Fiber-to-the-home (FTTH) services have overtaken ADSL services, which use telephone lines, to become the major broadband services in use in Japan. The existence of PON(Passive Optical Network) technology, which enables the realization of low-cost system architectures in which a single optical fiber can be shared by multiple users, is one factor in the rapid spread of FTTH. From STM (Synchronous Transfer Mode)-PON in the 1990s to today's standard, GE (Gigabit Ethernet)-PON, Mitsubishi Electric has been involved in the development of PON technology for an extended period, and has established itself a position as the industry leader. We can expect that, in the future, new applications and content will continue to appear on the scene, and that the amount of Internet traffic will continue to increase. Looking towards such future needs of society, Mitsubishi Electric has successfully developed a 10G-EPON system that increases the transmission speed of GE-PON tenfold, to 10 Gbps. We are continuing the development process, seeking to further increase the speed of the access networks that connect users with telephone exchanges, etc.

In addition to its two-way (upstream and downstream) 10 Gbps transmission speed, the fact that it can be introduced to environments using existing GE-PON systems is a major feature of the 10G-EPON system. The PON system upon which our new technology is based is a system in which a single optical fiber connected to the service provider's equipment (OLT) at the exchange is split using an optical coupler and connected to devices used in multiple subscribers' homes (ONU), creating an optical fiber network. In the case of the 10G-EPON system, if, for example, subscriber A uses 10G-EPON, even if subscriber B is using an existing GE-PON system, it is still possible to employ the same OLT. This characteristic is very important for the practical application of the system, because it will enable a smooth, low-cost transition to 10G-EPON while existing systems such as GE-PON optical fiber networks are still in use. In addition, the system conforms to the global standard, IEEE802.3av, with a view towards its diffusion both domestically and internationally.

The key to this development was the development of a new type of IC for use in the OLT at exchanges. In optical communications, the faster the optical signal is switched on and off, the more data can be transmitted within a specific timeframe, thus increasing transmission speed. Because light is switched on and off at a higher speed in 10G-EPON systems than in GE-PON systems, each optical signal is extremely small. The new IC therefore required superior sensitivity in order to capture these small optical signals. In addition, just as more distant light appears weaker and closer light appears stronger, optical signals arriving over an optical fiber from a long distance are weak, while those traveling a short distance are strong. In order to ensure that optical signals sent from subscribers' homes at different distances are accurately distinguished, it is necessary to equalize the signals by boosting the weak signals and attenuating the strong signals on the IC side. The coexistence of 10G-EPON and GE-PON systems was also a challenging issue for the development of the IC, because it was necessary to instantaneously judge the strength of the signals from the different systems, with their different speeds of switching light on and off, and process them. It would have been possible to resolve the issue simply by incorporating both a dedicated 10G-EPON IC and a dedicated GE-PON IC in the OLT, but the use of two IC would increase costs. We therefore achieved this complex feat of processing in a single IC, thereby also realizing a low-cost OLT.

The basic architecture of the 10G-EPON is identical to that of existing GE-PON, but of course the realization of a tenfold increase in speed necessitated not merely a new IC, but also a complete reconfiguration on the system side. For example, in PON systems the timing of data transmission from the exchange to a subscriber's home is specified, and a tenfold increase in speed also results in changes to the method of calculation of the timing. Calculation was particularly complex in the present case because of the coexistence of 1 Gbps and 10 Gbps transmission speeds. In addition, realizing a fair split between 1 Gbps and 10 Gbps users when setting data transmission timings was another issue. When the same volume of data is sent, for a 1 Gbps user the transmission speed is slower, meaning that user monopolizes the line for a longer period of time, and this situation is clearly not fair. Designing a system that is fair to all users and provides a faster and more convenient experience is very important for a PON system using shared optical fibers and devices, i.e. one in which costs are shared between users.