Visible Light Communication (VLC) benefit from array reception, which improve the receiver sensitivity, extend the transmission distance, and enhance the link reliability in mobile applications. In this paper, we design a VLC receiver architecture centered on a Silicon Photomultiplier (SiPM) array. To address the joint time-varying effect produced by transmitter and array position displacement, a two-step shot-noise-aware signal-processing framework at the receiver-side is developed. Then, a threshold-select detectability control for independent, power-invariant noise is presented, where a minimum detectable-power threshold per-pixel for the SiPM and an upper bound on the shot-noise fraction are imposed to select valid pixels. Building on these results, we propose the Edge Intensity Gradient Detection (EIGD) algorithm, which couples threshold detectability witDh noise-controlled weighting and outperforms classical array combining schemes under signal-dependent noise. The end-to-end performance of EIGD is validated by simulations and experiments, showing order-of-magnitude gains for EIGD over classical array schemes -10 to 10 dBm. EIGD improves the received performance by 10.36 dB and increases the Field-of-View (FoV) by 7.52 degrees. With the help of an SiPM array reception, the approach provides a reproducible, engineering-ready path to high-reliability VLC in industrial settings.

This paper proposes a dual-spectrum communication strategy for Industrial Internet of Things (IIoT) scenarios that integrates visible light communication (VLC) and ultraviolet communication (UVC). In the proposed approach, VLC leverages existing lighting infrastructure to deliver low-cost, short-range access, while UVC provides reliable backup in VLC dead zones. Given stringent delay requirements in IIoT, finite-blocklength coding is introduced to minimize end-to-end latency. Based on short-packet information theory, the system's achievable rate is analyzed, and the optimal rates under different channel conditions are determined via simulation. An adaptive large dynamic-range transmission scheme that combines UVC and VLC is designed. The spatial distribution of the rate field is characterized for the hybrid transmission strategy. We conduct bit-error-rate tests in an industrial workshop to validate the performance of the proposed approach, particularly its adequate coverage of UVC in VLC dead zones. It has been demonstrated that UVC can achieve a rate of 0.30 bits/symbol within VLC dead zones.

In this paper, we propose a novel computational method, termed Monte Carlo Integration with Common Volume Sampling (MCI-CVS), which enables direct photon sampling within the common scattering volume. This approach significantly accelerates the convergence of optical wireless scattering channel simulations. Although each sample in MCI-CVS incurs approximately 3.74 times the computational cost of conventional methods, numerical results for ultraviolet scattering channels demonstrate that it reduces the required number of samples by a factor of 1,000 compared with Monte Carlo Integration with Importance Sampling (MCI-IS). As a result, MCI-CVS achieves an overall efficiency gain of approximately 267.3 times faster than MCI-IS and about 1,206 times compared to the baseline Monte-Carlo Simulation (MCS) method. Furthermore, the proposed method effectively addresses inefficient photon path sampling in infrared scattering channels, where low scattering and absorption coefficients degrade sampling efficiency and thus result in slow convergence. By incorporating photon path reuse, MCI-CVS also enables fast generation of two-dimensional scattering fields on a standard personal computer.

Incremental optical encoders are widely used as photoelectric sensing components in direct current (dc) motor servo systems, but their inherent susceptibility to optical interference ultimately poses a critical threat to system stability and reliability in the Internet of Things (IoT) applications. This article focuses on the photoelectric security of incremental optical encoders under laser injection, characterizes the inherent photoelectric vulnerabilities of incremental optical encoders, and proposes an equivalent mathematical model based on transfer function theory. Based on this model, three possible photoelectric vulnerabilities are presented and the injection frequency leading to the worst case is derived. The motor speed after injection exhibits an inversely proportional relationship with the duty cycle of the injection signal for precise injection. Aiming at these vulnerable characteristics, a security enhancement strategy based on signal compensation is proposed to eliminate the influence of laser injection. A method for simulating the coupling of photoelectric signals is developed to simulate laser injection. Through simulation and experimental analysis, the correctness and rationality of the model and theory are verified, and the reliability of the security enhancement strategy under the worst case is proved. The fitting error of motor speed remains within 2% for precise injection. After implementing protection, the average speed error remains within 2.8%. This research aims to draw attention to the vulnerability of incremental optical encoders and provides insights for enhancing their security.

