In optical wireless communication (OWC) systems, the limited modulation bandwidth of commercial light-emitting diodes (LEDs) leads to severe inter-symbol interference (ISI). Conventional orthogonal frequency-division multiplexing (OFDM) relies on pilot-assisted channel estimation and equalization to mitigate this effect, at the cost of increased processing latency and pilot overhead. In this paper, we experimentally demonstrate a low-latency, channel state information (CSI)-free transmission scheme based on virtual polarization modulation (VPM) over a DCO-OFDM-based OWC link. By mapping data symbols onto the three-dimensional (3D) Poincaré sphere and assigning them to adjacent subcarrier pairs, the VPM scheme can remove the common channel gain in the Stokes space. Experimental results show that the 16-VPM scheme operates without pilot insertion and equalization. Despite subcarrier pairing, the proposed scheme maintains the bit error rate (BER) below the forward error correction (FEC) threshold under a 30 MHz transmission bandwidth, with an LED 3 dB bandwidth of 10 MHz. Compared with equalized 16-QAM, it exhibits improved robustness, making it a promising solution for latency-sensitive OWC applications.

In this work, the intelligent reconfigurable surface (IRS) has been proposed to relax the requirement of line-of-sight (LOS) channel gain of the cell-edge user in the non-orthogonal multiple access visible light communication (NOMA-VLC) system, in which the physical layer security (PLS) of the cell-edge user has been enhanced by optimizing the power allocation method at the transmitter. Besides, different mobility models have been adopted for the paired NOMA users to cope with the real indoor environment. The optimal power allocation method and non-silent probability (NSP) of the transmitter are mathematically derived by considering different cases of users’ channel gains. Through simulations, performances of the secrecy rate of the cell-edge legitimate user and NSP of the transmitter are analyzed in detail, where the impacts of the main system parameters are also studied. This work can serve as a good reference for further study of the secure VLC system.

This article presents a novel push-pull differential clamping Class E (PPDC-Class E) inverter and S/SP impedance compression compensation for wireless power transfer (WPT) systems. The proposed inverter incorporates voltage and current stress regulation and voltage-boosting capabilities, enabling configurable low stress levels and high voltage gain. Its auxiliary switches ensure load-independent zero-voltage switching (ZVS) and soft turn-off with minimal power dissipation. Furthermore, a systematic design approach for S/SP compensation is proposed to achieve impedance compression within WPT systems. Through parametric configuration, the voltage stress can be reduced to below 1.5 V-DC, the minimum current stress can approach I-DC, and the AC voltage gain can exceed 3. Furthermore, the proposed S/SP compensation extends the ZVS load range of the inverter's power switches. Finally, a 1-MHz, 500-W prototype has been constructed, confirming its effectiveness. The results demonstrate that the PPDC-Class E inverter exhibits wide-load-range ZVS operation and boost characteristics, with configurable switching voltage and current stresses through parameter selection. This inverter design achieves a peak efficiency of 97%.

This paper investigates reliability-constrained effective covert throughput for UWOC systems with Bob and Willie. By considering location-aware fading, outage probability, KL-divergence covertness, and duty-cycle transmission, numerical results reveal key reliability-covertness tradeoffs.

In this work, the sum rate of one non-orthogonal multiple access (NOMA)-based visible light communication (VLC) system enhanced by optical simultaneous transmission and reflection reconfigurable intelligent surface (OSTAR-RIS) has been investigated with the dynamic human blockages described by a random waypoint (RWP) mobility model for the first time. By jointly optimizing the user power allocation and the reflection and transmission coefficients of OSTAR-RIS elements, a sum rate maximization problem considering the impact of dynamic human blockages is formulated under practical constraints. To solve this non-convex optimization problem, the original problem is decomposed into the power allocation and OSTAR-RIS assignment subproblems. The power allocation subproblem is addressed via variable transformation and first-order Taylor series approximation, then it is solved by a penalty-assisted successive convex approximation (SCA) method. The OSTAR-RIS assignment subproblem is tackled by means of a greedy strategy and the alternating optimization (AO) algorithm is adopted to iteratively update the power allocation and OSTAR-RIS coefficients. Simulation demonstrates that, under various system settings, the proposed scheme significantly outperforms the benchmark approaches in terms of the system sum rate. This work will benefit the research of resource allocation of indoor NOMA-VLC system.

