System and method for an optical phase shifter

1. An optical phase shifter comprising:

a first waveguide phase shifter configured to phase shift a transverse electric (TE) polarized component of an input optical signal by a first phase shift to produce a TE polarized component of a first phase shifted optical signal, and configured to phase shift a transverse magnetic (TM) polarized component of the input optical signal by a second phase shift to produce a TM polarized component of the first phase shifted optical signal;

a first polarization rotator configured to rotate the TE polarized component of the first phase shifted optical signal to produce a TM polarized component of a rotated optical signal, and configured to rotate the TM polarized component of the first phase shifted optical signal to produce a TE polarized component of the rotated optical signal; and

a second waveguide phase shifter configured to phase shift a TE polarized component of the rotated optical signal by a third phase shift to produce a TE polarized component of a second phase shifted optical signal, and configured to phase shift the TM polarized component of the rotated optical signal by a fourth phase shift to produce a TM polarized component of the second phase shifted optical signal, wherein the first waveguide phase shifter, the first polarization rotator, and the second waveguide phase shifter are integrated on a single substrate.

2. The optical phase shifter of claim 1 , wherein the first phase shift plus the fourth phase shift is within n/ 16 of the second phase shift plus the third phase shift.

3. The optical phase shifter of claim 1 , further comprising a second polarization rotator configured to rotate the TE polarized component of the second phase shifted optical signal to produce a TM polarized component of an output optical signal, and configured to rotate the TM polarized component of the second phase shifted optical signal to produce a TE polarized component of the output optical signal.

4. The optical phase shifter of claim 1 , wherein the first waveguide phase shifter and the second waveguide phase shifter are passive waveguide phase shifters.

5. The optical phase shifter of claim 1 , wherein the first waveguide phase shifter and the second waveguide phase shifter are active waveguide phase shifters.

6. The optical phase shifter of claim 5 , wherein the first waveguide phase shift is configured to be adjusted by applying a voltage to the first waveguide phase shifter.

7. The optical phase shifter of claim 1 , wherein the substrate comprises silicon-on-insulator (SOI).

8. A method of optical phase shifting, the method comprising:

receiving a first received optical signal;

shifting, by a first waveguide phase shifter, a phase of a TE polarized component of the first received optical signal by a first phase shift to produce a TE polarized component of a first phase shifted optical signal;

shifting, by the first waveguide phase shifter, a phase of a TM polarized component of the first received optical signal by a second phase shift to produce a TM polarized component of the first phase shifted optical signal;

rotating, by a first polarization rotator, the TE polarized component of the first phase shifted optical signal to produce a TM polarized component of a first rotated optical signal;

rotating, by the first polarization rotator, the TM polarized component of the first phase shifted optical signal to produce a TE polarized component of the first rotated optical signal;

shifting, by a second waveguide phase shifter, a phase of the TM polarized component of the first rotated optical signal by a third phase shift to produce a TM polarized component of a second phase shifted optical signal; and

shifting, by the second waveguide phase shifter, a phase of the TE polarized component of the first rotated optical signal by a fourth phase shift to produce a TE polarized component of the second phase shifted optical signal, wherein the first waveguide phase shifter, the first polarization rotator, and the second waveguide phase shifter are integrated on a single substrate.

9. The method of claim 8 , further comprising:

rotating the TE polarized component of the second phase shifted optical signal to produce a TM polarized component of a second rotated optical signal; and

rotating the TM polarized component of the second phase shifted optical signal to produce a TE polarized component of the second rotated optical signal.

10. The method of claim 8 , further comprising adjusting the first phase shift and the second phase shift.

11. The method of claim 10 , wherein adjusting the first phase shift and the second phase shift comprises applying a voltage to the first waveguide phase shifter.

12. The method of claim 8 , further comprising:

splitting a first input optical signal to produce the first received optical signal and a second received optical signal;

transmitting the second received optical signal to produce a transmitted optical signal; and

combining the second phase shifted optical signal and the transmitted optical signal.

13. The method of claim 12 , wherein transmitting the second received optical signal comprises:

shifting a phase of a TE polarized component of the second received optical signal to produce a TE polarized component of a third phase shifted optical signal;

shifting a phase of a TM polarized component of the second received optical signal to produce a TM polarized component of the third phase shifted optical signal;

rotating the TE polarized component of the third phase shifted optical signal to produce a TM polarized component of a third rotated optical signal;

rotating the TM polarized component of the third phase shifted optical signal to produce a TE polarized component of the third rotated optical signal;

shifting a phase of the TM polarized component of the third rotated optical signal to produce a TM polarized component of the transmitted optical signal; and

shifting a phase of the TE polarized component of the third rotated optical signal to produce a TE polarized component of the transmitted optical signal.

14. The method of claim 12 , wherein transmitting the second received optical signal comprises:

shifting a phase of a TE polarized component of the second received optical signal to produce a TE polarized component of a third phase shifted optical signal;

shifting a phase of a TM polarized component of the second received optical signal to produce a TM polarized component of the third phase shifted optical signal;

rotating the TE polarized component of the third phase shifted optical signal to produce a TM polarized component of a third rotated optical signal;

rotating the TM polarized component of the third phase shifted optical signal to produce a TE polarized component of the third rotated optical signal;

shifting a phase of the TM polarized component of the third rotated optical signal to produce a TM polarized component of a fourth phase shifted optical signal;

shifting a phase of the TE polarized component of the third rotated optical signal to produce a TE polarized component of the fourth phase shifted optical signal;

rotating the TM polarized component of the fourth phase shifted optical signal to produce a TE polarized component of the transmitted optical signal; and

rotating the TE polarized component of the fourth phase shifted optical signal to produce a TM polarized component of the transmitted optical signal.

15. A Mach-Zehnder interferometer comprising:

an optical splitter comprising

a first output port, and

a second output port;

a first leg optically coupled to the first output port of the optical splitter, wherein the first leg comprises

a first waveguide phase shifter,

a second waveguide phase shifter, and

a first polarization rotator optically coupled between the first waveguide phase shifter and the second waveguide phase shifter;

a second leg optically coupled to the second output port of the optical splitter; and

an optical combiner comprising

a first input port optically coupled to the first leg, and

a second input port optically coupled to the second leg, wherein the first leg and the second leg are integrated on a substrate.

16. The Mach-Zehnder interferometer of claim 15 , wherein the first leg further comprises a third polarization rotator optically coupled to the second phase shifting waveguide.

17. The Mach-Zehnder interferometer of claim 15 , wherein the second leg comprises:

a third waveguide phase shifter;

a fourth waveguide phase shifter; and

a second polarization rotator optically coupled between the third waveguide phase shifter and the fourth waveguide phase shifter.

18. The Mach-Zehnder interferometer of claim 17 , wherein the first leg further comprises a third polarization rotator optically coupled to the second phase shifting waveguide, and wherein the second leg further comprises a fourth polarization rotator optically coupled to the fourth phase shifting waveguide.

19. The Mach-Zehnder interferometer of claim 15 , wherein the substrate is a silicon-on-insulator (SOI) substrate.

20. The Mach-Zehnder interferometer of claim 15 , wherein the first waveguide phase shifter and the second waveguide phase shifter are active waveguide phase shifters.