Iet Optoelectronics最新文献

The increasing development and utilisation of optical camera communications offer an excellent opportunity for the implementation of the smartphone-to-smartphone-based visible light communications (S2SVLC) system. In this study, the authors experimentally demonstrate that the S2SVLC system can support high-quality multimedia transmissions by the investigation of the mean square error estimation, peak signal-to-noise (PSNR) degradation, bit error rate (BER), and data rate achieved. The experimental analysis has been carried out for different typical practical background illuminations (i.e., normal illumination and dark condition), distances, tilting, and rotation angles. The PSNR and BER are determined for different frame sizes in the S2SVLC system to provide an insight of system performance. Those results indicate that the data transmission at different conditions significantly impacts the system's performance.

An algorithm for recovering transmitted static identifiers (IDs) in rolling shutter based Optical Camera Communication systems is proposed by the authors, considering a system comprised of a camera and a circular light source. The goal is to allow the correct decoding when the ID frame is only partially detected in the image. A baseline algorithm as reference for the frame recovery success rate (FRSR) and a reconstruction algorithm based on the idea of capturing multiple frame fragments and reassembling them is proposed in order to recover the transmitted ID not entirely seen on a single image. It was proven, by simulation, that the maximum distance at which the IDs recovery can be guaranteed is increased by 2.5 fold with the proposed algorithm, for 6-bit, 8-bit and 10-bit codewords. An experimental validation algorithm was also proposed, using image processing techniques to extract the bitstreams and test the ID recovery process. The proposed algorithm improves the FRSR for a given distance, even in the presence of considerable bit errors in the bitstreams extracted from the images.

Optical digital-to-analog converters (DACs) are key to overcoming the enormous power consumption caused by the slowdown of Moore's Law. In previous work, an optical DAC consisting of a signal generator and an intensity converter was presented. The generating component was integrated into the device, but a higher level of device integration is desirable. An optical DAC device with a built-in intensity converter for a 2-bit binary phase-shift keying (BPSK) signal is demonstrated. The integrated device consists of two delay line interferometers (DLIs) with silicon waveguides. The first is used to generate a quadrature PSK (QPSK) signal from two BPSK signals, and the second is used to convert the QPSK constellation into light intensities. Experimental results show that the 2-bit digital codes 00, 01, 10, and 11 can be successfully converted into four different light intensities depending on their pattern at 10 Gbps.

A method is proposed for optical characterisation of materials, which is a very important input for realistic channel simulation based on Monte-Carlo Ray-Tracing algorithms. This original approach consists first of all in carrying out some measurements of the optical power received after propagation in the environment containing the materials sought, using a simple and low-cost experimental setup. In a second step, this approach is based on an optimization algorithm. It takes as input the optical power measurements made, associated with the parameters of the measurement environment, such as the positions or properties of the sensors. This algorithm searches for the parameters of the material reflection models, minimising the difference between the optical measurement and the simulation. Two cost functions are studied to perform this search and showed that the correlation measure is the more robust one. To avoid uncertainties in the real input data, this approach is discussed using only a virtual configuration with well-controlled input data and thus a virtual measurement obtained by simulation. The results show that this method produces a correct estimate of the Bidirectional Reflectance Distribution Function (BRDF) albedos, provided that the chosen BRDF models correspond well to the reflection behaviour of the materials, and that the materials have a significant influence on the measured optical power.

Fast-OFDM-based intensity-modulation and direct-detection (IM/DD) has been proposed for deployment of cost-efficient optical access networks, due to its implementation simplicity and high spectral efficiency. In this article, the accuracy of the generalised memory polynomial (GMP) for the non-linear modelling of optical Fast-OFDM links is studied, including memory effects and considering different model parameters. After model validation using measured data of a 10 km single mode fibre link, the GMP is used for performance investigations of a distortion compensation approach to optical Fast-OFDM, for up to 16PAM modulation formats and different number of Fast-OFDM subcarriers. This study firstly reports the performance results of optical 16PAM-Fast-OFDM systems using either 2PAM- or 4PAM-based training signals for digital post-distortion and FFT-based channel estimation, and firstly investigates the influence of the zero padding (ZP) length on the performance of optical Fast-OFDM. Excellent performance improvements are achieved using the proposed distortion compensation scheme, relative to conventional system implementation.