The self-sweeping effect originates from dynamic gratings established when a doped fiber within a laser resonator is subjected to a standing-wave field. In the temporal domain, this effect can be classified into two distinct regimes: the microsecond-pulse (MP) state and the continuous-wave (CW) state, with the principal criterion of differentiation being whether the doped fiber responsible for dynamic grating formation is pump-excited. Elucidating the underlying generation mechanisms of these two self-sweeping laser regimes and realizing controllable switching between their temporal states constitute a critical research focus in this field. In this work, a CW self-sweeping output was achieved by inducing dynamic gratings in an unpumped doped fiber (UDF) incorporated within a unidirectional ring cavity, and controllable transition from the CW regime to the MP self-sweeping regime was subsequently realized by introducing pump excitation to the UDF. Systematic experiments were conducted under four conditions by independently regulating the pump powers of the gain-doped fiber (GDF) and UDF (pumping only GDF/only UDF, fixing GDF pump power to adjust UDF power, fixing UDF pump power to adjust GDF power). Furthermore, a theoretical model of the CW self-sweeping laser was formulated based on rate equations. By systematically varying the gain of the UDF, the transition mechanism from CW to MP self-sweeping operation was elucidated. Both theoretical and experimental results demonstrate that progressively increasing the UDF pump power induces a regime transition of the laser from the CW state to the MP state, accompanied by a pronounced enhancement of the pulse repetition rate throughout the transition. This investigation overcomes the inherent limitation of conventional lasers restricted to a single temporal operating mode, achieves controllable switching between CW and MP outputs, and thereby provides a novel paradigm for the development of high-performance self-sweeping laser sources.

Underwater wireless optical communication (UWOC) has emerged as a promising solution for short-range high-speed underwater data transmission in recent years. For what is believed to be the first time, this work presents a comprehensive secrecy performance analysis of a downlink non-orthogonal multiple access (NOMA)-UWOC system over the composite vertically stratified Weibull-generalized gamma (WGG) oceanic fading channel, in which the impacts of path loss, underwater turbulence, pointing errors, and angle-of-arrival fluctuations are considered. Specifically, the closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the vertically stratified WGG fading channel coefficient are derived analytically. Then, on the basis of these derivations, analytical frameworks for the key secrecy performance metrics, including secrecy outage probability, strictly positive secrecy capacity, and effective secrecy throughput, are obtained, taking into account the residual interference from successive interference cancellation (SIC), which are validated through Monte Carlo simulations. Finally, the effects of the number of layers, the thermohaline gradient and air bubbles, the residual power factor of imperfect SIC, the transceiver misalignment, and the angle-of-arrival deviation are investigated on this UWOC system. The presented results give valuable insights into the practical aspects of deployment of UWOC networks.

In this work, a satellite cluster-to-ship free space optical (FSO) system model over the composite doubly inverted gamma-gamma (IGGG) atmospheric turbulence channel has been proposed, considering the effects of path loss and ship mobility for what we believe is the first time. To quantify the impacts of satellite cluster orbital configurations, minimum separation distance (MSD), and ship velocity in different atmospheric turbulence regimes, the closed-form expressions of outage probability (OP), average bit error rate (ABER), and ergodic capacity (EC) have been derived and verified by Monte Carlo simulations. Results show that although the OP, ABER, and EC performances of both linear and circular orbital configurations will deteriorate as the atmospheric turbulence worsens, the circular orbital configuration consistently outperforms the linear orbital configuration. Besides, reducing the MSD of the satellite cluster will further enhance the system performances while it would be degraded as the ship velocity increases. Specifically, one communication experiment between a low Earth orbit (LEO) satellite and a ground station is carried out under pointing correction and fine-tracking closed-loop control, in which the received signal-to-noise (SNR) logs are recorded to obtain the practical downlink OP, therefore verifying the proposed theoretical OP model.

