Optical modulator and method of use

1. An optoelectronic device for quadrature-amplitude modulation (QAM), comprising:

an input waveguide;

a first intermediate waveguide, a second intermediate waveguide, a third intermediate waveguide, and a fourth intermediate waveguide, each coupled to the input waveguide via an input coupler; and

an output waveguide, coupled to each of the first to fourth intermediate waveguides via an output coupler,

wherein each intermediate waveguide includes a modulating component connected in series with a phase shifting component, and each modulating component is connected to a respective electronic driver, the respective electronic drivers together being operable to produce a QAM modulated output from light entering the optoelectronic device from the input waveguide,

wherein the input coupler or the output coupler comprises a first coupler comprising seven ports, a second coupler comprising three ports, and a third coupler comprising three ports, one of the seven ports of the first coupler being coupled to the input waveguide or the output waveguide, respectively,

wherein the remaining six of the seven ports of the first coupler are respectively coupled to the first intermediate waveguide, two of the three ports of the second coupler, two of the three ports of the third coupler, and the fourth intermediate waveguide,

wherein the remaining one of the three ports of the second coupler is coupled to the second intermediate waveguide, and

wherein the remaining one of the three ports of the third coupler is coupled to the third intermediate waveguide.

2. The optoelectronic device of claim 1 , wherein each of the respective electronic drivers is a PAM-4 electronic driver, such that the respective modulating component can operate in four modulation states.

3. The optoelectronic device of claim 1 , wherein the input coupler is configured to equally split input light between the first to fourth intermediate waveguides.

4. The optoelectronic device of claim 2 , further comprising a DC phase shifting intermediate waveguide, coupled to the input waveguide via the input coupler and coupled to the output waveguide via the output coupler, the DC phase shifting intermediate waveguide being configured to re-center a constellation corresponding to the QAM outputs available from the optoelectronic device.

5. The optoelectronic device of claim 2 , wherein a static phase difference between two of the first to fourth intermediate waveguides is set at 90° .

6. The optoelectronic device of claim 1 , wherein each of the phase shifting components is a DC phase shifter.

7. The optoelectronic device of claim 1 , wherein each of the respective electronic drivers is a binary non-return-to-zero driver, such that the respective modulating component can be operated in two modulation states.

8. The optoelectronic device of claim 1 , wherein the input coupler is configured to split input light between the first to fourth intermediate waveguides at a ratio of 2:1:2:1, such that two of the first to fourth intermediate waveguides receive twice the optical power of the other two of the first to fourth intermediate waveguides.

9. The optoelectronic device of claim 1 , wherein each modulating component is a phase modulator.

10. The optoelectronic device of claim 1 , wherein each modulating component is an amplitude modulator.

11. The optoelectronic device of claim 1 , wherein each intermediate waveguide includes two modulating components connected in series, the two modulating components being:

a phase modulator; and

an amplitude modulator.

12. A method of modulating an optical signal using the optoelectronic device of claim 1 and according to a QAM scheme, the method comprising:

providing an optical signal at the input waveguide;

splitting the optical signal into a plurality of intermediate waveguides including the first and second intermediate waveguides, each coupled to the input waveguide via the input coupler;

modulating the amplitude and phase of the optical signal present in each of the plurality of intermediate waveguides, according to the QAM scheme and by respective modulating components connected in series with respective phase shifting components, each of said modulating components being connected to and driven by a respective electronic driver; and

recombining the optical signals in each of the plurality of intermediate waveguides into the output waveguide, coupled to each of the plurality of intermediate waveguides via the output coupler.

13. The optoelectronic device of claim 1 , wherein the input coupler or the output coupler further comprises first and second coupling waveguides respectively coupling the two ports of the second coupler to the two corresponding ports of the first coupler, and

wherein a shape of the first coupling waveguide is different from a shape of the second coupling waveguide.

14. The optoelectronic device of claim 13 , wherein the shapes of the first and second coupling waveguides are configured such that light contributions input into the second coupler from the two corresponding ports of the first coupler, or input into the first coupler from the two corresponding ports of the second coupler, are in phase.

15. The optoelectronic device of claim 13 , wherein a width of the first coupling waveguide decreases along a guiding direction of the first coupling waveguide from the corresponding port of the first coupler to a point along the first coupling waveguide, and

wherein a width of the second coupling waveguide increases along a guiding direction of the second coupling waveguide from the corresponding port of the first coupler to a point along the second coupling waveguide.

16. The optoelectronic device of claim 15 , wherein the width of the first coupling waveguide increases along the guiding direction of the first coupling waveguide from the point along the first coupling waveguide to the corresponding port of the second coupler, and

wherein the width of the second coupling waveguide decreases along the guiding direction of the second coupling waveguide from the point along the second coupling waveguide to the corresponding port of the second coupler.

17. The optoelectronic device of claim 1 , wherein a static phase difference between the first intermediate waveguide and the second intermediate waveguide is 180°, and a static phase difference between the third intermediate waveguide and the fourth intermediate waveguide is 180°, and

wherein a static phase difference between the first intermediate waveguide and the third intermediate waveguide is 90°, and a static phase difference between the second intermediate waveguide and the fourth intermediate waveguide is 90°.

18. The optoelectronic device of claim 1 , wherein each of the first, second, and third couplers is a multimode interference (MMI) coupler.