Coherent Optics for Access Networks: From P2P to P2MP

Coherent optical communication is a game-changer optical fiber transport technology for high-speed data transmissions in long-haul networks and data center interconnects, enabling a widespread upgrade and new deployment of DWDM networks to speeds of 100 Gbps, 200 Gbps, and 400 Gbps per wavelength. Recently, the potential of using coherent optics in access networks incurs a lot of discussions in both industry and academia. Following the continuation of growing bandwidth demands in ultra-high-definition video streaming, cloud computing, immersive gaming, 5G, VR, and remote health care, we are pushing really hard on traditional intensity-modulation direct-detection systems and approaching their performance limit. On the other hand, with the progress of design simplification, silicon photonics, and semiconductor manufacturing process, the cost of coherent devices continues to reduce, which may enable coherent optics to replace direct-detection links in mobile fronthaul, aggregation nodes, and access networks. It is anticipated that, with the greatly improved receiver sensitivity and stronger robustness under chromatic dispersion, coherent optics could significantly enhance the transmission distance and number of connected users for next-generation passive optical networks (PONs). This migration model has been demonstrated in the optical industry before the DWDM system technology started in long haul and subsequently migrating to metro and edge access; forward error correction (FEC) encoding and decoding followed the same pattern. Benefiting from initial long-haul technology development, coherent optics for access networks is poised to follow the same natural progression. In this chapter, we reviewed the development, operation principles, and digital signal processing techniques of coherent optical systems. The key technologies to enable the future point-to-multipoint coherent optical access network have also been discussed.