Patent ID: 7405859

Claim:
A wavelength selecting apparatus comprising: a wavelength selecting filter that is a first acousto-optic tunable filter; a monitoring filter that is a second acousto-optic tunable filter like the first acousto-optic tunable filter; a light source that outputs light having a specific wavelength to the monitoring filter; a light receiving unit that detects a wavelength of light that has passed the monitoring filter; and a control unit that outputs, to the wavelength selecting filter, a control signal having a control frequency to selectively pass light of a desirable wavelength, wherein the light source includes a light emitting element that emits light of a wide wavelength band; and an optical filter having at least two transmission bands and through which the emitted light passes to be output to the monitoring filter, and the control unit outputs the control signal that has the control frequency that corresponds to the light of the desirable wavelength, based on at least two wavelengths of the light output by the light source.