The convergence of photonics and artificial intelligence is driving 6G and future communication systems toward Terabit-per-second (Tb/s) data rates, sub-millisecond latency, and ubiquitous intelligence. This evolution imposes stringent demands on Analog-to-Digital Converters (ADCs), challenging their sampling rate, resolution, bandwidth, and flexibility. This paper provides an overview of Photonic ADCs (PADCs), positioning them as important technologies for ultra-high-bandwidth optical interconnections and networks underpinning the 6G vision. Particularly, this work first quantifies ADC performance requirements in critical 6G optical scenarios. Then, we examine inherent physical limitations in conventional Electronic ADCs (EADCs) that make it increasingly difficult to achieve such metrics. Consequently, meeting these demands calls for a paradigm shift beyond established electronic frameworks. A comprehensive analysis of PADC architectures highlights their performance advantages over EADCs. These advantages stem from the intrinsic properties of photonics in speed, bandwidth, and jitter robustness. A dedicated case study on immersive extended reality, a quintessential 6G optical application, demonstrates the capability of a reconfigurable PADC architecture to process Tb/s-level real-time burst data while adaptively optimizing power-performance trade-offs. The accompanying simulation results suggest these advantages over adaptive EADC designs. Finally, we identify key challenges hindering PADC deployment and propose future research directions across device-, architecture-, and system-level innovations.

This paper studies the constellation optimization approach for multiple-input multiple-output (MIMO) visible light communication (VLC) systems with signal-dependent noise (SDN). We propose a constellation optimization method aiming at minimizing the system pairwise error probability. In order to obtain the transmitter constellation, we design the demapping rules from the perspective of energy efficiency and illumination uniformity. For the scenario where receiver randomly moves, the constellation lookup table is proposed to transform real-time optimization into table lookup operation, which effectively reduces the real-time computational complexity. Simulation results show that the optimized constellation leads to lower symbol error rate (SER) than the method of maximizing minimum Euclidean distance. In addition, the constellation lookup table operation shows negligible SER performance degradation.

Joint communication and positioning are increasingly demanded in mobile scenarios. But related works concerning integrated visible light communication and positioning systems mainly focus on the unilateral performance optimization, which restricts the efficiency and integral performance of the systems. This Letter exploits the cooperative enhancement mechanism between communication and positioning and proposes a cycling system framework to jointly implement the communication and positioning. An iterative method is designed to perform the mutual enhancement of positioning accuracy and received signal intensity by the system. Experimental results show that a positioning accuracy of 3.62 cm and a signal intensity improvement of 3-7 dB can be simultaneously achieved.

In this paper, we propose a robust received signal strength (RSS)-based indoor visible light positioning (VLP) scheme under limited receiving field-of-view (FOV). The position estimation in the time domain is complicated, and the time-frequency transform is first performed on the received time-domain signal to establish an equivalent frequency-domain RSS model, which simplifies the signal representation and problem solving. To realize robust VLP under limited receiving FOV, we consider the joint estimation of the receiver coordinate, light emitting diode (LED) validity indicator vector, signal phase vector and receiving coefficient based on the frequency-domain RSS vector. The original estimation problem is equivalently transformed into the optimization problem that maximizes the angle between the valid RSS modulus vector and the valid RSS feature vector. Experimental and simulation results verify the effectiveness of the proposed scheme under limited receiving FOV. Specifically, experimental results show that the proposed VLP scheme achieves a stable positioning accuracy below 5 cm under limited receiving FOV in a 60 cm x 60 cm positioning region with transceiver height 150 cm.

The capability of real-time mobile communication is highly desirable for underwater applications. However, there have been few reports on the underwater visible light communication (UVLC) systems with the ability to move, as their distance of reach is limited to a few meters and often rely on offline signal processing. In this paper, we propose a dynamic counting threshold (DCT)-based system for real-time underwater mobile communication to extend the reach beyond traditional adaptive feedback threshold (AFT)-based system. In the experiments, we achieved real-time underwater mobile communication at 2.0 Mb/s with a distance of reach up to 60 m under tap-water conditions. The proposed DCT-based system achieved a dynamic range of 15 m, representing a 5.8-fold improvement over the AFT-based system. In addition, we also demonstrate the real-time video transmission, showing that the receiver can move at a speed of 0.35 m/s while maintaining a BER below the FEC threshold at the same time.

