A method of transmitting a plurality n data streams comprises modulating an optical carrier using differential M-ary phase shift key (DMPSK) signaling in which M=2n. Advantageously the method comprises using differential quaternary phase shift keying in which n=2. A particular advantage of the method...http://www.google.com/patents/US8200099?utm_source=gb-gplus-sharePatent US8200099 - Demodulation of an optical carrier
