Consideration of most important parameters and selection of the laser for transmitting module of space laser communication system

Abstract

Laser communications through optical fibers move tens of terabits of data every second between cities and across oceans. But for the majority of Earth’s surface, where running fiber is impractical physically or financially, communication satellites in space provide connectivity—to remote ground users and also to mobile platforms such as aircraft, ships and even other satellites. These links rely on radio-frequency communications, which, while reliable, are orders of magnitude slower in moving data than optical fiber links, and have issues related to antenna footprint, power requirements and limited available spectrum. Also the requirements of a number of future planned space missions in low earth orbit, mainly in the field of earth observation, ask for high data rate capability to a geostationary data relay satellite. In the field of communication satellites, increasing traffic demand requires the use of inter—satellite links to conserve bandwidth and improve link quality by shorter transmission delays. The potential for the laser to overcome these issues in space was realized soon after its invention. Recent and upcoming deployments of satellite laser communication systems are bringing Internet-like speeds for data transmission in space. The result could be a revolution in communication, both on Earth and across the solar system. Laser communications uses collimated laser beams to transmit information at high data rates in the multigigabit regime, preventing interference problems and exhaustion of radio-frequency bandwidths. Laser transmitters, at wavelengths some 10,000 times shorter than RF waves, result in beams that are far narrower for the same unit aperture size—providing more concentrated communications power at the receiver with lower required transmitted power from smaller, lighter apertures. The upshot is a lower size, weight and power requirement for transmit and receive apertures of a laser communications terminal. Perhaps just as important, there is almost no spatial overlap among various users, so the optical spectrum of free-space optical communication is at present unregulated — a significant advantage for space-based users. In this article parameters of the transmitting module of laser cosmic space communication system are considered. These parameters require special attention, because they have the greatest influence on the quality of data transmission in such system. The laser with the more suitable parameters for applying it in the transmitter has been selected based on this information. Such parameters of the laser beam as sufficiently low divergence, high energy efficiency, high impulse density are very important for information transmission over long distances through laser energy. Since delivery of cargo into space is very expensive, before launching any device in space is important to be sure about effective use of its components so transmitting module of space communication system must be durable, energy efficient, must have a relatively small weight and size. The laser used in system have great influence on these parameters. Ref. 12, fig. 2, tabl. 1.

Keywords

References

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Copyright (c) 2018 Іван Анатолійович Голуб, Станіслав Володимирович Денбновецький (Автор)