Experimental Fiber-Optic Transmission System for Interoffice Trunks

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.