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Abstract A coherent optical receiver digital signal processing (DSP) scheme is proposed based on spectral clustering, which utilises spectral clustering to cluster the signals outputted by the DSP. Compared to existing blind DSP algorithms for coherent optical receivers operating at over 100Gbps with PM‐mQAM, the proposed scheme effectively suppresses various physical impairments, achieving lower bit error rates (BERs) at the same transmission distance, thus enabling longer transmission distances under the same forward error correction threshold. Furthermore, simulations of the proposed scheme on a 14GBaud PM‐16QAM coherent optical transmission system show that, at a BER of 1.9E‐2, the maximum transmission distance increases from 1700 to 2000 km, and at a BER of 3.8E‐3, it increases from 700 to 900 km.

Abstract This study analyses the interference effect in a visible light‐non‐orthogonal multiple access (VL‐NOMA) network that considers the signal power parameters performance for near and far users. The light‐emitting diode (LED) as a carrier transmits signals, and we investigate the interference effect. The interference effect challenge is a result of unaligned signal power parameters, thereby producing noise or echo during the signal transmission. The signal power parameters are successfully aligned, and NOMA techniques are deployed, which improves the signal performance in terms of bit‐error rate (BER), achieved data rate, and signal‐to‐interference plus noise ratio (SINR). Furthermore, the deployed NOMA techniques, such as power allocations (PA) to assign the signals appropriately, then superposition coding (SC) encodes the entire signal, and successive interference cancellation (SIC) cancels the interference within the signals. The signal behavior of the aligned and the unaligned signal power parameters performance are used to investigate the interference effect. We observed that unaligned signal power parameters reduce the signal performance of achieved data rate, BER, and SINR. Further, the aligned signal power parameter with NOMA techniques improves the signal performance. Moreover, in the aligned signal power scenario of NOMA, the near user performed better than the far user.

Abstract This study investigates the integration of dimmable constant weight polar‐coded non‐orthogonal multiple access (NOMA) with orthogonal space‐time block coding (OSTBC) in visible light communication (VLC) systems over Nakagami‐m fading environments. The proposed scheme aims to enhance the reliability of VLC systems by reducing the outage probability while accommodating dimming requirements. By allowing multiple users to utilize the same time‐frequency resources and adjust power levels based on individual channel conditions, the system optimizes resource utilization. Additionally, the OSTBC method provides effective communication among multiple users by leveraging transmit diversity to improve system performance. The efficacy of the proposed approach is demonstrated through analytical analysis and Monte Carlo simulations, showcasing superior outage probability performance compared to conventional Alamouti‐STBC schemes.

Abstract Solar cells are increasingly being utilised for both energy harvesting and reception in free‐space optical (FSO) communication networks. The authors focus on the implementation of a mid‐band p‐In0.01Ga0.99 N/p‐In0.5Ga0.5 N/n‐In0.5Ga0.5 N (PPN) solar cell, boasting an impressive 26.36% conversion efficiency (under 1.5AM conditions) as a receiver within an indoor FSO communication network. Employing a solar cell with dimensions of 1 mm in length and width, the FSO system underwent simulation using Optisystm software, while the solar cell's behaviour was simulated using SCAPS‐1D. The received power from the solar cell was then compared to that of four commercially available avalanche photodiode (APD) receivers. Exploring incident wavelengths spanning 400–700 nm within the visible spectrum, across transmission distances of 5, 10, 15, and 20 m, the study presented current‐voltage (IV) and power‐voltage curves. Notably, the InGaN solar cell exhibited superior electrical power output compared to all commercial APDs. In conclusion, the findings underscore that augmenting received power has the potential to enhance FSO network quality and support extended transmission distances.

Abstract The demand for miniaturized and integrated multifunctional devices drives the progression of high‐performance infrared photodetectors for diverse applications, including remote sensing, air defense, and communications, among others. Nonetheless, infrared photodetectors that rely solely on single low‐dimensional materials often face challenges due to the limited absorption cross‐section and suboptimal carrier mobility, which can impair sensitivity and prolong response times. Here, through experimental validation is demonstrated, precise control over energy band alignment in a type‐II van der Waals heterojunction, comprising vertically stacked 2D Ta2NiSe5 and the topological insulator Bi2Se3, where the configuration enables polarization‐sensitive, wide‐spectral‐range photodetection. Experimental evaluations at room temperature reveal that the device exhibits a self‐powered responsivity of 0.48 A·W−1, a specific directivity of 3.8 × 1011 cm·Hz1/2·W−1, a response time of 151 µs, and a polarization ratio of 2.83. The stable and rapid photoresponse of the device underpins the utility in infrared‐coded communication and dual‐channel imaging, showing the substantial potential of the detector. These findings articulate a systematic approach to developing miniaturized, multifunctional room‐temperature infrared detectors with superior performance metrics and enhanced capabilities for multi‐information acquisition.

