Method and apparatus for selecting wavelength

A wavelength selecting method of outputting a control signal having a control frequency that selectively allows transmission of a light of a desirable wavelength through a wavelength selecting filter of a pair of like acousto-optic tunable filters, the control signal being output based on a detected wavelength of a reference light of a specific wavelength when the reference light is passed through a monitoring filter of the pair of like acousto-optic tunable filters, the wavelength selecting method comprising:

• outputting light of a wide wavelength band as the reference light to the monitoring filter, through an optical filter having at least two transmission bands, from a light emitting element;
• detecting at least two wavelengths in the specific wavelength of the reference light transmitted through the monitoring filter;
• calculating characteristic information of the control signal based on at least two of the detected wavelengths and the frequency of the reference signal respectively corresponding thereto;
• obtaining the control frequency corresponding to the desirable wavelength based on the characteristic information;
• and
• outputting the control frequency to the wavelength selecting filter.