Mach-zehnder modulator

A Mach-Zehnder modulator comprising:

• a first arm waveguide including a first waveguide portion, a second waveguide portion and a third waveguide portion, the first waveguide portion extending in a direction of a first axis, the second waveguide portion extending in a direction of a second axis, and the third waveguide portion being curved so as to optically couple the first waveguide portion thereof to the second waveguide portion thereof;
• a second arm waveguide including a first waveguide portion, a second waveguide portion and a third waveguide portion, the first waveguide portion extending in the direction of the first axis, the second waveguide portion extending in the direction of the second axis, the third waveguide portion being curved so as to optically couple the first waveguide portion thereof to the second waveguide portion thereof, and the direction of the first axis being different from that of the second axis;
• and
• a differential signal line including a first signal conductor, a second signal conductor, and a reference potential conductor, the first signal conductor and the second signal conductor being coupled to drive the first arm waveguide and the second arm waveguide, respectively,
• the reference potential conductor having a first conductor portion extending in the direction of the first axis, and an intersecting conductor portion connected to the first conductor portion thereof,
• the first signal conductor having a first conductor portion extending in the direction of the first axis and connected to the first waveguide portion of the first arm waveguide, and a first intersecting conductor portion connected to the first conductor portion thereof,
• the second signal conductor having a first conductor portion extending in the direction of the first axis and connected to the first waveguide portion of the second arm waveguide, and a second intersecting conductor portion connected to the first conductor portion thereof,
• one of the first intersecting conductor portion and the second intersecting conductor portion including an upper conducting layer,
• the other of the first intersecting conductor portion and the second intersecting conductor portion including a lower conducting layer, and
• the upper conducting layer extending on the lower conducting layer apart from the lower conducting layer.