Optical spectrum analyzer

An optical spectrum analyzer for detecting a light output that is dependent on the frequency of light in a wavelength range of light to be measured, comprising:

• a waveguide acousto-optic tunable filter including a piezoelectric substrate, an optical waveguide provided on the piezoelectric substrate, and an IDT arranged to convert a mode of light being propagated in an approximate middle portion of the optical waveguide;
• a light source arranged to provide reference light having a specific wavelength outside of the wavelength range to the waveguide acousto-optic tunable filter;
• a driving circuit arranged to excite the IDT of the waveguide acousto-optic tunable filter by supplying a high frequency signal to the IDT;
• a photoreceptor that receives light that is output from the waveguide acousto-optic tunable filter;
• and
• an arithmetic device arranged to make a correction, based on the wavelength of selected light that is output when a mode of the reference light is converted by causing the reference light to be incident on the waveguide acousto-optic tunable filter and by applying high frequency waves having a predetermined frequency to the IDT and exciting the IDT, to a relationship between the frequency of the high frequency waves applied to the IDT and the wavelength of the selected light selected from the light to be measured.