Asynchronous Multiuser Coherent OCDMA System With Code-Shift-Keying and Balanced Detection

An optical code division multiple access (OCDMA) system with coherent coding, code shift keying (CSK) data modulation, and balanced detection (CSK OCDMA) is proposed and theoretically investigated in this paper. The proposed scheme has better multiuser capability, simpler threshold setting in the receiver, and particularly, enhanced security compares with conventional OCDMA systems. A multiuser CSK-OCDMA system with 511-chip superstructure fiber Bragg gratings and a multiport encoder/decoder (E/D) pair was experimentally demonstrated. A bit-error-rate of less than 10^-9 was achieved with up to ten and eight active users at data rates of 1.25 and 10.7 Gb/s, respectively, without any forward-error-correction or optical thresholding. The multiport E/D was used in a novel configuration to process multidimensional optical codes.