Optical access systems have been widely deployed to support the optical broadband service, so-called Fiber To The Home (FTTH). Considering the rapid progress of mobile broadband services as well as the future society in which everything is connected to the network and the cyber space and the physical space are converged, optical access systems are expected to evolve to the common access infrastructure for various equipment and systems, This special issue highlights several important technologies among various researches for the evolution of optical access systems.

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Broadband optical and wireless access networks play a critical role in providing attractive services to achieve an Internet of Things (IoT) society. In this paper, we firstly overview the trends in the IoT services and the requirements of the optical access network technology for supporting IoT societies, and then discuss such perspectives to develop and support their worldwide expansion in near future. Finally, we introduce our recent activity on optical wireless access technologies and describe the expected advances of the laser technology to boost the research and the development of the next-generation optical access networks.

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Future access networks consisting of various transmission media including optical fibers, millimeter- wave links, etc., would provide broadband connection for many base stations in 5G or beyond 5G mobile systems. This paper summarizes recent research trends by using a figure of merit to describe contribution to spectral congestion mitigation. As an example of networks based on convergence of radio and optical technologies, we focus on radio-over-fiber systems which can offer high-performance millimeter-wave transmission. Seamless connection between optical and radio signals would play very important roles in future access networks.

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In this paper, we describe technologies of commercialized optical access video distribution systems, such as low noise, low distortion, optical amplification, dispersion compensation, statistical system design, subcarrier multiplexing, and FM conversion. We also describe the latest research results and trends of QAM conversion and terrestrial digital OFDM conversion.

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10 Gbps-class PON systems, including 10G-EPON and XG(S)-PON, are being introduced to optical access networks. To reduce cost and improve system reliability, both a high-power budget and network protection are required. We developed OLT transceivers with a high launched power of +6.7 dBm that also achieved a good receiver sensitivity of −30.9 dBm by adopting an auto-switching fast/slow AGC circuit. In addition, N:1 Type B protection was demonstrated on a 10G-EPON system. We achieved hitless protection by providing fast protection switching in under 50 ms.

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Recently, due to the progress of mobile, there is a concern about the shortage of optical access system capacity. In order to realize an optical access system of over 100Gb/s, a WDM/TDM-PON system that uses WDM in addition to TDM is promising. In this paper describes the technology, standardization, and future trends of PON systems that enable WDM/TDM-PON systems that can provide large-capacity and various services.

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Transition from dedicated devices to general-purpose ones and modularization using a standardized interface has been progressed in various fields towards efficient development and cost reduction. In recent years, this movement comes in communication network equipment. This paper introduces the benefits of modularization and softwarization in optical access networks and reviews the recent works of them.

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