Free-space optical hybrid

Abstract

An exemplary optical hybrid includes a 50/50 un-polarized beam splitter, a folding prism, a beam shifter, a spacer and a phase shifter such that from an input S-beam (signal) and an L-beam (reference), four outputs, S+L, S−L, S+jL, S−jL, are produced. The phase difference of S and L at the four output ports is phi_0, phi_0+90-degrees, phi_0+180-degree, phi_0+270-degree, where the phase difference between S and L at the S+L port is an arbitrary number phi_0 and the phase difference between S and L at the other output ports, S−L, S+jL, S−jL, is 90, 180 and 270, respectively, shifted from phi_0.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a part of the disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

FIG. 1A shows a function diagram for a 90-degree optical hybrid.

FIG. 1B conceptually illustrates the operation of a 90-degree optical hybrid.

FIG. 2 shows an embodiment of the invention including a 50/50 un-polarized beam splitter, a folding prism, a beam shifter, a spacer and a phase shifter.

FIG. 3 shows a design that is similar to FIG. 2 without the circulators.

FIG. 4 illustrates a design having symmetrical cavities in the top and right arms.

FIG. 5 shows a design similar to that of FIG. 4, except that the path length ACE is lengthened.

FIG. 6A is a top view of a design integrated with a polarization beam splitter to provide a polarization diversity coherent detection system.

FIG. 6B is a side view of the design of FIG. 6A.

FIG. 7 shows a 2×4 optical hybrid implemented by 3 independent beam splitters.

FIG. 8A is a top view of a 2×8 optical hybrid that includes a PBS and a folding prism.

Claims

1. An optical hybrid, comprising: means for splitting a signal light beam (S) into a reflected signal light beam (RS) and a transmitted signal light beam (TS);means for splitting a reference light beam (L) into a reflected light beam (RL) and a transmitted light beam (TL); andmeans for combining pairs of said RS TS, RL and TL to produce a plurality of combined output beams comprising an S+L beam, an S+jL beam, an S−L beam and an S−jL beam, wherein the phase difference, between said S light beam and said L light beam in said S+jL beam, said S−L beam and said S−jL beam, with respect to the phase difference between said S light beam and said L light beam in said S+L beam, is about 90 degrees, 180 degrees and 270 degrees respectively.

2. The optical hybrid of claim 1, wherein said means for splitting a signal light beam and said means for splitting a reference light beam together comprise a first beam splitter comprising a first face, a second face, a third face, a fourth face and an internal reflecting/transmitting coating.

3. The optical hybrid of claim 2, wherein said means for combining comprises: a reflecting surface fixedly separated by a gap from said second face;means for adjusting the index of refraction N within said gap; anda beam shifter fixedly connected to said third face.

4. The optical hybrid of claim 1, wherein said beam splitter is selected from a group consisting of an unpolarized beam splitter and a beam splitter designed for only one polarization.

5. The optical hybrid of claim 4, wherein said unpolarized beam splitter comprises a cube.

6. The optical hybrid of claim 3, wherein said means for adjusting the index of refraction N comprises means for adjusting the index of refraction of a gas within said gap.

7. The optical hybrid of claim 3, wherein said means for adjusting the index of refraction N comprises at least one optical flat positioned within said gap.

8. The optical hybrid of claim 1, further comprising a first optical circulator positioned to receive and operatively align said S beam into said first face, wherein said S+L beam will exit said first optical circulator, said optical hybrid further comprising a second optical circulator positioned to receive and operatively align said L beam into said first face, wherein said S+jL beam will exit said second optical circulator.

9. The optical hybrid of claim 3, further comprising a second spacer fixedly attached to said third face, wherein said beam shifter is fixedly connected by said second spacer to said third face.

10. The optical hybrid of claim 9, wherein said third face, said spacer and said beam shifter form a second gap.

11. The optical hybrid of claim 10, further comprising means for adjusting the optical path length through said second gap.

12. The optical hybrid of claim 11, wherein said means for adjusting the index of refraction N comprises means for adjusting the index of refraction of a gas within said second gap.

13. The optical hybrid of claim 11, wherein said means for adjusting the index of refraction N comprises at least one second optical flat positioned within said second gap.

14. The optical hybrid of claim 9, further comprising an optical path addition fixedly attached to said folding prism.

15. The optical hybrid of claim 1, further comprising means for separating the polarizations of said S beam and said L beam prior to their being operatively aligned into said first face.

16. The optical hybrid of claim 15, wherein said means for separating the polarizations comprises a polarizing beam splitter (PBS) configured to transmit one polarization component (Y) into said first face and reflect an orthogonal polarization component (X), said means further comprising a folding prism operatively attached to said PBS to reflect X into said first face in a spatially separate parallel plane.

17. The optical hybrid of claim 3, wherein said reflection surface is part of a folding prism.

18. The optical hybrid of claim 2, wherein said means for combining comprises: a first optically transmitting element fixedly attached to said second face;a second beam splitter fixedly attached to said first optically transmitting element;a first folding prism attached to said second beam splitter;a first gap between said first beam splitter and said first folding prism;a second optically transmitting element fixedly attached to said third face;a second beam splitter fixedly attached to said second optically transmitting element;a second folding prism attached to said second beam splitter;a second gap between said first beam splitter and said second folding prism

19. The optical hybrid of claim 18, wherein at least one of said first beam splitter, said second beam splitter or said third beam splitter is selected from a group consisting of an unpolarized beam splitter and a beam splitter designed for only one polarization.

20. The optical hybrid of claim 19, wherein said unpolarized beam splitter comprises a cube.

21. The optical hybrid of claim 18, wherein said means for adjusting the optical path length comprises means for adjusting the index of refraction of a gas within at least one of said first cavity or said second cavity.

22. The optical hybrid of claim 18, wherein said means for adjusting the index of refraction N comprises at least one optical flat positioned within at least one of said first gap or said second gap.

23. The optical hybrid of claim 18, further comprising means for separating the polarizations of said S beam and said L beam prior to their being operatively aligned into said first face.

24. The optical hybrid of claim 23, wherein said means for separating the polarizations comprises a polarizing beam splitter (PBS) configured to transmit one polarization component (Y) into said first face and reflect an orthogonal polarization component (X), said means further comprising a folding prism operatively attached to said PBS to reflect X into said first face in a spatially separate parallel plane.

25. An optical hybrid, comprising: means for splitting a signal light beam (S) into a reflected signal light beam (RS) and a transmitted signal light beam (TS);means for splitting a reference light beam (L) into a reflected light beam (RL) and a transmitted light beam (TL); andmeans for combining pairs of said RS TS, RL and TL to produce a plurality of combined output beams comprising an S+L beam, an S+jL beam, an S−L beam and an S−jL beam, wherein the phase difference, between said S light beam and said L light beam in said S+jL beam, said S−L beam and said S−jL beam, with respect to the phase difference between said S light beam and said L light beam in said S+L beam, is about any number X, 180 degrees and X+180 degrees respectively.

26. A method, comprising: splitting a signal light beam (S) into a reflected signal light beam (RS) and a transmitted signal light beam (TS);splitting a reference light beam (L) into a reflected light beam (RL) and a transmitted light beam (TL); andcombining pairs of said RS TS, RL and TL to produce a plurality of combined output beams comprising an S+L beam, an S+jL beam, an S−L beam and an S−jL beam, wherein the phase difference, between said S light beam and said L light beam in said S+jL beam, said S−L beam and said S−jL beam, with respect to the phase difference between said S light beam and said L light beam in said S+L beam, is about 90 degrees, 180 degrees and 270 degrees respectively.