FIELD COMMUTATION RELATIONS IN OPTICAL CAVITIES

We introduce a simple quantum theory of the lossy beam splitter. When applied to describe a Fabry-Perot cavity this leads to apparently anom alous commutation relations for the intracavity operators. We show tha t these unfamiliar properties are nevertheless consistent with the fun damental canonical commutator for the vector potential and electric fi eld operators. This result is derived as a consequence of causality as applied to the properties of mirror reflection coefficients.