Search

Space laser communication technology has advantages such as high bandwidth and low interference, but the limitation of the load capacity of an unmanned aerial vehicle (UAV) makes it difficult for UAV clusters to have sufficient communication links to build a stable communication network. Aiming to address the problem of the low upper limit of the node degree of the self-organized network after the introduction of space laser communication technology for UAVs, a virtual node topology control (VNTC) algorithm is proposed for constructing an efficient and stable communication network structure. The algorithm is based on the unit disc graph model and achieves a lower-node-degree upper bound while maintaining connectivity through node pairing and virtual graph construction. The theoretical analysis and experimental results of the algorithm show that the algorithm can effectively deal with the topology control problem in UAV laser networks. In contrast to the XTC algorithm (exceptional topology control), the VNTC algorithm maintains the connectivity and most of the planarizability of the network, and, at the same time, it performs better in reducing the node degree and number of edges, thus providing an effective solution for low-connectivity topology control. [ABSTRACT FROM AUTHOR]

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 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.)

Space laser communication technology has advantages such as high bandwidth and low interference, but the limitation of the load capacity of an unmanned aerial vehicle (UAV) makes it difficult for UAV clusters to have sufficient communication links to build a stable communication network. Aiming to address the problem of the low upper limit of the node degree of the self-organized network after the introduction of space laser communication technology for UAVs, a virtual node topology control (VNTC) algorithm is proposed for constructing an efficient and stable communication network structure. The algorithm is based on the unit disc graph model and achieves a lower-node-degree upper bound while maintaining connectivity through node pairing and virtual graph construction. The theoretical analysis and experimental results of the algorithm show that the algorithm can effectively deal with the topology control problem in UAV laser networks. In contrast to the XTC algorithm (exceptional topology control), the VNTC algorithm maintains the connectivity and most of the planarizability of the network, and, at the same time, it performs better in reducing the node degree and number of edges, thus providing an effective solution for low-connectivity topology control.

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 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]

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]

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.

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.

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.

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]

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%.

The second node of the laser-based European Data Relay System (EDRS-C) was successfully launched on 6th August 2019. The EDRS-C satellite, developed, manufactured and tested by OHB System AG as prime contractor, has been procured in the frame of a Public Private Partnership (PPP) between the European Space Agency (ESA) and Airbus Defence and Space (ADS). The primary objective of the EDRS mission is to provide a data relay service to low-Earth-orbit satellites from geostationary orbit by means of optical and radio-frequency bands. A constellation of geostationary satellites will be linked to a network of ground stations and, using innovative laser communication technology, will receive data from Earth observation satellites from lower orbits and relay it to ground stations in Europe, in near real-time and at a rate of 1.8 Gbit/s. The geostationary EDRS-C satellite features laser communication terminal that significantly differentiates it from conventional telecom satellites. Laser Communication Terminal (LCT) was designed and manufactured by TESAT Spacecom. EDRS-C has been developed on the basis of the SmallGEO platform. In order to accommodate the LCT, adaptations to the existing platform design had been required, which implied a consolidation of the existing platform design, an extension of its competitiveness with reference to the application of optical payloads, and an important milestone in the development and industrialization of the generic SmallGEO platform product line. This paper presents the main design adaptations performed on the SmallGEO platform in order to provide the LCT with an environment that guarantees its full performances. Some selected assembly, integration and test matters specific to optical payloads, and in particular to an LCT, are summarized as well in this paper. • EDRS-C, 2nd node of the European data relay system, was launched on the 6th of August 2019. • EDRS System provides data relay service up to 1.8 Gbit/s for LEO satellites. • Major design challenge was to accommodate a laser instrument on a telecom spacecraft. • Typical verification and testing approach had to be tailored to the laser instrument. • In-orbit testing has confirmed the performances of the satellite as tested on ground. [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.

We mainly report an efficient approach to optimize the design of beaconless spatial laser acquisition. In order to analyze the influence of vibration environment on the beaconless spatial acquisition, a demonstration of an efficient method will be presented to simulate the level of satellite platform vibration. An important power spectral density (PSD) model of satellite platform vibration used by the European Space Agency is introduced. Then through LABVIEW, a simulated vibration waveform is generated, and the simulated PSD has a basic consistency with the in-orbit measurement spectral line, referring to the design of the filter, generating the Gaussian white noise sequence, filtering the pseudorandom signal and the whole processing procedure of parameter matching. The variation interval of the vibration amplitude is from -100 to 40 μrad. Then, the model of beaconless acquisition is proposed, which uses the spiral scan pattern, laser with a divergence angle of 80 μrad scan in an uncertainty cone (UC), and also the scan coupled with the simulated vibration is given. Through the beaconless acquisition program, the vibration is suppressed between -10.7 and 5.9 μrad; when the overlap factor is selected as 10%, it does not produce any leakage scanning area. It can be used for a wide variety of platforms. This new method will be good for analysis and test of beaconless spatial acquisition algorithm. Finally, the description of acquisition duration, which mainly includes the fast steering mirror spiral scan and the mechanical rotary table step scan, is introduced. And the corresponding optimal selection method of sub-region is proposed; the design of 1.6-mrad scanning pattern with 7 × 7 sub-regions in the 8-mrad acquisition UC is given. Through the actual measurement, the acquisition time is 18.21 s, the tracking error is better than 0.4 μrad.

