Metropolitan optical networks are undergoing significant transformations to continue being able to provide services that meet the requirements of the applications of the future. The current deployment of the 5G networks and the envisioned 6G cyber–physical systems would expand the possibilities for offering IoT applications, autonomous vehicles, and smart city services while imposing strong pressure on the physical infrastructure. In order to guarantee the strictest quality of service and quality of experience requirements for users, new architectures have been proposed in the literature for metropolitan optical networks, with a growing interest in the last five years. However, due to the proliferation of a dozen new architectures in the last years, many questions need to be investigated regarding the planning, implementation, and management of these architectures, before they could be considered for practical application. This work presents a comprehensive survey of the new proposed single-layer (purely optical) architectures for metropolitan optical networks. First, we discuss the structural organization of the new metro ecosystems. Second, the already established and novel architectures are presented, highlighting their characteristics and application. Third, we carry out a comparative analysis of these architectures to identify future technological trends. Finally, we have drawn outstanding research questions to help direct future research in the field.

城域光网络正在经历重大变革，以继续能够提供满足未来应用要求的服务。当前部署的 5G 网络和设想的 6G 网络物理系统将扩大提供物联网应用、自动驾驶汽车和智慧城市服务的可能性，同时对物理基础设施施加巨大压力。为了保证对用户最严格的服务质量和体验质量要求，文献中提出了城域光网络的新架构，在过去五年中引起了越来越多的兴趣。然而，由于过去几年十几个新架构的激增，许多关于规划、实施、和管理这些架构，然后才能考虑将它们用于实际应用。这项工作对城域光网络新提出的单层（纯光）架构进行了全面调查。首先，我们讨论新地铁生态系统的结构组织。其次，介绍了已经建立和新颖的架构，突出了它们的特点和应用。第三，我们对这些架构进行了比较分析，以确定未来的技术趋势。最后，我们提出了突出的研究问题，以帮助指导该领域的未来研究。首先，我们讨论新地铁生态系统的结构组织。其次，介绍了已经建立和新颖的架构，突出了它们的特点和应用。第三，我们对这些架构进行了比较分析，以确定未来的技术趋势。最后，我们提出了突出的研究问题，以帮助指导该领域的未来研究。首先，我们讨论新地铁生态系统的结构组织。其次，介绍了已经建立和新颖的架构，突出了它们的特点和应用。第三，我们对这些架构进行了比较分析，以确定未来的技术趋势。最后，我们提出了突出的研究问题，以帮助指导该领域的未来研究。