This article investigates the use of a visible light positioning system in an indoor environment to provide a three dimensional (3D) high-accuracy solution. The proposed system leveraged the use of a single light-emitting diode and an image sensor at the transmitter and the receiver (Rx) respectively. The proposed system can retrieve the 3D coordinate of the Rx using a combination of the angle of arrival and received signal strength (RSS). To mitigate the error induced by the lens at the Rx, a novel method is proposed and experimentally tested. The authors show that, the proposed method outperforms previously reported RSS under all circumstances and it is immune to varying exposure times within the standard range of 250 µs to 4 ms. The authors experimentally demonstrate that the proposed algorithm can achieve a 3D root mean squared error of 7.56 cm.

Optical camera communication is foreseen to have an essential role in future systems requiring wireless communication capability. In this regard, high-spectral-resolution cameras, such as multispectral (MS) cameras, present specific characteristics that can be exploited to provide new features to optical camera communication links. Using the MS cameras' features to take advantage of the light-emitting diode (LED) behaviour in a novel communication scheme is focussed. Notably, LED spectral response curves are different when their temperature changes. Therefore, these differences can be detected based on the MS cameras' spectral resolution. Thus, more than one communication channel can be attained using the same LED device since the camera can distinguish the different LED spectral signatures. This new approach is analysed in this work, including some equalisation techniques applied to the channel matrix in the receiver to improve the extraction of the transmitted signal reducing the inter-channel interference. For the specific MS camera employed in the experiments, up to two distinct channels could be obtained with the same transmitter at different temperatures, getting a bit error rate below the forward error correction limit. However, obtaining satisfactory results is highly dependent on the variation that temperature causes in the spectral signatures of the LEDs, so further experiments are recommended in future work with different devices.

Recently, reconfigurable intelligent surface (RIS) has gained research and development interests in modifying wireless channel characteristics in order to improve the performance of wireless communications, especially when the quality of the line-of-sight channel is not that good. In this work, for the first time in the literature, we have used simultaneously transmitting and reflecting RIS (STAR-RIS) in a non-orthogonal multiple-access visible light communication system to improve the performance of the system. Achievable rates of the users are derived for two data recovery schemes, single-user detection (SUD) and successive interference cancellation (SIC). Then, the sum-rate optimisation problem is formulated for two operating modes of STAR-RIS, namely energy-splitting and mode-switching cases. Moreover, a sequential parametric convex approximation method is used to solve the sum-rate optimisation problems. The authors have also compared energy-splitting and mode-switching cases and showed that these two modes have the same performance. Finally, numerical results for SUD and SIC schemes and two benchmarking schemes, time-sharing and max-min fairness, are presented, and spectral- and energy-efficiency, number of STAR-RIS elements, the position of users, and access point are discussed.

In this study, a surface plasmon resonance sensor for detecting haemoglobin concentration based on a D-type optical fibre with a graphene-gold surface architecture is proposed. The graphene-gold surface architecture included a 50 nm thick gold film and monolayer graphene film, which were decorated on a 10 mm long D-type sensing region. The proposed sensor worked in wavelength interrogation mode, with the light wavelength ranging from 400 to 1100 nm. The authors realised the D-type optical fibre surface polishing process, the gold film vacuum coating process, and the chemical-vapour-deposited graphene's wet transfer process. Furthermore, the fabricated sensors were used to detect the refractive index (RI) of haemoglobin samples, which varied from 1.331 to 1.346. Experiment results show that the fitted RI sensitivity of the sensor decorated with gold and graphene reaches 1874.41 nm/RIU, 4.995% higher than that of the sensor decorated only with gold. The concentration sensitivity of the sensor coated with gold and graphene film is 4.96 nm/(g/dL), and the proposed sensor can provide a resolution of 20.2 mg/dL for haemoglobin concentration detection.

This article presents a novel design for guiding terahertz (THz) waves, which utilises a photonic crystal fibre with a porous core (PC-PCF). This approach is substantiated by a Topas-based octagonal-shaped core with rectangular air slots. By utilising Finite Element Method and Perfectly Matched Layer boundary condition, the guiding properties of a structure consisting of octagonal air holes integrated with circular air slots in the cladding region have been investigated. The proposed structure exhibits a birefringence value of 0.05 and a low effective material loss of 0.013 cm⁻¹. Moreover, it exhibits flattened dispersion measuring $��0.6�\pm �0.16��p�s�/�T�H�z�/�c�m�$ at a wide-ranging frequency of 0.4 to 1.6 THz. In addition to that, the proposed structure offers 60% high core power fraction, 10⁻¹⁸ cm⁻¹ confinement loss at 65% porosity of 290 μm core diameter and 1.6 THz frequency. Other significant waveguide properties: effective refractive index, effective area, spot size, and beam divergence of the proposed fibre are numerically analysed and discussed rigorously along with the fabrication viability of the fibre with existing techniques.