This paper details the design and theoretical analysis of a novel thermo-optical modulator that leverages the unique phase transition characteristics of vanadium dioxide (VO<sub>2</sub>) and the plasmonic properties of graphene. Employing a combination of transmission and reflection mode structures, the study explores four configurations designed to optimize modulation depth and minimize insertion loss. The analysis conducted using COMSOL Multiphysics with the finite element method (FEM) highlights the significant influence of geometrical parameters on the modulator’s performance. The specific attention to the interaction between VO<sub>2</sub>’s phase transition at critical temperatures and graphene’s conductivity adjustment provides insights into the dynamic control of optical signals in the mid-infrared spectrum.
Links and knots are exotic topological structures that have garnered significant interest across multiple branches of natural sciences. Coherent links and knots, such as those constructed by phase or polarization singularities of coherent light, have been observed in various three-dimensional optical settings. However, incoherent links and knots - knotted or connected lines of coherence singularities - arise from a fundamentally different concept. They are hidden in the statistic properties of a randomly fluctuating field, making their presence often elusive or undetectable. Here, we theoretically construct and experimentally demonstrate such topological entities of incoherent light. By leveraging a state-of-the-art incoherent modal-decomposition scheme, we unveil incoherent topological structures from fluctuating light speckles, including Hopf links and Trefoil knots of coherence singularities that are robust against coherence and intensity fluctuations. Our work is applicable to diverse wave systems where incoherence or practical coherence is prevalent, and may pave the way for design and implementation of statistically-shaped topological structures for various applications such as high-dimensional optical information encoding and optical communications.
All-optical neural networks (AONNs) promise transformative gains in speed and energy efficiency for artificial intelligence (AI) by leveraging the intrinsic parallelism and wave nature of light. However, their scalability has been fundamentally limited by the high power requirements of conventional nonlinear optical elements. Here, we present a low-power nonlinear activation scheme based on a three-level quantum system driven by dual laser fields. This platform introduces a two-channel nonlinear activation matrix with both self- and cross-nonlinearities, enabling true multi-input, multi-output optical processing. The system supports tunable activation behaviors, including sigmoid and ReLU functions, at ultralow power levels (17 uW per neuron). We validate our approach through theoretical modeling and experimental demonstration in rubidium vapor cells, showing the feasibility of scaling to deep AONNs with millions of neurons operating under 20 W of total optical power. Crucially, we also demonstrate the all-optical generation of gradient-like signals with backpropagation, paving the way for all optical training. These results mark a major advance toward scalable, high-speed, and energy-efficient optical AI hardware.
Abstract Photoacoustic dual-comb spectroscopy (DCS), converting spectral information in the optical frequency domain to the audio frequency domain via multi-heterodyne beating, enables background-free spectral measurements with high resolution and broad bandwidth. However, the detection sensitivity remains limited due to the low power of individual comb lines and the lack of broadband acoustic resonators. Here, we develop cavity-enhanced photoacoustic DCS, which overcomes these limitations by using a high-finesse optical cavity for the power amplification of dual-frequency combs and a broadband acoustic resonator with a flat-top frequency response. We demonstrate high-resolution spectroscopic measurements of trace amounts of C2H2, NH3 and CO in the entire telecommunications C-band. The method shows a minimum detection limit of 0.6 ppb C2H2 at the measurement time of 100 s, corresponding to the noise equivalent absorption coefficient of 7 × 10−10 cm−1. The proposed cavity-enhanced photoacoustic DCS may open new avenues for ultrasensitive, high-resolution, and multi-species gas detection with widespread applications.
Unmanned Aerial Vehicle (UAV) remote sensing is a commonly used technical means in modern science and technology, but currently, remote sensing images captured by UAVs need to be spliced to obtain more comprehensive information. However, current image stitching techniques generally have shortcomings such as a small number of extracted features, low matching accuracy, and poor stability. To address the above issues, this study proposes an improved remote sensing image mosaic model on the bias of the Scale Invariant Feature Transform (SIFT) algorithm. Firstly, in this study, aiming at the problem that traditional SIFT cannot meet the requirements of feature extraction and matching for unconventional remote sensing images and special texture images, normalized cross correlation (NCC) and Forstner operator are introduced to optimize it, namely, a SIFT-NCC model is constructed. On this basis, for remote sensing images with high resolution and a wide range, this study further proposes a remote sensing image automatic mosaic model that combines point features and line features. That is, a linear segment detector (LSD) is introduced to extract the line features of remote sensing images. The experimental verification results of the final SIFT-NCC-LSD show that the matching accuracy for remote sensing images with different characteristics can reach over 95 %. Therefore, SIFT-NCC-LSD has good applicability.
