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Copyright of Control Theory & Applications / Kongzhi Lilun Yu Yinyong is the property of Editorial Department of Control Theory & Applications and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Study on Optical Communications / Guangtongxin Yanjiu is the property of Study on Optical Communications Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

【Objective】Affected by factors such as atmospheric attenuation and atmospheric turbulence, wireless laser communication will produce a certain degree of bit error, and it is often necessary to add error correction codes to improve the signal transmission quality. Low Density Parity Check codes (LDPC) have performance close to the Shannon's limit, and their error-correcting ability will increase significantly with the increase of codeword length. For codes with a large length of information segment, when each code corresponds to an Ethernet frame, its encoding efficiency will be seriously affected. Designing the transmission method for Ethernet frames in a way that allows both different speeds and lengths of Ethernet frames to fully leverage the encoding and decoding efficiency is crucial for enhancing the transmission rate of Ethernet data sources.【Methods】Based on the LDPC (4 050, 2 700) encoding with a data bit width of 16 bit, this paper designs a gigabit network service transmission method. The functions of each module are clearly divided, and the state machine is used in the design of the module. Therefore, the problems in the design process can be quickly located, and the development efficiency is very high. Setting an appropriate operational cycle at the transmitting end to process Ethernet frames, through operations such as framing, packet assembly, and filling with random sequences, enables Ethernet traffic of different frame lengths and rates to adaptively match the information segment length of the LDPC encoding module, thereby fully utilizing the efficiency of LDPC encoding. Each Ethernet frame can be finally recovered by deframing at the receiving end.【Results】Finally, this article verified the design scheme on the Field Programmable Gate Array (FPGA) board of XILINX, and tested the transmission rate of Ethernet data with different frame lengths by using a gigabit network tester. The results show that the data rate can reach the limit rate of 1 Gbit/s. Afterwards, different services such as video and files are successfully tested.【Conclusion】The article proposes an Ethernet service transmission method specifically designed for scenarios where the information segment length exceeds the Ethernet frame length, enabling it to accommodate Ethernet data transmission with varying lengths, rates, and types of services. The efficiency of the encoding module can be fully utilized to meet the demand for high-speed Gigabit Ethernet service transmission in wireless laser communication.

Light intensity flicker is the most basic and important effect of turbulence. Fiber coupling efficiency is the primary parameter that ensures the system's communication quality. The light intensity flicker effect caused by atmospheric turbulence significantly affects the coupling efficiency of space light in a single-mode optical fiber. Based on the principle of fiber coupling efficiency, this paper first establishes the relationship between light intensity flicker and spatial coherence radius, then analyzes the influence of light intensity flicker on fiber coupling efficiency through the spatial coherence radius. A laser communication system was built, and real-time measurement experiments on atmospheric light intensity flicker and optical fiber coupling efficiency at different transmission distances and altitudes above the ground were completed. The experimental results show that the constructed experimental system can simultaneously measure the scintillation index and fiber coupling efficiency. When the communication distance is 12,000 m and the height is 600 m above the ground, the scintillation index is measured to be 0.63, and the coupling efficiency is 0.05. The results of the study provide an experimental and theoretical basis and data support to promote the development of atmospheric laser communications. [ABSTRACT FROM AUTHOR]

【Objective】With the continuous advancements in satellite and communication technologies, the integration of space laser communication and ranging technology becomes more mature. As deep space exploration, satellite navigation, and other fields continue to develop, there is a growing demand for higher communication capacity and ranging accuracy between satellites. Thus, the need to achieve laser satellite high-speed communication while completing ranging and further improving ranging accuracy, under the premise of considering satellite payload and power consumption, has become an urgent issue.【Methods】This article designs and implements a coherent communication and ranging integrated system that supports both QPSK and BPSK, based on the principle of dual one way ranging. To further improve the ranging performance, the differential time sampling method is used to obtain the frequency difference and phase difference between the sending clock and the receiving clock through frequency and phase discrimination, thereby achieving higher clock accuracy and correcting the ranging value.【Results】The system can operate stably in an environment where the received optical power is greater than-48 dBm. Different rates can be set for different application requirements, with a maximum rate of 5 Gbit/s in QPSK mode and rates of 2.5 Gbit/s, 1.25 Gbit/s, and 625 Mbit/s in BPSK mode. The theoretical ranging accuracy of the system can reach a minimum of 53 ps. In normal communication, using Matlab and Vivado to calculate and process ranging data, the ranging accuracy of the system is verified to be less than 0.1 ns. Furthermore, using the differential time sampling method under simulation conditions, the ranging accuracy can be improved to the order of 10-3 of the symbol width, reaching±0.36 cm.【Conclusion】The proposed communication and ranging integrated system can achieve high-precision ranging while achieving high-speed communication, which is of practical significance for future applications of laser satellites.

