Coherent optical-fibre subscriber line

A laboratory bidirectional four-channel broadband coherent-type fibre-optic subscriber line (3.5 km) is reported. The carriers are centre-frequency-stabilised by a heterodyne spectroscope and demultiplexed by a tunable heterodyne receiver. In a very special state of the system, BER increases for nonlinear interaction between two counterpropagating narrowband lightwaves because of Brillouin scattering.