This lecture covers the impairments in optical fibers, including attenuation, dispersion, and nonlinear effects. It explains how fiber losses are quantified, intrinsic and extrinsic absorption mechanisms, scattering loss, Rayleigh scattering, and transmission windows for optical communications. The instructor also discusses other sources of loss such as fiber splices and connector losses, emphasizing the importance of loss management to compensate for fiber losses over long distances.