The operation of a laser in an optical repeater in an optical transmission system using an optical fiber cable is telemonitored at a terminal station by changing the mark ratio of the test signal which is transmitted from the terminal station to the circuit. Each of the repeaters has an optical-electrical...http://www.google.com/patents/US4313224?utm_source=gb-gplus-sharePatent US4313224 - Monitoring system of an optical power in an optical repeater
