A novel optical CDMA system using PAM-4 signaling with improved chromatic dispersion tolerance and spectral efficiency

In this paper, we propose a novel optical CDMA system that uses 4-level pulse amplitude modulation (PAM-4) signaling technique with bi-polar signature code scheme. This technique results in improved spectral efficiency and chromatic dispersion tolerance of the transmitted OCDMA signal over fiber. Moreover, an analog transversal filter-based decoder is proposed. This decoder reduces the power penalty induced by decoding processing and, as a result, larger number of users can be multiplexed with no need of additional optical amplifier (OA). Applying PAM-4 signaling to OCDMA results in having the original signal bandwidth and the use of lower speed optical components that enables a more cost-efficient implementation. In this paper, a thorough analysis of a 20Gbps throughput data transmission over 40 km single mode fiber (SMF) data rates is performed and the results show the benefits of the proposed technique.