Method and apparatus for transmitting information

A method of transmitting a signal comprising a number of frequency multiplexed channels, the method comprising generating a second version of the multiplex signal having frequencies different from those of the multiplex signals;

• and transmitting the two versions of the signal with orthogonal polarisations and with the portions of each signal corresponding to the same channel being transmitted simultaneously into an optical waveguide which can cause the signals to undergo random polarisation changes during propagation through the waveguide;
• and detecting said signals after propagation through the waveguide by means of a coherent optical receiver.

An optical network comprising an optical waveguide which can cause optical signals to undergo random polarisation changes during propagation through the waveguide, generating means for generating a pair of orthogonally polarised signals having different frequencies, each of which is identically modulated in accordance with information to be transmitted, and means for launching the signals simultaneously into the optical waveguide and a coherent detector for detecting said signals.

A network for transmitting a signal comprising a number of frequency multiplexed channels comprises means for generating a second version of the multiplex signal having frequencies different from those of the multiplex signal, and means for transmitting the two versions of the signal with orthogonal polarisations and with the portions of each signal corresponding to the same channel being transmitted simultaneously into an optical waveguide which can cause random polarisation changes during propagation through the waveguide and a coherent optical detector for detecting said signals.