Objective The integration of multiple-input multiple-output visible light communication (MIMO VLC) and intelligent reflecting surface (IRS) technologies shows great potential for enhancing communication capacity and coverage. However, traditional optimization methods face challenges such as high computational complexity, severe multipath interference, and inefficient resource allocation, making it difficult to approach the theoretical upper bound of the system achievable sum rate under practical conditions. To address these limitations, we aim to design a low-complexity joint optimization algorithm for IRS configuration and precoding matrix design. By jointly optimizing the phase control of IRS reflective units and the spatial resource allocation of the precoding matrix, the proposed algorithm significantly reduces computational overhead while overcoming bottlenecks such as signal coverage limitations and insufficient interference suppression in complex environments, thus maximizing the system achievable sum rate. In this paper, we not only provide an efficient and reliable performance optimization framework for MIMO VLC systems but also promote the cost-effective deployment of IRS technology in smart transportation, industrial IoT, and other scenarios, offering both theoretical innovation and practical value. Methods Building on the conventional MIMO VLC system model, we introduce an IRS and employ discrete matrices to characterize the interactions among LEDs, IRS units, and photodetectors (PDs). A joint optimization problem for IRS configuration and precoding matrix design is formulated with the goal of maximizing the system achievable sum rate. However, the resulting formulation is a highly non-convex mixed-integer optimization problem. To resolve this, the orthogonality constraints of IRS transceiver correlation vectors are first simplified based on the optical geometric characteristics of the MIMO-IRS system. Subsequently, an analytical expression for the optimal power allocation coefficients is derived using singular value decomposition (SVD)-based precoding to maximize total system capacity. Leveraging the orthogonal properties of IRS-reflected channels and matrix perturbation theory, a low-complexity approximate SVD of the channel matrix is proposed. This enables the design of a low-complexity traversal search algorithm for IRS configuration that efficiently identifies potential optimal regions. Within these regions, precise SVD operations are applied to achieve the maximum achievable sum rate. Results and Discussions In this paper, we address the complexity of jointly optimizing IRS configuration and precoding in MIMO VLC systems by proposing a low-complexity joint optimization algorithm. A unified optimization framework integrating IRS configuration and SVD precoding is established, enabling collaborative signal coverage enhancement and interference suppression. This contrasts with traditional approaches that optimize IRS configuration and precoding separately. By exploiting the orthogonality of IRS-reflected channels and matrix perturbation theory, a low-complexity approximate SVD of the channel matrix is developed. This approach maintains high precision in channel capacity calculation while significantly improving computational efficiency. Furthermore, a fast traversal algorithm evaluates all IRS configuration candidates using simplified SVD to estimate achievable sum rates, avoiding the local optimum trap inherent in heuristic search methods. As a result, the proposed method achieves near-global optimality while maintaining minimal computational overhead. Conclusions The proposed low-complexity joint optimization algorithm for IRS configuration and precoding matrix design strikes an optimal balance between search efficiency and accuracy. By rapidly traversing potential optimal regions and applying precise SVD operations, the algorithm achieves a near-maximum system achievable sum rate. The computational complexity of a single traversal is reduced by an order of magnitude compared to conventional SVD-based methods. Simulation results demonstrate that the proposed algorithm significantly outperforms traditional benchmark schemes in achievable sum rate, approaching global optimality while maintaining low computational complexity.

GaN-based light-emitting diodes (LEDs), which are regarded as one of the most important alternative light sources for visible light communication (VLC) systems, have been constrained by limited bandwidth. In this work, a vertically structured micro-LED array with trapezoidal AlInGaN electron blocking layer (EBL) has been proposed. This design weakens the blocking effect of charge carrier leakage through the EBL structure, improves the non-radiative recombination efficiency, significantly shortens the carrier lifetime, and thus enhances the -3 dB bandwidth. The as-prepared micro-LED arrays exhibit a light output power of 24.4 mW and a -3 dB bandwidth of 643 MHz with a transmission rate that can reach up to 4.2 Gb/s. The proper design of the EBL structure will expedite the implementation of GaN-based LEDs in the VLC system.

This study presents (Unmanned Aerial Vehicle-Free Space Optics) UAV-FSO, a drone-to-ground communication technology designed to enhance maneuverability and flight duration by reducing the drone's effective payload weight and power consumption. We introduce a multi-pixel joint likelihood estimation detection receiver method based on Silicon Photomultipliers (SiPM), emphasizing the system's high sensitivity to pointing errors. The evaluation of SiPM-based drones in FSO communications considered the impact of factors like communication distance, pointing errors, and reception angle. We developed a reception signal model for multi-pixel channels, incorporating atmospheric turbulence and multi-pixel channels reception. We analyzed the signal-to-noise ratio (SNR) and bit error rate (BER) under different pointing errors. Simulations validated the accuracy of our analytical models, and further analysis was conducted on the relationship between optimal system design and pointing errors. The simulations demonstrated that the SiPM-based method provides superior reception angles and increased channel capacity, showing enhanced robustness against pointing errors. Hence, this method offers a vital performance optimization strategy for UAV-FSO communication technology. In conclusion, the study proposes a SiPM-based multi-pixel joint likelihood estimation receiver method, evaluates its effectiveness in UAV-FSO communication technology, and confirms its accuracy and robustness through simulations, opening new avenues in drone communication applications.

