System and method for receiving coherent, polarization-multiplexed optical signals

1. An apparatus, comprising:

an optical device having a first and a second optical input and a first and a second optical output, said device being configured to separate an in-phase component and a quadrature component of a polarization-multiplexed received optical signal received at said first optical input, to transmit said polarization-multiplexed in-phase component to said first optical output, and to transmit said polarization-multiplexed quadrature component to said second optical output;

a local optical oscillator coupled to said second optical input;

a first polarization splitter coupled to receive light at said first optical output; and

a second polarization splitter coupled to receive light at said second optical output.

2. The apparatus as recited in claim 1 wherein each of said first and second polarization splitters produces one polarization component on an H optical output and an orthogonal polarization component on a V optical output, said local optical oscillator being coupled to said optical device such that light from said local optical oscillator is transmitted to said H and V optical outputs.

3. The apparatus as recited in claim 1 , wherein said local optical oscillator is polarization aligned to said first and second polarization splitters.

4. The apparatus as recited in claim 1 wherein said polarization-multiplexed in-phase component is a first polarization-multiplexed in-phase component and said polarization-multiplexed quadrature component is a first polarization-multiplexed quadrature component, and said optical device is configured to transmit a second polarization-multiplexed in-phase component to a third optical output and a second polarization-multiplexed quadrature component to a fourth optical output, said first and third optical outputs configured to function as a pair of polarization-multiplexed in-phase differential outputs and said second and fourth optical outputs configured to function as a pair of polarization-multiplexed quadrature differential outputs.

5. The apparatus as recited in claim 4 further comprising:

a third polarization splitter coupled to receive light from said third optical output; and

a fourth polarization splitter coupled to receive light from said fourth optical output.

6. The apparatus as recited in claim 1 wherein an optical path of said optical device comprises a 90° phase-shifter.

7. A polarization diversity receiver, comprising:

a polarization diverse optical hybrid having a first and a second optical input and a first and a second optical output, said hybrid being configured to separate in-phase and quadrature components of a received polarization-multiplexed optical signal received at said first optical input, to transmit polarization-multiplexed in-phase components of said received optical signal to said first optical output and to transmit polarization-multiplexed quadrature components of said received optical signal to said second optical output;

a local optical oscillator coupled to said second optical input;

a first polarization splitter coupled to receive light at said first optical output; and

a second polarization splitter coupled to receive light at said second optical output.

8. The receiver as recited in claim 7 wherein each of said first and second polarization splitters produces one polarization component on an H optical output and an orthogonal polarization component on a V optical output, said local optical oscillator being coupled to said polarization diverse optical hybrid such that light from said local optical oscillator is transmitted to said H and V optical outputs.

9. The receiver as recited in claim 7 wherein said local optical oscillator is polarization aligned to said first and second polarization splitters.

10. The receiver as recited in claim 7 wherein said polarization diverse optical hybrid is configured to transmit said in-phase components to said first optical output and a third optical output and said quadrature components to said second optical output and a fourth optical output, said first and third optical outputs configured to function as a pair of differential outputs and said second and fourth optical outputs configured to function as a pair of differential outputs.

11. The receiver as recited in claim 10 further comprising:

a third polarization splitter coupled to receive light from said third optical output; and

a fourth polarization splitter coupled to receive light from said fourth optical output.

12. The receiver as recited in claim 7 wherein an optical path of said polarization diverse optical hybrid comprises a 90° phase-shifter.

13. A method of receiving a received polarization-multiplexed optical signal, comprising:

separating polarization-multiplexed in-phase components and polarization-multiplexed quadrature components of said received polarization-multiplexed optical signal in an optical device;

transmitting said polarization-multiplexed in-phase components to a first optical output of said optical device;

receiving light at said first optical output into a first polarization splitter;

transmitting said polarization-multiplexed quadrature components to a second optical output of said optical device; and

receiving light at said second optical output into a second polarization splitter.

14. The method as recited in claim 13 further comprising:

producing plural polarization components of said polarization-multiplexed optical signal on plural H optical outputs of said first and second polarization splitters;

producing plural orthogonal polarization components of said polarization-multiplexed optical signal on plural V optical outputs of said first and second polarization splitters; and

transmitting light from a local optical oscillator to said H and V optical outputs.

15. The method as recited in claim 13 further comprising:

transmitting said polarization-multiplexed in-phase components to said first optical output and a third optical output; and

transmitting said polarization-multiplexed quadrature components to said second optical output and a fourth optical output, said first and third optical outputs configured to function as a pair of differential outputs and said second and fourth optical outputs configured to function as a pair of differential outputs.

16. The method as recited in claim 15 further comprising:

receiving light at said third optical output into a third polarization splitter; and

receiving light at said fourth optical output into a fourth polarization splitter.

17. The apparatus as recited in claim 2 , wherein said local optical oscillator signal is polarization-aligned to said first and second polarization splitters to result in a first ratio of optical power of said H and V optical outputs of said first polarization splitter being substantially the same as a second ratio of optical power of said H and V optical outputs of said second polarization splitter.

18. The receiver as recited in claim 8 , wherein said local optical oscillator signal and said first and second polarization splitters are polarization-aligned to result in a first ratio of optical power of said H and V optical outputs of said first polarization splitter being substantially the same as a second ratio of optical power of said H and V optical outputs of said second polarization splitter.

19. The method as recited in claim 14 , wherein a signal generated by said local optical oscillator is polarization-aligned with said first and second polarization splitters to result in a first ratio of optical power of said H and V optical outputs of said first polarization splitter being substantially the same as a second ratio of optical power of said H and V optical outputs of said second polarization splitter.

20. The apparatus as recited in claim 1 , wherein third and fourth polarization splitters are coupled to receive light at respective third and fourth optical outputs of said optical device, each of said third and fourth polarization splitters being configured to produce one polarization component on an H optical output and an orthogonal polarization component on a V optical output, said local optical oscillator being coupled to said optical device such that light from said local optical oscillator is transmitted to said H and V optical outputs of said third and fourth polarization splitters.