In recent years, progress in the generation of squeezed states of light,
mainly characterized by a reduced noise property, has stimulated
important work in relation to their potential use to improve the
sensitivity of optical communication systems. These notes are devoted to
the detection and information processing of optical signals at very low
levels of power. A survey of recent developments from the quantum and
classical points of view is presented. Ultimate limits of performance
under the criteria of detection and information are established. Some of
the results are detailed and may be utilized for the design of practical
systems of communication using present technology. The book addresses
physicists and engineers interested in present and future developments
in optical communications.