Propagation Of Visible Light Research Articles

Visible nonreciprocal light propagation based on titanium nitride and gold in tandem

The disappearance of the permittivity of epsilon-near-zero (ENZ) materials can significantly enhance the optical nonlinear absorption, which provides a feasible way to realize broadband optoelectronic devices. Here, we used titanium nitride (TiN) film with ENZ wavelength at 540 nm as the saturable absorber (SA), and hexagonal gold nanolayer as the reverse saturable absorber (RSA), which are arranged in tandem to fabricate a broadband nonreciprocal passive photonic diode, and the maximum nonreciprocity factor of 4.8 dB was obtained experimentally in the ENZ region. Our results show the potential applications of TiN in nonlinear optical devices, and may make inroads towards the ENZ-based high-performance broadband optoelectronic devices.

Near-fields of Butterfly Nanoantennas: A Comparative Simulation and Experimental Study

Optical nanoantennas demonstrate the ability to confine and enhance electromagnetic fields. This ability makes nanoantennas essential tools for high-resolution microscopy. The nanoantenna resonance and response can be tuned by changing their size, shape, and material as well as adjusting the probing conditions, e.g. excitation wavelength. In this paper we simulated the propagation and interaction of visible light with computer generated models of butterfly nanoantenna arrays using the finite-difference time-domain (FDTD) method. The simulations were used to understand and predict the experimental results obtained with scanning near-field microscopy (SNOM) on commercially available samples. Simulation parameters are chosen carefully to reflect the measurement conditions.

On the performance analysis of NOMA-based vehicular visible light communication systems

Communication-based vehicle safety applications have emerged as one of the best solutions to enhance road safety. In this area, visible light communication (VLC) has great potential for such applications, named Vehicular VLC (V-VLC). V-VLC is preferred due to its highly secure, low complexity, and radio frequency (RF) interference-free characteristics, exploiting the line of sight (LoS) propagation of visible light and usage of already existing vehicle light-emitting diodes. This research addresses the application of the non-orthogonal multiple access (NOMA) technique in V-VLC based vehicle-to-vehicle communication. In this study, we proposed a system integrating NOMA in V-VLC networks and comprehensively provided an analysis of the system. Subsequently, we derived theoretical achievable capacity and an exact bit error rate expression for the proposed scenario. This paper also covers discussions about system performance under the non-ideal NOAM at the receiver, the effect of transmitter-receiver distance, and the impact of different weather conditions. The derived analytical BER and channel capacity expressions are verified with the simulation results.

Four-dimensional indoor visible light positioning: A deep-learning-based perspective

Accurate indoor positioning has been a difficult problem as the last meter dilemma of localization and navigation due to lack of satellite navigation signals and complex characteristics of multipath and dynamic indoor channels. Indoor visible light positioning (VLP) provides a new possible paradigm for accurate and low-complexity indoor positioning using widely deployed light-emitting diodes (LED). In this paper, the received signal strength of the photodetector at a mobile terminal is utilized to extract the geometric features in order to infer the accurate position coordinate via deep learning. Specifically, a hybrid model, i.e., a convolutional-recurrent neural network (CRNN), is devised to learn the nonlinear mapping from the received signal strength to the position coordinates in the complex indoor visible light propagation environment. A four-dimensional (4D) VLP architecture based on CRNN is formulated to deal with the non-line-of-sight propagation of indoor visible light and different receiver orientation. Simulation results show that the proposed CRNN-based 4D VLP (CR4D-VLP) method can achieve centimeter-level positioning accuracy, and significantly outperforms other state-of-the-art deep-learning-based schemes in both line-of-sight and non-line-of-sight scenarios with various spatial patterns of LEDs and different room sizes.

Propagation of visible light in nanostructured niobium stripes embedded in a dielectric polymer

Abstract Nanometric metallic stripes allow the transmission of optical signals via the excitation and propagation of surface-localized evanescent electromagnetic waves, with important applications in the field of nano-photonics. Whereas this kind of plasmonic phenomena typically exploits noble metals, like Ag or Au, other materials can exhibit viable light-transport efficiency. In this work, we demonstrate the transport of visible light in nanometric niobium stripes coupled with a dielectric polymeric layer, exploiting the remotely-excited/detected Raman signal of black phosphorus (bP) as the probe. The light-transport mechanism is ascribed to the generation of surface plasmon polaritons at the Nb/polymer interface. The propagation length is limited due to the lossy nature of niobium in the optical range, but this material may allow the exploitation of specific functionalities that are absent in noble-metal counterparts.

