Optical waveguide modulator
A dual-differential optical modulator includes two optical waveguide arms, each including one or more phase modulating p/n junctions. The p/n junctions in each waveguide arm are electrically coupled between a same pair of single-ended transmission lines so as to be differentially push-pull modulated when the transmission line pair is connected to a differential driver. Either cathode or anode electrodes of the p/n junctions are AC coupled to the transmission lines and DC biased independently on the transmission line signals.
1. A modulator comprising:
a first waveguide arm for guiding input light along a first path;
a second waveguide arm for guiding input light along a second path;
a first phase modulator (PM) along the first waveguide arm, the first PM comprising a first anode electrode and a first cathode electrode;
a second phase modulator (PM) along the second waveguide arm, the second PM comprising a second anode electrode and a second cathode electrode;
a first transmission line (TL) extending along, at least, a first segment of the first waveguide arm and a second segment of the second waveguide arm and being electrically coupled to the first anode electrode and to the second cathode electrode; and
a second transmission line (TL) extending along, at least, a third segment of the first waveguide arm and a fourth segment of the second waveguide arm and being electrically coupled to the first cathode electrode and to the second anode electrode; and
a driver configured to feed electrical drive signals into the first and second transmission lines;
wherein the first transmission line and the second transmission lines cross each other at least once.
2. The modulator according to claim 1 , wherein the first waveguide arm and the second waveguide arm include electro-optic material; wherein the first PM comprises a p/n junction in the first waveguide; and wherein the second PM comprises a p/n junction in the second waveguide.
3. The modulator according to claim 1 , wherein the first waveguide arm and the second waveguide arm include electro-optic material; wherein the first PM comprises a plurality of first p/n junctions in the first waveguide; and wherein the second PM comprises a plurality of second p/n junctions in the second waveguide.
4. The modulator according to claim 1 , further comprising electrical circuitry for providing a DC bias voltage to at least one of the first cathode electrode, the second cathode electrode, the first anode electrode, and the second anode electrodes.
5. The modulator according to claim 4 , wherein the first cathode electrode is AC-coupled to the second transmission line; and wherein the second cathode electrode is AC-coupled to the first transmission line.
6. The modulator according to claim 5 , wherein the electrical circuitry includes a first resistor electrically connected to the first cathode electrode for DC biasing thereof, and a second resistor electrically connected to the second cathode electrode for DC biasing thereof.
7. The modulator according to claim 4 , wherein the first anode electrode is AC-coupled to the second transmission line; and wherein the second anode electrode is AC-coupled to the first transmission line.
8. The modulator according to claim 7 , wherein the electrical circuitry includes a first resistor electrically connected to the first anode electrode for DC biasing thereof, and a second resistor electrically connected to the second anode electrode for DC biasing thereof.
9. The modulator according to claim 4 , wherein the electrical circuitry includes a first coupling electrode electrically connected to the first cathode electrode, and capacitively coupled to the second transmission line; and a second coupling electrode electrically connected to the second cathode electrode, and capacitively coupled to the first transmission line.
10. The modulator according to claim 9 , wherein the first coupling electrode is disposed over or under the second transmission line with an insulating layer therebetween.
11. The modulator according to claim 10 , wherein the first TL includes an input end for receiving the electrical drive signals, wherein the second coupling electrode extends along the first TL for at least a portion of a length thereof, and wherein the first cathode electrode is electrically connected to the first coupling electrode at a distal end thereof farther away from the input end of the first TL.
12. The modulator according to claim 9 , wherein the first coupling electrode comprises a MiM structure disposed next to the second transmission line.
13. The modulator according to claim 4 , wherein the electrical circuitry includes a first coupling electrode electrically connected to the first anode electrode, and capacitively coupled to the second transmission line; and a second coupling electrode electrically connected to the second anode electrode, and capacitively coupled to the first transmission line.
14. The modulator according to claim 13 , wherein the first coupling electrode is disposed over or under the second transmission line with an insulating layer therebetween.
15. The modulator according to claim 14 , wherein the first TL includes an input end for receiving the electrical drive signals, wherein the second coupling electrode extends along the first TL for at least a portion of a length thereof, and wherein the first anode electrode is electrically connected to the first coupling electrode at a distal end thereof farther away from the input end of the first TL.
16. The modulator according to claim 13 , wherein the first coupling electrode comprises a MiM structure disposed next to the second transmission line.
17. The modulator according to claim 3 , wherein the plurality of first p/n junctions comprises two first p/n junctions of opposite polarity disposed on opposite sides of the TL crossing, and
wherein the plurality of second p/n junctions comprises two second p/n junctions of opposite polarity disposed on the opposite sides of the TL crossing.
18. The modulator according to claim 17 , wherein the first transmission line forms a first loop, and the second transmission line forms a second loop; and wherein the first loop overlaps the second loop forming a plurality of TL crossings.
19. The modulator according to claim 17 , further comprising electrical circuitry for providing a DC bias voltage to at least one of the first cathode electrode, the second cathode electrode, the first anode electrode, and the second anode electrodes; wherein the electrical circuitry includes a first coupling electrode electrically connected to the first cathode electrode of each of the plurality of first p/n junctions, and capacitively coupled to the second transmission line; and a second coupling electrode electrically connected to the second cathode electrode of each of the plurality of second p/n junctions, and capacitively coupled to the first transmission line.