We present new results obtained from the modeling of a <i>tulip-like</i> variable curvature mirror (VCM) in the case of a central force that reacts to its contour. From Nastran finite element analysis, we shows that 3-D optimizations, using <i>non-linear static flexural option</i>, with an appropriate solution sequence, provide an accurate <i>tulip-like</i> VCM thickness distribution. This allows us to take into account boundary conditions, including the thin outer collarette and its link to a rigid ring. Modeling with a quenched stainless steel chromium substrate provides diffraction-limited optical surfaces. Rayleigh’s quarter-wave criterion is performed over a <i>zoom range</i> from flat up to <i>f</i>/3.5 convexity over a 13 mm clear aperture and 10 daN central force. The optical testing results of a prototype <i>tulip-like</i> VCM elaborated from the previous analytic theory, show quasi-diffraction-limited figures for a zoom range up to <i>f</i>/5. The present modeling results should significantly help in the future construction of such VCMs with a zoom range extended up to <i>f</i>/3.5.
Mohd Salman Khan, B. Jahnavi Priya, Rathnala Aishika
et al.
An ultra-wideband (UWB) terahertz (THz) antenna is designed and numerically analyzed. A technique is implemented for obtaining the filtering characteristics in the antenna response. A graphene sheet is placed in antenna structure for achieving the filtering response. The variation in the surface conductivity of the covered area by graphene sheet provides the variable field confinement in antenna structure. This way helps in generating the filtering characteristics in UWB response of antenna. Also, the variation in the electrical properties of graphene material provides the tunability in the generated notched frequency band. The antenna utilizes the feeding with the orthogonal stubs associated with it which helps in providing the circularly polarized response. Furthermore, the antenna operation is verified with the electrical circuit model.
In this paper, an algorithm for the estimation of the linear inter-channel crosstalk in a dense-WDM polarization-multiplexed 16-QAM transmission scenario is proposed and demonstrated. The algorithm is based on the use of a feed-forward neural network (FFNN) inside the coherent digital receiver. Two types of FFNNs were considered, the first based on a regression algorithm and the second based on a classification algorithm. Both FFNN algorithms are applied to features extracted from the histograms of the in-phase and quadrature components of the equalized digital samples. After a simulative investigation, the performance of the channel spacing estimation algorithms was experimentally validated in a 3 × 52 Gbaud 16-QAM WDM system scenario.
Wen Qi Zhang, Zane Peterkovic, Stephen C. Warren-Smith
et al.
We propose a new concept to generate efficient one-third harmonic light from an unseeded third harmonic process in optical fibers. Our concept is based on the dynamic constant (Hamiltonian) of the nonlinear third harmonic generation in optical fibers and includes a periodic array of nonlinear fibers and phase compensation elements. We test our concept with a simulation of the nonlinear interaction between the fundamental and third harmonic modes of a realistic optical fiber, demonstrating high-efficiency one-third harmonic generation. Our work opens a new approach to achieving the so far elusive one-third harmonic generation in optical fibers.
Particles trapped by optical tweezers, behaving as mechanical oscillators in an optomechanical system, have found tremendous applications in various disciplines and are still arousing research interest in frontier and fundamental physics. These optically trapped oscillators provide compact particle confinement and strong oscillator stiffness. But these features are limited by the size of the focused light spot of a laser beam, which is typically restricted by the optical diffraction limit. Here, we propose to build an optical potential well with fine features assisted by the nonlinearity of the particle material, which is independent of the optical diffraction limit. We show that the potential well shape can have super-oscillation-like features and a Fano-resonance-like phenomenon, and the width of the optical trap is far below the diffraction limit. A particle with nonlinearity trapped by an ordinary optical beam provides a new platform with a sub-diffraction potential well and can have applications in high-accuracy optical manipulation and high-precision metrology.
The paper considers a problem of classifying Sentinel-2 multispectral satellite images for environmental monitoring of the Baikal Natural Territory (BNT). The specificity of the BNT required the creation of a new set of 12 classes, which takes into account current problems. The set was formed in such a way that the areas corresponding to these classes completely covered the BNT. A training dataset was formed using a web interface based on Sentinel-2 satellite images. The classification of satellite images was carried out using Random Forest algorithms and the ResNet50 neural network. The accuracy of the calculations showed that the classification results can be used to solve actual problems of the Baikal natural territory, in particular, to analyze changes in the forestland, assess the impact of climate change on the landscape, analyze the dynamics of development activities, create farmland inventory, etc.
Alberto Tibaldi, Mohammadamin Ghomashi, Francesco Bertazzi
et al.
We present a detailed simulation study on plasmonic-organic hybrid electro-optic modulators based on coupled symmetric or asymmetric plasmonic slots. An electro-optic polymer is exploited as an active material, and the device is compatible with a silicon photonics platform. The proposed device operates at 1550 nm wavelength, typical of data center or long-haul telecommunication systems. The device performance in terms of area, plasmonic losses, optical bandwidth, intrinsic modulation bandwidth and energy dissipation are comparable to already proposed Mach-Zehnder solutions, but with potentially better extinction ratio, coupling losses due to photonic-plasmonic transitions, and flexibility in exploiting, without any performance penalty, asymmetric slots to shift the ON and OFF states bias. Finally, the bias dependence of the modulation chirp is investigated, comparing through and cross-coupling configurations.
