Patent ID: 7340170

Claim:
A wavelength-division multiplexed passive optical network including a plurality of subscriber units, a central office having an end connected to a remote node, and said remote node having an end connected to said end of the central office, said network comprising: a composite feeder fiber, comprising a working feeder fiber and a protection feeder fiber, for connecting the central office to the remote node; a reflection unit provided said end of the remote node connected to the central office for reflecting a monitoring optical signal transmitted from the central office; an output monitor stage provided at said end of the central office connected to the remote node for detecting the reflected monitoring optical signal and generating a control signal based on the presence of abnormality in said composite feeder fiber; and a first optical switch for switching the working and protection feeder fibers based on said control signal wherein the output monitor stage is provided on the working and protection feeder fibers and the output monitor stage includes: an output monitor unit for detecting the presence of the monitoring optical signal branched and transmitted from one of the working and protection feeder fibers and transmitting the control signal based on the presence of the abnormality in said composite feeder fiber; and a first optical circulator for transmitting the monitoring optical signal to the output monitor unit, and transmitting said multiplexed 2N downstream optical signals to said composite feeder fiber.