Programmable FBG-based variable optical correlator for optical code division multiplexing

Programmable FBG-based optical correlators for optical code division multiplexing systems, which are able to change carrier phase of output pulses, are experimentally demonstrated. Phase shifts between adjacent FBGs are tuned thermally with small thermo-electric controllers by PWM signals from a microprocessor. Easy code adaptation with the programmable FBG-based optical correlator is successfully demonstrated with the open-loop control mode. The close-loop control mode gives better stability for ambient temperature variation, resulting in error free operation for an hour at 1 Gbit/s.