| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem that although an MZ modulator comprising two waveguides formed along different plane azimuths of a substrate performs phase modulation on respective demultiplexed branch light beams respectively in opposite-phase relation by two optical phase modulators so as to actualize a push-pull operation with one modulated signal, capacitance cannot be added to the electrodes, speeds of a light wave and a microwave electric signal cannot be sufficiently matched, and sufficient impedance matching cannot be made, so that fast wide-range modulation cannot be achieved.SOLUTION: An MZ optical modulator according to the present invention includes a sub electrode (branch electrode) which is electrically connected to a modulation electrode formed on a light guide having a mesa structure. The sub electrode branches off from a modulation electrode perpendicularly to the length direction thereof and separates from the modulation electrode, and then extends again substantially in parallel with the modulation electrode. A parallel part of the sub electrode includes a structure for adding capacitance for a waveguide similar to the light guides of the MZ modulator. A width of the sub electrode, a distance to the modulation electrode, constitution dimensions such as a length can be freely designed without taking functions of the light guides into consideration at all. |
