Optical control element, optical modulation device using same, and optical transmission apparatus
Provided is an optical control element that can minimize an optical path difference between branched waveguides while reducing a difference in structure between the branched waveguides by disposing an input portion and an output portion of an optical waveguide on the same side of a substrate on which the optical waveguide is formed. An optical control element includes a substrate 1 having an electro-optic effect, an optical waveguide 2 formed on the substrate, and a control electrode controlling a light wave propagating through the optical waveguide, in which an input portion (input light L 1 ) and an output portion (output light L 2 ) of the optical waveguide are formed on the same side of the substrate, the optical waveguide includes at least one Mach-Zehnder type optical waveguide portion (MZ) that has two branched waveguides ( 21, 22 ) branched from one optical waveguide and combines the two branched waveguides to form one optical waveguide, and the branched waveguides have an even number of turned-back potions (A 1 , A 2 ).
1. An optical control element comprising:
a substrate having an electro-optic effect;
an optical waveguide formed on the substrate; and
a control electrode controlling a light wave propagating through the optical waveguide, wherein
an input portion and an output portion of the optical waveguide are formed on the same side of the substrate,
the optical waveguide includes at least one Mach-Zehnder type optical waveguide portion that has two branched waveguides branched from one optical waveguide and combines the two branched waveguides to form one optical waveguide,
the branched waveguides have an even number of turned-back portions,
the control electrode includes a modulation electrode and a bias electrode,
the branched waveguides has a plurality of sections separated by the turned-back portions of the branched waveguides,
the modulation electrode and the bias electrode are provided in different sections of the branched waveguides,
the bias electrode is disposed in each of the sections before and after the turned-back portions,
the bias electrode has at least two wirings, each of which branches into a plurality of electrode portions,
in each of the sections, the wirings are arranged intersecting the branched waveguides,
in each of the sections, the electrode portions of the two wirings are arranged along the branched waveguides and opposite each other,
the electrode portions of one wiring and the electrode portions of the other wiring extend in opposite directions from each wiring along the branched waveguides, and
in each of the sections, the sign of the phase change formed by the bias electrode is set to be the same.
2. The optical control element according to claim 1 , wherein
optical path lengths of the branched waveguides are set to be same as each other.
3. The optical control element according to claim 1 , wherein
one optical waveguide is branched into a plurality of optical waveguides, each branched optical waveguide is provided with the Mach-Zehnder type optical waveguide portion, and the branched waveguides of the Mach-Zehnder type optical waveguide portion have an even number of turned-back portions in a state in which the Mach-Zehnder type optical waveguide portions are disposed in parallel.
4. An optical modulation device comprising:
the optical control element according to claim 1 ;
a case that accommodates the optical control element; and
an optical fiber through which light waves are input to and output from the optical control element.
5. The optical modulation device according to claim 4 , further comprising:
an electronic circuit that amplifies a modulation signal input to the optical control element and is provided inside the case.
6. An optical transmission apparatus comprising:
the optical modulation device according to claim 4 ; and
an electronic circuit that outputs a modulation signal for causing the optical modulation device to perform a modulation operation.
7. The optical control element according to claim 1 , wherein
the modulation electrode is formed in a linear shape from an input portion to an action portion, and is led from the action portion to an output portion in a direction away from the bias electrode.
8. The optical control element according to claim 1 , wherein
in one of sections before and after the turned-back portion, the electrode portions of one wiring are arranged so as to sandwich the electrode portion of the other wiring, and in the other one of sections, the other electrode portions of the other wiring is arranged so as to sandwich the other electrode portion of the one wiring.