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Study on Optical Communications / Guangtongxin Yanjiu is the property of Study on Optical Communications Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

There is a growing interest in the development of transportable optical ground station (TOGS) as an important component of laser communication network. The object of this paper is a TOGS designed for optical LEO satellite downlink as well as for long-distance aircraft downlink. A composite gravity compensation mount is proposed to simplify and efficiently suppress the low-order aberrations of an 800 mm aperture primary mirror with variable orientation of the optical antenna of a TOGS as it changes pointing. In this study, first we describe the composition of the TOGS and the utility of each part. Second, taking the minimization of the primary mirror deformation as the optimization objective, we employ the particle swarm optimization algorithm to find the optima of several key structural parameters by Isight software. Next, the annular Zernike polynomials are adopted to fit the wavefront error over the entire surface of the primary mirror for describing low-order aberrations, proving that the composite mount effectively suppresses the wavefront error to smaller than ⋋ /27, as the elevation angle changes from the horizontal to the vertical one. Finally, the ZYGO interferometer wavefront detections show that, after eliminating fabrication imperfections, the RMS of the wavefront error over the entire surface of the mirrors for horizontal and vertical axes, due to deformation, are 0.04⋋ and 0.035⋋, respectively. Compared to the results of the fitted wavefront error, the relative errors are 9.5% and 8.1%. The results show the validity and feasibility of the optimized composite mount and the wavefront fitting method, which can prove its reference significance for the budget and allocation of the systematic wavefront error in meter-scale optical antenna of the TOGS for satellite downlink. [ABSTRACT FROM AUTHOR]

Light intensity flicker is the most basic and important effect of turbulence. Fiber coupling efficiency is the primary parameter that ensures the system’s communication quality. The light intensity flicker effect caused by atmospheric turbulence significantly affects the coupling efficiency of space light in a single-mode optical fiber. Based on the principle of fiber coupling efficiency, this paper first establishes the relationship between light intensity flicker and spatial coherence radius, then analyzes the influence of light intensity flicker on fiber coupling efficiency through the spatial coherence radius. A laser communication system was built, and real-time measurement experiments on atmospheric light intensity flicker and optical fiber coupling efficiency at different transmission distances and altitudes above the ground were completed. The experimental results show that the constructed experimental system can simultaneously measure the scintillation index and fiber coupling efficiency. When the communication distance is 12,000 m and the height is 600 m above the ground, the scintillation index is measured to be 0.63, and the coupling efficiency is 0.05. The results of the study provide an experimental and theoretical basis and data support to promote the development of atmospheric laser communications.

The impact of tracking errors over the vibration interference is investigated. A novel expression is presented for the bidirectional laser tracking mechanism which takes in account both periscope communication terminal and beam acquisition process with beaconless technology. In this paper, platform microvibrations are measured and compensated to improve the tracking characteristics of the optical communication terminal. An experiment was conducted to verify the high precision tracking system with the combination of coarse and fine tracking technologies, which represents that the fine tracking error is suppressed to 2.1 μrad. This high precision implementation demonstrates the effectiveness of the tracking control loop, and will contribute to the space laser communication. [ABSTRACT FROM AUTHOR]

Copyright of Computer Measurement & Control is the property of Magazine Agency of Computer Measurement & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The success of laser communications heavily relies on the stiffness, dynamic properties, static performance, and manufacturability of the U-frame. The U-frame is a fundamental element in satellite-to-ground laser communication telescopes. However, there is currently a lack of research on the optimal design of U-frames, leading to a significant gap between ideal construction and practical manufacturability. To address these concerns, this study proposes a comprehensive approach that combines multi-objective topology optimization and multi-start size optimization techniques. This approach considers the multidisciplinary constraints imposed by mechanical, control, and optical systems. The objective is to achieve both the conceptual and detailed design of a novel U-frame, while also ensuring thorough consideration of the structure's manufacturability during the optimization process. The prototype of the optimized U-frame was successfully fabricated using laser welding processes. The tensile test conducted on the prototype supported the idea that laser welding can enhance the micro-grain size of the joint, leading to improved overall mechanical properties. In particular, the joint strength achieved through laser welding was found to be 1.5 times greater than that achieved through TIG (Tungsten Inert Gas) welding. Additionally, the results obtained from the free vibration experiment closely aligned with the simulation, confirming the feasibility of manufacturing the optimized structure. The optimized structure demonstrated an improvement of 7.13% in dynamic performance and 29.61% in static performance compared to the first-generation structure. Additionally, there was a reduction of 29.89% in mass without affecting the remaining performance aspects. The successful fabrication of the prototype validates the feasibility of the proposed welding process and highlights the superiority of the new U-frame. [ABSTRACT FROM AUTHOR]

