Space Laser Communication Research Articles

Tracking Performance of Mirrors in Space Laser Communication Networking

Tracking Performance of Mirrors in Space Laser Communication Networking

Experimental research on transmission performance on OAM beam and Gaussian beam in atmospheric turbulence channel

The transmission performance of orbital angular momentum(OAM) beam and Gaussian beam in atmospheric turbulent channel was studied and compared experimentally. The beam spreading, pointing error, power jitter and bit error rate of the two beams were measured respectively, the OAM beam loaded with modulated signals and the Gaussian beam were as carrier. The experimental results show that in the atmospheric turbulence channel, compared with Gaussian beam, beam spreading ratio of the OAM beams reduces by 10.5%, variance of power jitter falls 0.13, dispersion circle diameter of the pointing error decreases by 30.4%, and more focused on the distribution of the center of the beam axis. The lowest detection sensitivity of the OAM beam carrier system reaches −28.97 dBm, which improved 2.5 dB compared with that of Gaussian beam. The experimental results verify that OAM beam is less affected by turbulence than Gaussian beam in atmospheric turbulence channel, and the deterioration of beam quality of OAM beam is much less than Gaussian beam with the increase of turbulence intensity. The results of the experiment provide a reference for the development and application of free space laser communication in atmospheric turbulent channel.

Analysis and correction of geometrical error-induced pointing errors of a space laser communication APT system

The geometrical error caused pointing error is an inevitable problem in space satellite laser communication terminals which can affect the pointing accuracy of the APT (acquisition pointing and tracking) system greatly, in order to facilitate the assembling of the APT system and improve the performance of the laser communication system, the geometrical error sensitivity about the APT pointing accuracy is analyzed based on multi-body kinematics method in this paper, the error transformation matrix is derived and the geometrical error is analyzed, the simulation results provide some pointing error distribution regulars which are conductive to assembling. Based on the above research, the geometrical error correction experiment is performed and the pointing accuracy of the APT system is tested, the expectation value of the pointing error can reach 29.9 µrad which is greatly improved. This research can provide technical references for the design and analysis of space laser communication terminals.

Atmospheric Laser Communication Technology Based on Detector Gain Factor Regulation Control

Space laser communication, with its strong anti-jamming capability, high transmission rate and good adaptability, offers hope for the establishment of 5G mobile networks in areas that are not conducive to the erection of cables, such as islands and remote land areas. Turbulent scintillation effect is one of the important factors affecting the performance of laser communication, which can lead to the increase of communication BER and even communication interruption. Based on the working principle of the photoelectric detector in atmospheric turbulence, an optical communication receiving system based on the detector gain factor regulation control is designed, which calculates the scintillation variance according to the received signal in real time, establishes the function conversion relationship between the scintillation variance and the gain factor, realizes the closed-loop regulation control of the detector gain factor, and improves the SNR of the receiving system. A ground-based 13km static laser communication experiment was set up to test the reception performance, and the test results show that the system reduces the communication BER by more than two orders of magnitude and can be kept at 1E-6 under medium to weak turbulence (discriminated by flash variance) at a communication rate of 2.5Gbps. The technology was applied to the test of laser 5G signal transmission between the airship and the ground, and for the first time, the mobile communication (access network) signal transmission with a downlink speed of 1.230Gbps and an uplink speed of 76.4Mbps is realized, which verified the performance of mobile signal transmission between the mobile base station and the fixed station on the ground.

Control Technology of Slave Optical Transceiver in Space Laser Communication Network

Control Technology of Slave Optical Transceiver in Space Laser Communication Network

Design and analysis of a bi-axial centralized butterfly flexure hinge for fast steering mirrors

A bi-axial centralized butterfly flexure hinge for a fast steering mirror (FSM) was presented to adapt highly stabile accuracy of beam-pointing control performance in space laser communication. According to the requirements of two-dimensional reciprocating movements and high bandwidth provided for the FSM, the solid model of the bi-axial centralized butterfly flexure hinge was designed. By applying Castigliano’s displacement theorem, the numerical model was simplified and deduced. Furthermore, to quantify the numerical model, natural frequencies of the finite-element analysis (FEA) and experiments were carried out the results of which were compared with the analytic solutions. The experimental results show that the in-plane natural frequencies are 66.37 and 112.2 Hz, respectively. The comparison shows that the errors between numerical analytic and experimentation are 3.0% and 1.4%, respectively, and errors between FEA and experimentation are 1.7% and 2.4%, respectively. It is proven that the bi-axial centralized butterfly flexure hinge we built is an appropriate structure as a two-axis guide mechanism in two-dimensions for an FSM system with a large bandwidth of 225 Hz.