Featured Application: The research results in this paper are helpful for researchers to analyze and design the adaptive optics (AO) systems for atmospheric laser transmission and detection systems, such as free space optical communication and gas sensing lidar. The method in this paper can be used to study the residual margin allocation of AO system under different coupling efficiency thresholds. In this study, Zernike polynomials and optical fiber field theory are applied to build a mathematical model of coupling efficiency (CE) and spatial mode of aberrations. The theory built in this paper can be used to quickly calculate the CE affected by a single aberration as well as the aberrations caused by atmospheric turbulence. The aberrations are classified based on Zernike polynomials and the effects of aberrations on CE of different types and different spatial frequencies are analyzed. The influence of the effects of AO system residual errors is also analyzed. Adaptive optics (AO) equipment is applied to build a system on which the proposed theory was tested; the experimental results validate the theoretical analysis. [ABSTRACT FROM AUTHOR]

Laser technology has observed a great advancement over the last few decades. This technology is used for a wide range of applications including medical sciences, military, industrial manufacturing, electronics, holography, spectroscopy, astronomy and much more. Military operations often demand a secure and timely transmission of a massive amount of information from one place to another. Until now, the military has relied on the radio spectrum for effective communication, which is vulnerable to security threats and susceptible to electromagnetic interference (EMI). Also, this spectrum is hard-pressed to meet the current bandwidth requirement for high-resolution images, on-air video conferencing and real-time data transfer. Therefore, the focus has shifted to visible and infrared spectrum using laser technology which is capable of providing secure data transfer because of its immunity to EMI. The probability of intercepting a laser signal is very low due to its narrow beam divergence and coherent optical beam, making the laser a suitable candidate for secure military tactical operations. Besides the communication aspect, the highly directive nature of a laser beam is also used as a directed energy laser weapon. These highly powerful and light weighted directed energy laser weapons are very cost-effective countermeasures for airborne threats. Furthermore, laser sensors are deployed in the battlefield or in space for tracking the path of a wide range of military vehicles like missiles, unmanned aerial vehicles, fighter aircraft, warships, submarines, and so on. Advancements in space operations and laser technology have offered synergistic possibilities of using lasers from space-based platforms during military operations. In this paper, we are providing our readers with a comprehensive study of laser applications, used by the military, to carry out tactical operations on the ground or space-based platforms. Also, an intensive investigation on the development of laser technology for sensors, range-finders and target designators that are used for intelligence, surveillance and reconnaissance is presented in the paper. The advancement of laser communication for military purposes and its current state of the art is reviewed as well as some recent scientific developments in the area of high-energy directed laser weapons are discussed, which have revolutionized military battlefields. Therefore, this manuscript highlights recent trends and engineering breakthroughs for the use of lasers in tactical operations.

The Compressed Sensing (CS) camera can compress images in real time without consuming computing resources. Applying CS theory in the Laser Communication (LC) system can minimize the assumed transmission bandwidth (normally from a satellite to a ground station) and minimize the storage costs of beacon light-spot images; this can save more than ten times the typical bandwidth or storage space. However, the CS compressive process affects the light-spot tracking and key parameters in the images. In this study, we quantitatively explored the feasibility of the CS technique to capture light-spots in LC systems. We redesigned the measurement matrix to adapt to the requirement of light-tracking. We established a succinct structured deep network, the Compressed Sensing Denoising Center Net (CSD-Center Net) for denoising tracking computation from compressed image information. A series of simulations was made to test the performance of information preservation in beacon light spot image storage. With the consideration of CS ratio and application scenarios, coupled with CSD-Center Net and standard centroid, CS can achieve the tracking function well. The information preserved in compressed information correlates with the CS ratio; higher CS ratio can preserve more details. In fact, when the data rate is up than 10%, the accuracy could meet the requirements what we need in most application scenarios.

Background: Mast is mainly used for assisting the communication-vehicle-mounted optical transceiver to obtain a coarse tracking of objects rapidly and accurately, especially when objects are communicating among different regions. Methods: This study first conducts a force analysis of a vehicle-mounted mast specialized for laser communication and then derives dynamic characteristics of the mast under wind load. In order to validate tracking precision and the stabilization of the optical transceiver, and examine the wind disturbance resistance of the mast, a series of field experiments were carried out. Results and Conclusion: Finally, the test errors were analyzed in detail, and the experimental results demonstrated that the tracking error of the vehicle-mounted optical transceiver is less than 80μrad which means the optical transceiver satisfies the system requirements in terms of precision. Furthermore, both theoretical analysis and experimental results revealed that designed mast satisfies the technical requirements of the vehicle-mounted laser communication, thus the feasibility of the mast in vehicle-mounted communication was validated. [ABSTRACT FROM AUTHOR]

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%. [ABSTRACT FROM AUTHOR]

The registered history of laser technologies for space application starts with the first laser echoes reflected off the Moon in 1962. Since then, photonic technologies have become very prominent in most technical development. Their presence has also dramatically increased in space applications thanks to the many advantages they present over traditional equivalent devices, such as the immunity against electromagnetic interference, as well as their efficiency and low power consumption. Lasers are one of the key components in most of those applications. In this review, we present an overview of the main technologies involving lasers that are currently deployed in space, before reviewing the requirements for lasers to be reliable in that environment before discussing the advantages and drawbacks of replacing standard technologies by newly developed photonic laser-based devices.

In this study, Zernike polynomials and optical fiber field theory are applied to build a mathematical model of coupling efficiency (CE) and spatial mode of aberrations. The theory built in this paper can be used to quickly calculate the CE affected by a single aberration as well as the aberrations caused by atmospheric turbulence. The aberrations are classified based on Zernike polynomials and the effects of aberrations on CE of different types and different spatial frequencies are analyzed. The influence of the effects of AO system residual errors is also analyzed. Adaptive optics (AO) equipment is applied to build a system on which the proposed theory was tested; the experimental results validate the theoretical analysis.

Copyright of Iraqi Journal of Physics is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) 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.)