Patent ID: 8724933

Claim:
An optical device comprising: a substrate; a first optical branching filter on the substrate and dividing input light into first and second input lights; first and second Mach-Zehnder optical modulators on the substrate and respectively modulating the first and second input lights; and a first optical coupler on the substrate and combining light modulated by the first Mach-Zehnder modulator and light modulated by the second Mach-Zehnder optical modulator to produce modulated output light, wherein the first Mach-Zehnder optical modulator includes first and second optical waveguides, a first phase modulation electrode applying a first modulation voltage across the first optical waveguide to change phase of light propagating in the first optical waveguide, a second phase modulation electrode applying a second modulation voltage across the second optical waveguide to change phase of light propagating in the second optical waveguide, a first feed line and a first terminal line, respectively connected to opposite ends of the first phase modulation electrode, for supplying the first modulation voltage to the first phase modulation electrode, and a second feed line and a second terminal line, respectively connected to opposite ends of the second phase modulation electrode, for supplying the second modulation voltage to the second phase modulation electrode, the second Mach-Zehnder optical modulator includes third and fourth optical waveguides, a third phase modulation electrode applying a third modulation voltage across the third optical waveguide to change phase of light propagating in the third optical waveguide, a fourth phase modulation electrode applying a fourth modulation voltage across the fourth optical waveguide to change phase of light propagating in the fourth optical waveguide, a third feed line and a third terminal line, respectively connected to opposite ends of the third phase modulation electrode, for supplying the third modulation voltage to the third phase modulation electrode, and a fourth feed line and a fourth terminal line, respectively connected to opposite ends of the fourth phase modulation electrode, for supplying the fourth modulation voltage to the fourth phase modulation electrode, the first, second, third, and fourth feed lines and the first, second, third, and fourth terminal lines respectively extend to peripheral portions of the substrate, and the first and second phase modulation electrodes are both located on the substrate at locations closer to the first optical coupler than to the first optical branching filter, the third and fourth phase modulation electrodes are both located on the substrate at locations closer to first optical branching filter than to the first optical combiner, and the first and second phase modulation electrodes are not crossed by any straight line that is perpendicular to the first, second, third, and fourth optical waveguides and that crosses the third and fourth phase modulation electrodes.