Dual-side waveguide-based wavelength demultiplexer

• US 20020041734A1
• Filed: 08/06/2001
• Published: 04/11/2002
• Est. Priority Date: 08/21/2000
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Liu, Feng, Wood, Lance A., Worchesky, Terrance L.
• Granted Patent: US 6,549,708 B2
• Time in Patent Office: Days
• US Class Current: 385/37
• CPC Class Codes: G02B 2006/12107 Grating
• CPC Class Codes: G02B 2006/12121 Laser
• CPC Class Codes: G02B 2006/12123 Diode
• CPC Class Codes: G02B 6/12002 Three-dimensional structures
• CPC Class Codes: G02B 6/12004 Combinations of two or more optical elements
• CPC Class Codes: G02B 6/12007 forming wavelength selective elements, e.g. multiplexer, demultiplexer
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings

Abstract

A demultiplexer is disclosed. The demultiplexer incorporates a reflective grating that is associated with a first waveguide through which a multiplexed optical signal may be transmitted. Individual wavelengths of light that have been reflected by the reflective grating are able to pass through a barrier layer which separates the first waveguide from a second waveguide. A plurality of photodetectors are associated with the second waveguide to read out the individual, wavelength-specific optical signals. The reflective grating is preferably formed on a surface of the first waveguide which projects away from the second waveguide, while the photodetectors are preferably formed at least in part by processing a surface of the second waveguide that projects away from the first waveguide. Both polarities of light are preferably accounted for/collected by the grating as well.

Claims

1. A demultiplexer, comprising:

a first waveguide comprising first and second opposing surfaces;

a second waveguide comprising first and second opposing surfaces, wherein said second waveguide is disposed at a higher elevation than said first waveguide whereby said second surface of said first waveguide is disposed between said first surface of said first waveguide and said second waveguide, and wherein said first surface of said second waveguide is disposed between said second surface of said second waveguide and said first waveguide; and

a grating assembly disposed on said first surface of said first waveguide.

2. A demultiplexer, as claimed in claim 1, wherein:

said first waveguide comprises an input channel for a combined optical signal and said second waveguide comprises a plurality of output channels for a plurality of different individual wavelengths.

3. A demultiplexer, as claimed in claim 1, wherein:

said second waveguide comprises a plurality of second waveguide sections that are spaced in a general direction in which light travels through said first waveguide.

4. A demultiplexer, as claimed in claim 3, further comprising:

a photodetector associated with each said second waveguide section.

5. A demultiplexer, as claimed in claim 1, further comprising:

a barrier layer disposed between said second surface of said first waveguide and said first surface of said second waveguide.

6. A demultiplexer, as claimed in claim 5, wherein:

said barrier layer comprises means for limiting a passage of light between said first and second waveguides to light that is directed from said grating assembly toward said barrier layer and said second waveguide.

7. A demultiplexer, as claimed in claim 5, wherein:

said second waveguide comprises a plurality of spaced second waveguide sections, wherein said barrier layer comprises a plurality of spaced barrier layer sections.

8. A demultiplexer, as claimed in claim 7, wherein:

each of said plurality of spaced barrier layer sections are at least substantially identical.

9. A demultiplexer, as claimed in claim 5, wherein:

each of said second waveguide and said barrier layer are continuous structures.

10. A demultiplexer, as claimed in claim 1, wherein:

said first and second waveguides are asynchronous.

11. A demultiplexer, as claimed in claim 1, wherein:

said first and second waveguides have first and second refractive indices and first and second thicknesses between their respective first and second surfaces, respectively, wherein said first and second refractive indices are different and wherein said first and second thicknesses are different.

12. A demultiplexer, as claimed in claim 1, wherein:

said second waveguide comprises a plurality of second waveguide sections which are spaced in a general direction in which light travels through said first waveguide.

13. A demultiplexer, as claimed in claim 1, wherein:

said grating assembly comprises a plurality of grating subassemblies that are spaced at least generally in a general direction in which light travels through said first waveguide.

14. A demultiplexer, as claimed in claim 13, wherein:

each said grating subassembly comprises first means for directing light of a first polarity and a predetermined wavelength to said second waveguide and second means for directing light of a second polarity and said predetermined wavelength to said second waveguide.

15. A demultiplexer, as claimed in claim 13, wherein:

each said grating subassembly comprises first and second grating sections that are disposed at different longitudinal positions in relation to a general direction in which light travel through said first waveguide, wherein said first and second grating sections of each said grating subassembly use first and second grating spacings that are of different magnitudes.

16. A demultiplexer, as claimed in claim 15, wherein:

a difference between said first and second grating spacings of any said grating subassembly is significantly less than less than a difference in grating spacings in said first grating section of any adjacent pair of said grating subassemblies.

17. A demultiplexer, as claimed in claim 15, wherein:

said first and second grating spacings in each said grating subassembly differ by an amount that is within a range of about 0.1 microns to about 0.5 microns.

18. A demultiplexer, as claimed in claim 17, wherein:

a minimum difference in magnitude between each adjacent pair of said first grating spacings is about 1 micron.

19. A demultiplexer, as claimed in claim 13, further comprising:

a separate photodetector for each said grating subassembly.

20. A demultiplexer, as claimed in claim 1, wherein:

said grating assembly comprises a plurality of reflective gratings that are spaced in a general direction in which light travels through said first waveguide.

21. A demultiplexer, as claimed in claim 1, further comprising:

at least one photodetector associated with said second waveguide.

22. A demultiplexer, as claimed in claim 1, further comprising:

a plurality of photodetectors associated with said second waveguide, wherein each of said plurality of photodetectors are wavelength specific.

24. A demultiplexer, as claimed in claim 22, wherein:

said first waveguide comprises an input channel for a combined optical signal and said second waveguide comprises a plurality of output channels for a plurality of different individual wavelengths.

