Atlanta Fiber System Experiment: Optical Crosstalk Evaluation for Two End-to-End Lightguide System Installations

The Bell System uses many types of transmission media to carry telephone calls, computer data, and television signals. One of the newest telecommunications medium under development is the glass fiber lightguide medium. 1 The first telephone plant application of lightwave systems will probably be between central offices in metropolitan areas--where duct and manhole space are at a premium, the volume of traffic is high, and central offices are close enough so that manhole repeaters are not needed. In 1976 Bell Laboratories successfully demonstrated an experimental lightwave communications system at its facility shared with Western Electric in Atlanta. 2 This system, designated FT3, which uses solid-state 1759 lasers as light sources, could carry the equivalent of nearly 50,000 telephone calls through a one-half-in. diameter cable containing 144 fiber lightguides. Following this successful experiment, the Bell System's first lightwave system to be evaluated under actual service traffic conditions was installed in Chicago (Illinois Bell Telephone Company) in early 1977.3 Advantages of optical fibers over conventional copper links include small size, freedom from interference, immunity to ground-loop problems, large information capacity, and potential economy. Data available thus far on early lightwave systems have, for the most part, been limited to optical loss and signal distortion (pulse spreading), 4 which can be related directly to economic viability. However, for telecommunication applications in congested metropolitan areas, the trend is toward higher fiber packing density.