Patent ID: 7418211

Claim:
A control apparatus for an optical modulator, said optical modulator comprising: a first modulation section and a second modulation section connected in series; and a drive section that gives drive signals, phases of which are synchronized, to said first and second modulation sections, respectively, said second modulation section including a part branching an optical waveguide into a first branch optical waveguide and a second branch optical waveguide, and a part combining said first and second branch optical waveguides, that utilizes a first electrode and a second electrode respectively provided in said first and second branch optical waveguides to control refractive indexes of said first and second branch optical waveguides, and obtains a periodic optical intensity characteristic according to a difference between said refractive indexes, and said drive section capable of giving the drive signals to said first and second electrodes so that said second modulation section performs a modulating operation corresponding to one period of the optical intensity characteristic thereof, and said control apparatus comprising: an output monitoring section that photo-electrically converts a signal light outputted by said optical modulator to acquire the electric spectrum, and detects the intensity of said acquired electric spectrum over a frequency band thereof; and a control section that judges the phase shift between the drive signals given to said first and second electrodes of said second modulation section according to the intensity detected by said output monitoring section, and adjusts the phase of at least one of the drive signals given to said first and second electrodes of said second modulation section so as to maximize said intensity.