Study On Optical Communications
Co-Editors-in-Chief
Shaohua Yu
2025
Volume: 51 Issue 4
16 Article(s)
Tao ZHANG, Hao LIU, Peilei ZHANG, Zheheng LIU, Guangrui SHI, and Xiping FAN

【Objective】Aiming at the problems of poor feature extraction and low fault diagnosis efficiency in the study of submarine cable vibration signals, a fault diagnosis method for submarine cable is presented based on the combination of energy entropy features, Grey Wolf Optimizer (GWO) algorithm and Extreme Learning Machine (ELM).【Methods】Firstly, the finite element simulation software is used to simulate the vibration velocity signals of submarine cable optical unit under different working conditions. Secondly, the vibration signal is decomposed into four Intrinsic Mode Functions (IMF) using the Empirical Mode Decomposition (EMD) algorithm. These IMFs capture the inherent characteristics of the signal. Subsequently, the energy entropy of each IMF component is extracted and calculated. The energy entropy is used as an indicator to construct the eigenvectors. Finally, the eigenvector samples under different working conditions are input into the classifier using GWO-ELM method to judge the operation state.【Results】With a sufficient number of samples and multiple calculations for averaging, it is concluded that the accuracy of this method for recognizing different conditions of submarine cable can reach 97.4%. The recognition time is as low as 0.968 5 s, and multiple comparison groups with different algorithms have been established. The results show that the proposed method has good performance in extracting signal features and fault diagnosis.【Conclusion】The method proposed in the paper can accurately identify the real-time working status with better fault feature extraction while significantly reducing the difficulty of measurement.

Aug. 10, 2025
  • Vol. 51 Issue 4 240145 (2025)
  • Lin SUN, Meng MAO, Lu ZHANG, Weiye WANG, Ning LIU, and Gangxiang SHEN

    【Objective】Over 99% international data are transmitted over optical submarine cables. However, the main challenges of optical submarine communications are the feeding power and mechanical size limitation. Coupled Core-Multi Core Fibers (CC-MCF) are well-suited for submarine cable systems with physical space limitations, as they offer higher spatial multiplexing density and serve as an effective key transmission medium for expanding capacity. One of the critical impairments limiting the enhancement of transmission performance in CC-MCF is Mode Dependent Loss (MDL). This paper focuses on the mechanism of MDL in transoceanic transmission using coupled MCF, aiming to investigate the impact of Spatial Mode Dispersion (SMD) in heterogeneous CC-MCF on the estimation and mitigation of MDL.【Methods】Specifically, by establishing a coupled 4-core transoceanic transmission model and conducting self-consistent validation, this study explores the evolution of the accuracy of MDL estimation based on Multiple In Multiple Out (MIMO) taps under different SMD conditions. Additionally, it also investigates, for the first time, the MDL mitigation performance of a space-time coding technique based on the Hadamard transform under the influence of SMD.【Results】The results indicate a low level of SMD coefficient below 10 ps/km is helpful to the efficient MDL estimation and mitigation. Moreover, the use of Space Time Coding (STC) has provided a 5.5 dB Q factor gain to our 4-core CC-MCF transmission system.【Conclusion】This paper provides a comprehensive analysis of the actual transmission characteristics of CC-MCF. Its findings offer valuable insights into the potential development of next-generation CC-MCF submarine cable communication technologies, particularly those aiming for high spatial multiplexing density.

    Aug. 10, 2025
  • Vol. 51 Issue 4 240262 (2025)
  • Hongqiang YAN, and Ming JIANG

