The establishment of a high-precision optical link is a necessary condition for satellite-to-ground quantum communication experiments. Compared with conventional laser communications, a quantum experimental satellite needs to solve special requirements such as the great difference between the energy of quantum light and beacon light, and the establishment of optical links between one satellite and two ground stations. Based on the scientific demands of satellite-to-ground quantum communication, this paper proposes an overall scheme for an optical link establishing system with a combination of satellite pointing and load autonomous searching. By using a multiple-axis pointing control method, the requirements of high-precision optical tracking are met. We use the stare-stare capture method to achieve fast capture between the satellite and the ground stations. The high-precision alignment of the satellite and ground quantum beams is realized by using a method of joint scanning and system correction. Finally, in-orbit test results of the Mo-tse quantum experimental satellite are given. The experimental data show that all parameters in the establishment of optical links meet or exceed the expected requirements.
The establishment of a high-precision optical link is a necessary condition for satellite-to-ground quantum communication experiments. Compared with conventional laser communications, a quantum experimental satellite needs to solve special requirements such as the great difference between the energy of quantum light and beacon light, and the establishment of optical links between one satellite and two ground stations. Based on the scientific demands of satellite-to-ground quantum communication, this paper proposes an overall scheme for an optical link establishing system with a combination of satellite pointing and load autonomous searching. By using a multiple-axis pointing control method, the requirements of high-precision optical tracking are met. We use the stare-stare capture method to achieve fast capture between the satellite and the ground stations. The high-precision alignment of the satellite and ground quantum beams is realized by using a method of joint scanning and system correction. Finally, in-orbit test results of the Mo-tse quantum experimental satellite are given. The experimental data show that all parameters in the establishment of optical links meet or exceed the expected requirements.
To meet the requirement of high-accuracy pointing of quantum signals in satellite-to-ground quantum communication, this paper proposes a flexible satellite-based pointing method that changes the fine tracking point to solve the problem from point-ahead angle and ground beacon laser offset. This method does not require the use of a point-ahead mechanism and can detect the pointing angle in real time. Detailed algorithms and analysis are given. The method has been verified in orbit on the quantum science satellite Micius. The satellite-to-ground test results show that the quantum signal pointing accuracy is between 0.5∼1.0 µrad, which meets the efficiency requirements of satellite-to-ground quantum communication.
A satellite dedicated for quantum science experiments, has been developed and successfully launched from Jiuquan, China, on August 16, 2016. Two new optical ground stations (OGSs) were built to cooperate with the satellite to complete satellite-ground quantum experiments. OGS corrected its pointing direction by satellite trajectory error to coarse tracking system and uplink beacon sight, therefore fine tracking CCD and uplink beacon optical axis alignment accuracy was to ensure that beacon could cover the quantum satellite in all time when it passed the OGSs. Unfortunately, when we tested specifications of the OGSs, due to the coarse tracking optical system was commercial telescopes, the change of position of the target in the coarse CCD was up to 600μrad along with the change of elevation angle. In this paper, a method of reduce alignment error between beacon beam and fine tracking CCD is proposed. Firstly, OGS fitted the curve of target positions in coarse CCD along with the change of elevation angle. Secondly, OGS fitted the curve of hexapod secondary mirror positions along with the change of elevation angle. Thirdly, when tracking satellite, the fine tracking error unloaded on the real-time zero point position of coarse CCD which computed by the firstly calibration data. Simultaneously the positions of the hexapod secondary mirror were adjusted by the secondly calibration data. Finally the experiment result is proposed. Results show that the alignment error is less than 50μrad.
The development of space-based quantum communication is a critical step toward establishing global-scale secure networks. Quantum communication via satellites enables long-distance key exchange beyond the limitations of terrestrial fiber networks. To support such missions, robust optical ground stations are essential for maintaining high-fidelity quantum links with orbiting platforms. Commissioned in early 2024, the Singapore Optical Ground Station is the first dedicated facility of its kind located near the equator. Its equatorial position enables frequent access to satellites in a wide range of orbital inclinations, making it uniquely suited for supporting diverse global quantum networks. Its receiving optics can accommodate quantum links across a broad range of wavelengths and support various encoding schemes, including polarization and phase. In this work, detailed results from preliminary testing of the pointing, acquisition, and tracking system for low Earth orbit satellites are presented. For LEO satellites, a tracking accuracy reaching 50 microradians, approaching the local atmospheric seeing limit was achieved.Tracking stability is maintained using a hybrid feedback control loop designed to accommodate sporadic link losses caused by cloud cover. These results demonstrate the readiness of the SOGS to support current and future missions towards satellite quantum networks.
Designing a laser communications payload integral to a nano-satellite, capable of fine pointing, is a difficult task. Integrating this with a quantum key distribution payload for inter-satellite secure communication adds significant complexity, as does ground based communication with the moving objects in low Earth orbit. The advantages of low path length, secure, global communication make this an opportunity not to be missed. We report on developments of such a system. Beginning with a satellite demonstrator with a Pointing, Acquisition-and Tracking system that involves fine precision star-tracker, plasma and aerodynamic force interactions for steering, and an inter-satellite laser link demonstration on orbit using LED beacon for acquisition, and laser for communications link closure. Combining design studies for a nano-satellite quantum payload for transferring entangled photon-pairs between the satellites at long-range in Low Earth Orbit, and incorporating ground to space and space to ground laser communications, are described in the context of quantum optical ground station efforts within Australia.
To establish optical links between an optical ground station (OGS) and a quantum experiment satellite, a method of acquisition for the Micius satellite is proposed in this paper and the acquisition technological specification of the OGS system is analyzed. An acquisition strategy for the OGS is designed to meet the requirements of the quantum experiments. A method is designed to point accurately at the quantum satellite and improve the absolute pointing precision. The results show that the correction accuracy is better than 5 μrad, the acquisition time is less than 5 s, and the acquisition probability is 100% so far.
A worldwide growing interest in fast and secure data communications pushes technology development along two lines. While fast communications can be realized using laser communications in fiber and free-space, inherently secure communications can be achieved using quantum key distribution (QKD). By combining both technologies in a single device, many synergies can be exploited, therefore reducing size, weight and power of future systems. In recent experiments we demonstrated quantum communications over large distances as well as between an aircraft and a ground station which proved the feasibility of QKD between moving partners. Satellites thus may be used as trusted nodes in combination with QKD receiver stations on ground, thereby enabling fast and secure communications on a global scale. We discuss the previous experiment with emphasis on necessary developments to be done and corresponding ongoing research work of German Aerospace Center (DLR) and Ludwig Maximilians University Munich (LMU). DLR is performing research on satellite and ground terminals for the high-rate laser communication component, which are enabling technologies for the QKD link. We describe the concept and hardware of three generations of OSIRIS (Optical High Speed Infrared Link System) laser communication terminals for low Earth orbiting satellites. The first type applies laser beam pointing solely based on classical satellite control, the second uses an optical feedback to the satellite bus and the third, currently being in design phase, comprises of a special coarse pointing assembly to control beam direction independent of satellite orientation. Ongoing work also targets optical terminals for CubeSats. A further increase of beam pointing accuracy can be achieved with a fine pointing assembly. Two ground stations will be available for future testing, an advanced stationary ground station and a transportable ground station. In parallel the LMU QKD source size will be reduced by more than an order of magnitude thereby simplifying its integration into future free-space optical communication links with CubeSats.