially found for unveiling the existence of quantized electron spins, is now a general concept describing a state‐dependent separation. It is widely explored in optics to achieve a function of optical splitting, but the current schemes always require a polarization‐ or wavelength‐dependent process, thus showing limitations for broader applications. Here, spatial modes of an optical field are employed as another degree of freedom to demonstrate an SG effect. Two modes of a pair of coupled waveguides are found to be in analog to the electron spins. They are able to undergo a splitting upon a spatially‐dependent waveguide coupling, which plays the role of a non‐uniform magnetic field. In an experiment, such a splitting is realized in two coupled non‐parallel slab waveguides, and its strength is adjusted at ease by varying the parameters of this proposed structure. This SG‐related optical splitting may find applications in the field of optical sensing and signal processing.

Lithography‐Free Method to Synthesize Quasiperiodic Silicon Inverted‐Pyramid Arrays: A Broadband Light Trapper for High‐Efficiency Thin Silicon Solar Cells

Thin silicon solar cells can be a low‐cost effective photo‐conversion device, if the device can efficiently absorb the solar spectrum. Herein, a new lithography‐free technique is developed for the fabrication of quasiperiodic silicon inverted‐pyramids arrays (SiIPAs), which show a high‐light‐trapping phenomenon in the ultraviolet–visible—near‐infrared (300–2000 nm). Fabricated SiIPA samples show a significant reduction of reflectance (3%) in the silicon absorption band (300–1000 nm). A unique additional absorption of 33–44% compared to the planar silicon is observed in the sub‐bandgap region of silicon (1100–2000 nm) for these samples. Photocurrent response measurement confirms the generation of additional electron–hole pairs in the sub‐bandgap region of silicon for the SiIPA samples in comparison with planar sample. In these results, the effect of field confinement and the creation of optical resonance modes within these structures, qualitatively supported by numerical simulation, are signified. The estimated short‐circuit current density using the experimental absorption spectrum of SiIPAs is 55.46 mA cm−2, which is far higher than the Lambertian limit of ≈43 mA cm−2. The theoretical efficiency of the solar cell can be achieved up to 35.22%, which surpasses the Shockley–Queisser limit of 33.7%.

Photon Number Splitting Attack – Proposal and Analysis of an Experimental Scheme

AbstractPhoton‐number‐splitting (PNS) is a well‐known theoretical attack on quantum key distribution (QKD) protocols that employ weak coherent states produced by attenuated laser pulses. However, beyond the fact that it has not yet been demonstrated experimentally, its plausibility and effect on quantum bit error rate are questioned. In this work, an experimental scheme is presented for PNS attack employing demonstrated technological capabilities, specifically a single‐photon Raman interaction (SPRINT) in a cavity‐enhanced three‐level atomic system. Several aspects of the proposed implementation are addressed, analytically and simulatively, and the eavesdropper's information gain by the attack is calculated. Furthermore, it is analytically shown that the scheme results in a small (yet non‐zero) quantum bit error rate, and a comparison to purely theoretical analyses in the literature is presented. It is believed that the inherent nonlinearity of the PNS attack unavoidably affects the optical modes sent to the receiver, and accordingly will always result in some error rate.

Nonlinear ray tracing in focused fields, part 2. Tracing the flux: tutorial

In this three-part paper series, we develop a method to trace the lines of flux through a three-dimensional wavefield by following a direction that is governed by the derivative of the phase at each point, a process that is best described as flux tracing but which we interchangeably name “nonlinear ray tracing.” In the first part we focused on the high-speed calculation of focused three-dimensional complex wavefields in the paraxial approximation for TEM00 and TEM01 laser modes. The algorithms developed in the first paper are first used to generate the three-dimensional grid of samples of the complex wavefield in the focal region. In this second part, we focus on tracing a flux through this three-dimensional point cloud. For a given “ray” at an arbitrary position in the 3D volume, interpolation of the three-dimensional samples is applied to determine the derivative of the phase (normal to the direction of propagation) at the ray position, which is then used to direct the ray as it “propagates” forward in a straight line over a short distance to a subsequent plane; the process is repeated between consecutive planes. The initial origin of the ray can be chosen arbitrarily at any point, and the ray can then be traced through the volume with appropriate interpolation. Results are demonstrated for focused wavefields in the absence of aberrations, corresponding to the cases highlighted in the first paper. Some of the most interesting results relate to focused Laguerre-Gaussian beams, for which the rays are found to spiral at different rates of curvature. In the third paper we extend the application of this algorithm to the investigation of lens aberration.