Analysis of scintillation effects along a 7 km urban space laser communication path.

In this study, the scintillation effects along a 7 km space laser communication path in an urban area were examined, including the relationship between the scintillation and bit error rate and the variation of the scintillation index with changes in the transmitting and receiving apertures. It was concluded that multi-aperture transmitting technology can effectively reduce the scintillation caused by atmospheric turbulence. For the investigated urban link, the scintillation index could meet the communication requirements for adjusting the receiving aperture. These results will facilitate space laser communication improvement and turbulence suppression along horizontal urban paths.

Characterization of film-evaporating microcapillaries for water-based microthrusters

Compact micronewton thrusters can provide attitude control for small satellites to increase mission duration and enable constellation flying. Micronewton thrust control can also enhance missions that require precision pointing such as space telescopes, laser interferometers, and laser communication relays. Film-Evaporating MEMS Tunable Array (FEMTA) is a novel micropropulsion device that generates thrust by heating a micron-scale water capillary to induce controlled film-evaporation. Thrust stand tests under high vacuum have shown that FEMTA can produce controllable thrust of 150μN at 70s specific impulse using 0.65W of electrical power and ultra-pure deionized water as propellant. An undesired quiescent propellant loss rate is inherent to the current FEMTA design which limits its life span and reliability. To derive mitigations to this issue, the behavior of the fluid interface within the FEMTA micronozzle was characterized through direct experimentation. A test-bed FEMTA design was created which enabled direct observation of the liquid within the micronozzles and precise control over critical nozzle dimensions. These test-bed devices were used to measure contact angle, Laplace pressure, and total quiescent propellant loss rates for multiple nozzle configurations. Finally, a next generation FEMTA design was derived from the findings of these studies and its propulsive performance was measured under high vacuum on a micronewton thrust stand. Microfabrication was performed at Purdue’s Birck Nanotechnology Center and vacuum testing was completed at Purdue’s High Vacuum Lab.

Integrated Multichannel Lithium Niobate Waveguides for Quantum Frequency Conversion

Lithium niobate photonic chip could realize diverse optical engineering for various applications benefiting from its excellent optical performances. In this letter, we demonstrate monolithic photonic chips for multi-channel sum-frequency conversion based on reverse-proton-exchange periodically poled lithium niobate waveguides, with the different channels showing uniform and excellent conversion efficiencies. To obtain a robust device and provide a convenient interface for applications, the integrated chip is fiber coupled with two fiber arrays. The packaged chip then forms the core of a multi-channel up conversion single photon detector. In each channel the input signal interacts with a 1950-nm single frequency pump laser and the sum frequency output is spectrally filtered and detected by a silicon avalanche photodiode. Average detection efficiency (DE) of 23.2 % and noise count rate (NCR) of 557 counts per second (cps) are achieved, with a standard deviation of 2.73 % and 48 cps over the 30 channels, as well as optical isolation (OI) between nearby channels of more than 71 dB, which are excellent for the extensive applications of monolithic photonic chips in fields including deep space laser communication, high-rate quantum key distribution and single-photon imaging.

