The first lightwave communications system that provides a wide range of telecommunications services to customers has been carrying commercial traffic in the Chicago Loop area since early May, 1977. The exploratory system furnishes POTS (plain old telephone service), analog data, and digital data services from the Franklin central office (CO) to customers in the Brunswick building, over an optical cable approximately 0.6 mi long. Picturephone®meeting service, a 4-MHz video service, is delivered over an optical cable from the Wabash CO to the Franklin CO, then on to the Brunswick building, a total distance of 1.6 mi. The optical cable was placed inside a small plastic pipe, which had been installed previously along the cable route. The plastic pipe, or innerduct, was used to reduce pulling tensions and provide environmental protection. The optical cable was installed using a novel 2-way installation technique by which the two ends of each section were fed successively in opposite directions from an intermediate manhole toward the splicing manholes. The connectorized optical cable was then spliced in five manholes along the cable route. This paper describes the installation and splicing of the lightguide cable and the transmission characteristics of the installed medium. It also contains a discussion of the manner in which the various telecommunication services are provided and a performance evaluation of the lightwave transmission system to date.

This paper discusses in a general way the design of, and realization of, an experimental transmission system using optical fibers. Aimed at interoffice trunk applications in metropolitan areas, the design demonstrates the performance expected for a practical system. Included in the experimental system is a translation from standard digital hierarchy signal formats to a format more suitable for simple optical modulation and considerations for system maintenance and fiber reassignments. The design approach uses essentially conventional electronics to amplify, reshape, and regenerate the digital signal with GaAIAs injection lasers for sources and avalanche photodiodes for detectors. Light output of the laser is monitored and electronically controlled and the gain of the detector is controlled by varying its bias supply. In the descriptions of the electronic and optical components of the design, emphasis is placed on the properties peculiar to optical fiber applications.