Copyright of Telecommunication Engineering is the property of Telecommunication Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The signal-receiving end of acquisition, pointing, and tracking (APT) systems applied to intersatellite laser communication terminals usually uses a fast-steering mirror (FSM) to control the fiber-coupling process, has a complex structural design, and induces large errors in the nonideal coaxial optical path. Herein, we propose a fiber-optic nutator using a piezoelectric ceramic tube (PCT) as the driving unit that allows scanning in the focal plane of the light signal to achieve active fiber coupling in the APT system. Specifically, this article describes the structural design principle of a PCT-based fiber optic nutator, establishes a simulation model of the mechanism, and proves the correctness of the simulation model by measuring the deflection angle of a PCT based on a parallel light collimator. The minimum accuracy of the designed nutator was 0.145 μm, the maximum nutation radius R was 20.09 μm, and the maximum nutation bandwidth was 20 kHz, as determined through simulation. Finally, the design parameters of the nutator were evaluated. The PCT-based fiber optic nutator, which met the design parameters, structurally replaced the fiber optic coupling component FSM and fine tracking camera in conventional APT systems successfully. Therefore, the PCT-based fiber optic nutator allows the active coupling control of signal light to a single-mode fiber (SMF) based on energy feedback on a theoretical basis and promotes the lightweight design of relay optical paths in APT systems. In addition, with future work in optimization of the nutation control algorithm, the scanning range and accuracy of the nutator can be improved. [ABSTRACT FROM AUTHOR]

Underwater optical communication is a new and feasible underwater communication technology, which has developed rapidly in recent years. To build a high-performance and practical underwater optical communication system, it is necessary to consider and optimize the design from the device to the system, from the internal modulation to the external environment. This paper summarizes the current problems of underwater optical communication from the aspects of underwater optical communication system transmitter and receiver, modulation format and underwater channel. The paper also classifies and summarizes the three key technologies of improving underwater optical communication distance, communication rate and communication stability, and gives the possible solutions. It provides reference for the follow-up system design and experimental research.

In order to optimize space laser communication networking, the 2:1 transmissions for all reflectors on a multi-address transceiver can be removed. However, without the 2:1 transmissions, the reflectors exhibit doubled optical coupling effect in rotation, which reduces the numerical calculation precision of the attitudes of the reflectors' lines-of-sight (LOS). In the present study, using Snell's law of reflection and Euler's theorem, a mathematical model for the attitudes of the LOS of multiple reflectors without 2:1 transmissions was established, and a method was proposed for an indirect numerical calculation of the attitudes of the LOS by creating a Snell transformation matrix. This method eliminates the influence of the doubled optical coupling effect on the numerical solution of the line-of-sight attitudes of multi-reflectors. Compared to the direct numerical calculation method using the angular velocity, the calculation precisions achieved using the proposed method exhibited improvements of 3, 5, and 3 orders of magnitude in the three conical motions, respectively. The indirect calculation method and the numerical calculation model proposed in the present study, therefore, provide a theoretical basis for applying reflectors without 2:1 transmissions to multi-address transceivers. [ABSTRACT FROM AUTHOR]

We investigated the effect of solar radiation noise on the performance of a long-range atmosphere-ocean laser communication system. To model an inhomogeneous channel in the atmosphere-ocean system, a Monte Carlo (MC) simulation method was utilized in combination with measured underwater chlorophyll profiles. We conducted field measurements to accurately assess the effects of background noise, specifically solar radiation at different underwater depths and times. The influence of different scenarios on the system's signal-to-noise ratio (SNR) was then scrutinized based on the detector type. Additionally, a comprehensive analytical model was proposed for diverse background light noises, enabling the exploration of the effects of solar noise and Photomultiplier Tube (PMT) on the communication link's performance in terms of Pulse Position Modulation (PPM) demodulation symbol error rate (SER). The results indicate that expanding the receiver's field of view (FOV) from 1° to 15° can enhance the system's communication depth by 11 m, while increasing the receiver's radius from 1 cm to 20 cm can elevate the communication depth by 37 m. Moreover, the study investigates the impact of transmit power and the multi-aperture receiving technique on communication depth, providing valuable insights for designing atmosphere-ocean laser communication links and offering robust support for the practical implementation of the Free-Space Optical (FSO) - Underwater Optical Communication (UWOC) system. • Using actual measurements of solar radiation intensity at different depths in oceanic waters. • Using Monte Carlo simulations, combined with regional seawater chlorophyll profiles and bubble models. • Consider the DC saturation effect of PMT and model the output using actual measurements, enhancing the practicality. • Evaluating the optimal demodulation algorithm and exploring the system performance in different cases from the SER. [ABSTRACT FROM AUTHOR]

