| 摘要 |
PURPOSE:To attain quick formation of a bypass having a high reliability, at the production of a failure, by weakly coupling a main transmission line and a sub- transmission line at each section of communication stations. CONSTITUTION:A main transmission line 1 and a subtransmission line 2 for optical signals are installed in parallel. Communication stations 31-3n are provided for suitable locations of the main transmission line 1. The subtransmission line 2 is provided with substantial optical signal attenuators 41-4n corresponding to the stations 31-3n. Bidirectional weak coupling sections 51-5n-1 (e.g., half mirrors) are provided to each section of the communication stations between the lines 1 and 2. Both ends of the lines 1 and 2 are connected for looping so that the attenuation of optical signal attenuators 41-4n can be small toward the return and large toward the opposite direction. Thus, the output of the station 3n is returned to the station 31 through the line 2. Further, the reliability can be improved through by-pass. |
