Fiber Bundles in Transceivers to Mitigate Scintillation Effects on Free-Space Optical Networks

摘要

Accuracy of alignment is a key factor for successfully establishing and maintaining connections in networks of free-space optical links, and is particularly critical when one or both of the transceivers are moving. Scintillation and other atmospheric effects create beam deflections that further complicate the alignment process. This paper studies the use of a fiber-optic bundle at the transmitter and receiver to mitigate the atmospheric effects on the link up-time. The bundle at the transmitter allows fast, non-mechanical steering of the optical beam to track and correct for relative motion. The bundle at the receiver allows for a significant improvement in misalignment tolerance, particularly to angular misalignment. Laboratory experiments and theoretical analyses were conducted on a free-space link to determine the inter-relationship between spacing of the fibers within the bundle, the focal lengths of the transceiver lenses, the beam deflection angle, and the misalignment tolerance for varying atmospheric conditions. A shorter focal length lens at the transmitter provides greater coverage, while a moderate focal length lens at the receiver reduces the bundle size required to improve misalignment tolerance. A smaller overall system size is possible, provided that sufficient power is used to overcome the greater spatial spreading and subsequent loss of peak power at the receiver.