Patent ID: 6947630

Claim:
A control method for a variable wavelength optical filter that permits a wavelength division multiplexing signal light including a plurality of optical signals having mutually different peak wavelengths at which a maximum power of light is provided, respectively, to be input thereto, and selectively separates, in collective, the plurality of optical signals of different peak wavelengths from the wavelength division multiplexing signal light, for changing a drive condition of said variable wavelength optical filter, and controlling a wavelength characteristic of said variable wavelength optical filter to become closer to a wavelength characteristic corresponding to a preset plurality of selected wavelengths, based on power of monitor light taken out from said variable wavelength optical filter, comprising: taking out in collective to receive the monitor light corresponding to the plurality of optical signals having different peak wavelengths selectively separated by said variable wavelength optical filter from the wavelength division multiplexing signal light, and generating a monitor signal of a level which is changed corresponding to the power of said received monitor light; extracting an alternating current component of said generated monitor signal; and controlling the drive condition of said variable wavelength optical filter based on a level change in said extracted alternating current component.