    【Objective】As communication network technologies rapidly evolve towards the 6th Generation Mobile Communication Technology (6G), the future may see the emergence of an integrated internet of everything that covers space, sky, land, and sea scenarios. In this context, cross-water Visible Light Communication (VLC) has emerged as one of the key enabling technologies to support such a new network.【Methods】In this paper, we address the shortcomings of existing Water-to-Air (W2A) VLC systems with a Deep Learning (DL) aided Link Alignment (LA) scheme for a W2A-VLC system communication between Unmanned Aerial Vehicle (UAV) and Autonomous Underwater Vehicles (AUV), based on the proposed extended W2A (eW2A) VLC channel model. Upon the aligned optical link between the transmitter and receiver, we further design a signal detection scheme based on a wind speed estimator and a channel classifier operating in a channel with unknown wind speeds.【Results】The results show that the fitted eW2A channel model based on Lognormal and Gamma distributions matches well with the channel data generated by Monte Carlo simulations, accurately modeling the cross-water VLC channel. Simulation results show that under high Signal-to-Noise Ratio (SNR) conditions and different wind speeds, the angle estimation accuracy of the four angular layers located between 2~30° for the UAV can reach 100%. The results exhibit good convergence and can effectively support the UAV path decision-making in the DL-LA scheme. Additionally, in the wind speed range of 1~10 m/s, the Wind-speed Estimation (WE) and Channel Classification (CC) aided Symbol Detection (SD), namely the WE-CC-SD scheme, can work under untrained unknown wind speeds. This scheme can achieve a high accuracy of WE and a Bit Error Rate (BER) performance close to that achieved under ideal channel state conditions.【Conclusion】The above results validate the superiority of the proposed DL-LA and WE-CC-SD schemes over traditional methods. The findings can provide valuable references for the improvement and development of cross-water VLC technologies.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250001 (2025)
  • 【Objective】In bidirectional Underwater Wireless Optical Communication (UWOC) system, backscattering is one of the major factors which affect its stability. In a full-duplex UWOC system, such noise could be removed by optical filter in the receiver. However, because the transmission wavelength of filter would be“blue shift”with incident angle of light, the backscattering angle will affect the noise suppression performance.【Methods】In this paper, a theoretical model is constructed by Monte Carlo method to qualitatively study the angle distribution characteristics of backscattering noise and its influence on UWOC performance.【Results】The results show that, angle distribution of backscattering noise is relatively dispersed in full-duplex UWOC system with large divergence angle and filed. It has a great influence on the equipment whose transmitting wavelength is smaller than the receiving one. In engineering applications, without affecting the link establishment efficiency, equipment structural complexity, and effective communication distance of the UWOC system, the impact can be mitigated by appropriately reducing the communication transmission angle, receiver aperture, and field of view, increasing the spacing between the transmitter and receiver in the communication equipment, and enlarging the wavelength interval of the bidirectional optical signals. Using this method, a full-duplex UWOC system is built with about 50° transmitting angle and field based on 450 and 520 nm blue-green light. In the communication distance of 2.2~13.2 m, the file transmitting rates are 89.6 and 84.8 Mbit/s for the two transmission links respectively.【Conclusion】The research results in this paper are helpful to design a full-duplex UWOC system with large transmitting and receiving angles.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250003 (2025)
  • Yunpeng SUN, Guoxiang XU, Rendong XU, Huiling KANG, Chang WANG, and Wei YIN

    【Objective】Submarine cables, as a key enabler of global connectivity, carry over 99% of the world's communication data traffic. With the continuous growth of international communication services and the vigorous development of the marine digital economy, the capacity for transoceanic communication is facing a severe challenge. Currently, with the maturation of capacity-expansion technologies such as higher-order modulation, Wavelength Division Multiplexing (WDM), and Polarization Division Multiplexing (PDM), the bottleneck problem of traditional fiber-optic transmission capacity is becoming increasingly evident. As a new generation of Space Division Multiplexing (SDM) fiber, 200 μm fine diameter fiber can meet the future Pbit capacity demand and reduce the per bit cost of submarine optical cable system.【Methods】The article focuses on the research and development of key technologies for thin-diameter optical fibers. By leveraging the inherent characteristics of optical fibers, a residual length model for thin-diameter fibers is established, and the boundary conditions for the residual length of thin-diameter fibers in submarine cables are solved. At the same time, the three factor and four level orthogonal experimental design is used to optimize the fusion parameters of fine diameter fiber, and the optimal fusion parameter combination of fine diameter fiber is obtained by defining the one-time qualification rate of fiber fusion.【Results】Finally, the development of key technologies for the cabling of fine diameter fiber submarine cable is completed. The additional attenuation of fine diameter fiber cabling is less than 0.003 dB/km, which realizes the balance control between the additional attenuation of cabling and the reliability life. At the same time, the one-time qualification rate of fine diameter fiber fusion is controlled to be more than 90%, meeting the requirements of ultra long-distance transoceanic communication. The developed submarine cable has passed the key performance test of submarine cable recom-mended by International Telecommunication Union-Telecommunication Standardization Sector (ITU-T) G.976 and the 5 km deep sea trial test, and the change of light transmission performance is far less than 0.05 dB.【Conclusion】The performance indicators of the high fiber count and low additional attenuation fine diameter fiber submarine cable developed in this paper meet the technical requirements of submarine cable communication systems, providing important technical support for the development of the next generation of fine diameter fiber submarine communication systems.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250010 (2025)
  • Weijie DAI, Xiaofeng SU, Xiaoqian LIU, Liyan ZHANG, Tiankuo WEI, Jian SONG, and Yuhan DONG

