Patent ID: 7292787

Claim:
A selected-wavelength tuning apparatus comprising: an acoustic optical tunable filter (AOTF) receiving a wavelength division multiplexed (WDM) light including a plurality of lights at different wavelengths multiplexed together, and branching the WDM light into a selected-wavelength light and light with other wavelengths in accordance with a radio-frequency signal applied to the AOTF; a radio-frequency signal generating means for generating said radio-frequency signal; a light intensity detecting means for detecting light intensity of light from said acoustic optical tunable filter; and a radio-frequency signal controlling means for controlling said radio-frequency signal generating means so as to select light of a predetermined wavelength in accordance with an output of said light intensity detecting means, wherein said radio-frequency signal controlling means comprises a maximum value discriminating means for discriminating the maximum value of said light intensity with respect to light of a predetermined wavelength by receiving said light intensity from said light intensity detecting means while changing the frequency of said radio-frequency signal generated by said radio-frequency signal generating means, and a frequency controlling means for controlling said radio-frequency signal generating means so as to generate the radio-frequency with the frequency which makes the maximum light intensity discriminated by said maximum value discriminating means, said frequency controlling means generates a frequency which is smaller than the frequency of said radio-frequency signal generated by said radio-frequency signal generating means and said radio-frequency signal generating means superimposes said frequency generated by said frequency controlling means with said radio-frequency signal.