Optical waveguide crossings

1. A system for transmitting an optical signal across an optical obstruction, comprising:

a first optical waveguide optically coupled to a first surface grating coupler (SGC);

a second optical waveguide optically coupled to a second SGC, the second optical waveguide being a separate waveguide from the first optical waveguide; and

a reflector configured to reflect an optical signal for free-space propagation from the first SGC to the second SGC without an optical waveguide between the reflector and the first SGC and without an optical waveguide between the reflector and the second SGC, a reflecting surface of the reflector being parallel to a direction of propagation of the optical signal through the first optical waveguide and to a direction of propagation of the optical signal through the second optical waveguide.

2. The system of claim 1 , wherein the reflector comprises a specular reflector.

3. The system of claim 2 , wherein the specular reflector comprises a diffraction grating.

4. The system of claim 1 , wherein the reflector comprises a metal mirror.

5. The system of claim 1 , wherein the reflector comprises a dielectric interference filter.

6. The system of claim 1 , wherein the first SGC is disposed on a first substrate and the second SGC is disposed on a second substrate.

7. The system of claim 6 , wherein one of the first substrate and the second substrate comprises silicon-on-insulator.

8. The system of claim 6 , wherein one of the first substrate and the second substrate comprises a compound semiconductor.

9. The system of claim 1 , further comprising at least one support member supporting the reflector.

10. The system of claim 9 , wherein the support member comprises a copper pillar.

11. The system of claim 9 , wherein the support member comprises a cement.

12. The system of claim 11 , wherein the cement comprises an epoxy.

13. The system of claim 1 , wherein the reflector comprises a broadband mirror.

14. The system of claim 1 , wherein the reflector comprises a wavelength selective mirror.

15. The system of claim 1 , wherein the first optical waveguide optically coupled to a first surface grating coupler (SGC) is in a first optical chip and the second optical waveguide optically coupled to a second SGC is in a second optical chip.

16. A network component configured for transmitting and receiving optical signals, the network component comprising:

a photonic integrated circuit (PIC), wherein the PIC comprises:

a first optical waveguide optically coupled to a first surface grating coupler (SGC);

a second optical waveguide optically coupled to a second SGC, the second optical waveguide being a separate waveguide from the first optical waveguide; and

a reflector configured to reflect an optical signal for free-space propagation from the first SGC to the second SGC without an optical waveguide between the reflector and the first SGC and without an optical waveguide between the reflector and the second SGC, a reflecting surface of the reflector being parallel to a direction of propagation of the optical signal through the first optical waveguide and to a direction of propagation of the optical signal through the second optical waveguide.

17. The network component of claim 16 , wherein the reflector comprises a specular reflector.

18. The network component of claim 16 , wherein the reflector comprises a metal mirror.

19. The network component of claim 16 , wherein the reflector comprises a dielectric interference filter.

20. The network component of claim 16 , wherein the first SGC is disposed on a first substrate and the second SGC is disposed on a second substrate.

21. The network component of claim 20 , wherein the one of the first substrate and the second substrate comprises silicon-on-insulator.

22. The network component of claim 20 , wherein the one of the first substrate and the second substrate comprises a compound semiconductor.

23. The network component of claim 16 , wherein the reflector reflects the optical signal across an optical obstruction separating the first optical waveguide from the second optical waveguide.

24. The network component of claim 16 , wherein the PIC comprises a first PIC and a second PIC and wherein the first PIC comprises the first optical waveguide and the second PIC comprises the second optical waveguide.

25. A method for transmitting an optical signal across an optical obstruction in an photonic integrated circuit (PIC), comprising:

propagating an optical signal through a first optical waveguide to a first surface grating coupler (SGC) optically coupled to the first optical waveguide;

reflecting with a reflector the optical signal received from the first SGC to a second SGC, the optical signal propagating in free space from the reflector to the second SGC without an optical waveguide between the reflector and the first SGC and without an optical waveguide between the reflector and the second SGC; and

propagating the optical signal received at the second SGC through a second optical waveguide optically coupled to the second SGC, the second optical waveguide being a separate waveguide from the first optical waveguide, and a reflecting surface of the reflector being parallel to a direction of propagation of the optical signal through the first optical waveguide and to a direction of propagation of the optical signal through the second optical waveguide.

26. The method of claim 25 , further comprising deflecting, with the first SGC, the optical signal out of a plane of propagation toward the reflector before the optical signal reaches an optical barrier separating the first optical waveguide from the second optical waveguide.

27. The method of claim 26 , wherein the reflector is situated out of a plane defined by the first SGC, the second SGC, and the optical barrier.

28. The method of claim 26 , wherein the optical barrier comprises one of a gap, a waveguide, and a deep isolation trench.

29. The method of claim 25 , wherein propagating the optical signal received at the second SGC through the second optical waveguide comprises collecting the reflected optical signal at the second SGC and focusing the collected signal onto the second optical waveguide.

30. The method of claim 25 , wherein the reflector comprises one of a dielectric and a metal.

31. The method of claim 25 , wherein the reflector comprises a broadband mirror.

32. The method of claim 25 , wherein the reflector comprises a wavelength selective mirror.