Single-laser bidirectional coherent PON with hybrid SC and DSC transmission for flexible and cost-effective optical access networks

Coherent passive optical networks (PONs) are a promising solution for next-generation optical access networks, offering high capacity, extended reach, and improved spectral efficiency. This paper presents a single-laser bidirectional (BiDi) coherent PON architecture that supports hybrid single-carrier (SC) and digital subcarrier (DSC) transmission, enabling cost-effective coherent PON implementation and adaptive resource allocation within the same network. The system was experimentally evaluated over a 50 km optical distribution network (ODN) using multiple split ratio configurations, reflecting practical PON deployment scenarios, for both 25 GBd SC and 6.25 GBd DSC transmissions, demonstrating negligible back-reflection penalties compared to conventional full-duplex BiDi schemes. An upstream burst digital signal processing (DSP) framework is proposed, featuring a simple modulation format selection method based on burst rising edge detection and synchronization peak index information, supporting flexible-rate burst-mode upstream transmission across multiple optical network units (ONUs). Experimental results validate the system’s performance across various link distances and split ratios, achieving robust transmission with minimal inter-subcarrier interference. The proposed system offers a cost-effective and scalable solution for next-generation high-speed optical access networks.