Strip loaded waveguide with low-index transition layer

• US 20030059190A1
• Filed: 09/09/2002
• Published: 03/27/2003
• Est. Priority Date: 09/10/2001
• Status: Active Grant

• Current Assignee: California Institute of Technology
• Original Assignee: California Institute of Technology
• Inventors: Scherer, Axel, Gunn, Lawrence Cary III
• Granted Patent: US 6,834,152 B2
• Time in Patent Office: Days
• US Class Current: 385/130
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 2006/12038 Glass (SiO2 based materials)
• CPC Class Codes: G02B 2006/12061 Silicon
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12109 Filter
• CPC Class Codes: G02B 2006/12116 Polariser; Birefringent
• CPC Class Codes: G02B 2006/12145 Switch
• CPC Class Codes: G02B 2006/12147 Coupler
• CPC Class Codes: G02B 6/10 of the optical waveguide type G02B6/02, G02B6/24 take precedence; devices or arrangements for the control of light by electric, magnetic, electro-magnetic or acoustic means G02F1/00; transferring the modulation of modulated light G02F2/00; optical logic elements G02F3/00; optical analogue/digital converters G02F7/00
• CPC Class Codes: G02B 6/12004 Combinations of two or more optical elements
• CPC Class Codes: G02B 6/122 Basic optical elements, e.g. light-guiding paths
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices
• CPC Class Codes: G02B 6/132 by deposition of thin films
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: G02F 1/0147 based on thermo-optic effects G02F1/132 takes precedence
• CPC Class Codes: G02F 1/3133 the optical waveguides being made of semiconducting materials
• CPC Class Codes: G02F 2202/10 semiconductor
• CPC Class Codes: G02F 2203/15 involving resonance effects, e.g. resonantly enhanced interaction

Abstract

A strip loaded waveguide comprises a slab and a strip, wherein the strip is separated from the slab. Nevertheless, a guiding region is provided for propagating an optical mode and this guiding region extends both within the strip and the slab. A layer of material having an index of refraction lower than that of the strip and the slab may be disposed between and separate the strip and the slab. In one embodiment, the slab comprises a crystalline silicon, the strip comprises polysilicon or crystalline silicon, and the layer of material therebetween comprises silicon dioxide. Such waveguides may be formed on the same substrate with transistors. These waveguides may also be electrically biased to alter the index of refraction and/or absorption of the waveguide.

Claims

1. A strip loaded waveguide comprising:

a slab portion having a first refractive index (n₁),

a strip portion having a second refractive index (n₂), and

a transition portion between the slab portion and the strip portion, the transition portion having a third refractive index (n₃) that is less than the first refractive index (n₁) and the second refractive index (n₂).

2. The waveguide of claim 1, wherein the transition portion comprises silicon dioxide.

3. The waveguide of claim 1, wherein the slab portion comprises semiconductor.

4. The waveguide of claim 3, wherein the slab portion comprises single crystal silicon.

5. The waveguide of claim 1, wherein the strip portion comprises polysilicon.

6. The waveguide of claim 1, wherein the strip portion comprises single crystal silicon.

7. The waveguide of claim 1, wherein the strip portion comprise silicon nitride.

8. The waveguide of claim 1, wherein the slab portion and the strip portion comprise substantially the same material.

9. The waveguide of claim 1, further comprising a substrate that supports said slab and said strip.

10. The waveguide of claim 9, wherein the substrate comprises a silicon wafer.

11. The waveguide of claim 9, wherein the substrate comprises sapphire.

12. The waveguide of claim 1, further comprising a lower cladding layer adjacent said slab, said lower cladding layer having a refractive index less than the first refractive index (n₁) of said slab.

13. The waveguide of claim 12, wherein the difference between first refractive index (n₁) of said slab and said refraction index of said lower cladding layer is at least about 1.

14. The waveguide of claim 13, wherein the difference between first refractive index (n₁) of said slab and said refraction index of said lower cladding layer is at least about 2.

15. The waveguide of claim 12, wherein said lower cladding layer comprises a layer of silicon dioxide.

16. The waveguide of claim 12, wherein said lower cladding layer comprises a layer of silicon nitride.

17. The waveguide of claim 12, further comprising an upper cladding adjacent said slab and said strip, said upper cladding has a refractive index that is less than both the first refractive index (n₁) and second refractive index (n₂).

18. The waveguide of claim 17, wherein the difference between a refractive index of said upper cladding and said first refractive index (n₁) of said slab and said second refractive index (n₂) of said strip is at least about 1.

19. The waveguide of claim 18, wherein the difference between a refractive index of said upper cladding and said first refractive index (n₁) of said slab and said second refractive index (n₂) of said strip is at least about 2.

20. The waveguide of claim 17, wherein the upper cladding comprises glass.

21. The waveguide of claim 17, wherein the upper cladding comprises silicon dioxide.

22. The waveguide of claim 17, wherein the upper cladding and the lower cladding comprise substantially the same material.

23. The waveguide of claim 1, wherein said strip has a width and thickness, and said slab and transition regions have respective thicknesses so as to support a fundamental optical mode with a cross-sectional power distribution profile having two intensity maxima.

24. A strip loaded single-mode waveguide for propagating light having a wavelength, comprising:

a slab portion,

a strip portion disposed with respect to the slab portion to form a guiding region, a first portion of the guiding region being in the strip portion, and a second portion of the guiding region being in the slab portion, the guiding region configured to propagate light of the wavelength only in a single spatial mode and only in a transverse electric mode.

25. The strip loaded single-mode waveguide of claim 24, wherein said slab portion and strip portion comprise single crystal silicon.

26. The strip loaded single-mode waveguide of claim 25, wherein said slab portion has a thickness of approximately 90 nm and said strip portion has a thickness of approximately 40 nm.

27. The strip loaded single-mode waveguide of claim 24, further comprising a transition portion between the slab portion and the strip portion, such that a third portion of the guiding region is located in the transition portion.

28. A strip loaded waveguide comprising:

a slab portion,

a strip portion disposed with respect to the slab portion to form a guiding region, a first portion of the guiding region being in the strip portion, and a second portion of the guiding region being in the slab portion, the guiding region propagating light in a single spatial mode with a cross-sectional power distribution profile having two intensity maxima, one of which is located in the slab portion and the other of which is located in the strip portion.

29. The strip loaded waveguide of claim 28, wherein the slab comprises semiconductor.

30. The strip loaded waveguide of claim 29, wherein the slab comprises silicon.

31. The strip loaded waveguide of claim 30, wherein the strip comprises silicon.

32. The strip loaded waveguide of claim 28, further comprising a transition portion positioned between the slab portion and the strip portion, such that a third portion of the guiding region is location in the transition portion.

33. The strip loaded waveguide of claim 32, wherein said transition portion comprises oxide.

34. A waveguide having a guiding region for guiding light through the waveguide, the guiding region comprising a layer of polycrystalline silicon juxtaposed with a layer of crystal silicon.

35. The waveguide of claim 34, wherein said layer of crystal silicon comprises a slab and said layer of polycrystalline silicon comprises a strip formed thereon, said strip and said slab forming a strip waveguide.

36. The waveguide of claim 35, wherein said strip has a width and a thickness and said slab has a thickness to support a single optical mode.