Optical add drop multiplex (oadm)

The invention claims a optical network loop is OADM, wherein the light from grades socket is for preventing node fault and optical fibre fault subnode or the subnode system and method. The network a control loop and spare loop; each sub-node a selecting optical filter device and optical 2×2 switching system and optical amplifying device. The method and system further - comprising: And spare loop the input and output of the sub-node to work loop for monitoring through monitoring device, device according to generating alarm signal to in subnode detection. As the response of alarming, so the alarm subnode and an alarm function with of the first phase transition to one of multiple types of possibilities situations, therefore selects a combined switch capable of the plug according to the new of antithetical couplet detecting node is at.