Optical edge coupler with controllable mode field for photonic chip

• US 10,345,524 B2
• Filed: 12/22/2016
• Issued: 07/09/2019
• Est. Priority Date: 12/22/2016
• Status: Active Grant

• Current Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Huawei Technologies Co., Ltd. (Huawei Investment & Holding Co., Ltd.)
• Inventors: Jiang, Jia, Bernier, Eric
• Primary Examiner(s): Bedtelyon, John
• Application Number:
  US15/388,861
• Publication Number:
  US 20180180818A1
• Time in Patent Office: 929 Days
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: G02B 6/305 and having an integrated mode-size expanding section, e.g. tapered waveguide

Abstract

An optical coupler at an edge of a photonic integrated circuit (PIC) is provided and configured to match a mode of a waveguide of the PIC to a mode of an external optical fiber. A core of the waveguide terminates prior to the edge and can include an inverted taper for mode enlargement. The waveguide cladding includes an inverted taper and is surrounded by an outer cladding material of lower refractive index, forming a second waveguide. The cladding and outer cladding cooperate to guide light between the core and the edge while the inverted taper contributes to mode enlargement. The outer cladding material is selected to have a refractive index which facilitates the mode matching to optical fiber. The coupler can be provided using lithography. Material underneath the waveguide cladding can be removed by an undercutting process and the outer cladding material deposited in place thereof.

Claims

1. An apparatus for providing optical coupling between a photonic integrated circuit (PIC) and an external optical transmission line at an edge, the apparatus comprising:

a first elongate region formed of a first material having a first refractive index, the first elongate region forming a core of a main portion of a waveguide;

a second elongate region formed of a second material having a second refractive index lower than the first refractive index, the second elongate region decreased in dimension toward the edge, the second elongate region surrounding at least a portion of the first elongate region and forming a core of a secondary portion of the waveguide, the second elongate region configured to gradually adjust a diameter of a mode of light propagating in the secondary portion of the waveguide and within a region separate from the main portion of the waveguide; and

a third material having a third refractive index lower than the second refractive index, the third material at least partially surrounding and adjacent to a portion of the second elongate region which extends beyond a terminus of the first elongate region, the third material forming a cladding of the secondary portion of the waveguide.

2. The apparatus of claim 1, wherein the first elongate region is decreased in dimension toward the edge.

3. The apparatus of claim 1, wherein the third material is adjacent to two opposing side faces of the portion of the second elongate region which extends beyond the terminus of the first elongate region.

4. The apparatus of claim 3, wherein the third material is adjacent to a top face of the second elongate region connecting the two opposing side faces.

5. The apparatus of claim 3, wherein a bottom face of the second elongate region is adjacent to an elongate base region formed of the second material.

6. The apparatus of claim 5, further comprising:

a first further layer disposed on top of the elongate base region, the first further layer being proximate to one of the opposing side faces of the second elongate region by a first space; and

a second further layer disposed on top of the elongate base region, the second further layer being proximate to the other of the opposing side faces of the second elongate region by a second space, wherein the third material at least partially surrounds the second elongate region, the first further layer and the second further layer and fills the first space and the second space.

7. The apparatus of claim 6, wherein each of the first further layer and the second further layer comprises a region made of the first material interposing between a lower region and an upper region, the lower region and the upper region being made of the second material.

8. The apparatus of claim 6, further comprising a substrate adjacent to the bottom of the elongate base region.

9. The apparatus of claim 8, wherein the substrate is made of the first material.

10. The apparatus of claim 1, wherein the third material is adjacent to top, bottom and opposing side faces of at least the portion of the second elongate region which extends beyond the terminus of the first elongate region.

11. The apparatus of claim 10, further comprising:

a substrate having an undercut region, wherein the undercut region comprises;

a first side surface proximate to one of the opposing side faces of the second elongate region by a first space;

a second side surface proximate to the other of the opposing side faces of the second elongate region by a second space; and

a bottom surface proximate to the bottom face of the second elongate region by a third space;

a first further layer disposed on top of a substrate top surface along the first side surface of the undercut region; and

a second further layer disposed on top of the substrate top surface along the second side surface of the undercut region, wherein at least one of the further layers being connected to the second elongate region by one or more bridges.

12. The apparatus of claim 11, wherein the third material at least partially surround the second elongate region, the first further layer and the second further layer, and fills the first space, the second space and the third space.

13. The apparatus of claim 11, wherein each of the first further layer and the second further layer comprises a region made of the first material interposing between a lower region and an upper region, the lower region and the upper region being made of the second material.

14. The apparatus of claim 11, wherein the substrate is made of the first material.

15. The apparatus of claim 1, wherein the second elongate region terminates at the edge.

16. The apparatus of claim 1, wherein a portion of the third material is located between the second elongate region and the edge and the portion of the third material is located along a main axis of the second elongate region.

17. The apparatus of claim 1, wherein the first material is silicon.

18. The apparatus of claim 1, wherein the second material is silica.

19. The apparatus of claim 1, wherein the third material is polymer, sol-gel organic-inorganic hybrid material, or phosphorous boron doped silica.

20. The apparatus of claim 1, wherein some or all of the first material, the second material, and the third material are Type III, Type IV or Type V materials.

21. The apparatus of claim 1, wherein the edge is an edge of the photonic integrated circuit.

22. The apparatus of claim 1, wherein the first elongate region and the second elongate region form an end of the waveguide operatively coupled to one or more devices of the photonic integrated circuit comprising the apparatus.

23. The apparatus of claim 1, wherein the waveguide is a single-mode strip waveguide, a single mode rib waveguide, or a multimode rib waveguide.

24. A photonic integrated circuit comprising the apparatus of claim 1.

25. The apparatus of claim 1, wherein the third material is adjacent to the portion of the second elongate region which extends beyond the terminus of the first elongate region.

26. An optical coupler at an edge of a photonic integrated circuit, comprising:

an optical waveguide having a first core and a cladding, the first core comprising a terminus located at a first distance from the edge and the cladding comprising a first inverted taper, the first inverted taper extending beyond the terminus of the first core and decreasing in dimension toward the edge, wherein the extension of the first inverted taper forms a second core of the optical waveguide, and wherein the cladding is configured to gradually adjust a diameter of a mode of light propagating in the second core of the optical waveguide within a region separate from first core; and

a material at least partially surrounding and adjacent to a portion of the first inverted taper which extends beyond the terminus of the first core, the material forming a cladding around the second core of the optical waveguide and having a refractive index which is lower than a refractive index of the cladding.

27. The optical coupler of claim 26, wherein the first core comprises a second inverted taper ending at the terminus, the second inverted taper decreasing in dimension toward the edge.

28. The optical coupler of claim 26, wherein the first inverted taper of the cladding forms a core of a rib waveguide having a base and a ridge, the ridge being surrounded by the material on a top face and two opposing side faces.

29. The optical coupler of claim 26, wherein the first inverted taper of the cladding forms a core of a strip waveguide, the material surrounding and adjacent to the core of the strip waveguide.