The process by which a beam of radiant electromagnetic energy is lined up to minimize divergence or convergence. Ideally, a collimated beam is a bundle of parallel rays perfectly lined up along an optical line-of-sight (LOS) between a transmitter and receiver, perhaps through, and in perfect parallel with, a waveguide. In a fiber optic transmission system (FOTS), a perfectly collimated optical beam would be perfectly lined up with the fiber core. See also LOS.