Iet Optoelectronics最新文献

An enhanced transmission is presented in a multiple-input-multiple-output (MIMO) dense-wavelength division multiplexed (DWDM) free-space-optical (FSO) communication link using diversity coding techniques under the effect of turbulent weather phenomenon. The findings show good performance with an (8 channels × 2.5 Gbps data rate/channel) 20 Gbps 1500 m transmission distance. The bit-error-rate (BER), outage probability (OP), and signal-to-noise ratio (SNR) of the diversity combining techniques using maximum-ratio combining (MRC), selection combining (SC), and equal-gain combining (EGC) technique are evaluated in this work. The obtained results illustrate that Alamouti, space-time coding (STC), space-time block coding (STBC), space-time trellis code (STTC), orthogonal STBC (O-STBC), and quasi-orthogonal STBC (QO-STBC) on the minimum mean-square-error, and MRC are worth implementing on the DWDM-FSO wireless communication systems. The mitigation of atmospheric turbulence is achieved using MIMO diversity combining techniques coding. The simulation results for diversity coding techniques using QO-STBC/STTC and SC/MRC in the MIMO-DWDM FSO communication system can improve BER performance, OP, and SNR. The MRC exhibits the lowest OP and BER when compared with the SC and EGC. The numerical results demonstrate that the FSO communication link using DWDM QO-STBC/STTC improves the power penalty at both BER values under varying atmospheric turbulence conditions for ST, MT, and WT, in comparison to FSO systems without DWDM QO-STBC/STTC diversity coding techniques.

The authors analyse the influence of reference sphere on the test accuracy of Ritchey–Common method during testing of flat mirror surface. A simulation model is established to simulate the influence of different radii of curvature of reference sphere on system wavefront. Then, the difference between the flat mirror surface result with reference sphere surface error to the actual flat mirror surface is examined by this model. The test accuracy of flat mirror result can be effectively improved by eliminating the influence of the surface error of reference sphere. When the surface accuracy of the reference sphere is better than 0.01 λ, the influence on RMS test accuracy is within 0.01 λ. R–C test path is built to test a 100 mm-diameter flat mirror surface, and its results are compared with those of the flat mirror surface without surface error of reference sphere and with the test result of the interferometer. When the surface accuracy of the actual used area of reference sphere is better than 0.01 λ, the effect on flat mirror RMS accuracy is within 0.01 λ. The RMS test accuracy can reach 0.01 λ, when the surface error of reference sphere is retained. The experiment verifies the correctness of the simulation results and guarantees the improvement in the test accuracy of R–C method.

The authors theoretically designed a highly sensitive SPR biosensor with a hybrid structure using two-dimensional nanomaterials (BP-WS₂). Using the transfer matrix method (TMM), the performance of the sensor in terms of reflection, sensitivity, detection accuracy, and quality factor is investigated, and by changing the structural parameters of the sensor, the obtained results are further analysed so that an optimal structure with optimal performance can be achieved. The sensor was optimised with four layers of BP and a single layer of WS₂. This composite structure is placed on a 50 nm thick gold layer and concluded with a maximum sensitivity of 234 deg/RIU with a FOM of 26.53 RIU⁻¹. This biosensor is designed by considering the advantages and characteristics of biosensors in their resistance and high electrical properties, as well as the ability to detect diseases quickly.

In rapid development, Selective Laser Sintering (SLS) creates prototypes by processing industrial materials, for example, polymers. Such materials are usually in powder form and fused by a laser beam. The manufacturing quality depends on the interaction between a high-energy laser beam and the powdered material. However, in-homogeneous temperature distribution, unstable laser powder, and inconsistent powder densities can cause defects in the final product, for example, Powder Bed Defects. Such factors can lead to irregularities, for example, warping, distortion, and inadequate powder bed fusion. These irregularities may affect the profitable SLS production. Consequently, detecting powder bed defects requires automation. An ensemble learning-based approach is proposed for detecting defects in SLS powder bed images from this perceptive. The proposed approach first pre-processes the images to reduce the computational complexity. Then, the Convolutional Neural Network (CNN) based ensembled models (off-the-shelf CNN, bagged CNN, and boosted CNN) are implemented and compared. The ensemble learning CNN (bagged and boosted CNN) is good for powder bed detection. The evaluation results indicate that the performance of bagged CNN is significant. It also indicates that preprocessing of the images, mainly cropping to the region of interest, improves the performance of the proposed approach. The training and testing accuracy of the bagged CNN is 96.1% and 95.1%, respectively.

