Patent ID: 7773833

Claim:
An optical modulation device comprising: an optical modulation unit in which first and second sub-Mach-Zehnder optical waveguides are formed in two arms of a main Mach-Zehnder optical waveguide supplied with a beam having a frequency f 0 , and in which a first phase difference adjusting member adjusts an intensity of respective output beams passing through the sub-Mach-Zehnder optical waveguides by applying a phase difference to the beam passing through both arms of at least one of the sub-Mach-Zehnder optical waveguides, a second phase difference adjusting member applies a phase difference of a bias to the respective beams passing through the two arms of the main Mach-Zehnder optical waveguide, and a modulation member modulates a frequency of the beam into a modulation frequency f m to output a beam having a component of frequency f +1 =f 0 +f m and a component of frequency f −1 =f 0 −f m from the main Mach-Zehnder optical waveguide; a division unit which divides the output beam of the optical modulation unit into two beams; a filter unit which extracts the component of frequency f 0 from one divided beam; a first optical detector which measures a beam reception power of the filtered beam having the component of frequency f 0 ; and a second optical detector which measures a beam reception power of the other divided beam having the components of frequencies f 0 , f +1 , and f −1 , wherein in the optical modulation unit, the first and second phase difference adjusting members are controlled so that the beam reception power measured by the first optical detector becomes a minimum value and the beam reception power measured by the second optical detector becomes a maximum value.