The rapid evolution of communication technologies such as 5G and beyond, rely on optical networks to support the challenging and ambitious requirements that include both capacity and reliability. This chapter begins by giving an overview of the evolution of optical access networks, focusing on Passive Optical Networks (PONs). The development of the different PON standards and requirements aiming at longer reach, higher client count and delivered bandwidth are presented. PON virtualization is also introduced as the flexibility enabler. Triggered by the increase of bandwidth supported by access and aggregation network segments, core networks have also evolved, as presented in the second part of the chapter. Scaling the physical infrastructure requires high investment and hence, operators are considering alternatives to optimize the use of the existing capacity. This chapter introduces different planning problems such as Routing and Spectrum Assignment problems, placement problems for regenerators and wavelength converters, and how to offer resilience to different failures. An overview of control and management is also provided. Moreover, motivated by the increasing importance of data storage and data processing, this chapter also addresses different aspects of optical data center interconnects. Data centers have become critical infrastructure to operate any service. They are also forced to take advantage of optical technology in order to keep up with the growing capacity demand and power consumption. This chapter gives an overview of different optical data center network architectures as well as some expected directions to improve the resource utilization and increase the network capacity.

翻译：通信技术（如5G及未来演进）的快速发展依赖光网络来支撑兼具容量与可靠性的严苛需求。本章首先概述光接入网演进历程，重点介绍无源光网络（PON），阐述面向更长传输距离、更多用户支持及更高带宽的PON标准与需求演变，并引入PON虚拟化作为灵活性增强技术。随着接入与汇聚网段带宽的提升，骨干网亦呈现演进趋势（本章第二部分详述）。物理基础设施扩容需高额投资，故运营商正探索优化现有容量利用的替代方案。本章介绍路由与频谱分配、再生器与波长转换器部署等不同规划问题，并探讨多类故障的恢复机制，同时概述控制与管理技术。此外，鉴于数据存储与处理重要性日益凸显，本章还聚焦光数据中心互连技术。数据中心已成为运营各类服务的关键基础设施，需借助光技术应对持续增长的容量需求与功耗压力。本章综述多种光数据中心网络架构，并展望提升资源利用率与网络容量的潜在方向。