Abstract
Free-space laser communication is characterized by high communication speed, strong anti-jamming ability, high confidentiality, and flexible configuration. In this paper, a pointing, acquisition, and tracking (PAT) system based on a two-stage (i.e., coarse and fine) composite tracking mechanism is proposed to solve the optical axis alignment problem, which is common in free-space laser communications. The acquisition probability of the PAT system is ensured by designing two tracking modules, a coarse tracking module which combines passive damping with active suppression and a fine tracking module based on an electromagnetic galvanometer. Both modules are combined by using a dynamic scanning mechanism based on the gyroscope signal. Finally, a free-space laser communication test with a long range and a high speed is conducted by two fixed-wing Y12 aircrafts equipped with the proposed PAT system. Experimental results show that the coarse tracking precision of the airborne PAT system is 10 μrad (1σ), and the fine tracking precision is 8 μrad (1σ) during flights which are much improved as compared with the indoor tests. This indicates that the system can achieve a high precision for PAT during high-speed and long-range laser communications in the free-space. This also verifies the tracking capability and the environmental adaptability of the proposed laser communication PAT system.
Highlights
An aircraft furnished with an array of sensors can act as a flexible reconnaissance platform, enabling it to continuously acquire information about the ground, sea, and free-space which can be disseminated to ground stations over high-speed links [1, 2]
Theoretical analysis from the above tables show that the coarse tracking error is less than 41 μrad and the fine tracking error is less than 6.2 μrad
The PAT system consisting of a biaxial-quad-frame coarse tracking module and a fine tracking unit based on piezo-ceramic galvanometer is adopted in this paper
Summary
An aircraft furnished with an array of sensors can act as a flexible reconnaissance platform, enabling it to continuously acquire information about the ground, sea, and free-space which can be disseminated to ground stations over high-speed links [1, 2]. The TT Company of USA conducted an aircraft-to-ground station laser communication test to achieve a 1 Gbps data rate at a flight height of 1.1 km while communicating over the 20 km ‒ 30 km range [4,5,6]. The atmosphere boundary layer brings a great difficulty to the wireless laser communications, which may seriously restrict the communication speed and distance This is because, when the laser passes through the atmosphere, the power of the laser beam received by the detector fluctuates and is attenuated due to the rapid changes because of the mentioned factors [11, 12].
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