    【Objective】Atmospheric and oceanic turbulence causes the mode fading of optical Orbital Angular Momentum (OAM), thus being one of the main factors that deteriorate the performance of OAM-based Free-Space Optical Communications (FSOC) systems. Anti-turbulence effect has long been a pursuit of researchers in the field of OAM-FSOC.【Methods】In the context of high-capacity optical wireless communication based on the OAM mode, turbulence causes symmetric diffusion of the OAM spectrum. Traditional turbulence mitigation schemes require complex wavefront sensing and combining solutions. However, in a partially coherent light field, the coexistence of twisted phase and vortex phase leads to an asymmetric diffusion behavior of the OAM spectrum, providing a new approach for turbulence mitigation. This work highlights the paradigm shift of information transmission inspired by asymmetrical OAM spectra, aiming to utilize the controllable asymmetry caused by the twist factor for mode augmentation. Based on this, we further propose novel mode encoding scheme at the transmitter and mode combining scheme at the receiver. The proposed schemes bring significant improvements in terms of the average capacity, aggregate capacity, and Bit Error Rate (BER) of OAM-FSOC systems.【Results】Numerical results show significant performance improvements consistent with theoretical predictions, including the actual capacity, capacity upper bound, and available link distance in turbulent channels, as well as the ability to suppress turbulence.【Conclusion】The proposed solution in the paper is not only the application of twisted partially coherent light fields in OAM-FSOC systems but also the utilization of the physical fact of controllable asymmetric diffusion of the OAM spectrum. The paper demonstrates the significant potential for the application of cutting-edge optical wave physics theories, exemplified by the regulation of twisted phase partially coherent light fields, in next-generation optical wireless communications.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250021 (2025)
  • Xuehua LI, Tong XI, Xin WANG, and Xiang HUANG

    【Objective】With the rapid growth of business volume in the nearshore area, the demand for bandwidth is showing an exponential growth trend. The resources of the 5th Generation Mobile Communication Technology (5G) and Beyond-5G (B5G) Next Generation Radio Access Network (NG-RAN) that carry the business are about to be exhausted. Wavelength Division Multiplexing-Passive Optical Network (WDM-PON), with its advantages such as high bandwidth, has become an effective solution to support 5G/B5G NG-RAN. However, the complex and variable offshore environment poses severe challenges for the deployment of WDM-PON networks. These challenges include high deployment costs, substantial path losses, and harsh underwater conditions. There is an urgent need to optimize network deployment strategies to reduce costs, risks, and transmission losses in order to build a network that is suitable for the offshore environment.【Methods】This study proposes a Multi-Head Attention enhanced Multi-Agent Deep Q-Network (MHA-MAD) algorithm. It efficiently extracts key features of the network environment using multi-head attention mechanism and assigns dynamic weights to different features, thereby improving modeling accuracy. Simultaneously, the multi-agent structure allows multiple agents to collaborate and make synchronized decisions within a shared network environment, promoting global optimization in network deployment.【Results】Compared to other benchmarks, the MHA-MAD algorithm improves performance in network deployment by nearly 42%, with results approaching the theoretical optimum. Furthermore, compared to multi-agent Deep Q-Network (DQN) method without the multi-head attention, MHA-MAD algorithm improves the performance by nearly 8% in the joint optimization objective of minimizing overall network deployment costs, node power consumption, link attenuation, and network deployment risk probabilities.【Conclusion】MHA-MAD provides new insights for the deployment and optimization of WDM-PON to support 5G/B5G NG-RAN in offshore scenarios.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250076 (2025)
  • Li ZHAO, and Chunbo MU