The paper proposes an inverse design method for the holographic metasurface antennas (HMSAs) to enhance the aperture efficiency (AE) based on deep learning. To overcome the limitations of scalar impedance modulation, a novel anisotropic tensor unit is introduced to achieve flexible wavefront control, but this inevitably brings high-dimensional optimization challenges. To address this, a differentiable cascaded surrogate model comprising a convolutional autoencoder and an electromagnetic response predictor is constructed. This framework enables the efficient optimization of tensor parameters within a compressed latent space via gradient descent to maximize the AE. Validated by a 12-GHz prototype, the measured results agree well with simulations, and an AE of 44.16% and peak gain of 18.36 dBi are presented. The proposed approach offers an effective solution for the AE enhancement of the HMSA.

In the field of wireless communications, the integrated communication and sensing system is quite essential for beyond fifth generation (B5G) and sixth generation (6G) communication. This work focuses on the optical intelligent reflecting surface-assisted (OIRS-assisted) integrated lighting, sensing and communication (LiSAC) system for the first time. Specifically, a joint optimization problem involving power allocation, slot selection and OIRS orientation-angle selection has been established to minimize the total transmitted power, which is mainly subject to the lighting, sensing and communication constraints. The lighting constraint is first transformed into power threshold constraint by solving the convex optimization problem only subject to lighting constraint. Then, the joint optimization problem is divided into two subproblems according to sensing and communication constraints. Through cyclic minimization algorithm (CMA) and successive convex approximation (SCA), these two subproblems are transformed into convex optimization problems. The multi-layer nested cyclic joint slot and angle selection and power allocation (MNC-JSASPA) and the low-complexity channel gain-based slot selection and power allocation (CGSSPA) algorithms are thus proposed to solve those convex problems. Simulation results show that introducing OIRS and enlarging the scale of OIRS can effectively improve the performance of LiSAC system with these two proposed algorithms. Both MNC-JSASPA and CGSSPA algorithms are very effective with different layouts of light source. In particular, compared with the benchmark algorithms, the MNC-JSASPA algorithm demonstrates the best performance while the CGSSPA algorithm with lower complexity shows comparable performance to that of MNC-JSASPA algorithm.

In dynamically varying optical wireless communication (OWC) links, conventional quadrature amplitude modulation (QAM) in optical orthogonal frequency-division multiplexing (OFDM) requires frequent channel estimation and equalization, incurring pilot overhead and processing latency. This paper proposes a virtual polarization modulation (VPM)-based direct-current-biased optical OFDM (DCO-OFDM) scheme that maps each data symbol onto the three-dimensional Stokes space and places its corresponding Jones vector across two adjacent OFDM subcarriers. Using a rotation-based analytical framework, closed-form symbol error rate (SER) expressions are derived for arbitrary spherical constellations, along with upper and lower bounds and high signal-to-noise ratio (SNR) approximations. The framework is further extended to practical OWC scenarios with frequency-selective channels and atmospheric turbulence. Monte Carlo (MC) simulations validate the theoretical results. The results show that under practical OWC impairments, VPM outperforms QAM with least-squares (LS) channel estimation and minimum mean square error (MMSE) equalization. At a target SER of 10^-5, 16-VPM achieves SNR gains of approximately 7.5 dB and 4 dB over equalized 16-QAM and 8-QAM, respectively, in frequency-selective channels, and a 6 dB advantage over equalized 16-QAM under atmospheric turbulence. By eliminating the need for channel state information, the proposed VPM-based DCO-OFDM provides a robust and low-latency solution for dynamic OWC links.

This study presents a high-efficiency wireless power transfer (WPT) system designed to overcome the severe eddy current losses and magnetic shielding effects inherent in sealed rotating metal cavities. Achieving a 1:1 distance-to-diameter ratio, the system integrates a multi-layered, high-permeability ferrite gradient magnetic circuit with a loss-optimized planar hollow-coil architecture. To mitigate quality factor degradation under weak coupling conditions, a symmetrical L-type dual-resonant network is employed to facilitate high-frequency impedance matching at a 500 kHz operating frequency. Comprehensive electromagnetic and thermal co-design ensures robust performance under continuous load. Experimental validation demonstrates an AC-AC transmission efficiency of 95.3% across a 30 cm air gap at a 5 kW power output. Furthermore, the system sustains a DC-DC efficiency exceeding 90.2% over a 0.5-5 kW operating range, effectively constraining the maximum temperature rise to 42.3 °C. Rotational coupling tests confirm extreme robustness to angular deviation, limiting efficiency fluctuations to within 1%. This electromagnetic-thermal collaborative design provides a highly reliable, maintenance-free alternative to mechanical slip rings for demanding aerospace and industrial rotary applications.

