Development of optical transmission module for access networks

Alongside the spread of the Internet in recent years, high-speed data transmission services for subscriber networks (access networks) have taken root in a real way. This has been accompanied by a growth in fibre-optic communications networks. Fig. 1 illustrates an optical communications network. The core DWDM (Dense Wavelength Division Multiplexing) optical network is connected to LANs (Local Area Networks), metro (metropolitan) networks, metro access networks, and access networks. Conversion of access networks to optical technology, which enables much faster services, is widely anticipated. In addition, Passive Optical Network (PON) systems are also being introduced, providing real-time communications of greater capacity, at a reasonable cost. In these systems, the adoption of single-fibre bi-directional communications methods reduces the number of fibres required, and by sharing network-sides and fibre transmission paths between a number of users, faster services can be achieved at the same low cost of metal cable systems. Early installation of optical access networks is eagerly awaited worldwide, and the ITU-T and IEEE are actively discussing standardization in this field. The ITU-T has proposed standards for ATM-PON (G983.1) and B-PON (Broadband-PON) (G983.3). G983.1 relates to networks with a transmission path rate of 155 Mb/s or 622 Mb/s. In G983.3, these signals are multiplexed with CATV or other video signals. This essay starts with a brief discussion of B-PON systems, and goes on to introduce the 155 Mb/s OLT/ONT optical transmission module developed by Oki, which is a key device in optical systems of this kind. We will also look briefly at burst signal reception, which is a core technology in our transmission modules for optical access networks.