Rotatable joints for communication lines

Abstract

A communication line joint arrangement comprising two parts between which relative rotation and the transmission of at least two channels using electromagnetic energy such as light is facilitated, each part comprising polarising beam splitter means operatively associated with quarter wave plate means, wherein the polarising beam splitter means of the two parts are arranged to pass two orthogonally related polarised input channel signals to the quarter wave plate means associated therewith, so as to produce two corresponding circularly polarised channel signals of opposite directional sense which are transmitted between the quarter wave plate means, across an interface between the parts, so as to produce two corresponding orthogonally polarised output channel signals from the polarising beam splitter means. By arranging that the two channel signals are circularly polarised in opposite senses as they traverse the interface between the two relatively rotatable parts, mutual interference between channels and/or breakdown of communication in the presence of rotation between the parts is thereby obviated.

Dependencies are inferred from the claim text.