Polarization diverse optical receiver using a polarization-dependent beam splitter

• US 20050259907A1
• Filed: 05/18/2004
• Published: 11/24/2005
• Est. Priority Date: 05/18/2004
• Status: Active Grant

• Current Assignee: Agilent Technologies, Inc.
• Original Assignee: Agilent Technologies, Inc.
• Inventors: Haney, Doug, Tan, Tun S., Tan, Tun S, McAlexander, William Ian
• Granted Patent: US 7,280,770 B2
• Time in Patent Office: Days
• US Class Current: 385/11
• CPC Class Codes: H04B 10/61 Coherent receivers
• CPC Class Codes: H04B 10/614 comprising one or more polarization beam splitters, e.g. polarization multiplexed [PolMux] X-PSK coherent receivers, polarization diversity heterodyne coherent receivers H04J14/06 takes precedence
• CPC Class Codes: H04B 10/64 Heterodyne , i.e. coherent receivers where, after the opto-electronic conversion, an electrical signal at an intermediate frequency [IF] is obtained

Abstract

A receiver and method for using the same to process optical signals is disclosed. The receiver includes an optical coupler and a polarization dependent beam splitter. The optical coupler combines an input signal and a local oscillator signal into a first combined signal. The optical coupler includes a polarization filter that operates on the local oscillator to provide a linearly polarized signal having a predetermined LO polarization direction.

Claims

1. A receiver comprising:

an optical coupler for combining an input signal and a local oscillator signal into a first combined signal;

a polarization-dependent beam splitter for generating first and second component signals from said first combined signal, said first component signal having a polarization that is orthogonal to said second component signal, said first component signal being spatially displaced from said second component signal in a displacement direction, said displacement direction being at an angle greater than zero and less than ninety degrees with respect to said LO polarization direction.

a first detector for converting said first component signal into a first electrical signal; and

a second detector for converting said second component signal into a second electrical signal.

2. The receiver of claim 1 wherein said optical coupler further comprises a polarization filter for filtering said local oscillator to provide a linear polarized signal having an LO polarization direction.

3. The receiver of claim 1 wherein said optical coupler comprises a polarization-maintaining waveguide coupler.

4. The receiver of claim 3, wherein said polarization-maintaining waveguide coupler has a birefringence axis that is parallel to said LO polarization direction.

5. The receiver of claim 1 wherein said polarization-dependent beam splitter comprises a rutile walk-off crystal.

6. The receiver of claim 1 wherein said angle is chosen such that said local oscillator signal is divided into components having orthogonal polarizations and substantially equal amplitudes by said polarization-dependent beam splitter.

7. The receiver of claim 1 further comprising third and fourth detectors, and wherein said optical coupler further combines said input signal and said local oscillator signal into a second combined signal and wherein said polarization-dependent beam splitter further generates third and fourth component signals from said second combined signal, said third and fourth component signals having polarizations that are orthogonal to one another and separated spatially from each other and from said first and second component signals, said third detector converting said third component signal into a third electrical signal and said fourth detector converting said fourth component signal into a fourth electrical signal.

8. A method for characterizing an input optical signal comprising:

providing a local oscillator signal polarized in a LO polarization direction;

combining said local oscillator with said input optical signal to provide a first combined signal;

spatially separating said first optical signal into first and second component optical signals, said first component signal being spatially displaced from said second component signal in a displacement direction, said displacement direction being at an angle greater than zero and less than ninety degrees with respect to said LO polarization direction; and

converting said first and second component signals into first and second electrical signals.

9. The method of claim 8 wherein said local oscillator signal and said input optical signal are combined in a polarization-maintaining waveguide coupler.

10. The method of claim 9, wherein said polarization-maintaining waveguide coupler has a birefringence axis that is parallel to said LO polarization direction.

11. The method of claim 8 wherein said first optical signal is separated into first and second component optical signals in a rutile walk-off crystal.

12. The method of claim 8 wherein said angle is chosen such that said local oscillator signal is divided into components having orthogonal polarizations and substantially equal amplitudes by said polarization-dependent beam splitter.

13. The method of claim 8 wherein said input signal and said local oscillator signal are further combined into a second combined signal and wherein said second combined signal is separated into third and fourth component signals, said third and fourth component signals having polarizations that are orthogonal to one another and separated spatially from each other and from said first and second component signals, said third and fourth component signals being converted to third and fourth electrical signals.