Apparatus and method of generating multilevel quadrature amplitude modulated signal using electro-absorption modulators

1. An apparatus, comprising:

an optical modulator including a parallel-nested pair of Mach-Zehnder Interferometers, each arm of the Mach-Zehnder Interferometers including one or more Electro-Absorption Modulators therein; and

an electronic controller electrically connected to drive the Mach-Zehnder Interferometers such that the optical modulator outputs an optical carrier modulated according to a quadrature amplitude modulation constellation with at least five different symbols, wherein the electronic controller is connected to apply intermediate voltages to drive each of the Mach-Zehnder Interferometers to modulate the optical carrier with one positive amplitude on a quadrature-phase component of the optical carrier and with a different positive amplitude on an in-phase component of the optical carrier.

2. The apparatus of claim 1 , wherein one of the arms of a first of the Mach-Zehnder Interferometers includes a first phase shifter and one of the arms of a second of the Mach-Zehnder Interferometers includes a second phase shifter.

3. The apparatus of claim 1 , wherein each of the Mach-Zehnder Interferometers is connected to combine portions of Electro-Absorption Modulator modulated optical carriers from first and second arms thereof with a relative phase shift of 180 degrees ±5 degrees.

4. The apparatus of claim 1 , wherein the optical modulator is connected to combine modulated optical carriers from the two Mach-Zehnder Interferometers with a relative phase.

5. The apparatus of claim 4 , wherein the relative phase has a magnitude of 90 degrees ±5 degrees.

6. The apparatus of claim 1 , further including first optical couplers connected to ends of the arms of the parallel-nested pair and second optical couplers to connecting the first optical couplers on same ends of the arms to each other.

7. The apparatus of claim 1 , wherein the optical modular and the electronic controller are on a substrate as part of an electronic-photonic device.

8. An apparatus, comprising:

an optical modulator including a parallel-nested pair of Mach-Zehnder Interferometers, each arm of the Mach-Zehnder Interferometers including one or more Electro-Absorption Modulators therein; and

an electronic controller electrically connected to drive the Mach-Zehnder Interferometers such that the optical modulator outputs an optical carrier modulated according to a quadrature amplitude modulation constellation with at least five different symbols; and

wherein the electronic controller is connected to apply intermediate voltages to drive a first of the Mach-Zehnder Interferometers to modulate the optical carrier to have at least three different modulation amplitudes.

9. The apparatus of claim 8 wherein, the electronic controller is connected to drive a second of the Mach-Zehnder Interferometers to modulate the optical carrier to have the at least three different modulation amplitudes.

10. The apparatus of claim 8 , wherein one of the arms of the first of the Mach-Zehnder Interferometers includes a first phase shifter and one of the arms of a second of the Mach-Zehnder Interferometers includes a second phase shifter.

11. The apparatus of claim 8 , wherein each of the Mach-Zehnder Interferometers is connected to combine portions of Electro-Absorption Modulator modulated optical carriers from first and second arms thereof with a relative phase shift of 180 degrees ±5 degrees.

12. The apparatus of claim 8 , wherein the optical modulator is connected to combine modulated optical carriers from the two Mach-Zehnder Interferometers with a relative phase.

13. The apparatus of claim 12 , wherein the relative phase has a magnitude of 90 degrees ±5 degrees.

14. The apparatus of claim 8 , wherein the optical modular and the electronic controller are on a substrate as part of an electronic-photonic device.

15. An apparatus, comprising:

an optical modulator including a parallel-nested pair of Mach-Zehnder Interferometers, each arm of the Mach-Zehnder Interferometers including one or more Electro-Absorption Modulators therein; and

an electronic controller electrically connected to drive the Mach-Zehnder Interferometers such that the optical modulator outputs an optical carrier modulated according to a quadrature amplitude modulation constellation with at least five different symbols; and

wherein the electronic controller is connected to apply intermediate voltages to drive a first of the Mach-Zehnder Interferometers to modulate the optical carrier to have at least three different modulation phases.

16. The apparatus of claim 15 wherein, the electronic controller is connected to drive a second of the Mach-Zehnder Interferometers to modulate the optical carrier to have the at least three different modulation phases.