The increasing interests in integrating ultraviolet communication (UVC) into uncrewed aerial vehicles (UAVs) introduce novel security threats to terrestrial non-line-of-sight (NLOS) UVC systems, as aerial jammers can exploit line-of-sight links to disrupt communications. This letter investigates the average bit-error rate (ABER) performance of on-off keying-based terrestrial NLOS UVC systems under aerial jamming. The jammer transmits optical pulses with a random duty cycle, for which the probability density function is first formulated. The turbulence effect in the jamming link is modeled using a log-normal distribution, and a closed-form ABER expression is further obtained. Monte Carlo simulations validate the accuracy of the theoretical model. The influence of different jammer positions, beam widths, turbulence strengths, silent rates, and jamming-on durations on ABER performance is analyzed and discussed. Finally, the detection rate of random-duty-cycle jamming is compared with that of periodic jamming. This work contributes to the design of NLOS UVC systems under jamming conditions.

An integrated visible light positioning and communication (VLPC) system has been proposed on the basis of non-orthogonal multiple access (NOMA), in which the direct current (DC) and alternating current (AC) components of the signal are adopted for positioning and communication, respectively. Specifically, biphase coding, majority vote, and two-stage positioning strategies are introduced to mitigate message randomness, receiver noise, and fingerprinting errors. Besides, the achievable sum rate and energy efficiency (EE) are obtained, and the optimal DC power setting is derived to achieve the best communication performance. Results show that the positioning accuracy improves with the number of light-emitting diodes (LEDs) and as user moves closer to the room center, follows an inverted U-shaped trend with user height, and could achieve the same accuracy as the AC-based positioning method using metaheuristic algorithms but in less time. Moreover, under perfect and imperfect successive interference cancellation (pSIC/ipSIC), both the system sum rate and EE initially increase with DC power and then decrease. A small-scale experiment is also carried out to verify the proposed DC-based positioning method. This letter offers a good reference for VLPC system research.

In this work, the performance of dual-client free space optical (FSO) system with simultaneous transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) mounted by unmanned aerial vehicle (UAV) has been investigated under energy splitting (ES) protocol. Specifically, it is assumed that the path loss induced by atmospheric absorption and scattering is described by the Beer-Lambert’s law, the optical signal fluctuations due to atmospheric turbulence follow the inverted GG-Gamma (IGGG) distribution, and the random jitter of buildings and UAV follows Gaussian distribution, which would cause the geometric and misalignment losses (GML). The exact expressions of outage probability (OP) and ergodic capacity (EC) for each client as well as the joint outage probability (JOP) of this proposed system are derived with the help of Meijer G-function, and then the asymptotic expressions of OP and EC for the reflection client and transmission client are also presented, which are also verified by Monte Carlo simulations. Besides, the annealing algorithm has been adopted to optimize the outage performance of this system with the constraints of the deployment position and energy allocation coefficients of FSO communication system with UAV-mounted STAR-RIS. Furthermore, the effects of atmospheric turbulence intensity, random jitter intensity, and energy allocation coefficient on the system performance are analyzed. Results demonstrate that the OP and EC performances of the reflection and transmission clients are both positively correlated with the energy allocation coefficient. When the STAR-RIS is placed at the origin, the JOP will decrease as the value of transmission coefficient approaches that of the reflection coefficient. Moreover, to improve the OP performance of this system, the optimal location of the STAR-RIS is in close proximity to the transmitter with the optimal transmission energy coefficient about 0.7. This study will benefit the design and research of the advanced FSO system for 5G and 6G communication networks.

