A phase modulation technique able to increase the transmission capacity of an optical channel is presented. It is based on spatial soliton switching properties. The modulator device accepts as inputs two streams of amplitude modulated pulses and generates an output stream of phase modulated pulses whose phase values depends on the different input combinations, coding properly the input streams and increasing the transmission capacity of the optical channel that carries this information. The modulator device can be properly cascaded, generating a unique stream of pulses capable of carrying the information of a certain number of input channels. A proper demodulator device is also presented. It is capable of accepting as input a phase modulated stream of pulses, generating as outputs the original amplitude modulated pulse streams.
Fabio Garzia, Concita Sibilia, and Mario Bertolotti, "New Phase Modulation Technique Based on Spatial Soliton Switching," J. Lightwave Technol. 19, 1036- (2001)