Space Laser Communication Research Articles

Nonmechanical two-user tracking method of space-polarization division using the liquid crystal optical phased array

We propose a two-user tracking method called space-polarization division to enable simultaneously multiple terminals tracking in the field of free space laser communications. This method is based on the nonmechanical beam steering device of liquid crystal optical phased array, which is capable of continuously laser beam pointing and multiple beams generating. An optical architecture of two-user access is presented to show a one-to-two communication link between the relay satellite terminal and user terminals. The two-user tracking strategy is modeled numerically and experimentally verified to show the feasible and agile two-user tracking with a good accuracy less than 50 microradians which meet the requirements of coarse tracking.

Initial Pointing Technology of Line of Sight and its Experimental Testing in Dynamic Laser Communication System

The initial pointing unit of the line of sight (LOS) operating in the open-loop mode is an important part of the space laser communication system, which directly determines the size of the field of uncertainty (FOU) and the length of the scan time. In this paper, the composition and working principle of the initial pointing of the LOS in the dynamic laser communication system are studied in detail. The initial pointing angle (IPA) of the LOS is derived by applying the principle of coordinate transformation, and the factors affecting the size of the FOU are analyzed. It is proposed to introduce the extended Kalman filtering technique into the initial pointing to reduce the size of the FOU. In the demonstration experiment of the dynamic laser communication (including airship–ship and aircraft–aircraft), the dual-antenna global positioning system/inertial navigation system composite device is applied to obtain position, attitude, and other parameters in real-time to realize the performance test of the initial pointing system. The size of the FOU is measured with a target-viewing camera, and the filtered and unfiltered results were compared.

Highly efficient coherent conformal projection system based on adaptive fiber optics collimator array

Coherent beam combination (CBC) of fiber laser array, which is a promising approach to overcome the power scaling limitations of the single fiber laser and to achieve high-brightness laser with good beam quality, can be employed in coherent conformal projection system (CCPS) for beam projection and free space laser communication system with enormous potential. To date, all the demonstrated CBC system through several kilometers atmospheric turbulence have employed collimated beams, which significantly decrease the final CBC effect because of the inefficient wavefront overlap. On the other hand, focused CCPS has lots of advantages over collimated projection system since the wave front of the projected beam is closer to that of a convergent spherical wave. In this paper, we design and manufacture focused CCPS based on an adaptive fiber optics collimator array for the first time, which is achieved by introducing controllable spherical aberration through the adaptive fiber optics collimator. A CBC system is setup to evaluate and validate its performance. Results show that compared with the collimated CCPS, the energy portion of the central lobe could be increased by a factor of 44%, which agrees well with the theoretical analysis.

Investigation of isolation for free space laser communication in the mono-wavelength optical T/R channels

Favorable isolation performance in optical transmitting-receiving (T/R) channels is key to establishing full-duplex bi-directional laser communication links when designing mono-wavelength laser communication terminals. This study proposes a novel design scheme for T/R channels that use a single laser wavelength. The system includes measures such as the deflection at λ/4 wave plate angles, light trap installation at a polarization beam splitter, and removal of polarization analyzers in optimized systems. A mathematical model describing isolation in the optical T/R channels is presented. Three types of factors that affect the isolation of optical T/R channels were analyzed and simulated in detail. The present simulation results show that the roughness of the λ/4 wave plate and the solid angle of the detector field of view are exponentially related to T/R isolation, which can thus be regarded as the most significant factors affecting isolation. According to the present design scheme, the prototype T/R channel was developed for measuring isolation. The measured value (77.8 dB) agrees well with the result determined using the established mathmatical model (77.3 dB). Conclusively, the present theoretical model can provideguidance for optimizing isolation in a mono-wavelength optical channel. Thus, it can be applied extensively in laser communication systems, including inter-satellite networks.

Research on APT Spot Detection Algorithm in Space Optical Communication

In space laser communication system, the coarse tracking accuracy of the APT system directly affects the field of view selection and accuracy of fine tracking system, and the accuracy of the selection of the spot center position directly affects the accuracy of the coarse tracking system. Therefore, the selection of reasonable spot detection algorithm is an important guarantee for the stable establishment of APT system. Centroid method, hough transform method, and circle fitting method are often used in the analysis of spot center and the realization of spot tracking. In order to improve the detection accuracy and anti-jamming performance, this paper compares and analyzes several commonly used spot detection methods, and obtains the applicable conditions of each algorithm.