17. The apparatus of claim 15 , wherein at least two of the at least three different modulation phases differ from each other by 90 degree phase increments.

18. The apparatus of claim 15 , wherein the electronic controller is connected to drive the first of the Mach-Zehnder Interferometers to modulate the optical carrier to have three different modulation amplitudes.

19. The apparatus of claim 15 , wherein one of the arms of the first of the Mach-Zehnder Interferometers includes a first phase shifter and one of the arms of a second of the Mach-Zehnder Interferometers includes a second phase shifter.

20. The apparatus of claim 15 , wherein each of the Mach-Zehnder Interferometers is connected to combine portions of Electro-Absorption Modulator modulated optical carriers from first and second arms thereof with a relative phase shift of 180 degrees ±5 degrees.

21. The apparatus of claim 15 , wherein the optical modulator is connected to combine modulated optical carriers from the two Mach-Zehnder Interferometers with a relative phase.

22. The apparatus of claim 21 , wherein the relative phase has a magnitude of 90 degrees ±5 degrees.

23. The apparatus of claim 15 , wherein the optical modular and the electronic controller are on a substrate as part of an electronic-photonic device.

24. An apparatus, comprising:

an optical modulator including a parallel-nested pair of Mach-Zehnder Interferometers, each arm of the Mach-Zehnder Interferometers including one or more Electro-Absorption Modulators therein;

an electronic controller electrically connected to drive the Mach-Zehnder Interferometers such that the optical modulator outputs an optical carrier modulated according to a quadrature amplitude modulation constellation with at least five different symbols; and

wherein the electronic controller is electrically connected to:

deliver a modulating drive voltage to a first of the Electro-Absorption Modulators in a first arm of a first Mach-Zehnder Interferometer of the parallel-nested pair such that an optical carrier passing through the first Electro-Absorption Modulator of the first Mach-Zehnder Interferometer has one of two or more different non-null levels of optical phase and optical amplitude modulation, and

deliver a paired drive voltage to a second of the Electro-Absorption Modulators in a second arm of the first Mach-Zehnder Interferometer of the parallel-nested pair such that the optical carrier passing through the second Electro-Absorption Modulator of the first Mach-Zehnder Interferometer is reduced to a substantially null amplitude.

25. The apparatus of claim 24 , wherein the paired drive voltage delivered to the second Electro-Absorption Modulator of the first Mach-Zehnder Interferometer is a differentially complementary voltage of the modulating drive voltage delivered to the first Electro-Absorption Modulator of the first Mach-Zehnder Interferometer.

26. The apparatus of claim 24 , wherein, the electronic controller is connected to:

deliver a second modulating drive voltage to the first of the Electro-Absorption Modulators of a second Mach-Zehnder Interferometer of the parallel-nested pair such that the optical carrier passing through the first Electro-Absorption Modulator to the first arm of the second Mach-Zehnder Interferometer has one of the three or more different levels of optical phase and optical amplitude modulation, and,

deliver a second paired drive voltage to the second of the Electro-Absorption Modulators in the second arm of the second Mach-Zehnder Interferometer of the parallel-nested pair such that the optical carrier passing through the second Electro-Absorption Modulator to the second arm of the second Mach-Zehnder Interferometer is reduced to substantially null amplitude.

27. The apparatus of claim 26 , wherein the paired drive voltage to the second Electro-Absorption Modulator of the second Mach-Zehnder Interferometer is a differentially complementary voltage of the modulating drive voltage to the first Electro-Absorption Modulator of the second Mach-Zehnder Interferometer.

28. The apparatus of claim 26 , wherein the electronic controller is configured to deliver the modulating drive voltage, the paired drive voltage, the second modulating drive voltage and the second paired drive voltage over substantially a same time period.

29. The apparatus of claim 26 , wherein the modulating drive voltage includes a first data stream and the second modulating drive voltage includes a second different data stream.

30. The apparatus of claim 24 , wherein the optical modular and the electronic controller are on a substrate as part of an electronic-photonic device.