Tip of the hat

Researchers from China have proposed a hollow top-hat beam (HTB) diffractive optical element (DOE) shaping method, for use in space uplink chaotic communications systems (SUCCS). Simulation results show that by shaping the beam into a HTB, the bit error-rate (BER) improvement is substantial when compared to the traditional hollow Gaussian beam (HGB). The results could be significant for the optimisation of designs relating to SUCCS. Laser communication is a type of communication technique that, unsurprisingly, uses laser beams as a signal carrier, allowing the transmission of images, sound and other data in free space. It has been conceptualised since the development of the first lasers in the 1960s. When compared to more traditional microwave communication, laser communication has the advantages of allowing faster transmission due to higher data-rate (in principle anywhere from 1,000 to 100,000 times faster), a larger communication capacity, smaller terminal size and lower power consumption. It is anticipated that, due to its higher data-rate, laser communication will be the preferred candidate for the problem of bottlenecking when it comes to space uplink communications. Prof Mi Li (left of centre) and his research group. (a) original Gaussian distribution of laser beam (b) hollow Gaussian beam (HGB) shaped by DOE (c) hollow top-hat beam (HTB) shaped by DOE. Space chaotic laser communication system. Reducing the complexity of designing laser communications systems is a hot topic in the research field of free-space communication. Optical antennas play an important role, where they function as beam collators, expanders and convergers – all of which can improve the performance of free-space communication. One of the most commonly used antennas is the Cassegrain reflective optical antenna, featuring a short mirror body, high magnification and elimination of spherical aberrations (which result in blurry images due to numerous undesired focal points). Cassegrain antennas do come with a drawback, however, in that the secondary mirror can block part of the transmission beam, affecting the transmission efficiency of the optical system. The work presented in this issue of Electronics Letters is applicable to space chaotic laser communications systems, which are more complex than ground optical fiber chaotic communication systems. The authors use a DOE to shape a carrier beam into a hollow, top-hat shape (see inset images). DOEs have been widely used in the field of beam-shaping due to the advantages of high diffraction efficiency, flexible design and simple structure. Intelligent shaping of the beam can eliminate the problem of secondary mirrors in a Cassegrain antenna blocking part of the transmission beam. It can also be used to improve the transmission efficiency of the optical sub-system, meaning that the design pressure on other sub-system parameters is eased. DOEs can be used to shape and split laser beams in an energy-efficient manner and are often used in production facilities for laser material processing, or in medical laser treatments and diagnostics. They also see use in lighting, printing and lithography. In short, DOEs are frequently used in areas where shaping and splitting with minimal light loss is necessary. In order to effectively demonstrate how their suggested HTB improves the quality of the communication system, the authors use BER to evaluate their work. They also compare the HTB to a HGB, which they used in previous research works, to see if there is any difference in quality when considering the two shapes for SUCCS. The research considers strong and weak atmospheric conditions, as atmospheric turbulence also plays a role in the BER of signals moving between Earth and orbit. The work shows that, at higher beam power, BER is reduced by around 10−0.9 when using the HTB shaping method at a low chaotic mismatch and 10−1.5 at a high chaotic mismatch. In both scenarios the HTB shaping outperforms the HGB shaping, showing that the HTB is more suitable for SUCCS. In recent years there have been a number of exciting achievements in the free-space laser communication field. Laser communication has moved from concept to practice, Mbps rates to Gbps rates and we are now seeing the next iteration of communication technology. Research scientists are carrying out research work on small-size, high-speed laser communication stations. The work presented here not only improves the efficiency of the beam, but also makes steps towards reducing the design difficulty of other sub-systems within the communication terminal. The authors hope that this work will also allow a meshing of 5G ground wireless communications and space laser communications networks, and even pave the way for easier realisation of 6G in the future.

Point ahead angle prediction based on Kalman filtering of optical axis pointing angle in satellite laser communication

Point ahead angle (PAA) prediction is important in space laser communication, but the existing methods have low accuracy and complicated calculation processes. In this paper, a new PAA prediction method is proposed based on Kalman filtering of the optical axis pointing trajectory. The proposed method uses the high precision of fine tracking to improve the accuracy of predictive filtering. Taking ground-satellite laser communication as the research background, the beam transmission process in a typical acquisition, pointing, and tracking (APT) system is derived, then the Kalman filter model is established, and a simulation of the model is performed. The results show that the PAA can be predicted accurately and the error of the PAA can be reduced effectively the maximum prediction error is 3.8 μrad only, and the method does not need to take the complex satellite perturbations into consideration. The proposed approach improves the accuracy of PAA prediction and contributes to the design of space laser communication systems.

Recent Trends in Space Laser Communications for Small Satellites and Constellations

Free-space optical communications in space can realize broadband and large-capacity communications using smaller and lower-power-consumption onboard equipment. Recently, many mega-constellation systems have been planned and launched from various countries. Although the frequency spectra will soon be exhausted, optical communications have potentially wider bandwidths in the optical spectrum and are a viable alternative. Because optical communications do not have regulatory restrictions or licensing issues, this technology can revolutionize the space system architecture. This article describes the recent trends and future prospects of space laser communications.

Tm-doped fiber laser with multiwavelength output and switchable wavelength difference based on nonlinear polarization rotation effect

In this paper, we report on the characteristics of multiwavelength output and wavelength difference switching in a Tm-doped fiber laser based on the nonlinear polarization rotation effect. The multiwavelength output and wavelength difference switching were realized through joint action of nonuniform intensity-dependent loss caused by the nonlinear polarization rotation effect and the polarization controller intertwined with Tm-doped fiber. Under dual-wavelength state, one wavelength could be switched within wavelength intervals of 44.7, 58.0, 68.2, and 73.1 nm, and the position of the other wavelength nearly remained unchanged in the switching process. The fiber laser with switchable wavelength difference has a broad application prospect in laser space communication and optical fiber sensing.