    International submarine cables are a global public infrastructure that connects the information and communication networks of various countries. In recent years, the demand for their construction and the associated security risks have both been on the rise. This article systematically reviews the policy trends of submarine cables in major countries and regions around the world. It elaborates on how regulatory and developmental policy changes impact the construction and maintenance cooperation of submarine cables. The insights provided offer valuable references for the development of international submarine cable construction in our country.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250084 (2025)
  • Xueyong CHEN, Renshan XIA, Xiaojun SUN, Xiaoming ZONG, and Yuliang CAO

    【Objective】In the construction of large-scale underwater interconnection projects for submarine engineering, the underwater wet-mateable hybrid optoelectronic connector is a key component. To break the monopoly of foreign technologies and products and achieve self-reliance and controllability, the paper analyzes its key technologies and develops the product.【Methods】The paper employs key technologies such as isobaric balance, rotary sealing, oil-filled cable sealing connection, multi-stage guided precise docking and position recognition, non-contact optical contacts, and fiber core adjustment to develop an underwater wet-mateable hybrid optoelectronic connector. The connector is subjected to high-pressure underwater mating and unmating tests, oscillation and tension tests of oil-filled cables, and maximum offset mating and unmating tests. Additionally, the paper conducts simulation analyses on the critical static and dynamic sealing issues of the underwater wet-mateable connector, as well as the contact pressure during dynamic mating and unmating processes.【Results】The test results show that the insertion loss (0.5 dB) and insulation resistance (≥50 GΩ) of the connector are qualified after 100 times of plugging and unplugging under the pressure of 45 MPa. Tensile capacity and end connection reliability of oil-filled cable cone sealing structure meet the requirements. The simulation analysis results indicate that during the dynamic mating and unmating process of the underwater wet-mateable connector, the contact pressure of the rolling shaft is always greater than the water pressure, ensuring dynamic sealing and preventing leakage. For static sealing structures, when the water pressure is 70 MPa, there will be no seawater leakage into the equipment interior. However, as the gap increases, the deformation, stress, and contact pressure of the Oring with the wall surface all show an increasing trend. For dynamic sealing structures, the faster the pin movement speed, the greater the seawater pressure, and the greater the leakage amount.【Conclusion】The obtained results in the paper can provide theoretical guidance for the design of underwater wet plugin optoelectronic hybrid connectors.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250088 (2025)
  • Kun WU, Mingnian WU, Qingqing CHEN, Zhengming WU, Shuhong XIE, Daogen WANG, and Songlin LI

    【Objective】The traditional discrete measurement mode of submarine cable burial depth, which relies on external devices, has the drawbacks of high monitoring costs, discrete spatial coverage, and delayed timeliness. It is difficult to obtain the real-time burial status of the submarine cable route. Additionally, the physical modeling method based on heat conduction equation is limited by the problem of coupled heat transfer in multiphase media under the sea floor. This study aims to develop a submarine cable burial depth analysis and calculation method using Brillouin Optical Time Domain Analysis (BOTDA) to enable efficient and convenient monitoring of burial depth.【Methods】The article proposes an intelligent monitoring method that integrates BOTDA with Backpropagation Neural Network (BPNN). It investigates the reconstruction of the communication fibers embedded in submarine cables into a distributed temperature sensor array and leverages machine learning techniques to break through the traditional technological framework. Using BOTDA equipment, the center frequency offset data of Brillouin scattering from a 24 km long submarine cable is collected. This data is then converted into temperature distribution data for the entire cable route through a frequency shift-temperature/strain coupling equation, and a standardized dataset is established. Based on this dataset, a BPNN model is constructed. Through machine learning, the model automatically identifies temperature distribution characteristics to establish a mapping relationship between the temperature of the submarine cable and its burial depth status. The model takes the measured temperature data as input and calibrates the model parameters through field experiments and historical data. After training and optimization, it outputs the predicted burial depth status.【Results】The proposed BPNN model can effectively capture the nonlinear relationship between the temperature change and the buried depth of the submarine cable, and obtain the relationship between the buried depth state of the submarine cable with the distance, so as to realize the prediction of the buried depth state of the submarine cable.【Conclusion】The results show that the burial depth measurement method based on distributed optical fiber temperature-strain sensing technology and BPNN can achieve precise monitoring of the submarine cable burial depth status, with the detection accuracy reaching 97%.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250097 (2025)
  • Hong ZHANG, Mingnian WU, Daogen WANG, Zhangjian MU, Shuhong XIE, Zhengming WU, Songlin LI, and Qingqing CHEN