Abstract Quantum communication networks pose immense potential for revolutionising secure communications for several applications such as banking, defence, etc. The majority literature on quantum networks deals with the problems of networking and resource allocation using Software Defined Networks (SDNs). SDNs, however, introduce several issues, such as app manipulation attacks and scalability issues. We propose a novel scheme of implementing quantum communication networks that are hardware routed rather than software defined by labelling qubit photons using laser communications. We provide a comprehensive implementation of the new scheme and propose two novel algorithms—Bandwidth sharing and Equitable bandwidth sharing to implement the hardware routed quantum network. The algorithms result in a key rate increase of 118% and improved network resource utilization of 147% as compared to the First Come First Serve algorithm.

In order to achieve underwater wireless dynamic optical communication, a laser communication system is proposed based on Pulse Position Modulation (PPM). In order to achieve underwater laser communication accurately, the mathematical model of underwater laser communication was constructed with small angle analysis. The pulse position modulation demodulation algorithm is designed, and the workflow of modulation and demodulation is given in the transmit module and the receive module. In the experiment, Lumileds-470 nm light source was selected for data communication for testing at a communication rate of 15 Mbp/s. In the servo control process, the square wave signal used for stepping motor drive had a stable amplitude output and a stable time width. It can well simulate the testing process of underwater dynamic scanning. In the experiment, laser light spots were obtained under different attenuation states, and the characteristics of the light spot distribution were analyzed. The numerical reconstruction of the light spot energy was completed in MATLAB. Three types of light attenuators, 1.0%, 0.1%, and 0.01%, were used to simulate different light attenuations underwater. The test results show that the system error rate is better than 10−6 when attenuation chip is 1.0%. When attenuation chip is 0.1%, the error rate of the system is reduced to 10−4. When attenuation chip is 0.01%, a valid signal cannot be obtained by the system. The feasibility of the system is verified.

In order to improve the data sharing and comprehensive information processing capabilities between multi-microgrids in the power system, the multi-microgrids scheduling system based on laser communication has been proposed. In order to reduce the error rate of laser communication and reduce the impact of atmospheric turbulence on signal acquisition, an adaptive modulation algorithm has been designed. A mathematical model for laser communication modulation and demodulation based on adaptive modulation algorithm has been constructed. In simulation analysis, the target signal was extracted from the original signal superimposed with atmospheric turbulence noise through filtering and demodulation. The energy fluctuation of the extracted signal decreased from 47.3 to 5 mV. The energy attenuation trend of communication lasers within the range of 0–6 km was experimentally tested. Within 2.0 km, the energy demodulation results of both algorithms are similar, both below 10%. After exceeding 2.0 km, the calculation error of the adaptive modulation algorithm remains basically unchanged, while the error of traditional algorithms increases by about twice. For the APD response value, the adaptive modulation algorithm demodulation has a higher response range concentration ratio and the higher envelope recognition. Under different nominal atmospheric turbulence values, the maximum error rates of the adaptive modulation algorithm are 5.8 × 10−8, 8.9 × 10−8, and 1.2 × 10−7, respectively, while the maximum error rates of the amplitude coherent algorithm are 2.9 × 10−5, 6.3 × 10−5, and 1.05 × 10−4, respectively. It can effectively suppress the impact of atmospheric turbulence on the error rate of laser communication by adaptive modulation algorithm.

A free space optical module is used in laser communication to transport a signal from the transmitter to the receiver. Free Space Optical Communication (FSOC) is a Line of Sight connectivity that sends a highly narrow beamwidth. FSOC provides high bandwidth and data rates greater than 10 Gbps. Although FSOC technology has several advantages, it is inefficient for long-distance transmission because of many constraints caused by atmospheric variables. In FSOC connections, turbulence-induced scintillation is a severe problem that significantly reduces link performance. Keeping this problem in mind, the objective of this study is to enhance FSOC performance in terms of energy efficiency, spectral efficiency and long-distance transmission. To achieve this, a study is employed using a hybrid combination of Higher-order Gaussian filter (HGF), post-amplification and a homodyne detection method. Precisely, the simulative study of 32-channel wavelength division multiplexing (WDM) FSOC has used channel model Gamma-Gamma with single-beam (SB), dual-beam (DB), four multiple-beam (MB4) and eight multiple-beam (MB8) techniques. The proposed framework has achieved a Channel capacity of more than 320 Gbps. The transmission range enhancement of 112% and reduction in transmitted power of 100% are achieved, which are considerably more significant compared with state-of-the-art literature studies. The OptiSystem platform is used to gather the outcomes. The performance is based on parametric analysis of bit error rate (BER), Quality (Q) factor and eye height.