Optimization of Electronic Data Investigation Mode Based on Intelligent Perception and Positioning Technology

The exploration reported here is aimed at obtaining the geographic information and ecological information of the user’s specific location to understand the real-time needs of the user and provide users with accurate and timely services. Firstly, intelligent sensing and positioning technology is introduced under the background of big data. Then, the Geographic Information Systems (GIS) and Location-Based Service (LBS) technology are sketched out. Besides, an environmental intelligent perception and positioning model is proposed based on the GIS technology, LBS technology, and visible light propagation model. Finally, the proposed model is verified by experiments. The research results demonstrate that the environmental intelligent perception and positioning model can improve the positioning ability and efficiency of the users’ location and significantly enhance the accuracy of the location of the target. The positioning accuracy of the positioning system based on GIS combined with LBS reaches more than 80%, meeting the positioning requirements in daily life. Therefore, the research reported here provides a new perspective and new method for intelligent perception, makes a guarantee for further improving the efficiency of user work and life, and sets an example for future research.

A dual channel and node mobility based cognitive approach to optimize wireless networks in coal mines

This study investigates the network capability by introducing a self-adaptive cognition approach that can sense and dynamically configure the communication channel requirements to optimize the wireless links in coal mines. The cognitive scheme based on dual-channel is initiated to sense the optimal channel of transmission and the multi-node mobility system is employed to cover the area of the network where signal strength is below the threshold level. The searching model of target nodes is presented to locate the field of intermittent link and cognitive controlled mobile nodes are utilized to restore the site of intermittent link. The visible light communication (VLC) and radio frequency (RF) channels are integrated into a cognition access point and the channel modeling of both links is performed to evaluate their performance in the hostile environment of coal mines. Multi-mode waveguide and geometrical optic (GO) models are employed in the modeling of RF signal propagation and the ray-tracing approach based on Lambertian radiation pattern (LRP) is utilized to characterize the visible light propagation. The estimation of received signal power and other evaluating parameters of communication reveals the significance of the proposed study against the challenges of intermittent links in coal mines.

Intermixed Time-Dependent Self-Focusing and Defocusing Nonlinearities in Polymer Solutions.

Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the solvent. We show how the self-focusing and defocusing responses can be captured by a nonlinear propagation model using local spatial and time-integrating responses. We realize a remarkable pattern formation in ternary solutions and model it assuming a linear combination of the self-focusing and defocusing nonlinearities in the constituent solvents. This versatile response of solutions to light irradiation may introduce a new approach for self-written waveguides and patterns.

Machine Learning Based Channel Modeling for Vehicular Visible Light Communication

Vehicular Visible Light Communication (VVLC) is preferred as a vehicle to everything (V2X) communications scheme due to its highly secure, low complexity and radio frequency (RF) interference free characteristics, exploiting the line of sight (LoS) propagation of visible light and usage of already existing vehicle light emitting diodes (LEDs). Current VVLC channel models based on deterministic and stochastic methods provide limited accuracy for path loss prediction since deterministic methods heavily depend on site-specific geometry and stochastic models average out the model parameters without considering environmental effects. Moreover, there exists no wireless channel model that can be adopted for channel frequency response (CFR) prediction. In this paper, we propose a novel framework for the machine learning (ML) based channel modeling of the VVLC with the goal of improving the model accuracy for path loss and building the CFR model through the consideration of multiple input variables related to vehicle mobility and environmental effects. The proposed framework incorporates multiple measurable input variables, e.g., distance, ambient light, receiver inclination angle, and optical turbulence, with the exploitation of feed forward neural network based multilayer perceptron neural network (MLP-NN), radial basis function neural network (RBF-NN) and decision tree based Random Forest learning methods. The framework also includes data pre-processing step, with synthetic minority over sampling technique (SMOTE) data balancing, and hyper-parameter tuning based on iterative grid search, to further improve the accuracy. The accuracy of the proposed ML based channel modeling is demonstrated on the real world VVLC vehicle-to-vehicle (V2V) communication channel data. The proposed MLP-NN, RBF-NN and Random Forest based channel models generate highly accurate path loss predictions with 3.53 dB, 3.81 dB, 3.95 dB root mean square error (RMSE), whereas the best performing stochastic model based on two-term exponential fitting provides prediction accuracy of 7 dB RMSE. Moreover, MLP-NN and RBF-NN models are demonstrated to predict VVLC CFR with 3.78 dB and 3.60 dB RMSE, respectively.

