| 摘要 |
PURPOSE:To obtain an electric output signal with a desired level by allowing an optical modulator to utilize a 1st order Bragg diffracted light so as to control the intensity of transmitted light through the optical modulator. CONSTITUTION:An optical modulator 1 utilizing the 1st order Bragg diffracted light so as to vary the intensity of transmitted light by means of a modulation frequency, a voltage comparator 3 outputting a voltage in response to a voltage difference with respect to an input voltage over a reference voltage 7, and an oscillator 4 are provided. An optical input signal 5 inputted to the optical modulator 1 is attenuated by an attenuation rate depending on the modulation frequency and converted into an electric signal 6 by a photodetector 2. The electric signal 6 is given to the voltage comparator 3, where it is compared with a reference voltage 7 set to a desired maximum level and its output varies the oscillated frequency of the oscillator 4. Thus, the diffraction efficiency of the optical modulator 1 is varied based on the output of the modulator 4 to obtain an electric output of a desired level.
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