In this paper, a laser communication antenna with two mirrors is designed. The decenters of the secondary mirror do not introduce field-linear coma, which reduces the antenna's sensitivity to misalignment, and we call it coma insensitive system. The conic coefficients of the primary and secondary mirrors of the coma insensitive system are different from those of the Cassegrain and Ritchey–Chretien systems. We derive the calculation formula of the coma insensitive system in detail based on the nodal aberration theory. Through a design example, the performance of the coma insensitive, Cassegrain and Ritchey–Chretien system in the nominal state and the secondary mirror decentered state is compared, and it is found that the aberration performance of the Cassegrain and Ritchey–Chretien system in the nominal state is much better than that of coma insensitive system. However, when the secondary mirror is decentered, the performance of Cassegrain and Ritchey–Chretien system is obviously inferior to coma insensitive system, and their rms spot diameter is about 2.8 times that of coma insensitive system. [ABSTRACT FROM AUTHOR]

The success of laser communications heavily relies on the stiffness, dynamic properties, static performance, and manufacturability of the U-frame. The U-frame is a fundamental element in satellite-to-ground laser communication telescopes. However, there is currently a lack of research on the optimal design of U-frames, leading to a significant gap between ideal construction and practical manufacturability. To address these concerns, this study proposes a comprehensive approach that combines multi-objective topology optimization and multi-start size optimization techniques. This approach considers the multidisciplinary constraints imposed by mechanical, control, and optical systems. The objective is to achieve both the conceptual and detailed design of a novel U-frame, while also ensuring thorough consideration of the structure’s manufacturability during the optimization process. The prototype of the optimized U-frame was successfully fabricated using laser welding processes. The tensile test conducted on the prototype supported the idea that laser welding can enhance the micro-grain size of the joint, leading to improved overall mechanical properties. In particular, the joint strength achieved through laser welding was found to be 1.5 times greater than that achieved through TIG (Tungsten Inert Gas) welding. Additionally, the results obtained from the free vibration experiment closely aligned with the simulation, confirming the feasibility of manufacturing the optimized structure. The optimized structure demonstrated an improvement of 7.13% in dynamic performance and 29.61% in static performance compared to the first-generation structure. Additionally, there was a reduction of 29.89% in mass without affecting the remaining performance aspects. The successful fabrication of the prototype validates the feasibility of the proposed welding process and highlights the superiority of the new U-frame.

The signal-receiving end of acquisition, pointing, and tracking (APT) systems applied to intersatellite laser communication terminals usually uses a fast-steering mirror (FSM) to control the fiber-coupling process, has a complex structural design, and induces large errors in the nonideal coaxial optical path. Herein, we propose a fiber-optic nutator using a piezoelectric ceramic tube (PCT) as the driving unit that allows scanning in the focal plane of the light signal to achieve active fiber coupling in the APT system. Specifically, this article describes the structural design principle of a PCT-based fiber optic nutator, establishes a simulation model of the mechanism, and proves the correctness of the simulation model by measuring the deflection angle of a PCT based on a parallel light collimator. The minimum accuracy of the designed nutator was 0.145 μm, the maximum nutation radius R was 20.09 μm, and the maximum nutation bandwidth was 20 kHz, as determined through simulation. Finally, the design parameters of the nutator were evaluated. The PCT-based fiber optic nutator, which met the design parameters, structurally replaced the fiber optic coupling component FSM and fine tracking camera in conventional APT systems successfully. Therefore, the PCT-based fiber optic nutator allows the active coupling control of signal light to a single-mode fiber (SMF) based on energy feedback on a theoretical basis and promotes the lightweight design of relay optical paths in APT systems. In addition, with future work in optimization of the nutation control algorithm, the scanning range and accuracy of the nutator can be improved.

Fast steering mirrors (FSMs) driven by piezoelectric ceramics are actuators of pointing, acquiring, and tracking (PAT) systems in free space laser communications. However, the inherent hysteresis nonlinearity of the FSM significantly degrades the performance of the PAT system, especially the so called rate-dependent hysteresis in high frequency. This paper presents a systematic framework for modeling rate-dependent hysteresis. The rate-dependent hysteresis curve can be viewed as a superposition of the rate-independent hysteresis curve and the rate-dependent term. The proposed method is transformed into a control algorithm that can work in real-time for satellite optical communications. Meanwhile, the corresponding parameter identification methods are reasonably presented. Applying a feed-forward control strategy, the presented algorithm compensates for the rate-dependent hysteresis effect of the FSM at low and medium frequencies. The results demonstrate that the proposed algorithm effectively suppresses the rate-dependent hysteresis nonlinearity of the FSM. After the rate-dependent hysteresis effect of the FSM is compensated, the actual spiral scan trajectory of the FSM accurately tracks the target trajectory, which validates the effectiveness of the proposed compensation algorithm. [Display omitted] • Achieving modeling and compensation of dynamic hysteresis in fast steering mirrors. • Presenting a rate-dependent hysteresis model possessing a simple structure. • Development of a rate-dependent hysteresis compensation algorithm. • Establishment of a parameter identification method for the proposed hysteresis model. [ABSTRACT FROM AUTHOR]

