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Proceedings Paper

Ground to survey aerostatic platform bidirectional free space optical link
Author(s): F. J. López Hernández; M. A. Geday; G. del Campo; D. Martin-Fuertes; A. Carrasco-Casado; P. Munuera
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Paper Abstract

The mass and the power consumption are the most constrictive restrictions in an Aerostatic Platform. We present in this work a bidirectional link based on a liquid crystal retro-modulator (LCRM). The use of this device displaces to the terrestrial station the tasks of powering the laser, and the pointing mechanism. Also, due to the non-conductive characteristic of the LCRM, the power requirements are low. The beam aperture of the upward link can be tailored with the compromise between the aperture losses, and the tracking mechanics. The range of the distances for the system presented is from 2 to 20 km, being the lower limit for the tests and checking of the system, and the higher the final system for a stratospheric survey Aerostat. The system will be modified to fulfill the requirements associated to the increasing distances, although the main characteristics (modulation schemes, modulator, etc.) will be maintained. The system uses two modulation schemes for each direction: in the uplink a carrier constant envelope FSK modulation is used. For the down link, part of the optical signal is polarization modulated and reflected to the earth. For increasing the data rate, a multi-polarization modulation is used. Actually, 32 polarization levels are used, increasing the data rate in a 5-fold factor. The use of differential scheme, i.e. the State of Polarization (SOP) change defines the data, not the SOP, avoids the necessity of SOP maintenance in the transmitter.

Paper Details

Date Published: 5 October 2007
PDF: 7 pages
Proc. SPIE 6736, Unmanned/Unattended Sensors and Sensor Networks IV, 673616 (5 October 2007); doi: 10.1117/12.737897
Show Author Affiliations
F. J. López Hernández, Univ. Politécnica de Madrid (Spain)
M. A. Geday, Univ. Politécnica de Madrid (Spain)
G. del Campo, Univ. Politécnica de Madrid (Spain)
D. Martin-Fuertes, Univ. Politécnica de Madrid (Spain)
A. Carrasco-Casado, Univ. Politécnica de Madrid (Spain)
P. Munuera, Ingenieria y Servicios Aeroespaciales (Spain)

Published in SPIE Proceedings Vol. 6736:
Unmanned/Unattended Sensors and Sensor Networks IV
Edward M. Carapezza, Editor(s)

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