A "dual-ring" network configuration is proposed in wavelength-division multiplexing (WDM) metropolitan area network (MAN). In the proposed architecture, a "sub-ring" using two fibers is added to the existing metropolitan WDM ring for flexible and cost effective addition of new nodes.

Optical signal processing is one of essential technologies for improving the flexibility of all-optical network. Above all, recently there have been a lot of studies regarding all-optical 2R/3R regeneration technology. However, there are few studies about all-optical 2R/3R technologies that are carried out in field environment. In this paper, we report the successful results of field trials of an all-optical 2R regeneration system based on an electro-absorption modulator for 40-Gbit/s WDM transmission systems with optical add/drop multiplexing. It was made sure that by applying the all-optical 2R regeneration system to the optical add/drop multiplexer in the 320-km-long transmission systems the transmission characteristics of the express signal after 320-km transmission and those of the dropped signal at 160-km can be made nearly the same. It is quite important that the transmission characteristics are equal for both the dropped and express channel from a point of view of the system design, and the results in this paper suggests one possible solution for this matter.