US Patent 9559782 Optical receiver for multimode communications

An optical receiver (20) for multimode communications comprises:a mode demultiplexer (21) having an input connected to a multimode link (22) and a plurality of output lines (231-234), wherein the mode demultiplexer is adapted to couple each of the modal components of the optical signal substantially into a selected one of the output lines,a plurality of coherent optical detectors (251-254) respectively connected to the output lines to produce a set of electrical digital signals each comprising an in-phase component and a quadrature-phase component,a plurality of independently adjustable optical delay devices (241-244) arranged on the output lines to impart a selected delay to each of the corresponding modal components, anda signal processing device (26) adapted to process the digital signals to recover the independent modulations of the respective modal components by inverting a mode-mixing characteristic of the multimode link.