Patent ID: 8437068

Claim:
An optical modulator which makes polarized waves orthogonal to each other between light pulses corresponding to adjacent bits on a time axis, the optical modulator comprising: first and second light modulation unit which are driven with the same modulation frequency; an optical waveguide element which has a first waveguide through which a first modulated light beam by the first light modulation unit propagates and a second waveguide through which a second modulated light beam by the second light modulation unit propagates, the first waveguide being formed obliquely to an outgoing end surface, and the second waveguide being formed obliquely to both the first waveguide and the outgoing end surface; a lens which makes parallel optical paths of the first modulated light beam outgoing from the first waveguide and the second modulated light beam outgoing from the second waveguide; a phase delay element which applies a phase delay to at least one of the first and second modulated light beams; a polarization beam rotating unit which rotates at least one polarized wave of the first and second modulated light beam to make the polarized waves orthogonal to each other between the two modulated light beams; and a polarization beam combining element which is provided at the back of the lens, and combines the first modulated light beam and the second modulated light beam whose polarized waves are made orthogonal to each other, wherein the thickness of the phase delay element in the light propagation direction is set to a thickness at which a light pulse of the first modulated light beam and a light pulse of the second modulated light beam by a phase difference due to the phase delay element and a phase difference due to the polarization beam combining element are bit-interleaved.