부산대학교 도서관

A beam-steered Gigabit Ethernet (GbE) bidirectional OWC system with user-hosted automatic self-calibrated alignment of the upstream beams has been designed and realized, using stepper motor translators, miniature retro-reflectors and a novel self-alignment center-of-gravity (CoG) algorithm. Broadband receivers with a Field-of View (FoV) >10 degree are used, which relaxes beam alignment. The accuracy of the CoG algorithm and the impact of lens aberrations in the upstream beam launching is analyzed. A good accuracy of the automated upstream beam steering within 200 μm relative to the center of the upstream receiver's aperture has been found up to a beam incident angle of 10 degree; this is well within the 25 mm aperture and the FoV of the upstream receiver. Hereto a relatively simple low-aberration triplet lens is used at the user site. The upstream beam alignment takes less than 10 seconds. The full system laboratory setup provides individual narrow beams for high user densities. It also includes automatic self-calibrated alignment of the downstream beams using similar retroreflector technology and a wavelength-tuned beam steering. TCP measurements show transfer speeds of 940 Mbit/s per user within 10 degree FoV. Real-time high-definition GbE video streaming to laptop computers via individual bidirectional OWC links has been demonstrated.