Abstract The enhanced capacity of optical networks is a significant advantage within the global telecommunications industry. Optical networks provides transmission of information over large distances with reduced latency. However, the growing intricacy of network topologies poses a significant challenge to network adaptability, network resilience, device compatibility, and service quality in the contemporary era of technology and 5G networks. In light of these challenges, recent studies leverages on disaggregation in the context of Software Defined Network (SDN) and network service orchestrators as a viable remedy. Disaggregated optical systems offer SDON (Software‐Defined Optical Networking) enhanced control options and third‐party dynamism streamlining upgrades and diminishing single vendor dependency. Although, the advancement of disaggregation improves network flexibility and vendor neutrality of Software Defined Optical Networking (SDON), this improvement comes at the cost of reduced scalability and network controllability performance. The current research paper posits two potential resolutions to the aforementioned challenge. The authors present recommendations and an enhanced architecture that leverages Open Network Operating System (ONOS) containers and Kubernetes orchestration to improve scalability inside the Software‐Defined Optical Networking (SDON) architecture. The suggested architectural design has underlining novel flow charts and algorithms that enhances scalability performance by 33% while also preserving flexibility and controllability in comparison to pre‐existing SDON architectures. This architecture also makes use of the Mininet‐Optical physical‐layer architecture to simulate a real‐time scenario, as well as yang models from the Open Disaggregated Transport Network (ODTN) working group, the pioneers of SDONs. A detailed analysis of the rules and procedural processes involved in the implementation of the proposed architecture. In order to demonstrate the practical application of this architectural framework to a real‐world Software‐Defined Optical Network (SDON) system, the pre‐existing SDON ONOS architecture within the Optical Transport Domain Networking (OTDN) working group was adjusted and refined. This adaptation aimed to illustrate the use of ONOS in conjunction with established optical network systems, highlighting the advantages it offers.

Abstract Turbulence effects can cause performance degradation for underwater optical wireless communication (UOWC) system. In this paper, a hybrid modulation (modulation–modulation, M–M) is presented to resist turbulence‐induced fading and improve the transmission performance of UOWC systems. The proposed differential phase shift keying‐multiple pulse position modulation (DPSK‐mPPM) is adopted as hybrid modulation to improve the bit error rate (BER) performance over UOWC turbulence channel of Gamma–Gamma distribution. Subsequently, the closed‐form average BER expressions of mPPM and hybrid DPSK‐mPPM modulation are derived and investigated, which are related to the oceanic turbulence parameters. The influence of the variation of anisotropy factor of ocean turbulence is analysed for the UOWC system over strong Gamma–Gamma turbulent channels. Finally, the numerical simulation results demonstrate the effectiveness of proposed DPSK‐mPPM to improve the BER performance compared to the traditional single modulation over UOWC channel under the same conditions. Furthermore, the work of this paper improves the practicality of the proposed DPSK‐mPPM scheme for underwater communication in complex oceanic environments.

Abstract 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.

Abstract The authors propose to arrange the light emitting diodes (LEDs) on the ceiling for an indoor visible light communication system in order to minimise the secrecy outage probability (SOP) at the location of the legitimate user (LU). More precisely, by deriving the secrecy capacity for a multiple‐input single‐output‐VLC system, we evaluate the SOP at the LU's location which is used as the appropriate metric to determine the position of the LEDs on the ceiling. To mitigate the effect of the eavesdropper, we derive the optimal beamforming coefficients which are used at the transmitter LED array with the aim of maximising the signal‐to‐noise ratio at the LU. Simulation results show that for a SOP of 10−4, the proposed SOP‐based LED arrangement with optimal beamforming offers up to 3 dB gain in transmit power compared to the classical uniform LED arrangement with sub‐optimal zero‐forcing beamforming. Moreover, they show that by using the proposed method, the SOP is kept below a desired threshold, over a wider area inside the indoor environment compared to classical methods.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract 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.

