激光通信技术

Modeling of Fine Tracking Sensor for Free Space Laser Communication Systems

Hu Zhen,Song Zhengxun Tong Shoufeng, Zhao Xin, Song Hongfei, Jiang Huilin School of Electronics and Information Engineering Space Institute of Photo-Electronic Technology

Changchun University of Science and Technology

No. 7089, Weixing Road, Changchun, P. R. China, 130022

zhu@

Abstract—The optical communication networks comprised of ground stations, aircraft, high altitude platforms, and satellites become an attainable goal, however, some challenges need to be overcome. One of challenges involves the difficulty of acquisition, tracking, and pointing (ATP) a concentrated beam of light arriving from another platform across the far reach of space. To meet the pointing accuracy requirement, the basic method of tracking between the terminals of optical communication systems includes the use of a beacon laser and tracking system with a quadrant detector sensor on each terminal. In some future optical communication networks, it is plausible to assume that tracking system and communication receiv ers will use the same sensor. In this paper, the architecture of the fine tracking assembly of the designing optical communication terminal (OCT) is described, and the fine tracking assembly sensor is modeled based on the correlation coefficient. The simulation and experiment results of the sensor show that the detecting accuracy satisfies the design demand for our developing OCT.

Keywords-modeling; quadrant detector; fine tracking sensor; optical communication networks

I.I NTRODUCTION

Communication from one place to another on Earth is an attractive goal. To achieve this aim, the communication net-works that cover the globe are established. Future optical

communication network is pictured in Figure 1.

Figure 1. Future optical communication network [1].

The optical communication networks comprised of ground stations, aircraft, high altitude platforms, and satellites become an attainable goal, however, some challenges need to be overcome. Laser-based communication links between a satellite and another satellite or a high flying aircraft have been investigated for free-space communication systems They include European Space Agency’s (ESA) Artemis, Japan Aerospace Exploration Agency’s (JAXA) OICETS and the Department of Defense’s (DoD) TSAT [2]. Laser communication systems offer greater capabilities than RF systems, such as smaller size and weight of the terminals, less transmitter power, higher immunity to interference, and larger data rate, but present greater challenges in implementation. One of challenges involves the difficulty of acquisition, tracking, and pointing (ATP) a concentrated beam of laser arriving from another platform across the far reach of space [3].

To meet the pointing accuracy requirement the optical communication terminals (OCT) mounted on satellite or other platforms use the Ephemeredes data (the position of the satellite according to the orbit equation) or navigation system for rough pointing, and a tracking system for fine pointing to another OCT. The basic method of tracking between OCT includes the use of a beacon laser and tracking system with a quadrant detector sensor on each OCT. In some future optical communication networks, it is plausible to assume that tracking system and communication receivers will use the same sensor. The reason is the possibility to design simple OCT at a reduced cost, mass, and volume in order to implement very compact, lightweight and low-power consumption precision beam-steering technologies. In view of this, a 4-quadrant detector (4QD) will be adapted in our developing OCT. Having a good mathematical description of the sensor is crucial for successful implementation of the tracking system, as it allows testing various control techniques prior to building a hardware prototype. This paper described the architecture of the fine tracking assembly of the designing OCT, proposed an approach to mathematical modeling of the fine tracking assembly sensor, and performed a number of experiments to validate the derived models.

The remainder of this paper is organized as follows. Section II described the ATP subsystem architecture, the fine tracking assembly components briefly. The operating principle of 4QD, the operation of the position detecting sensor, the transfer characteristics for the different spot in sizes, and mathematical model of the sensor are presented in Section III. Section IV gives the simulation and experiment results of the sensor. Finally, our work is summarized in Section V.

Supported by High-Tech Research and Development Plan of China (863).

978-1-4244-4412-0/09/$25.00 ©2009 IEEE