Patent ID: 7151875
Filing Date: 2006-12-19
Classification: H04J

Abstract:
1. An optical add drop multiplexer (OADM) comprising: an input port for receiving a WDM optical signal that includes a plurality of signal wavelengths; at least one drop port for extracting one of the plurality of signal wavelengths from the WDM optical signal; at least one add port for inserting an add wavelength into the WDM optical signal; an output port for transmitting to an external element the WDM optical signal with the add wavelength present and the extracted one of the plurality of wavelengths absent; a first monitoring arrangement for monitoring an average power level of the signal wavelengths in said WDM optical signal; a second monitoring arrangement for monitoring a power level of the add wavelength; a comparator for comparing the average power level of the signal wavelengths in said WDM signal to the power level of the add wavelength; and a variable optical attenuator coupled to the add port for adjusting optical attenuation of the add wavelength in response to a control signal received from the comparator, wherein said first monitoring arrangement includes: a first optical tap located at the input port; an optical splitter having an input coupled to the first optical tap for receiving a portion of WDM optical signal therefrom; an optical tunable filter coupled to a first output of the optical splitter; a firsts photodetector coupled to the optical tunable filter; a second photodetector coupled to a second output of the optical splitter; an electric circuit receiving first and second reference signals from the first and second photodetectors, respectively, and generating a third reference signal that is provided to a first input of the comparator.