25. A demultiplexer, as claimed in claim 22, wherein:

said second waveguide comprises a plurality of second waveguide sections that are spaced in a general direction in which light travels through said first waveguide.

26. A demultiplexer, as claimed in claim 24, further comprising:

a photodetector associated with each said second waveguide section.

27. A demultiplexer, as claimed in claim 22, wherein:

one of said first and second grating sections of each said grating comprises means for directing light of a first polarity and a predetermined wavelength to said second waveguide and the other of said first and second grating section of each said grating subassembly comprises means for directing light of a second polarity and a predetermined wavelength to said second waveguide.

28. A demultiplexer, as claimed in claim 22, wherein:

a difference between said first and second grating spacings of any said grating subassembly is significantly less than less than a difference in grating spacings in said first grating section of any adjacent pair of said grating subassemblies.

29. A demultiplexer, as claimed in claim 22, wherein:

said first and second grating spacings in each said grating subassembly differ by an amount that is within a range of about 0.1 microns to about 0.5 microns.

30. A demultiplexer, as claimed in claim 29, wherein:

a minimum difference in magnitude between each adjacent pair of said first grating spacings is about 1 micron.

31. A demultiplexer, as claimed in claim 22, further comprising:

a separate photodetector for each said grating subassembly.

23. A demultiplexer, comprising:

a first waveguide comprising first and second opposing surfaces;

a second waveguide disposed in stacked relation to said first waveguide; and

a grating assembly associated with said first waveguide, wherein said grating assembly comprises a plurality of grating subassemblies that are spaced at least generally in a general direction in which light travels through said first waveguide, wherein each said grating subassembly comprises first and second grating sections that are disposed at different longitudinal positions in relation to a general direction in which light travel through said first waveguide, wherein said first and second grating sections of each said grating subassembly use first and second grating spacings that are of different magnitudes.

32. A demultiplexer, comprising:

a first waveguide comprising first and second opposing surfaces;

a second waveguide disposed in stacked relation to said first waveguide; and

a grating assembly associated with said first waveguide, wherein said grating assembly comprises first means for directing light of a first polarity and a predetermined wavelength to said second waveguide and second means for directing light of a second polarity and a predetermined wavelength to said second waveguide.

33. A method for making a demultiplexer, comprising the steps of:

forming a first waveguide layer in overlying relation to a first substrate;

forming a barrier layer in overlying relation to said first waveguide layer;

forming a second waveguide layer in overlying relation to said barrier layer;

processing a first surface of said second waveguide layer which is opposite said barrier layer to at least complete a definition of one of first and second demultiplexing subassemblies, wherein said first demultiplexing subassembly comprises a grating assembly, and wherein said second demultiplexing subassembly comprises a photodetector assembly, wherein said first substrate, said first waveguide layer, said barrier layer, and said second waveguide layer define a stack;

mounting said stack on a second substrate such that said first surface of said second waveguide layer projects toward said second substrate;

removing said first substrate; and

processing a surface of said first waveguide layer that is exposed by said removing said first substrate step to at least complete a definition of the other of said first and second demultiplexing subassemblies.

34. A method, as claimed in claim 33, further comprising the step of:

forming a first etch stop layer in overlying relation to said first substrate before said forming a first waveguide layer step.

35. A method, as claimed in claim 34, further comprising the step of:

removing said first etch stop layer after said removing said first substrate layer and before said processing a surface of said first waveguide layer step.

36. A method, as claimed in claim 33, wherein:

each of said first waveguide layer, said barrier layer, and said second waveguide layer are epitaxial.

37. A method, as claimed in claim 33, wherein:

each of said forming a first waveguide layer step, said forming a barrier layer step, and said forming a second waveguide layer step are selected from the group consisting of using molecular beam epitaxy, metal organic chemical vapor deposition, and liquid phase epitaxy.

38. A method, as claimed in claim 33, wherein:

said forming a first waveguide layer step, said forming a barrier layer step, and said forming a second waveguide layer step are each executed within a first processing chamber, and wherein said processing a first surface of said second waveguide layer step, said mounting step, said removing said first substrate step, and said processing a surface of said first waveguide layer step are each executed at a location other than in said first processing chamber.

39. A method, as claimed in claim 38, wherein:

said forming a first waveguide layer step, said forming a barrier layer step, and said forming a second waveguide layer step are each completely executed without ever being removed from said first processing chamber, and wherein said processing a first surface of said second waveguide layer step, said mounting step, said removing said first substrate step, and processing surface of said first waveguide layer step are each executed only after each of said forming a first waveguide layer step, said forming a barrier layer step, and said forming a second waveguide layer step have been completely executed.

40. A method, as claimed in claim 33, wherein:

said forming a first waveguide layer step, said forming a barrier layer step, and said forming a second waveguide layer step, are each executed without using any regrowth.

41. A method, as claimed in claim 33, wherein:

said processing step used for said first demultiplexing subassembly comprises executing a controlled etch step.

42. A method, as claimed in claim 33, wherein:

said processing step used for said first demultiplexing subassembly comprises etching without any etch stop layer.

43. A method, as claimed in claim 33, wherein:

said processing step used for said second demultiplexing subassembly comprises patterning said first or second waveguide layer.

44. A method, as claimed in claim 33, wherein:

said processing step used for said second demultiplexing subassembly comprises forming a plurality of spaced photodetectors.

45. A method, as claimed in claim 33, wherein:

said mounting step comprises bonding said stack to said second substrate.

46. A method, as claimed in claim 33, further comprising the step of:

selecting said second substrate to have a coefficient of thermal expansion which at least generally matches a coefficient of thermal expansion of an adjacent portion of said stack.