| 摘要 |
In a data transmission system where a computer side and a terminal side are connected with the aid of an optical fiber cable (FK), unauthorized tapping of light energy from some fiber in the cable can be detected. The transmitted signals are assumed to be shot-noise limited, i.e. the transmitted light is heavily superposed, whereby a large part of the transmitted light must be tapped off for listening. The computer side and terminal side contain level-sensing circuits (NVK1,NVK2) connected to respective receiver units (MD,MT) which send an alarm when tapping takes place. An optical fiber relay (RK) is connected between the fiber cable (FK) and the terminal side for short-circuiting this side in the case where a power failure can occur. |