Abstract A visible light positioning (VLP) system for multi‐cell networks based on multi‐colour LED that combines frequency division multiplexing with the received signal strength and a trilateration method is proposed. First, it employs experimental measurements to model the designed visible light communication (VLC) system under the characteristics of the target scenario. Second, it introduces a low‐cost VLC transmitter that exploits the chromatic space to transmit the VLP information. Third, it characterizes the VLC transmitter and proposes a linearization for electro‐optical responses of RGB LED. An RGB digital colour sensor and simple method calibrate the chromatic emission. The experimental results show that the proposed VLP multi‐cell architecture achieves a positioning accuracy lower than 6cm.

Abstract Downlink data transmission of multi‐user indoor optical wireless communications and its corresponding fairness analysis is studied by the authors. It is assumed that access points (APs) may use infrared beam (IR‐beam) laser or light emitting diodes (LEDs) for data transmissions. For the case of APs with IR‐beams, since the bandwidth of the transmitted optical signal can be very large than that of the LED’s, a typical time‐division multiple access (TDMA) scheme is utilised to serve multiple users and the respective achievable rates are derived. Then, for a general fairness‐scheduling utility function with the capability of adjusting the degree of fairness known as α‐proportional fairness, optimal time‐sharing coefficients are analytically derived in closed‐forms. To compare the performance of the IR‐based communications for the LED‐based APs, two non‐cooperative and cooperative data transmission schemes are also studied and the corresponding achievable rates are presented based on the classical superposition coding. Finally, to compare the performance of the two types of APs, per user data rate of the proposed systems are compared through numerical results for different scenarios to highlight advantages and drawbacks of the two types of APs. Also, by considering the Jain's index as a fairness metric, the impact of the system parameters on the fairness is discussed through numerical results.

Abstract The intractable brittleness and opacity of the crystalline semiconductor restrict the prospect of developing low‐cost imaging systems. Here, infrared visualization technologies are established with large‐area, semi‐transparent organic upconversion devices that bring high‐resolution invisible images into sight without photolithography. To exploit all photoinduced charge carriers, a monolithic device structure is proposed built on the infrared‐selective, single‐component charge generation layer of chloroaluminum phthalocyanine (ClAlPc) coupled to two visible light‐emitting layers manipulated with unipolar charges. Transient pump‐probe spectroscopy reveals that the ClAlPc‐based device exhibits an efficient charge dissociation process under forward bias. This process is indicated by the prompt and strong features of electroabsorption screening. Furthermore, by imposing the electric field, the ultrafast excited state dynamic suggests a prolonged charge carrier lifetime from the ClAlPc, which facilitates the charge utilization for upconversion luminance. For the first time, >30% of the infrared photons are utilized without photomultiplication strategies owing to the trivial spectrum overlap between ClAlPc and the emitter. In addition, the device can broadcast the acoustic signal by synchronizing the device frequency with the light source, which enables to operate it in dual audio‐visual mode. The work demonstrates the potential of upconversion devices for affordable infrared imaging in wearable electronics.

Abstract Polarization dynamics in spin‐polarized vertical‐cavity surface‐emitting lasers (spin‐VCSELs) with high birefringence have recently been demonstrated to offer very high potential for optical data‐transmission systems that outperform their counterparts based on conventional direct current modulation by far. For polarization dynamics in spin‐VCSELs, the birefringence determines the resonance frequency and thus the modulation bandwidth. In previous work, birefringence was controlled using mechanical strain, which lacks the ability to be integrated in standard VCSEL manufacturing processes. In this work the polarization dynamics of a VCSEL with an integrated birefringence control mechanism is demonstrated based on custom designed integrated surface gratings. It is found that, despite the surface grating which is commonly known to stabilize the polarization, the presented spin‐VCSELs are able to generate polarization oscillations with frequencies corresponding to the birefringence induced by the surface grating and show polarization dynamics up to 68 GHz.

Abstract A novel method that converts blue light into the white‐light for illumination and provides the high‐speed visible light communication link is introduced. Typical phosphors for creating white‐light cause low bandwidths and restrictions on changing correlated colour temperatures. The proposed method deals with such issues by utilising combinations of photo‐luminescence lights from cost‐effective fluorescent acrylic sheets. Characteristics of the light generated from the proposed method show that white‐lights with various correlated colour temperatures can be straightforwardly generated whilst providing orders of magnitude higher bandwidth than that from the conventional approaches using the phosphors. A high‐speed white‐light visible light communication demonstration based on a blue laser‐diode and the fluorescent acrylic sheets is presented, showing the data‐rate of 2.16 Gb/s with a bit‐error‐rate less than 3.8 × 10−3 by using an optical orthogonal frequency division multiplexing scheme.

