Fig. 1. (a) Point-to-multipoint schematic of the CPON system; (b)–(d) present the three key advancements in next-generation CPON, low cost, wide coverage, and high flexibility.

Fig. 2. (a) Intensity signal with coherent detection and DSP; (b) amplitude signal with coherent detection and DSP; (c) PAM-4 ASK signal coherent detection and DSP.

Fig. 3. The concept of coherent receiver simplification schemes. (a) A DP-intradyne receiver; (b) a DP-heterodyne receiver; (c) a 2 × 2 coupler and single-ended PD (SPD)-based heterodyne receiver; (d) a single polarization heterodyne coherent receiver with a 3 × 3 coupler; and (e) an Alamouti single-polarization heterodyne receiver.

Fig. 4. The system diagram based on Alamouti coding.

Fig. 5. Advanced DSP in both upstream and downstream.

Fig. 6. Two examples of the possible implementation of LO power adjustment: (a) adjustment based on the detected photocurrent output from the photodiodes; (b) adjustment based on the optical input signal power.

Fig. 7. BER performance versus different ROP with or without LO adjustment in (a) QPSK, (b) 16QAM, and (c) 64QAM.

Fig. 8. Schematic of a hybrid PS (HPS)-based flexible CPON system without any optical amplifiers.

Fig. 9. The architecture of simplified TFDM CPON with adaptive rate.