Patent ID: 9444573
Filing Date: 2016-09-13
CPC Classification: H04B,H04J,H04Q

Claim Text:
1. A frequency modulated signal detection circuit that receives an optical signal on which a frequency modulated signal is superimposed, the frequency modulated signal detection circuit comprising: an optical filter configured to filter the optical signal; a filter controller configured to control a passband of the optical filter based on a change of power of the optical signal; a signal detection unit configured to detect the frequency modulated signal based on the change of the power of the optical signal filtered by the optical filter; and a state decision unit configured to decide a state of an optical transmission path through which the optical signal is transmitted based on the change of the power of the optical signal, wherein the state decision unit decides whether the passband of the optical transmission path for the optical signal is shifted to a long wavelength side or a short wavelength side with respect to a center wavelength of the optical signal, and when the passband of the optical transmission path is shifted to the long wavelength side, the filter controller allocates the passband of the optical filter on the long wavelength side of the center wavelength of the optical signal, and when the passband of the optical transmission path is shifted to the short wavelength side, the filter controller allocates the passband of the optical filter on the short wavelength side of the center wavelength of the optical signal.