Optical Add-Drop Multiplexers for Metro/Access Networks

Presently, high-speed and wide-bandwidth broadband access systems such as ADSL, CATV and FTTH have become widespread. With respect to the data sent and received in such systems, those not only of text but also from multi-media fields --such as moving images and audio-have grown in volume, and tend to increase hereafter. Thus, metro/access networks that connect subscribers with a trunk network are required to have scalability enabling rapid changes of communications capacity in response to the requirement of subscribers, in addition to transmission capacity enhancement and cost reduction, so that WDM systems have begun to be introduced. Many metro/access networks adopt a ring configuration where the nodal bases are connected to form a ring, taking into consideration the reliability, transmission efficiency and ease of operation. At each nodal base, required signals are separated from a large amount of signals to carry out sending and receiving of information with the users. See Figure 1. Consequently, when conventional systems based on optical-electrical signal conversion are used, an enormous scale of equipment would be required, leading to an increase in system maintenance costs. Recently, the coarse WDM (CWDM) communications technology is drawing attention since the technology allows a network configuration using devices with lower costs. However, because mutual entry between CWDM and the dense WDM (DWDM) for trunk networks is impossible, it is required to provide optical-electrical-optical conversion at switching nodes between the CWDM and DWDM systems. To reduce the cost of large capacity transmission, whereas conventionally most signal processing has been done after optical-to-electrical conversion, it is required to process signals in optical form. Optical add/drop multiplexOptical Add-Drop Multiplexers for Metro/Access Networks