NTT Research and Development 2008 Review of Activities

The service area of broadband optical access networks in Japan is expanding, and it will include an estimated 20 million customers by 2010. We have already developed an optical fiber line testing system that reduces construction and maintenance costs. If water penetrates an underground optical closure, it will increase optical loss and degrade the mechanical strength of the fiber cables contained in it. To indicate when maintenance is necessary, we attached a water sensor module to one fiber in the optical fiber cable in each underground optical closure. If water penetrates the underground optical closure, the material encasing the water sensor module expands and applies a bending loss to the optical fiber. Water penetration can be monitored by performing a periodic OTDR^*1 test using this system. However, the optical testing module (OTM) for this system is not installed in the central office of rural areas. This means a worker must travel to the central office and measure the optical fiber cable when undertaking periodic OTDR tests.

Figure shows our new optical fiber line testing system with a small-scale FS^*2. The central office of a metropolitan area is equipped with an OTM and large-scale FS. The OTM consists of an OTDR, frame and test equipment selector (FTES) for selecting a test equipment, and controller for the OTDR, FTES and FS. The large-scale FS can select a target fiber from thousands of optical fibers. The central office of the rural area is equipped with a small-scale FS that accommodates a few fibers for monitoring water penetration. The small-scale FS is controlled by the OTM via a virtual private network (VPN). The test light of the OTM passes through the trunk line optical cable, and the small-scale FS selects the target fiber to monitor. With these technologies, we can expand the application range of optical fiber line testing systems to rural areas.

We will continue researching and developing technologies for reducing maintenance costs.

• *1 OTDR: Optical Time Domain Reflectometer
• *2 FS: Fiber Selector