The impacts of many-body effects, which include the Hartree potential, exchange-correlation potential, depolarization effect, and excitonic effect, on the n-type periodic β-(Al0.3Ga0.7)2O3/Ga2O3 quantum cascade structure with four quantum wells of different widths have been theoretically investigated. The conduction band structure and wave functions of the device were obtained by iteration of the Schrödinger and Poisson equations to describe the bound-to-bound electronic transport processes. The results show that the many-body effects make a significant contribution to the energy band parameters, especially the energy level and wave function of subbands in the active wells. By considering many-body effects, the peak absorption coefficient increases from 6.14 × 10−4 to 1246.93 cm−1. The depolarization and excitonic effects lead to a peak response wavelength shift of approximately 1.33 μm. When the temperature increases from 77 to 300 K, the peak responsivity of the long wavelength infrared β-(AlGa)2O3/Ga2O3 quantum cascade detector (QCD) only decreases 22.87% and the peak response wavelength remains almost constant, indicating an excellent temperature stability. Moreover, the room-temperature dark current of proposed QCD is 1.46 × 10−15 A, which is much lower than that of QCDs based on some materials and operating at similar wavelengths. This work would benefit the research and development of β-(AlGa)2O3/Ga2O3 QCDs.

In this work, optical intelligent reflecting surface (OIRS) is introduced into the hybrid non-orthogonal multiple access (NOMA)/orthogonal frequency division multiple access (OFDMA) visible light communication (VLC) system with mobile users and dynamic blockages for the first time, to our knowledge. Specifically, the dynamic blockages are modeled by the random way-point (RWP) model, and two cases of movement patterns are considered for the mobility of users. The theoretical symbol error rate (SER) expressions for different users are derived and validated by Monte Carlo (MC) simulation, and one optimization problem is formulated with four critical parameters. A joint mirror array and power allocation (JMAPA) algorithm is then proposed to minimize the average SER. The superiority of the JMAPA algorithm is demonstrated by comparing the SER performance with other power allocation algorithms and different OIRS designs. Then, the impact of distance separation between APs on the SER performance is investigated with the JMAPA algorithm. Results show that with the assistance of OIRS, the SER performance of this hybrid system will be markedly enhanced, and compared to other bench algorithms and different OIRS designs, the JMAPA algorithm achieves superior SER performance and shows the best adaptability to different transmit power, while its effectiveness in optimizing the orientation of OIRS units is also validated. Moreover, the increases in the radius, height, and number of dynamic obstacles will degrade the overall SER performance with this algorithm while an increase in the velocity of the obstacles will enhance the SER performance in the dynamic environment. Furthermore, the distance separation between APs has an obvious effect on the SER performance.

This study successfully realized a single-frequency erbium-doped fiber laser operating at 1600.05 nm by harnessing fiber-based saturable absorber filtering effects. To mitigate adverse impacts of the fiber-based saturable absorber's length on laser loss, threshold, and cost, suitable fiber components were meticulously selected, facilitating the achievement of both single-frequency laser output and the desired power level. Spectral and frequency analysis revealed that the resultant single-frequency fiber laser demonstrates a specific power output range, with a maximum output power exceeding 10 mW. The average linewidth, measured using the delayed self-heterodyne method, was approximately 679.8 Hz, validated by the perfect Lorentz linear signal. During one hour of stability monitoring, the wavelength and power fluctuations were observed to be 1.51 pm and 0.082 %, respectively. Furthermore, we meticulously observe and quantify the laser spectrum and power dynamics during the experiment, and contrast the outcomes of various linewidth signals. This approach offers a novel perspective for observing and expressing the parameters of narrow linewidth lasers, particularly those equipped with extended fiber cavities.

In this article, a novel secondary reconfigurable S/SP (R-S/SP) compensation network and parameter design method are proposed. The proposed compensation network can reconfigure the S/SP circuits by switching to implement load-independent constant-current mode (CCM) and constant-voltage mode (CVM), respectively, without the need for communication. The derivation of a generalized design methodology is given in detail based on the two-port network transfer matrix approach. By adjusting the parameter factors, the R-S/SP topology can maintain both the zero-voltage switch (ZVS) characteristic in the Class-D inverter's wide load range and the stability of the voltage and current gains under misalignment tolerance. Also, the gains are tunable in this topology. Finally, a 0.6 MHz, 108 W inductive power transfer (IPT) prototype is developed with a CVM output of 72 V and a CCM output of 1.5 A. The experimental results show that load-independent switching of CCM and CVM can be implemented. The system can operate at a lateral offset of +/- 21%, with CCM gain fluctuations of less than 6.8% and CVM gain fluctuations of less than 9.9% over the full impedance range. The ZVS is realized throughout the process, and the system efficiency reaches 91.1% at maximum power.