Method and apparatus for aligning telescopes within a free-space optical communication system

Abstract

A free space optical communication system is disclosed whereby a transmit telescope and a receive telescope are aligned such that the point of maximum power of the received light beam is incident upon the optical fiber located at a specific point on the focal plane of the receive telescope. Such incidence is achieved by causing the transmitted beam to diverge by moving the transmit optical fiber to a point in front of the focal plane of the transmit telescope until at least a portion of the beam is incident upon the receive optical fiber. The transmit telescope and/or the receive telescope (or, alternatively, only the respective optical fibers of those telescopes) are then moved such that the point of maximum received power for that degree of divergence is incident upon the receive optical fiber. The transmit optical fiber, in response to received power measurements at the receive telescope, then incrementally moves back toward the focal plane of the transmit telescope thereby reducing the degree of divergence and achieving a greater signal per unit area at the receive telescope. As the divergence is reduced, the position of the either the transmit telescope and/or the receive telescope (or, respectively, the optical fibers) is incrementally adjusted to maximize the received power of the received signal which is incident upon the receive optical fiber for each degree of divergence. By monitoring received signal power this iterative process continues until the transmit and receive telescopes are aligned such that the transmitted beam is focused so as to maximize the received power that is incident upon the receive optical fiber.