Fano resonance arises from the superposition of a narrow discrete resonance with a continuous state. In this paper, a Fano resonance-based plasmonic refractive index sensor based on nanoscale metal-insulator-metal (MIM) waveguides is proposed and evaluated by applying the two-dimensional finite-difference time-domain (2D FDTD) method. An MIM-based single stub vertically attached to an MIM waveguide is considered as the unit cell of the waveguide system of the proposed structure. A transfer matrix of transmission and coupling complex coefficients is defined for the unit cell of the waveguide system of the proposed sensor, and the conditions for the authenticity of its modeling based on the transmission line theory are evaluated. A system of triplet coupled stub resonators (TCSRs) attached to an MIM waveguide is coupled with a disk resonator to induce Fano resonances in the transmission spectrum of the sensor. Fano resonance and its characteristics are utilized to improve the essential operating parameters of the sensor, such as full width at half maximum (FWHM) and figure of merit (FOM). In optimized conditions, for the system of TCSRs coupled to a disk resonator, a resonance with a sensitivity of 684 nm/RIU and an FOM of 621.8 1/RIU exhibited. Also, for the system of TCSRs coupled to a ring resonator, a resonance with a sensitivity of 3524 nm/RIU and an FOM of 35.24 1/RIU was achieved. Eventually, the numerically achieved results for the operating parameters of the sensor are validated using governing analytical methods.

In the known field of topological photonics, what remains less so is the breakdown effect of topological phases deteriorated by perturbation. In this study, the authors investigate the variance on topological invariants for a periodic Kekulé medium perturbed in unit cells, which was a gyromagnetic photonic crystal holding topological phases induced by synchronised rotation of unit cells. Two parameters for geometric and material perturbation are respectively benchmarked to characterise the topological degradation. Our calculation demonstrates that such a periodic perturbation easily destructs the topological phase and thus calls for further checkups on robustness under such unit-cell-perturbation in realisation.

Light-fidelity (Li-Fi) is a promising solution to provide high-rate, secure, and green communications to be used in the next generation of wireless networks. Since visible or infrared (IR) light-emitting diodes (LEDs) are used as the optical source and have a non-linear transfer function, the transmitted modulated signal can be distorted if the signal has a high peak-to-average power ratio (PAPR). Recently, a new modulation scheme called Hadamard-coded modulation (HCM) is proposed which has no PAPR concern since it produces symbols with discrete levels. In the HCM technique, the symbol levels can be created using multiple LEDs. Therefore, each LED operates in its linear region and just switches on or off. A low-complexity transceiver architecture for the HCM-based communication links is proposed and a complete synchronisation procedure based on the spread-spectrum techniques is presented. Finally, the bit error rate of the system is evaluated by Monte Carlo simulations, and effects of system parameters such as preamble length, fall and rise time of optical devices, and timing jitter on the bit error rate of the link are discussed.

Green energy transition and climate change have gathered significant momentum in the world because of the rising population and increased clean energy demands. For this reason, renewable energy alternatives such as inexhaustible photo energy from the sun appear to be the ultimate solution to the world's energy needs. Formamidinium tin tri-iodide (HC(NH₂)₂SnI₃)-based perovskites are found to be more efficient and stable than their methylammonium tin tri-iodide (MASnI₃) counterparts because of its wider bandgap and better temperature stability. A device simulation of FASnI₃-based solar cell is numerically performed using solar cell capacitance simulator (SCAPS-1D). The focus is to investigate the effect of changing working temperature, metal back contact, absorber thickness, defect density, and doping concentration on the performance of the proposed solar cell device. The optimised solar cell parameters of the proposed solar cell were: short-circuit current density (Jsc) of 28.45 mAcm⁻², open-circuit voltage (Voc) of 1.0042 V, fill factor of 63.73%, and power conversion efficiency of 18.21% at 300 K, thus, paving the way for novel perovskite solar cells which are environmentally benign because they are lead-free, have better absorption efficiency, and can be injected into the production work flow for commercial applications.

Visible light communication can be leveraged to establish a wireless link between neurons in spiking networks even when neural areas are in relative motions. In electro-optical spiking neural networks (SNN), parallel transmission is often achieved through wavelength division multiplexing (WDM). However, WDM can be prohibitive in certain applications due to the need for multiple narrow-band transmitters and receivers with optical bandpass filters. Instead of WDM, an alternative approach of using non-orthogonal multiple access is explored (NOMA) with a pulse amplitude modulation (PAM) scheme in optical axons to enable parallel neural paths in an SNN. To evaluate NOMA with PAM, the authors implement an electro-optical SNN that controls the force of two anthropomorphic fingers actuated by the shape memory alloy-based actuators. An optical reference channel is used to dynamically adjust the optical receiver's gain to improve the receiver's decoding performance. Experimental results demonstrate that the electro-optical SNN can maintain control over the fingers and hold an object under varying channel conditions. Hence, the proposed system offers robustness against dynamic optical channels induced by the relative motion of neurons.