Fundamental spatial mode high power 808 nm double trench wide ridge waveguide laser

—Lasers operating at a wavelength of 808 nm, with watt-level output power and high beam quality in the fundamental spatial mode, have garnered significant attention due to their potential applications across various fields. Transverse optical confinement in double trench ridge waveguide lasers is determined by the width of the ridge and the refractive index difference between the ridge and trench. In this study, we have designed and fabricated a wide ridge laser operating at 808 nm with high power output and stable fundamental spatial mode based on this principle. The fundamental spatial mode operation was successfully achieved with an 8 μm ridge waveguide laser, producing an impressive output power of 1.3 W. The device exhibits a stable far-field as the current was increased from 0.3 A to 1.8 A. The laser's output power exhibits a 14% reduction with an increase in temperature of 80 °C, demonstrating a decrease rate of only 1.25 mW/°C and a wavelength variation rate of 0.22 nm/°C, indicating low sensitivity to temperature changes.

CiteNet: Cross-modal incongruity perception network for multimodal sentiment prediction

Multimodal sentiment prediction poses a formidable challenge that necessitates a profound understanding of both visual and linguistic cues, as well as the intricate interactions between them. The current achievements of modern systems in this domain can plausibly be attributed to the development of sophisticated cross-modal fusion techniques. Nevertheless, such solutions often handle each modality equally, neglecting the discordant predictions arising from sentiment incongruity in unimodal sources, which may result in performance degradation in conventional extraction-fusion scenarios. In this work, we take a different route–introducing an extraction-estimation-fusion paradigm aimed at exploring more reliable multimodal representations under the supervision of unimodal sentiment prediction. To this end, we propose a Cross-modal IncongruiTy pErception NETwork, named CiteNet, for multimodal sentiment detection. In CiteNet, we initially develop a cross-modal alignment module tailored to synchronize modality-specific representations through contrastive learning. Subsequently, with a refined cross-modal integration module, CiteNet can achieve a synergistic and comprehensive multimodal representation. In addition, we explore a cross-modal incongruity learning module from an information-theoretic perspective, capable of estimating inherent sentiment disparities by analyzing modal distributions. This incongruity score is then employed as a crucial factor in the adaptive fusion of unimodal and multimodal representations, culminating in enhanced accuracy in sentiment prediction. Experimental results on two datasets demonstrate that CiteNet outperforms prior methods by a significant margin of approximately 1%–11% in accuracy.

Orbital-angular-momentum-dependent speckles for spatial mode sorting and demultiplexing

Characterizing the orbital-angular-momentum (OAM) modes is critically important for OAM-encoded data transfer. However, traditional characterizing approaches rely on either complex and precise experimental configurations or complicated prior information processing. In these scenarios, the correlation features of OAM-dependent speckles from the scattering effect have received little attention. Here, we investigate the cross-correlation characteristics of the OAM speckles resulting from a scattering medium and propose an appealing alternative for spatial mode sorting and demultiplexing based on the OAM-dependent speckles. We demonstrate theoretically and experimentally that the cross-correlation operation between two different OAM-dependent speckles can uniformly derive an annulus pattern, whose dimension is determined by the absolute topological charge difference value between the two corresponding OAM modes. Based on this mechanism, the original coherent OAM modes can be easily sorted by implementing the cross-correlation operation between incoherently measured OAM-dependent speckles. To fully capitalize on the orthogonal feature of the OAM-dependent speckles, we also construct OAM mode demultiplexing experiments using a ground glass diffuser, where both 8-bit grayscale and 24-bit RGB OAM-encoded data demultiplexing are successfully demonstrated with superior error rates. Results show that the OAM-dependent speckles, previously treated as a nuisance for practical applications, can be surprisingly utilized as a competitive candidate for OAM mode sorting and demultiplexing, thus opening new directions in optical communication and information processing.