The delay jitter in the visible light communication (VLC) network is analyzed in this work. First, the delay jitter under single-user and multi-user scenarios is investigated and a closed-form expression is obtained, whose accuracy is verified by simulation. Second, through analyzing the delay jitter under two typical indoor light emitting diode (LED) layouts, we find that the mean user delay jitter under cellular layout is a little lower than that of square layout. Then, we study the delay jitter for mobile users, and the relationship among user movement speed, arrival rate and delay jitter in different scenarios. The delay jitter performance is evaluated assuming perfect coordinated multiple points (CoMP) transmission strategy in VLC network. Simulation results show that in the context of VLC, static users can experience an average delay jitter of up to $10^{-6}$ s, while mobile users can experience an average delay jitter of up to $10^{-5}$ s. Therefore, VLC network can provide users with good delay jitter performance and customized services to meet the higher service quality requirements of future users.

The industrial Internet of Things (IIoT) environment involves multiple production items, such as robots and automated guided vehicles (AGVs), among others. The practical industrial scenario requires communication of production items while also considering mobile recognition and positioning. Hence the perception approach requires not only combining communications but also realizing the recognition and positioning of multiple communication cells. This Letter proposes a multi-optical cell recognition and positioning framework based on LED image features. The LED images are obtained by a CMOS image sensor. This framework utilizes convolutional neural networks (CNN) to train LED images for recognition between multiple optical cells and locates precise positions through region recognition within the optical cells. The experimental results show that the mean accuracy of the CNN model for two LED cells is above 99%, and the mean accuracy of region recognition within the optical cell is as high as 100%, which is significantly better than other traditional recognition algorithms. Therefore, the proposed framework can provide location-aware services for visible light communication and has a wide application prospect in IIoT.

Reconfigurable intelligent surfaces (RIS) supply high-speed and in-depth coverage wireless networks for visible light communication (VLC) systems, improving the system adaptability to mobile scenarios. But the angle-related efficiency loss caused by the diffraction effect of RIS as well as the angular response of the lens-enhanced optical receiver severely affects the practical performance of the RIS-assisted VLC system, which have not draw the attention of researchers. By the influences of these adverse properties, the beam angle configuration method should be further explored. In this paper, a RIS-assisted optical receiver model that jointly considering the angle-related characteristics of both the RIS reflector and the receiver is proposed. Based on the model, the receiver property is characterized, and the beam angle optimization to achieve the maximum optical power is presented. The results of simulations verify the validity of the obtained optimal reflected angle, and test the practical detecting range of the optimally configured RIS-assisted receiver.

Covert communications hide the information transmission from a watchful adversary (Willie) while ensuring a satisfactory decoding performance at a legitimate receiver (Bob). In this paper, we propose a covert transmission scheme based on narrow signal waveband and nonlinear suppression effect of avalanche photodiodes (APDs) for water-to-air (W2A) optical wireless communication (OWC) systems. Narrow signal waveband is selected based on a given wavelength selection pattern which is negotiated by the transmitter and receiver. Willie’s detection performance is investigated under APD characteristics and ambient radiation. Under the covertness constraints on Willie’s detection performance, the covert throughput between Alice and Bob is maximized by optimizing the power and blocklength of transmitted signals. Except for the case of Alice with knowledge of Willie’s position and optical filter passband-width, we explore a more practical scenario where the knowledge is not available to Alice. The optimal passband-width of Willie’s filter is calculated by taking into account both overlapped waveband and detection performance, and a covert region is established to limit Willie’s detection range. Numerical and experimental results indicate that strong ambient radiation and narrow signal waveband can enhance the signal covertness significantly.

In general, visible light communication (VLC) uses LEDs as transmitters. However, LEDs can serve as receivers to construct a simple duplex VLC system that uses only two LEDs instead of one LED and one photo-diode (PD). There is a lack of effective equivalent analysis models for characterizing and evaluating the inherent behavioral characteristics of LEDs used as receivers. This paper presents an equivalent analysis model for GaN LEDs as receivers. First, based on the proposed receiving equivalent circuit model, a third-order signal transmission mathematical analysis model is established, revealing the transmission relationship between the photocurrent and output voltage. Further research is conducted on the impact of parameter changes on the bandwidth, and the model can be simplified into a first-order low-pass mathematical analysis model under specific conditions, providing theoretical support for improving the bandwidth of LED receiving applications. The experimental results also confirm the theoretical predictions. This research result holds significant importance for revealing the intrinsic mechanisms and the improved optical communication performance of LEDs for effective reception.

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