Laser diode optical wavelength control apparatus

DETAILED DESCRIPTION It an object of the present invention to provide a photodiode optical wavelength control apparatus which, even when the optical center wavelength is largely shifted to fall outside the range of the optical low-pass filter or optical high-pass filter, can restore it to a controllable optical wavelength, thereby preventing an uncontrollable state.
In order to achieve the above object, according to the present invention, there is provided a laser diode optical wavelength control apparatus comprising a laser diode, optical branching means for branching a laser beam emitted by the laser diode into first, second, and third branched laser beams, a narrow-band first optical filter for receiving the first branched laser beam and transmitting a laser beam having a specific optical wavelength therethrough as a transmitted beam, second and third optical filters for receiving the second and third branched laser beams and transmitting laser beams having specific optical wavelengths therethrough as transmitted beams, first, second, and third photodiodes for converting output beams from the first, second, and third optical filters into electrical signals and outputting the electrical signals as analog voltages, comparator means for comparing the analog voltages output from the second and third photodiodes and outputting a signal representing a comparison result, differential amplifier means for performing differential amplification of a reference analog voltage obtained from the first photodiode and the output signal from the comparator means and outputting a control signal, a temperature adjustment element provided in tight contact with the laser diode and generating heat, a temperature of which is externally controlled, and temperature adjustment means for controlling the temperature of the heat from the temperature adjustment element on the basis of the control signal output from the differential amplifier means.