Optical fiber order wire system

Abstract

An order wire system which can be used during installation and maintenance of an optical fiber communication system comprises an optical fiber order wire to which engineers can connect at remote sites communication sets each of which includes a microphone and earphone allowing the engineers to communicate with each other. Full duplex and multi-party operation can be achieved with the sets according to the invention and, because the signals are regenerated, the range of operation is considerable. Both analog and digital communication is contemplated and different specific circuits are proposed. In a typical analog configuration, the microphone output is fed to first and second frequency modulators operating respectively at first f.sub.1 and second f.sub.2 center frequencies. The outputs of the modulators are summed and passed to a laser driver and laser which is optically coupled both to the upstream and the downstream side of the order wire. Optical detectors are respectively connected to the upstream and downstream sides of the order wire and the outputs of these are fed through first and second bandpass filters to respective frequency demodulators. One of the filters passes only f.sub.1 frequencies and the other only f.sub.2 frequencies. The outputs of the demodulators are fed to the earphone and also back to the respective modulators for regeneration.