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 Amplifiers (OA). Applying PAM-4 signaling to OCDMA results in halving the original signal bandwidth and the use of lower speed optical components that enables a more cost-effective implementation. In this paper, a thorough analysis of a 20 Gbps throughput data transmission over 40 Km Single Mode Fiber (SMF) using 8 multiplexed channels at OC-48 (2.488 Gbps) data rates is performed and the results show the benefits of the proposed technique.