Optical modulator

An optical modulator comprising:

• a Mach-Zehnder optical waveguide including first and second optical waveguides;
• a buffer layer covering the first and second optical waveguides;
• and
• an electrode layer including first and second ground electrodes and a signal electrode positioned between the first and second ground electrodes in a plan view, wherein
• an insulating layer provided between the buffer layer and the electrode layer, the insulating layer having first and second openings positioned above the first and second optical waveguides, respectively,
• the signal electrode has a first lower surface covering the first optical wave guide through the buffer layer, the signal electrode including an upper part formed in the electrode layer and a lower part embedded in the first opening, and
• the first ground electrode has a first lower surface covering the second optical waveguide through the buffer layer and a second lower surface positioned above the first lower surface thereof, the first ground electrode including an upper part formed in the electrode layer and a lower part embedded in the second opening, wherein
• a gap between the signal electrode and the second ground electrode is larger than a gap between the signal electrode and the first ground electrode, and wherein
• a width of the upper part of the first ground electrode is larger than a width of the lower part of the first ground electrode.