Free Space Optical (FSO) communication systems have extensively invaded the speed of smart city evolution due to the current surge in demand for wireless communication spots that can match recent challenges due to high technical leaps in smart city evolution. As the number of users is vastly increasing throughout all networks in the form of machines, devices, and variously distinct objects, FSO is a hugely recommended robust communication system that mitigates a lot of RF disadvantages on the field with no need for licensing, fast rollout time, and low cost. This paper shows an exploit of a Low Power Field Programmable Gate Array (FPGA) based FSO communication system designed for Line of Sight (LOS) Building to Building Communication over a distance of 12 m using a 650 nm Visible Light (VL) red laser source via On-Off Keying (OOK) and higher-level Intensity Modulation (IM)/Pulse Width Modulation (PWM) schemes. The implemented system reached a doubled data rate than OOK of 230 kbps using the IM technique. Traffic monitoring and building security status can be frequently updated between adherent buildings, each scanning its zone real-time conditions and sharing them with the neighboring links. [ABSTRACT FROM AUTHOR]

Stochastic parallel gradient descent (SPGD) algorithm is one of the most promising methods for effective coherent beam combination. However, the algorithm also has some disadvantages, such as slow convergence speed and local extremum. This paper proposes an AdaDelSPGD algorithm, which combines an AdaDelta algorithm with a SPGD algorithm, and improves the traditional AdaDelta algorithm with adaptive gain coefficient. It is worth noting that the adaptive gain coefficient can be adjusted in real time to improve the convergence rate. The effectiveness of the proposed algorithm is verified by relevant simulation experiments, and the results show that the proposed algorithm can significantly improve the convergence speed. Following the experiments with the fiber laser-phased array multiplex communication system, we can draw the conclusion that the addition of communication modulation reduces the beam quality, and the higher the modulation frequency, the worse the beam quality. However, adding the SPGD algorithm can improve the beam quality. The AdaDelSPGD algorithm proposed in this paper can further improve the beam quality, and the bit error rate of communication is also decreased after testing. This provides a foundation for further research on the fiber laser-phased array multiplex communication system. [ABSTRACT FROM AUTHOR]

The pointing accuracy of the Risley prisms beam-steering system mainly depends on the accuracy of the solution method and the impact of the error on the solution. To improve pointing accuracy, the impact of systematic errors on the inverse solution precision is investigated and a correction method is proposed. First, a more accurate error model for Risley prisms is established, and the errors are obtained by the parameter identification method, which corrects the forward solution error. Second, we explain the reason for the error generated by the inverse solution and analyze the variation of the inverse solution error magnitude with the beam deflection angle. A correction method based on pointing-field transformation is proposed. Finally, simulations and experiments are performed to verify the feasibility of the method. Experimental results show that when the beam deflection angle is equal to 0.1°, the maximum and RMS values of the pointing error are reduced by 94.08% and 95.18%, respectively. [ABSTRACT FROM AUTHOR]

This article deals with the proposed design of a 10 GHz optical wireless communication (OWC) link using 1550 nm Laser source for long range communication channel. Optical communication is the backbone of next generation gigabit class communication system and optical fiber communication plays an important role to fulfill the requirement of gigabit communication. But OWC is very useful where optical fibers cannot be laid off. A 10 GHz communication channel bandwidth has been designed in this article using very low power (2 mW) 1550 nm laser diode. A long range communication channel of 3 km has been considered with maximum bit-error-rate (BER) of 10−9. This system has been designed to withstand high atmospheric attenuation up to 11.67 dB/km, without affecting the BER and link range. An auto alignment method and automatic laser power control method have also been described with all necessary design parameters of the system.

