Patent ID: 9071378
Filing Date: 2015-06-30
Classification: H04B,H04J

Abstract:
1. A superimposed signal detection circuit that detects a signal superimposed on an optical signal in a WDM system, the superimposed signal detection circuit comprising: an optical filter having wavelength-dependent loss configured to filter a plurality of optical signals on which a corresponding superimposed signal is superimposed by frequency modulation; a photo detector configured to convert the plurality of optical signals filtered by the optical filter into an electric signal; and a detector configured to obtain information indicated by the superimposed signal respectively superimposed on the plurality of optical signals from the electric signal obtained by the photo detector, wherein a transmittance of the optical filter is tilted at and around a center wavelength of respective wavelength channels with respect to wavelength for the respective wavelength channels of at least one of the plurality of optical signals, and the detector detects a value of the superimposed signal based on a change in power of output light from the optical filter for the respective wavelength channels of at least one of the plurality of optical signals, and the frequency of the optical signal is modulated according to a value of the superimposed signal and the optical filter is configured to provide different transmittances for respective wavelengths corresponding to frequencies that correspond to respective values of the superimposed signal.