An optical-code-division-multiple-access (OCDMA) system with a novel modulation scheme for simultaneous generation of time-domain spectral phase encoding/decoding (SPE/SPD) and differential phase-shift keying (DPSK) data modulation that can be potentially rapidly reconfigured using only a single-phase modulator (PM) is proposed and experimentally demonstrated. The time-domain SPE is realized by stretching and compressing the ultrashort optical pulse through two-chirped fiber Bragg gratings with opposite dispersion and a high-speed PM for optical code (OC) generation and data modulation. The SPD has similar configuration as the SPE counterpart but using another PM synchronously driven by the complementary code pattern for OC recognition. Simulation investigation and experimental results both show that the code transition, dispersion mismatch between the encoding and decoding side, and the transmission fiber dispersion have detrimental effect on the en/decoding performance. In the experiment, 16-chip, 40-Gchip/s OC pattern and 2.5-Gb/s DPSK data modulation have been simultaneously generated using a single PM. The 2.5-Gb/s DPSK data have been successfully decoded and transmitted over 34 km fiber with BER < 10(-9) for five OCs. The proposed scheme employs similar setup for transmitter and receiver, exhibiting the potential to simplify the architecture of the whole system, and improve the flexibility and confidentiality of OCDMA system.
- Fiber optics
- optical-code-division-multiplexing (OCDM)
- phase modulation (PM)
- secure optical communication
- spectral phase encoding/decoding (SPE/SPD)