The quadrant detector (QD) faces the limitation of a restricted field of view, which is effectively circumvented by implementing a QD array. Despite the potential advantages, there has been a scarcity of research on positioning methods for QD arrays. In this letter, we present a novel method for QD arrays utilizing a neural network approach. This method eliminates the need for intricate preprocessing of the signal in accordance with the array's architecture and demonstrates the capability to predict the radius of the incident beam with high accuracy. This technique holds promising potential for addressing contemporary challenges in space laser communication systems. [ABSTRACT FROM AUTHOR]

In recent years, the diffractive optical systems have developed rapidly. Diffractive devices such as binary optical device and membrane-based lens are equivalent to fixed phase shifters of microwave antennas. Thus, the mature theories and methods of a microwave phased-array antenna could be used for diffractive devices’ performance analysis. Both laser Synthetic Aperture Radar (SAR) and laser communication feature a single color and long wavelength, and they are specifically suitable for non-imaging diffractive optical systems. A signal wave front control realized by a diffraction device reduces the focal length and the weight of a system. Research on laser SAR and laser communication technology has important theoretical significance and application value for diffractive optical system. In this paper, we provide a phased-array interpretation of a diffractive optical system and introduce research that has been conducted on airborne and spaceborne laser SAR with respect to diffractive optical systems. We propose the concept of shipborne 1 m diffraction aperture laser communication and an interferometric positioning system and analyze its performance. The results indicated that, using a 10 m short baseline, this system can reach 400 million km with a corresponding positioning accuracy of 6 km that is suitable for use during deep space probes. We also discuss the sparsesampling laser-imaging problem using a laser to illuminate the target, transforming the laser image signal into the frequency domain with Fourier lens, using the small-scale detector to perform sparse sampling in the lowfrequency domain, and reconstructing the target image using a computer. Some preliminary simulation results are provided.

The change in the temperature of an underground water pipeline and its surrounding environment caused by a leakage has been detected by a variety of devices. Among the most popular technologies are infrared cameras, distributed temperature sensing using fiber optic cables, and analog active temperature sensors. In this paper, a novel low-cost leakage detection system composed of two analog active temperature sensors is presented. The proposed system detects water leakages by comparing the readings of two analog active temperature sensors, one at the surface at a depth of 2 cm of a sand layer covering a buried water pipeline and the other is adjacent to the first sensor at the same depth in a thermally insulated portion by a polystyrene barrier. The results of the heat flow simulation developed with FEMM (Finite Element Method Magnetics) 4.2, which is free, open source, cross-platform capable of solving heat flow problems, showed that the addition of the insulation is expected to increase the difference between the readings of the sensors from 0.011 to 0.063 K (°C) when there is a leakage, and thus the addition of the insulation can be effective in making the effect of leaked water on the surface temperature more detectable. Experimental results indicated the capability of the proposed system in detecting water leakage which caused a temperature difference of 1.47 °C after 30 minutes of running a leaking water system. Furthermore, a laser communication system was built to allow for the transmission of an alarm signal from the sensing node above the underground pipeline to a master node which should have an internet connection to upload information to a cloud storage which can be accessed by different users.

An integrated space-earth information network is an important symbol of a strong country in science and technology.According to China’s overall plan,an information network with global coverage,on-demand services,local access and security and credibility will be built by 2030 to serve national defense and social development.Space laser communication is an important means to realize high speed information transmission and security.Firstly,space-earth integration network was introduced from three aspects:concept connotation and system architecture,research status and development trend,overall goal and main difficulties.Then,the concept,characteristics,research status and development trend of space laser communication were summarized in order to provide useful reference for the construction of space-earth integrated information network in China.

Free Space Optical (FSO) communication systems have extensively invaded the speed of smart city evolution due to the current surge in demand for wireless communication spots that can match recent challenges due to high technical leaps in smart city evolution. As the number of users is vastly increasing throughout all networks in the form of machines, devices, and variously distinct objects, FSO is a hugely recommended robust communication system that mitigates a lot of RF disadvantages on the field with no need for licensing, fast rollout time, and low cost. This paper shows an exploit of a Low Power Field Programmable Gate Array (FPGA) based FSO communication system designed for Line of Sight (LOS) Building to Building Communication over a distance of 12 m using a 650 nm Visible Light (VL) red laser source via On-Off Keying (OOK) and higher-level Intensity Modulation (IM)/Pulse Width Modulation (PWM) schemes. The implemented system reached a doubled data rate than OOK of 230 kbps using the IM technique. Traffic monitoring and building security status can be frequently updated between adherent buildings, each scanning its zone real-time conditions and sharing them with the neighboring links.