    【Objective】The article presents an algorithm utilizing optical fibers and Distributed Acoustic Sensing (DAS) technology for monitoring anchor-induced damage events in submarine cables. The algorithm enables feature-threshold-based identification of anchor hazards in data-scarce scenarios, circumventing the high costs associated with anchor damage data acquisition while enhancing the algorithm's broad applicability.【Methods】Based on the characteristic attributes of anchor damage events (high intensity, long-range impact, and prolonged duration), the algorithm processes two-dimensional spatiotemporal vibration data obtained through DAS measurements of submarine cable fibers. It first extracts event data profiles using average power feature masking, then calculates contour area and anchor damage confidence to filter profiles. Subsequently, morphological feature curves are computed for profiles at equally spaced time intervals, enabling identification of anchor intrusion events through intensity and temporal distribution analysis of these curves.【Results】Simulation experiments demonstrate significant differences in morphological feature curves between normal interference and simulated anchor damage events. The combined computation of multiple feature curves effectively distinguishes profile defects in event contours. By setting morphological feature thresholds, anchor damage events can be rapidly identified. In the tests using one anchor damage dataset alongside two non-damage datasets, the algorithm effectively distinguished the anchor damage data by employing filtering techniques based on the intensity and duration of feature curves, as well as by detecting profile defects in these curves.【Conclusion】The submarine cable anchor damage monitoring algorithm proposed in this article primarily utilizes the OpenCV computer vision framework for its implementation. It features fast computation speed and high accuracy, meeting the real-time monitoring requirements for submarine cable anchor damage detection. The morphological feature curves used in the algorithm effectively represent the temporal distribution of event contours. As the core feature of the anchor damage algorithm, they expand the application scenarios of morphological features and hold significant practical value.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250098 (2025)
  • Xuechao NIU, Jianjia LU, Ziwei CHEN, Shuhong XIE, Chunfei GU, Jie SUN, Zhenzhen Chen, and Bing MAO

    【Objective】The umbilical cable is one of the core pieces of equipment for marine scientific exploration. It typically uses high-strength steel wires as the load-bearing elements. However, steel wires have a high density, and as the operating water depth increases, the proportion of the umbilical cable's own weight in the safe working load also increases, reducing the safety margin for ultra-deep water applications. Therefore, there is a need for lightweight design of umbilical cables.【Methods】The light-weight umbilical cable replaces steel wires entirely with low-density, high-hardness aramid Fiber Reinforced Polymer Compsite Materials (FRP) in its innermost layer. In the middle layer, steel wires are partially replaced at intervals, while the outermost layer maintains a full steel wire structure to enhance overall wear resistance and facilitate heat dissipation through the gaps in the loadbearing layer when seawater seeps in. To mitigate interlayer wear, a wear-resistant layer is extruded on the surface of the FRP, thereby increasing its fatigue resistance for long-term use.【Results】Firstly, compared with steel wire umbilical cables, light-weight umbilical cables reduce the unit weight by 30.50% in air and 37.29% in seawater, and increase the static water depth by 27.6%, expanding the application scenarios of umbilical cables. Secondly, the finite element method is used to analyze and compare the stiffness, tensile strength, and heat dissipation performance of lightweight umbilical cables and steel wire umbilical cables. It is found that the tensile stiffness of lightweight umbilical cables is 16.7% lower and the bending stiffness is 20.0% lower. Both types of cables can reach the theoretical fracture tensile load, and the stress of both materials is less than the fracture strength. At this time, the elongation of the cables is 1.45%. Under the same current in seawater, the temperature of the light-weight umbilical cable core is 0.7 ℃ higher, which is 2.9% higher than the steel wire umbilical cable. Finally, the prototype cable was manufactured and subjected to tensile tests based on common failure modes, as well as tests for fatigue under alternating loads and tension-bending fatigue. The test results confirm that after 2 000 cycles of fatigue, the lightweight umbilical cable still has high strength and minimal interlayer wear.【Conclusion】Under the premise of unchanged outer diameter, lightweight umbilical cables can significantly increase the application water depth. Two different load-bearing materials with different characteristics can simultaneously exert maximum tensile performance. Through testing, it has been verified that the lightweight umbilical cables have high reliability.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250100 (2025)
  • Xin WAN, Haochuan WANG, Yang YE, Zhihong ZENG, Min LIU, Min LENG, and Chen CHEN