On Increasing the Accuracy of Star Trackers to Subsecond Levels

Modern star trackers are based on photodetector arrays such as CCD or CMOS arrays. The accuracy of commercially available devices is ~1–3 arcseconds. However, the development of the space industry calls for higher orientation accuracies, which are needed in laser space communications, monitoring of near-Earth space and space debris, high-precision global mapping, and remote sensing of the Earth. The problems associated with enhancing the accuracy of modern star trackers are discussed.

Optical chaotic secure algorithm based on space laser communication

The traditional drive response synchronization control method has the poor robustness, which results in the low security performance of the optical chaotic secure communication. To address this problem, an optical chaotic secure algorithm based on space laser communication is proposed in this paper. With the advantage of space laser communication and full consideration of the influence of complex environment on signal transmission of laser wireless communication, a laser wireless communication channel model is built. Based on this, a hybrid self-synchronization chaotic system model is proposed. It can reduce the information needed for transmission, and only need to transmit a small amount of error correction signals on the channel to achieve synchronization of the receiving and the transmitting system, which greatly suppress the drawback of the traditional method. On the basis of chaotic synchronization, the erbium-doped fiber laser is used for information transmission. Different encryption techniques are used to achieve optical chaotic secure communication within the allowable range of error. Numerical simulation results show that the proposed algorithm has good security and robustness, and can realize the secure communication for different signals.

Radiation-induced mismatch effect on performances of space chaos laser communication systems.

Chaotic modulation serves as an excellent scheme to enhance the confidentiality of space laser communication systems. Considering radiation and intensity scintillation, we establish bit error rate (BER) computation models for both an inter-satellite chaos laser communication system and a satellite-to-ground chaos laser communication system. Based on such models, numerical simulations are conducted to investigate the mismatch effect on BER performance of these two typical systems. For an inter-satellite system, radiation can induce great parameter mismatches. For a satellite-to-ground system, the BER only slightly rises due to intensity scintillation being a more dominant deterioration effect than radiation. Our work has good reference value for the practical design of space chaos laser communication systems.

Polarization properties of calibration reflector system in the polarization-modulated space laser communication

Abstract S-polarization light and p-polarization light are mutually cross orthogonal, which can be used as signal light for emitting and receiving in the polarization-modulated space laser communication, respectively. Due to the retro reflection characteristics of the corner cube retroreflector (CCR), it is widely used as a calibration reflector system in the polarization-modulated space laser communication. The polarization states of the incident light will be change owing to the total internal reflection (TIR) of uncoated rear surface, in addition, each of the six propagation trips will in general produce a different output polarization. For the calibration reflector system in the polarization-modulated space laser communication, the polarization state of the received light, especially the intensity ratio of the p-polarization component, needs to be clarified. In this paper, a framework is presented to calculate polarization by ray tracing through CCR with arbitrary input polarization states and incident angles. On this basis, the relationships between intensity ratio of the p-polarization component in the received light of each propagation trip and the incident light with different polarization states at normal incidence as well as the circular polarized light at incident angles within ± 15°analyzed. Theoretical analysis and experiments have guiding significance for the development of the polarization-modulated space laser communication.

Temperature analysis of Cassegrain optical antenna for space laser communication

The thermal stability of optical antennas is a key parameter determining the performance of satellite optical communication links. The effects of uniform temperature changes on the performance of a Cassegrain optical antenna are discussed. In addition, a simple theoretical model is proposed to describe the defocusing distance and wavefront aberration (power) as a function of temperature. Through the theoretical model, the thermal stability can be quickly assessed in the optical design stage. The alignment data and thermal experimental results are consistent with the theoretical model.

Influence mechanism of repetition frequency on pulse position modulation in deep space laser communication

Taking the deep space laser communication as the application background, based on multi-pulse position modulation and differential pulse position modulation, a new differential multi-pulse position modulation (DMPPM) mode is proposed. The DMPPM theory model is set up, and a comparative study and analysis of four modulation schemes of PPM, DPPM, MPPM and DMPPM has been developed. The simulation results show that the repetition rate of the pulse laser has a great influence on the four modulation modes. DMPPM has the characteristics of the smallest average symbol length, the largest average transmitting power, the maximum peak transmitting power, the maximum unit transmission rate, the smallest bandwidth demand and a higher transmission efficiency. The analysis shows that DMPPM is greatly influenced by the repetition frequency of the laser. It is very necessary to improve the repetition rate of the laser under the premise of ensuring the peak power of the pulse laser. DMPPM can become one of the excellent modulation schemes for deep space laser communication.

