Patent ID: 9503211
Filing Date: 2016-11-22
CPC Classification: H04B,H04J

Claim Text:
1. A signal detection circuit comprising: a first optical filter configured to filter a WDM optical signal including a plurality of optical signals respectively carrying frequency modulated signals; a second optical filter configured to filter the WDM optical signal; a first photo detector configured to convert the output light of the first optical filter into a first electrical signal; a second photo detector configured to convert the output light of the second optical filter into a second electrical signal; a difference circuit configured to output a signal representing a difference between the first electrical signal and the second electrical signal; and a detector configured to detect respective frequency modulated signals carried by the plurality of optical signals based on the output signal of the difference circuit, wherein the plurality of optical signals are arranged substantially at a fixed wavelength spacing, optical transmittance of each of the first and second optical filters is changed substantially periodically with respect to the wavelength, a plurality of transmission bands of the first optical filter are arranged on the long wavelength side with respect to the corresponding center wavelengths of the spectrum of the optical signal in the WDM optical signal, and a plurality of transmission bands of the second optical filter are arranged on the short wavelength side with respect to the corresponding center wavelengths of the spectrum of the optical signal in the WDM optical signal.