| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical transmission system of high reliability, which does not require periodical maintenance and inspection. <P>SOLUTION: The optical signal pi of an optical transmitter 11 is sent to a normal transmission line 21 through an optical switch 12 as an optical signal pad, and the transmitted optical signal pad is sent out to the optical receiver 31 of a subscriber device 30 through an optical coupler 24 as an optical signal pm and branched by the optical coupler and output as branch light pn. The branch light pn is branched into return light pau and return light pbu by an optical coupler 25. The return light pau is transmitted to the optical switch 12 through the normal transmission line 21, and the return light pbu is transmitted to the optical switch 12 through a spare transmission line 22. When the reception level of the return light pau becomes lower than a first threshold in the optical switch 12 due to occurrence of a fault or the like in the normal transmission line 21, the optical signal pi is sent out to the spare transmission line 22 as an optical signal pbd in the case that the reception level of the return light pbu is equal to or higher than a second threshold. <P>COPYRIGHT: (C)2009,JPO&INPIT |