The application of ultramicroscope with high precision in light and small laser communication system for micro-nano satellite

With the rapid development of space laser communication technology, it is possible to realize mass data transmission between satellites in low orbit. Micro-nano satellite is the first choice of low orbit communication satellite because of its lightweight, small size and low cost. Laser scanning technology is a kind of technology that can accurately control the direction of laser beam. It has been widely used in the field of space laser communication. In this paper, after analyzing the technical requirements of the scanning mirror with APT system for microsatellite, a kind of miniature scanning mirror is selected to realize the accurate pointing of the beam.

Research on acquisition and tracking technology for the four-quadrant detector

Aiming at the space laser communication system requirement of miniaturization, this paper proposes a scheme of using the four-quadrant detector to complete the acquisition and tracking. By analyzing the position distribution of the spots on the four-quadrant detector (4QD), the acquisition models are derived for the three kinds of spots distribution. Through the calculation of the position of the spots and the accurate calibration of the tracking mechanism, the high precision tracking is realized. Then besed on the laserteco and system test platform the capture and tracking scheme and detection performance of the 4QD are experimentally verified. The test results show that under the laboratory dynamic conditions, using 4QD as the capture and tracking detector, the capture probability is up to 100%, and tracking accuracy is better than 3μrad, which verifies the feasibility of the scheme and lays a foundation for the miniaturization design of the laser terminal.

像差对空间激光通信系统发射光束远场分布的影响

像差对空间激光通信系统发射光束远场分布的影响

Progress and Prospect of Space Laser Communication Technology

Progress and Prospect of Space Laser Communication Technology

Model analysis and resonance suppression of wide-bandwidth inertial reference system

In the fields of earth observation, deep space detection, laser communication, and directional energy weapon, the target needs to be observed and pointed at accurately. Acquisition, tracking, and pointing (ATP) systems are usually designed to stabilize the line of sight (LOS) within sub-micro radian levels. In the case of an ATP system mounted on a mobile platform, angular disturbances experienced by the mobile platform will seriously affect the LOS. To overcome the problem that the sampling frequency of detectors is usually limited and achieving several hundreds of hertz is difficult, the wide-bandwidth inertial reference system (WBIRS) and fast steering mirror are usually integrated into ATP systems to mitigate these angular disturbances. To reduce the structural stress, a flexible support providing two rotational degrees of freedom is usually adopted for the system. However, the occurrence of resonant points within the bandwidth will be inevitable. Measurements have to be taken to compensate these low-frequency resonant points to realize a wide bandwidth and high precision. In this paper, the low-frequency resonant points of a system were simulated using finite element analysis and tested by a system identification method. The results show that the first-order resonance happened at 34.5 Hz with a gain of 28 dB. An improved double-T notch filter was designed and applied in a real-time system to suppress the resonance at 34.5 Hz. The experimental results show that the resonance was significantly suppressed. In particular, the resonance peak was reduced by 79.37%. In addition, the closed-loop system settling time was reduced by 36.2%.

High Speed Laser Information Transmission Technology of Deep Space Between Moon and Earth

The application of light wave for deep space information transmission will have the advantages of smaller terminal volume,mass and low power consumption under the same data rate,and the receiving sensitivity is high during the transmission process. Because of the narrow beam width,it can make the energy centralized and reach a long transmission distance. Using light wave as the information carrier of deep space exploration will have the advantages that the microwave band does not have. The feasibility of technology is described, and the research status of the moon earth laser information transmission technology is summarized,providing a reference for the development and engineering application of deep space laser communication in China.

Shipborne Acquisition, Tracking, and Pointing Experimental Verifications towards Satellite-to-Sea Laser Communication

Acquisition, tracking, and pointing (ATP) is a key technology in free space laser communication that has a characteristically high precision. In this paper, we report the acquisition and tracking of low-Earth-orbit satellites using shipborne ATP and verify the feasibility of establishing optical links between laser communication satellites and ships in the future. In particular, we developed a shipborne ATP system for satellite-to-sea applications in laser communications. We also designed an acquisition strategy for satellite-to-sea laser communication. In addition, a method was proposed for improving shipborne ATP pointing error. We tracked some stars at sea, achieving a pointing accuracy of less than 180μrad.We then acquired and tracked some low-Earth-orbit satellites at sea, achieving a tracking accuracy of about 20μrad. The results achieved in this work experimentally demonstrate the feasibility of ATP in satellite-to-sea laser communications.