Space laser communication optical antennas have very high requirements for the stability and uniformity of the temperature field. The GEO satellite-borne laser communication is affected by the violent alternating solar heat flow, which causes the thermal disturbance of the in-orbit temperature field of the extra-satellite optical antenna to become unstable. Reduce optical communication time. For this reason, the paper proposes a “sun window” as a solar spectral filter device to shield solar radiation, combined with the thermal design of the optical antenna system, based on thermal simulation analysis to study the effectiveness of the solar window to suppress the thermal disturbance of the optical antenna temperature field. The research results show that the thermal control optimization design of the optical antenna system based on the "sun window" has a significant effect in suppressing the thermal disturbance of the optical antenna temperature field: the stability of the temperature field of the primary mirror is increased by 2.2 times, the stability of the temperature field of the secondary mirror is increased by 10.6 times. The uniformity of the temperature field of the secondary mirror is increased by about ten times, and the time that meets the requirements of the stability and uniformity of the optical communication antenna temperature field can be up to 24 hours per day, which is more than three times that of the solution without the "sun window". [ABSTRACT FROM AUTHOR]

Laser Communication is the most evolving arenas in the field of wireless communication. Presently, laser commutation is espoused in the satellite communication for the purpose of space research related activities because of its benefits such as less power consumption, low cost, flexibility and resistance to the radio interferences. This work is an application of laser communication for transmitting data between two ends. Laser Communication needs the transmitter and receiver to be aligned in line-of-sight. The carrier which transmits the signal is produced by a laser diode. The main objective of this work is to transmit audio signal from transmitter to receiver by using the laser beam as a medium. The complete system for this work consists of a transmitter and a reciever capable of transmititng and recieving the analog signal respectively. The results shows that input signal frequencies are preserved at the output with less distortion. However there is decrease in the amplitude of the received signal which can be increased at the output end and the original signal can be recovered. Signal to Noise Ratio is used as a performance metric and it is derived from experimentation that, for higher frequencies Signal to Noise Ratio is more, and for lower frequencies Signal to Noise Ratio is less. [ABSTRACT FROM AUTHOR]

We study the influence of altitude and speed on aero-optic imaging quality degradation of new laser communication system "Multi-Aperture Transmission and Diversity Reception" of surface-to-air missile. The 3D modeling and meshing of surface-to-air missile are obtained by ANSYS software. The density field distribution around the optical system was analyzed by FLUENT and the nonuniform refractive-index field around is calculated, in view of the Gladstone–Dale relation. The point spread function (PSF), Strehl ratio (SR), encircled energy, and modulation transfer function (MTF) are provided for the imaging quality evaluation of optical system. The altitude ranges from 0 to 20 km, and the speeds of missile are 5 and 3 Ma. The results show that, at the constant speed, with increase in the altitude, the refraction index and the radius of dispersion spot including 80% energy are gradually decreasing; the SR results and the curve of MTF are gradually increasing, and the PSF is concentrated. At the constant altitude, with increase in the speed, the aerodynamic flow field becomes more and more complex. Therefore, the higher the altitude, the better the receiving quality, and the smaller the speed, the better the receiving quality. [ABSTRACT FROM AUTHOR]

Stochastic parallel gradient descent (SPGD) algorithm is one of the most promising methods for effective coherent beam combination. However, the algorithm also has some disadvantages, such as slow convergence speed and local extremum. This paper proposes an AdaDelSPGD algorithm, which combines an AdaDelta algorithm with a SPGD algorithm, and improves the traditional AdaDelta algorithm with adaptive gain coefficient. It is worth noting that the adaptive gain coefficient can be adjusted in real time to improve the convergence rate. The effectiveness of the proposed algorithm is verified by relevant simulation experiments, and the results show that the proposed algorithm can significantly improve the convergence speed. Following the experiments with the fiber laser-phased array multiplex communication system, we can draw the conclusion that the addition of communication modulation reduces the beam quality, and the higher the modulation frequency, the worse the beam quality. However, adding the SPGD algorithm can improve the beam quality. The AdaDelSPGD algorithm proposed in this paper can further improve the beam quality, and the bit error rate of communication is also decreased after testing. This provides a foundation for further research on the fiber laser-phased array multiplex communication system.

In this contribution, large-scale commercial aeronautical ad-hoc networks are evaluated. The investigation is based on a simulation environment with input from 2016 flight schedule and aircraft performance databases for flight movement modelling, along with a defined infrastructure of ground gateways and communication satellites. A cluster-based algorithm is used to build the communication network topology between aircraft. Cloud top pressure data can be considered to estimate cloud height and evaluate the impact of link obscuration on network availability, assuming a free-space optics-based communication network. The effects of communication range, satellite availability, fleet equipage ratio and clouds are discussed. It is shown how network reach and performance can be enhanced by adding taps to the network in the form of high-speed satellite links. The effect of adding these is two-fold: firstly, network reach can be increased by connecting remote aircraft clusters. Secondly, larger clusters can effectively be split into smaller ones in order to increase performance especially with regard to hop count and available overall capacity. In a realistic scenario concerning communication range and with moderate numbers of high-speed satellite terminals, on average, 78% of all widebody aircraft can be reached. With clouds considered (assuming laser links), this number reduces by 10%.