• Corpus ID: 32560171

Optical Links for Fast and Secure Communications on Ground and in Space

@inproceedings{Mottini2016OpticalLF,
  title={Optical Links for Fast and Secure Communications on Ground and in Space},
  author={Sergio Mottini},
  year={2016}
}

• S. Mottini
• Published 2016
• Physics

The interest in fast and secure optical communication link has grown in the last years driven by the increasing demand in data throughput for applications spanning from small satellites for global services to large satellites for secure communications, from Earth Observation distributed sensing networks to CubeSat constellations for in-orbit inspections of large satellites; in addition particular interest is also demonstrated by military market. Moreover, besides speed, in modern information society the secure communications are of the utmost importance: confidential and authenticated transfer of data between companies, financial institutions, military operators and public administration is crucial for maintaining the competitiveness of industry and increasingly it is also important for individuals. And optics offer new revolutionary tools to provide security in an unprecedented manner. This paper shows how this objectives are going to be reached. 1.0 INTRODUCTION The market for optical data link constellations and HTS feeder links is very active and competitive; there is a new diffused tendency to propose the use of mini and micro satellites for the space activities related to optical data link networks. The interest on satellite optical communication link has grown also in the science domain, driven by the increasing demand in data downlink for scientific, planetary exploration and earth observation missions; in addition particular interest is also demonstrated by military and commercial market not only for the high data rates achievable but also for the security levels: low probability of intercept, quantum cryptography. And all this in a wide variety of possible scenarios: space-space, space-ground, space-aircraft, groundground links, suitable to different kind of users with different purposes. Free space optical communication systems (FSO) answer to specific needs for satellite communication technologies, fitting with the objective of moving towards the Terabit-throughput satellite systems or target constellations in lower Earth orbit, making use of laser-based optical communication terminals. FSO communications is the technology which offers the possibility of breaking the bottleneck of radio frequency link by using an optical carrier with a frequency 10,000 times higher than in RF. Today optical communication systems using optical fibres already reach even beyond 1 Terabit/s capacity thanks to the dense wavelength division multiplexing (DWDM) technology. FSO demonstrators above 1 Tbps have been realized on ground. The activities described in this paper aim at extending the use of these technologies into space, as already planned (and funded) by most of the NATO Member States and by NASA and the STO-MP-SCI-283 2 1 PUBLIC RELEASE PUBLIC RELEASE Optical Links for Fast and Secure Communications on Ground and in Space European Space Agency (e.g. the ARTES programme). 2.0 OPTICAL VS. RF FSO communications are based on similar concept developed for radio frequency communication systems (RFS), in terms of system architecture and physical parameters that provide the communication behaviour. The main difference between the two systems is that FSO uses light (frequencies of hundreds of Thz) as carrier to transfer information while RFS uses electromagnetic waves with a much longer wavelength (in the MHz and GHz domain). The propagation channel properties in the two cases (optical and RF) lead the application fields and mission scenario of the two communication systems (FSO and RFS). A remarkable advantage is represented by the fact that optical communications working at optical frequencies permits to use devices with very large modulation and demodulation bandwidth allowing much higher bit rate inaccessible to RF communications. The expected bit rate for a typical FSO link is in the range between some hundreds Mbps (for deep space communications) to some tens of Gbps depending on distance, laser output power and telescopes (optical antenna) size. These transmission speeds cannot be reached with an equivalent RF transmission systems (i.e. same dimensions, mass and power). To cope with similar bit rate, an RF communications system would need larger antennas for both terminals (in order to reduce beam divergence) and / or greater power in the transmitter (which means, for space applications, larger S/C with larger power systems). Ground antennas are already large, but intensifying power also the side lobes become energetic as well, and the problem of interception (e.g. for military applications) becomes a concern. FSO systems are free from all these problems. The increase in high-speed data link and data handling capability of satellites and planned satellite clusters has reached a point that calls for the wide implementation of free-space laser communication links. The advantage related to the possibility of dealing with a huge data volume is related to the positive impact on the expanded content of the mission (or the reduction of mission duration) and on the duration of the required on-board processing (also considering that raw data are always more interesting as they may contain hidden significant information). Also the possibility of a faster data uplink has advantages, related to faster upload of observation planes, of planned SW upgrades and of SW bug fixing activity. Then, also the possibility to use mobile portable Optical Ground Stations (OGS) increases flexibility of this technique, allowing e.g. a laboratory to receive directly data originated by its instrument. The characteristics of laser communication beam in FSO implies the following considerations: • The relative small beam aperture and the high gain of the transmitter and receiver antenna (implemented with telescope) in the optical domain mean narrower beam width with respect to RF systems, making difficult the possibility of intercepting the data stream. As counterpart, it requires an accurate tracking acquisition and pointing system, one order of magnitude more accurate compared to the RF Systems • FSO, which is highly directional, is a typical point to point communication; broadcast requires an additional optical communication networks (e.g. satellites constellation) • In general, power budget is proportional to the system communication carrier frequency squared, so being FSO frequency carrier much higher with respect to RF system case, less transmitter power and larger link distances can be attained while maintaining the same performance From above considerations, it is clear that an optical communications network provides, besides the increased data throughput, additional competitive advantages compared to conventional RF systems: Optical Links for Fast and Secure Communications on Ground and in Space 2 2 STO-MP-SCI-283 PUBLIC RELEASE