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Unformatted text preview: Satellite Optical Communications A highly secure optical communications link is to be established bewteen a low- orbit satellite and a ground station on earth. A block diagram of the optical system is shown below. The signal is to be pulse-code modulated and have a data rate of 1 . GB/sec . The satellite is at an altitude of L 4 = 160 km above the surface of the earth (of diameter 12 , 875 km ). The transmitter uses a mode-locked neodymium YAG laser of fundamental wavelength of 1 . 0641 m . The fundamental wavelength of this laser is then frequency doubled for data communications. The beam exiting the frequency doubler has a di- ameter of L 1 = 2 . 00 mm . Then the laser beam is expanded and collimated using a beam-expanding telescope. Finally, the beam is directed down to the ground station. A circlular area with a diameter of only L 3 = 0 . 80 m is illuminated on the earths surface by this laser beam....
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- Spring '08