Patent ID: 7729613

Claim:
A node for a wavelength division multiplexing (WDM) communication system, the node being connectable to other nodes of the system by first and second optical paths along which WDM radiation propagates in opposite directions between the nodes, the node comprising: a) an add/drop multiplexer for adding and dropping at least one WDM channel at the node; b) at least one optical shutter including a power monitor for monitoring power of the WDM radiation input to the node along the first path and for generating a corresponding radiation power indicative signal, and a radiation dropping coupler succeeding the power monitor along the first path, the coupler being operative for diverting from the first path a portion of the WDM radiation after the WDM radiation has been monitored by the power monitor, the portion of the WDM radiation corresponding to a supervisory channel carrying supervisory information for use in controlling the system; c) a controller for comparing the indicative signal with a threshold value to generate a control signal; and d) a switch for selectively substantially transmitting the WDM radiation output from the node along the second path without amplification and substantially blocking the WDM radiation output from the node along the second path comprising radiation input to the node along the second path, in response to the control signal.