MAC/PHY Comprehensive Visible Light Communication Networks Simulation.

In this paper, the effect of channel conditions on the global behavior of a wireless Visible Light Communications (VLC) optical network are studied. It presents a system-level simulator that considers jointly a channel propagation model and the MAC mechanisms to have a realistic description of the network, even in situations where the emitted signal is heavily affected by reflections in any close surface or obstacle. The resulting platform also accurately evaluates both Line-Of-Sight (LOS) and Non-LOS (NLOS) contributions on each node and enables the effective use of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) schemes as defined by IEEE 802.15.7r1 standard, as well as allows a correct evaluation of lifelike problems such as the effect of hidden nodes. This work shows the necessity of accurately modeling VLC MAC layer performances, taking also into account the physical nature of visible light propagation in indoor scenarios.

Study of Al2O3 thin films by ALD using H2O and O3 as oxygen source for waveguide applications

Atomic Layer Deposition (ALD) is an advantageous technique to obtain alumina (Al2O3) optical waveguides based on the trimethylaluminum-water (TMA-H2O) process. However, the influence of ozone (O3) as oxygen source on pure Al2O3 ALD waveguides has not been studied yet. In this work, the optical design, fabrication and characterization of slab optical waveguides based on Al2O3 thin films using water (Al2O3–H2O) or ozone (Al2O3–O3) as oxygen source is presented. Ellipsometry measurements show a refractive index of 1.64 for Al2O3–H2O and of 1.65 for Al2O3–O3 waveguides. The intensity distribution at the waveguides output demonstrates propagation of visible light (λ = 632.8 nm) for both type of waveguides. Optical propagation losses are smaller for O3 than for H2O waveguides, the lowest value for Al2O3–O3 is 0.51 dB/cm and 3.03 dB/cm for Al2O3–H2O. Fourier transform infrared spectroscopy (FTIR) analysis shows a prominent band for bulk OH group in water oxidized samples, which may be associated with the increase of propagation losses. X-ray photoelectron spectroscopy (XPS) show no differences in chemical composition (supplementary material).

Received signal strength assisted perspective-three-point algorithm for indoor visible light positioning.

In this paper, a received signal strength assisted perspective-three-point positioning algorithm (R-P3P) is proposed for visible light positioning (VLP) systems. Due to the directional propagation of visible light, the orientations of light-emitting diodes (LEDs) and receivers can affect the positioning accuracy seriously. To circumvent this challenge, R-P3P is proposed to mitigate the limitation on LEDs' and receiver's orientation in VLP systems. The basic idea of R-P3P is to jointly utilize visual and strength information to estimate the receiver position using 3 LEDs regardless of the orientations of LEDs and receivers. Simulation results show that R-P3P can achieve positioning accuracy within 10 cm over 70% of an indoor area with low complexity.

Optimal frequency reuse scheme based on cuckoo search algorithm in Li‐Fi fifth‐generation bidirectional communication

Huge demand for bandwidth and capacity is exhibited by various wireless users and applications, for that purpose now the light-fidelity (Li-Fi)-based technologies are developing. In visible light communication, the hybrid networks based on Wi-Fi and Li-Fi has emerged recently. It is based on the concept of integrating small cell Li-Fi networks with large coverage radio frequency (RF) communication systems. For bidirectional data communication, the access links use shared bandwidth since the link of wireless backhaul invokes in the visible light spectrum. Due to the RF spectrum shortage, the bandwidth of Wi-Fi access point (AP) and the coverage of Li-Fi AP are limited in the outdoor environment. To tackle this issue, the authors propose a swarm intelligence-based improved cuckoo search into the frequency reuse of a hybrid Wi-Fi–Li-Fi network in the outdoor environment. The proposed approach employed bidirectional visible light propagation with non-orthogonal multiple access (NOMA) which is an effective approach towards fifth-generation wireless networks. The NOMA can help various users at the same time with the same frequency and multiple power levels. The system throughput and spectral efficiency are improved with dynamic frequency reuse scheme. The simulation results are compared with conventional techniques to show its effectiveness.

