An apparatus and method are provided for monitoring the Q-factor of a plurality of main signals that are simultaneously transmitted across a fiber optic line using wave division multiplexing. In particular, the includes an optical tap, a tunable optical bandpass filter, and a Q-detection circuit. The...http://www.google.de/patents/US6532087?utm_source=gb-gplus-sharePatent US6532087 - Multiple signal Q-tester
