Patent ID: 7224899

Claim:
A system comprising: a closed loop topology adapted to WDM signal light obtained by wavelength division multiplexing a plurality of optical signals; and a plurality of nodes arranged along said closed loop topology; each of said nodes comprising: a first optical amplifier for amplifying input signal light; an optical demultiplexer for separating signal light output from said first optical amplifier into a plurality of optical signals; an optical switch adapted to operate on a plurality of optical signals output from said optical demultiplexer; an optical multiplexer for wavelength division multiplexing a plurality of optical signals output from said optical switch; a second optical amplifier for amplifying signal light output from said optical multiplexer; and a control unit for controlling said first and second optical amplifiers; said control unit comprising: first means for transmitting the number of channels of WDM signal light to be output from a corresponding node to a node immediately downstream of the corresponding node; second means for controlling said first optical amplifier so that an output from said first optical amplifier becomes constant, according to the number of channels of WDM signal light received from the node immediately upstream of the corresponding node; and third means for controlling said optical switch so that the optical signals other than one or more optical signals added to the corresponding node are not output from the corresponding node until the control by said second means is converged.