Optical and Superhydrophilic Characteristics of TiO2 Coating with Subwavelength Surface Structure Consisting of Spherical Nanoparticle Aggregates

It is expected that the applications of photocatalytic coatings will continue to extend into many areas, so it is important to explore their potential for enhanced functionality and design flexibility. In this study, we investigated the effect of a subwavelength surface structure in a TiO2 coating on its optical and superhydrophilic characteristics. Using submicron-scale spherical aggregates of TiO2 nanoparticles, we fabricated a TiO2 film with a subwavelength surface structure. Optical examination showed the enhanced transmittance of visible light compared to that of a plain surface. This was considered to be a result of a graded refractive index at the air–TiO2 interface. The effect of the subwavelength surface structure on optical transmittance was also demonstrated by the numerical simulation of visible light propagation in which Maxwell’s equations were solved using the finite-difference time-domain method. In addition, superhydrophilic behavior without ultraviolet light illumination was observed for the subwavelength-structure film via the measurement of the contact angle of a water drop. Furthermore, it was confirmed that the photocatalytic activity of the proposed film was comparable with that of a standard TiO2 film. It was suggested that the control of the subwavelength surface structure of a TiO2 film could be utilized to achieve novel properties of photocatalytic coatings.

Chaos‐based physical‐layer encryption for OFDM‐based VLC schemes with robustness against known/chosen plaintext attacks

The technology of visible light communication (VLC) is regarded as an appealing technique for upcoming wireless indoor multimedia communications. Considering the broadcast aspect of visible light propagation, the visible light interface is exposed and approachable to both licensed and unlicensed parties settled within the illuminated region. In this study, the authors present a chaos-based physical-layer encryption method for orthogonal frequency division multiplexing (OFDM)-based VLC schemes with the ability to counter known-plaintext attacks (KPAs) and chosen-plaintext attacks (CPAs). A logistic map is utilised for the chaos mapping. The presented method produces dynamic ciphertexts by employing the random quality of the chaotic keys and input data. It uses a multiple-fold encryption protocol which implements chaotic scrambling of the subcarrier distribution in time and frequency domains, as well as chaotic polarity inversion of subcarriers. To generate the secret key, a chaotic key creation approach is introduced by including the position-sensitive and real-valued channel state information of the VLC channel. The presented method provides supreme confidentiality for the OFDM-based VLC schemes to counter KPAs, CPAs, brute-force attacks, and statistical attacks. The secrecy capacity of the presented method is improved by applying a pre-equalisation technique at the transmitter instead of the receiver.

FIBONACCI OPTICAL LATTICE: A FRACTAL BIOMODULATION DEVICE

Natural scenes or structures share fractal-like geometries with scale-invariant statistical patterns that exhibit useful functional physiological properties in humans. This paper explores the self-assembling of alumina microelements on a nanostructured silica-embedded PET substrate and the application of Fibonacci fractal geometry as a photonic wave-guiding device. Two concentric Fibonacci circles impinged on the top of embedded silica clusters were investigated using fractal analysis. Calculating the fractal dimension of spatial scaling properties demonstrated the potential of a fractal photonic element. Simulating the propagation of spectral visible or low NIR incident light through the fractal trajectory shows that the fractal scaling properties generate novel nonlinear and double-twisted electromagnetic waves with biophilic interconnecting potential.

