Patent ID: 7945173

Claim:
A control apparatus for an optical modulator that comprises: 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 for branching an optical waveguide into a first branch optical waveguide and a second branch optical waveguide, and a part for 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 a drive signal to at least one of 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, wherein said control apparatus comprises: a phase shift detection section that compares phases of the respective drive signals given to said first and second modulation sections to detect the phase shift; and a control section that controls said drive section so as to minimize the phase shift detected in said phase shift detection section.