    【Objective】Lightwave-based Retroreflective Optical Integrated Sensing and Communication (RO-ISAC) systems have the advantages of large communication capacity and high sensing accuracy, which can offer communication and sensing capabilities for the underwater activities. However, the limited Field of View (FOV) of the Corner Cube Reflector (CCR) in underwater RO-ISAC systems greatly limits the effective sensing range of the system. Hence, how to increase the FOV of the CCR to expand the effective sensing range of the system is a subject that needs to be solved urgently. Moreover, the impact of underwater turbulence on the communication and sensing performance of the RO-ISAC system also remains to be further explored.【Methods】For the limited FOV issue of the CCR, we propose a CCR array scheme based on an angle diversity structure. The proposed angle diversity CCR array consists of a central CCR unit and multiple side CCR units distributed in a circle, where each side CCR unit has a certain tilt angle. In the underwater RO-ISAC system based on the angle diversity CCR array, Orthogonal Frequency Division Multiplexing (OFDM) is adopted as the ISAC waveform, and the communication and sensing performance of the RO-ISAC system in the underwater turbulence channel is studied through Matlab software simulation.【Results】Simulation results show that, under the condition of the same equivalent reflection area, the angle diversity CCR array can significantly increase the FOV of the CCR. Moreover, as the number of side CCR units in the angle diversity CCR array increases, the equivalent FOV also increases, and the sensing (i.e., ranging) performance of the underwater RO-ISAC system improves accordingly. At the same time, there is an optimal interval for the tilt angle of the side CCR units in the angle diversity CCR array, which is highly related to the incident angle of the optical signal. In addition, in the underwater RO-ISAC system based on the OFDM waveform, underwater turbulence has a great impact on the Bit Error Rate (BER) performance of the system. When the turbulence is stronger, the BER performance is worse. In contrast, underwater turbulence has no obvious impact on the ranging performance of the system.【Conclusion】The proposed angle diversity CCR array can significantly expand the effective sensing range of the under-water RO-ISAC system and improve the sensing accuracy. At the same time, the underwater RO-ISAC system based on the OFDM waveform can effectively overcome the adverse effects of underwater turbulence on the sensing performance.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250103 (2025)
  • Yifan WANG, Litian LIU, and Junyuan LIU

    With the increasing demand for ocean exploration, the construction of an integrated space-air-ground-sea network has become extremely important. However, due to the different properties of air and seawater, as well as the complex and variable marine environment, achieving cross-domain communication between air and sea faces many technical challenges. To deeply explore the current state of innovation and future development trends in air-sea cross-domain communication, the paper constructs a dataset based on patent search results. It investigates the overall patent landscape, global geographical distribution, and key innovative entities. The core patents and technological evolution of three technical branches-direct air-sea cross-domain link-level communication, air-sea cross-domain relay communication, and air-sea cross-domain communication networking are analyzed. The paper also offers development suggestions to Chinese innovative entities in terms of core technology breakthroughs and patent protection and utilization.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250116 (2025)
  • Jiale WANG, Kaiwen ZHENG, and Jie LIAN

