Stabilizing device for optical modulator

Abstract

A device for stabilizing a modulation operation of an optical modulator is provided, the optical modulator having an optical waveguide provided on a substrate and an electrode provided so as to correspond to the optical waveguide, modulating light inputted to the optical waveguide by a voltage corresponding to a physical amount to be measured which is inputted to the electrode, and outputting the modulated light. The device includes: an optical detecting device for outputting signal corresponding to intensity of light outputted from the optical modulator; a control signal outputting device for, on the basis of the output signal of the optical detecting device, outputting a control signal which compensates a phase bias fluctuation of the optical modulator; a light source device for outputting control light corresponding to the control signal; and a voltage applying device, provided in contact with the electrode of the optical modulator, for applying voltage corresponding to the control light to the electrode. Accordingly, the light source device illuminates to the voltage applying device a control light corresponding to a driving signal which negatively feeds back a phase bias fluctuation signal. In this way, the voltage applying device applies a voltage which is set so as to offset variation in phase bias fluctuation in accordance with bias fluctuation, and the phase bias fluctuation is offset.