Dynamic tracking and pointing accuracy measurement method of space laser communication system

Dynamic tracking and pointing accuracy measurement method of space laser communication system

空间激光通信最新进展与发展趋势

空间激光通信最新进展与发展趋势

Overview of deep space laser communication

The deep space probe is a vital technology for observing andexploring the universe. It is thus intensifying as an aerospace researchfocus on an international scale. Despite improving the frequency band,the conventional microwave communication technique has difficultysatisfying the increased demand for the enormous volume of scientific datareturning to the Earth. With a carrier frequency that is several orders ofmagnitude higher than the microwave, free-space optical communication is arobust and promising method for achieving both high bit rates and longdistances in deep space communication. In this article, the history of thistechnology is summarized and the objective laws are formulated, while keytechniques and development trends are analyzed. Finally, useful concepts andsuggestions are proposed for the development of deep space lasercommunication in China.

Satellite-to-ground quantum-limited communication using a 50-kg-class microsatellite

Recent rapid growth in the number of satellite-constellation programs for remote sensing and communications, thanks to the availability of small-size and low-cost satellites, provides impetus for high capacity laser communication (lasercom) in space. Quantum communication can enhance the overall performance of lasercom, and also enables intrinsically hack-proof secure communication known as Quantum Key Distribution (QKD). Here, we report a quantum communication experiment between a micro-satellite (48 kg and 50 cm cube) in a low earth orbit and a ground station with single-photon counters. Non-orthogonal polarization states were transmitted from the satellite at a 10-MHz repetition rate. On the ground, by post-processing the received quantum states at an average of 0.14 photons/pulse, clock data recovery and polarization reference-frame synchronization were successfully done even under remarkable Doppler shifts. A quantum bit error rate below 5% was measured, demonstrating the feasibility of quantum communication in a real scenario from space.

Networking optical antenna of space laser communication

Laser communication network technology has not been broken through and it needs to meet the demands of “high-speed, real-time, dynamic and big range” among platforms, which seriously restricts large-scale engineering application and space network system. To solve the problem of communication platform for networking, a new solution based on rotating parabolic model and a new scheme of laser communication networking antenna system has been put forward in the paper. Depending on the operation mode of the system, multiple mathematical optimization models have been established. Tracking communication range, emission energy efficiency, and receiving energy efficiency have been analyzed and optimized. Relationship among opening up and low apertures, lens unit aperture, focal length of lens unit as well as rotating parabolic focal length have been analyzed. After preliminary optimized design of the system, demand of three satellites in 1000 km, 360° circumferential range, pitch range greater than 20° under the condition of network communication can be reached. Under the background of three LEO (low earth orbit) satellites within 1000 km distance of 2.5 Gbps rate in networking, communication link energy is analyzed and calculated to meet the smallest and the lightest of laser emission energy. Relationship between track angle and receiving as well as emission energy is analyzed. Conclusions can promote various fields of engineering, large-scale applications, and updated generations.

空间激光通信中四象限光电探测器环形光斑检测及误差补偿

空间激光通信中四象限光电探测器环形光斑检测及误差补偿

空间激光通信离轴两镜反射望远镜自由曲面光学天线设计

The coaxial two-mirror reflective structure has the disadvantage of small receiving field of view and low emission efficiency when being used as optical antenna in space laser communication. At the same time, the energy loss caused by central obscuration will greatly reduce the aiming and capturing probability of communication system. For this inherent defects, an off-axis two-mirror reflective structure with freeform surface was designed to improve the performance of space laser communication. The initial structure of the off-axis two-mirror reflective structure was deduced according to the basic aberration theory. Zernike polynomial freeform surface was introduced to improve the ability of designing freedom and balancing the freeform surfaces aberration. A design example was given whose coaxial and off-axis two-mirror reflective system had same pupil aperture and focal length, and the modulation transfer function, spot diagram, diffraction encircled energy and wavefront error were compared. The results show that the image quality of the off-axis two-mirror reflective antenna with freeform surface is better than that of the coaxial, thus, the structure of the off-axis two-mirror reflective antenna structure could improve entire performance of space laser communication system.

大气湍流对空间激光通信跟踪系统的影响

大气湍流对空间激光通信跟踪系统的影响

基于液晶光学相控阵的空间激光通信PID跟踪方法

基于液晶光学相控阵的空间激光通信PID跟踪方法