Optical interference and the related effects are key elements which could exhibit the properties of both classical and quantum optical systems. Usually, the interference between different optical paths may produce intriguing effects, such as the electromagnetically induced transparent (EIT) and so on. In this work, we study the interference effects in directly coupled whispering-gallery mode (WGM) micro-resonators, in which the emergence of EIT and electromagnetically induced absorption (EIA) could be observed. We find by tuning the coupling strength between the resonators, the modulation phase may control the appearance and disappearance of EIT (EIA). Furthermore, we prove the existence of fast and slow light, and propose a scheme for effective switching between them. This work provides a new strategy for obtaining slow light and quantum storage in the WGM micro-resonators.
The influence of thermo-optic effects on shape profiles of soliton crystals in optical Kerr microresonators is investigated. The study rests on a model that consists of the Lugiato-Lefever equation, coupled to the one-dimensional heat diffusion equation with a source term proportional to the average power of the optical field. Using appropriate variable changes the model equations are transformed into a set of coupled first-order nonlinear ordinary differential equations. These equations are solved numerically with emphasis on the influence of thermo-optic effects on the amplitude and instantaneous frequency of the optical field, as well as on the temperature profile in the microresonator cavity. It is found that thermo-optic effects do not prevent soliton crytals from forming in optical Kerr microresonators, however, a strong thermal detuning will decrease the soliton-crystal amplitude. The model predicts a temperature profile in the microresonator cavity which is insensitive to the specific spatio-temporal profile of the soliton crystal propagating in the microresonator, a feature peculiar to the model.
The effect of the width of the angular spectrum (numerical aperture) of a broadband-frequency wave-field probing a layered object on the signal of an autocorrelation low-coherence interferometer (ALCI) under spatially coherent and incoherent illumination of the entrance pupil is considered. It is found that under incoherent illumination an increase in the width of the angular spectrum of the field leads to a decrease in the amplitude, a change in the shape and position of the measuring signals of the interferometer due to decorrelation of the object field partial components which have reflected from various interlayer boundaries inside the object. In the case of coherent illumination, the ALCI signal is formed in a confocal mode, which leads to the amplitude extraction of the measurement signals are determined by the mutual correlations between a partial component reflected from the boundary on which the probing field was focused, and partial components of this field which have reflected from other boundaries within the object. This effect makes it possible to determine parameters of the internal layered structure of an object doing without apriori structure-related information. In this case, an increase in the numerical aperture of the probing light beam leads to an increase in the systematic error in determining the optical thicknesses of the layers, which can be estimated on the basis of the obtained expressions.
Silicon nanoparticles (Si-NPs) with initial sizes of the order of 100 nm were prepared by femtosecond laser
ablation-fragmentation of microcrystalline silicon in water followed by drying and resuspending in water
or in aqueous solutions of dextran. The prepared aqueous suspensions of Si-NPs without dextran and with
dextran coating were investigated by means of the scanning electron microscopy, dynamic light scattering
and optical absorption spectroscopy in the spectral range from 250 to 800 nm. The optical absorption of
uncoated Si-NPs in an aqueous medium with different pH-level varied from 4 to 8 was found to decrease
with time because of a process of the dissolution of those NPs in water. The dissolution rate depended
nonmonotonically on the solution acidity (pH level) and the corresponding times were in the range from 50
to 180 hours. The addition of dextran into the solution was found to significantly decrease the dissolution
rate of Si-NPs to 300 hours because of the coating of NPs with a polymer shell. The obtained results can
be useful to develop new biomedical technologies involving Si-NPs as stabilized theranostics (therapy and
diagnostics) agents.
Key words: nanoparticles, dextran, biopolymer, optics, absorbance.
Linear optical multiports are widely used in photonic quantum information processing. Naturally, these devices are directionally-biased since photons always propagate from the input ports toward the output ports. Recently, the concept of directionally-unbiased linear optical multiports was proposed. These directionally-unbiased multiports allow photons to propagate along a reverse direction, which can greatly reduce the number of required linear optical elements for complicated linear optical quantum networks. Here, we report an experimental demonstration of a 3 x 3 directionally-unbiased linear optical fiber multiport using an optical tritter and mirrors. Compared to the previous demonstration using bulk optical elements which works only with light sources with a long coherence length, our experimental directionally-unbiased 3 x 3 optical multiport does not require a long coherence length since it provides negligible optical path length differences among all possible optical trajectories. It can be a useful building block for implementing large-scale quantum walks on complex graph networks.
Optical trapping describes the interaction between light and matter to manipulate micro-objects through momentum transfer. In the case of 3D trapping with a single beam, this is termed optical tweezers. Optical tweezers are a powerful and non-invasive tool for manipulating small objects, which have become indispensable in many fields, including physics, biology, soft condensed matter, amongst others. In the early days, optical trapping were typically used with a single Gaussian beam. In recent years, we have witnessed the rapid progress in the use of structured light beams with customized phase, amplitude and polarization in optical trapping. Unusual beam properties, such as phase singularities on-axis, propagation invariant nature, have opened up novel capabilities to the study of micromanipulation in liquid, air and vacuum. In this review, we summarize the recent advances in the field of optical trapping using structured light beams.
We demonstrate that the singular value decomposition algorithm can be combined with the fast Fourier transform or finite difference procedures to generate straightforward and accurate one-way Helmholtz equation electric field propagation methods.