PhD defence of Zixian Wei – Coherent Optical Access Networks

Thursday, June 13, 2024 10:00to12:00
McConnell Engineering Building Room 603, 3480 rue University, Montreal, QC, H3A 0E9, CA


Coherent technology is a competitive candidate for next-generation 100/200-G passive optical networks (PON) with 40 km coverage. The characteristics of linear optical field conversion, digital compensation, and superior receiver sensitivity enable coherent PON (CPON) to have higher capacity, larger coverage extended reach, and higher density support. The evolution of access networks' scale, scalability, and flexibility leads to a series of dynamic behaviors in CPON. In this thesis, the selected topics related to potential business issues, including rate flexibility, parameters monitoring, dynamic encryption, and service fairness of downstream links over CPON are analyzed and demonstrated emphatically.

This thesis first explores and demonstrates point-to-point (P2P) and point-to-multipoint (P2MP) coherent optical communication systems and access networks. A time-variant entropy-regulated probabilistic constellation shaping (PCS) 64-quadrature amplitude modulation (64-QAM) scheme is proposed. Then, an active learning-aided entropy-tunable automatic modulation identification (AL-aided ET-AMI) scheme is demonstrated. The dynamic time-varying entropy is embedded in the constellation diagram and is re-extracted at the receiver. A 10-km/ 350 ~ 550-Gb/s result is achieved over a 10-km link within hard-decision-forward error correction (HD-FEC). For an entropy tuning step with 0.1, the recognition accuracy of AL-aided ET-AMI can reach 98% with data aggregation. This scheme was subsequently extended to P2MP access networks. Our proposed scheme can provide an abundant system loss budget and fast graphical monitoring for flexible coherent optical transmission systems and networks.

Physical layer security is becoming an important topic in the commercial deployment of ultra-100-G optical access networks. With the regulation of initial entropies, the PCS-based optical link can realize a bit stream with a tunable data rate, which facilitates mass multi-rate access. Digital signal processing (DSP) chaotic encryption attracts more and more attention in fiber-optic networks. We first demonstrate a chaotic-encrypted transmission on a PCS-based rate-flexible CPON. The transmitted signal with various entropy is encrypted and converted into a cipher via mapping from PCS-64-QAM to pseudo-m-QAM format. Net rate tuning from 211.80 Gb/s to 348.12 Gb/s with a step size of 3.408 Gbps/pol./λ is achieved by 0.1-step entropy interval at an ROP of -15 dBm, encrypted by different parallel chaotic sequences. This work provides a feasible solution for next-generation >100-G rate-flexible and physical layer security-enhanced optical transmission.

Finally, a time division multiplexing non-orthogonal multiple access scheme is proposed for high-capacity and dense-access CPON. The scheme is experimentally demonstrated between two far-near ONUs over CPON within a single timeslot with different transmission distances and split ratios. Different fairness indexes are defined and adopted to verify the fairness of the service from the OLT to the two far-near users. Four experiments are demonstrated with four coherent PON application scenarios. A 400-Gb/s rate is achieved for two far-near users within HD-FEC and flexible HD-FECs. The signal-to-interference noise ratios or bit-error rates of far-near two users are almost the same. Our proposed scheme can provide a fair service for next-generation wide-coverage coherent optical access systems.

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