    【Objective】With the rapid development of the marine economy, the underwater Internet of Things (IoT) is facing urgent demands for intelligence and convenience. The separation of traditional communication and sensing modules has led to large device sizes and high costs, which restrict the overall system performance. This has spurred the development of Integrated Sensing and Communication (ISAC) systems, especially Optical ISAC (OISAC) systems based on Underwater Wireless Optical Communication (UWOC), which have become a current research hotspot. Although OISAC systems offer the advantages of high spectral efficiency and low latency, they still face challenges in clock synchronization and hardware implementation in practical applications.【Methods】To address these issues, the paper proposes an Optical Integrated Communication and Ranging (OICAR) system based on spread-spectrum signals. The paper employs a spread-spectrum communication scheme to transmit communication information, which effectively combats channel fading caused by the transmitter light source and the transmission channel, thereby ensuring the successful transmission of communication information. Additionally, the paper incorporates timestamp information into the chips of the duplex spread-spectrum signals. By utilizing the timestamp information of the master and slave transceivers, the autocorrelation properties of the spread-spectrum code, and the Frequency Control Word (FCW), the system achieves high-precision underwater ranging with asynchronous transceivers. Furthermore, the paper constructs a real-time hardware implementation system using Light Emitting Diode (LED) arrays and a Field Programmable Gate Array (FPGA) processing system, providing a hardware verification platform for the development of the underwater OICAR system.【Results】Communication and ranging experiments are conducted on the OICAR real-time system in a towing tank. Results demonstrate that the designed system achieves a maximum underwater communication distance of 63.5 m while maintaining ranging accuracy within ±0.25 m.【Conclusion】These findings indicate that the proposed OICAR system can realize efficient underwater communication and precise ranging functions in real time.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250133 (2025)
  • Jingjing Lü, Qing SHI, Bingjie WANG, and Li LIU

    【Objective】Underwater Photon Counting Wireless Communication (UPCC) is capable of achieving weak signal detection. It can effectively mitigate the impact of optical signal attenuation induced by complex underwater environments and extend the communication range. The absorption and scattering of light in underwater channels lead to signal attenuation, while turbulence gives rise to fluctuations in signal amplitude. Both of these phenomena can degrade the Bit Error Rate (BER) of the UPCC systems. It is crucial to reasonably evaluate the comprehensive impact of these factors on the bit error performance of the UPCC system based on the underwater joint channel model that takes into account the effects of absorption, scattering and turbulence simultaneously.【Methods】In this study, the random phase screen model is employed to simulate the impact of turbulence effects on the transmitted beam. The turbulence phase screen model is further extended to the Monte Carlo (MC) numerical simulation framework for underwater channels. Subsequently, a more comprehensive joint channel model of absorption, scattering, and turbulence, incorporating the influence of the seawater environment, is constructed. Additionally, based on the Single-Photon Avalanche Diode (SPAD) and On-Off Keying (OOK) modulation methods, an UPCC system is developed.【Results】Utilizing the established joint channel model, a comparative analysis is conducted on the bit error performance of the UPCC system under diverse parameters, including water quality conditions, link distance, and turbulence intensity.【Conclusion】The results of the simulation indicate that in the environments of pure seawater and clean seawater with excellent water quality, the impact of turbulence on the communication performance of the system cannot be ignored. Specifically, the communication distance is significantly attenuated, and the BER of the system increases. For instance, under the ideal conditions of pure seawater and the absence of turbulence, the maximum communication distance of the system can reach approximately 500 m. Under weak turbulence, it reduces to about 400 m, and under strong turbulence, it further shrinks to approximately 200 m. As the water quality deteriorates, the absorption and multiple scattering effects emerge as the primary factors influencing the communication performance of the system. In the seawater of the port with the poorest water quality, the farthest communication distance of the system under different turbulence intensities ranges from approximately 25~30 m. Moreover, the influence of different turbulence intensities on the BER of the system is nearly negligible.

    Aug. 10, 2025
  • Vol. 51 Issue 4 250172 (2025)
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