Abstract Pixelated two‐dimensional (2‐D) optical wireless communication systems, with intensity‐modulation and direct‐detection (IM/DD), are capable to transmit data at high data rates by modulating the data into image intensities at the transmitter. Frequency division modulation (FDM) and space‐domain modulation (SDM) are two common modulation schemes in a 2‐D pixelated system. Generally, FDM is preferred because FDM benefits from the capability of controlling the spectrum of transmitting signals so that the output signal could be shaped according to the characteristics of a particular optical channel. However, the computational complexity of FDM is relatively high and complex computation is needed at both the transmitter and the receiver. In this work, a fast orthogonal frequency‐division multiplexing (FOFDM) modulation which employs 2‐D inverse discrete cosine transform (IDCT2) instead of 2‐D inverse Fourier transform (IFFT2) is presented. As the image intensities must be real and positive, two schemes are hereby introduced to generate unipolar image intensities. The proposed FOFDM is simulated and discussed in terms of key characterisations including the signal spectrum, spectral efficiency, peak to average power ratio (PAPR), bit error ratio (BER) and computational complexity. Compared with traditional spatial orthogonal frequency‐division multiplexing (OFDM) based on IFFT2, the proposed FOFDM has similar BER performance, twice the spatial efficiency for the same constellation size, lower computational complexity and a much simpler structure in the transmitter.

Abstract Satellite‐based, long‐distance free‐space quantum key distribution has the potential to realise global quantum secure communication networks. Detecting faint quantum optical pulses sent from space requires highly accurate and robust classical timing systems to pick out signals from the noise and allow for reconciliation of sent and received key bits. For such high‐loss applications, a fault‐tolerant synchronisation signal coding and decoding scheme based on de Bruijn sequences is proposed. A representative synchronisation timing system was tested in laboratory conditions and it demonstrated high fault tolerance for the error‐correction algorithm even under high loss. The performance limitations of this solution are also discussed, and the maximum error tolerance of the scheme and the estimated computational overhead are analysed, allowing for the possibility of implementation on a real‐time system‐on‐chip. This solution not only can be used for synchronisation of high‐loss channels such as channels between satellites and ground stations but can also be extended to applications with low loss, high bit error rate, but require reliable synchronisation such as quantum and non‐quantum communications over terrestrial free space or fibre optic channels.

Abstract A large area photo‐diode based homodyne detector for free‐space quantum coherent communication is reported. The detector's performance is studied in terms of the detection bandwidth and electronic noise for shot‐noise limited quantum signal detection. Using large area photo‐diodes increases the signal collection efficiency from turbulent atmospheric channels, in comparison with thetypical fibre‐based free‐space homodyne detectors. Under identical atmospheric turbulence and receiver aperture conditions, over a 700‐km free‐space link at 90° elevation angle, our homodyne detector based on a diameter of 1mm photo‐diode experiences 0dB loss due to turbulence, while a 10‐um fibre‐based detector experiences 13.5dB of signal loss.

With the development of modern weapon techniques, radio frequency integrated technology has attracted widespread attention as a key technology to improve the informationalised level of missiles. Radar and communication are two typical electronic types of equipment, and their integration can support and promote the development of radio frequency integrated technology. In this study, experimental verification of an integrated radar–communication system is carried out. Firstly, the key technologies to achieve radar–communication integration are theoretically analysed. The solutions of the key issues, including signal separation, time synchronisation and frequency synchronisation, are proposed. Furthermore, a radar–communication demo is implemented and the experimental verification is carried out here to verify the feasibility of the proposed methods.

Fast Fourier transform (FFT) and inverse FFT (IFFT) are the fundamental algorithms at the heart of optical orthogonal frequency division multiplexing (OOFDM) transceivers. The high digital signal processing (DSP) complexity has become one of the most significant obstacles to experimentally demonstrating real-time high-capacity OOFDM transceivers. In this study, extensive numerical explorations are undertaken, for the first time, of the impacts of each individual transceiver DSP element on the inverse error vector magnitude (IEVM) performance of the OOFDM transceivers incorporating full-parallel pipelined FFT/IFFT architectures. More importantly, FFT/IFFT stage-dependent minimum bit resolution maps are identified, based on which minimum bit resolutions of individual DSP elements of various FFT/IFFT stages can be easily selected according to chosen analogue-to-digital converter/digital-to-analogue converter resolutions. The validity and high accuracy of the identified maps are experimentally verified in field programmable gate array (FPGA)-based platforms. In addition to great ease of practical OOFDM transceiver designs, the maps also significantly reduce the FPGA logic resource usage without degrading the overall transceiver IEVM performance.