Signal transmission system

摘要

A signal transmission system uses an optical signal for carrying traffic information by modulating the brightness of the optical signal at a high frequency. A lower frequency optical overhead signal also modulates the optical signal, and a detector having a fall time characteristic of substantially longer duration than its rise time characteristic and which is of substantially longer duration than the longest bit period of the traffic is used to recover the overhead signal. The optical overhead signal modulates the maximum brightness of the signal, but not its minimum brightness so that the signal can be recarried even if the system is AC coupled.