Simulation of Formation, Propagation and Interaction with Light of Nanoporous Structures in Indium Phosphide during Anodisation in Aqueous KOH

In semiconductor materials, electrochemical processes during anodization can cause localized etching to occur.1,2 This localized etching leads to dissolution of material in a way that creates complex porous structures. Such structures are of considerable interest. With silicon, crystals can be engineered that behave as though they have a direct bandgap, which is of interest in photonics.2,3 Metals such as aluminium and titanium can also be used to form tubular structures, via localized etching of oxide layers that form at the surface.4-6 The resulting structures have high surface area and so are of interest for a range of applications. Under many circumstances, it is possible to etch crystallographically-oriented pores. As the term suggests, these pores align themselves with certain crystallographic directions, such as <100> or <111>. Such pores lead to the formation of very regular porous structures.3,7-12 The III-V semiconductors, such as gallium arsenide (GaAs) and indium phosphide (InP), exhibit pore propagation along <111> crystallographic directions, more specifically <111>A, the directions of bonds from A atoms (gallium or indium) to B atoms (arsenic or phosphorus).8,9 This crystallographic pore propagation is interesting from a theoretical modelling point of view. The case of InP anodized in potassium hydroxide (KOH) is of particular interest because the etching is purely electrochemical, i.e. simple models can be easily compared with actual experiments. These regular structures also exhibit intriguing optical properties. In the case of InP, typical pore width is an order of magnitude smaller than the wavelength of visible light, so pores cannot be resolved optically, but the features of the porous structure do cause constructive and destructive interference.13 Furthermore, interference patterns are also observed on the surface of anodized InP electrodes.14 In this presentation, we will investigate computational modelling of pore formation and propagation during anodisation of InP in aqueous KOH solutions and describe the propagation of visible light in such porous structures by modelling of the propagation of waves.

Light positioning: A high-accuracy visible light indoor positioning system based on attitude identification and propagation model

With the booming development of green lighting technology, visible light-based indoor localization has attracted a lot of attention. Visible light-based indoor positioning technology leverages a light propagation model to pinpoint target location. Compared with the radio localization technology, visible light-based indoor positioning not only can achieve higher location accuracy, but also no electromagnetic interference. In this article, we propose LIPOS, a three-dimensional indoor positioning system based on attitude identification and visible light propagation model. The LIPOS system takes advantage of the existing lighting infrastructures to localize mobile devices that have light-sensing capabilities (e.g. a smartphone) using light emitting diode lamps as anchors. The system can accurately identify the attitude of a smartphone using its integrated sensors, distinguish different light emitting diode beacons using the fast Fourier transform algorithm, construct a position cost-function based on a visible light radiative decay model, and apply a nonlinear optimizing method to acquire the optimal estimation of final location. We have implemented the LIPOS system and evaluated it with a small-scale hardware testbed, as well as moderate-sized simulations. Extensive experiments are performed in three representative indoor environments—open-plan office, cubicle, and corridor, which not only demonstrate that the LIPOS can effectively avoid the negative effects of dynamic change of a smartphone’s attitude angle, but also show better locating accuracy and robustness, and obtain sub-meter level positioning accuracy.

Comparison of Radio Frequency and Visible Light Propagation Channels for Vehicular Communications

Comparison of Radio Frequency and Visible Light Propagation Channels for Vehicular Communications

Three-dimensional all-dielectric metamaterial solid immersion lens for subwavelength imaging at visible frequencies.

Although all-dielectric metamaterials offer a low-loss alternative to current metal-based metamaterials to manipulate light at the nanoscale and may have important applications, very few have been reported to date owing to the current nanofabrication technologies. We develop a new "nano-solid-fluid assembly" method using 15-nm TiO2 nanoparticles as building blocks to fabricate the first three-dimensional (3D) all-dielectric metamaterial at visible frequencies. Because of its optical transparency, high refractive index, and deep-subwavelength structures, this 3D all-dielectric metamaterial-based solid immersion lens (mSIL) can produce a sharp image with a super-resolution of at least 45 nm under a white-light optical microscope, significantly exceeding the classical diffraction limit and previous near-field imaging techniques. Theoretical analysis reveals that electric field enhancement can be formed between contacting TiO2 nanoparticles, which causes effective confinement and propagation of visible light at the deep-subwavelength scale. This endows the mSIL with unusual abilities to illuminate object surfaces with large-area nanoscale near-field evanescent spots and to collect and convert the evanescent information into propagating waves. Our all-dielectric metamaterial design strategy demonstrates the potential to develop low-loss nanophotonic devices at visible frequencies.