INTEGRATED PHOTONICS MODE EXPANDER

• US 20160170142A1
• Filed: 02/23/2016
• Published: 06/16/2016
• Est. Priority Date: 08/30/2011
• Status: Active Grant

• Current Assignee: Skorpios Technologies Inc.
• Original Assignee: Skorpios Technologies Inc.
• Inventors: Lambert, Damien, Li, Guoliang, Zyskind, John, Krasulick, Stephen B.
• Granted Patent: US 9,977,188 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G02B 2006/12061 Silicon
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12152 Mode converter
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/132 by deposition of thin films
• CPC Class Codes: G02B 6/136 by etching
• 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

A method of fabricating a waveguide mode expander includes providing a substrate including a waveguide, bonding a chiplet including multiple optical material layers in a mounting region adjacent an output end of the waveguide, and selectively removing portions of the chiplet to form tapered stages that successively increase in number and lateral size from a proximal end to a distal end of the chiplet. The first optical material layer supports an input mode substantially the same size as a mode exiting the waveguide. One or more of the overlying layers, when combined with the first layer, support a larger, output optical mode size. Each tapered stage of the mode expander is formed of a portion of a respective layer of the chiplet. The first layer and the tapered stages form a waveguide mode expander that expands an optical mode of light traversing the chiplet.

Claims

1. A method of fabricating a waveguide mode expander, the method comprising:

providing a silicon on insulator (SOI) substrate comprising a waveguide, wherein;

the waveguide defines a waveguide thickness and terminates at an output end, and

the waveguide supports an optical mode of an initial mode size at the output end;

forming a mounting region adjacent the output end of the waveguide;

providing a multi-layer chiplet comprising one or more optical materials, wherein

a first layer of the one or more optical materials defines a first layer thickness that supports an input optical mode size substantially the same size as the initial mode size, and

one or more overlying layers define thicknesses that, when combined with the first layer, support an output optical mode size that is larger than the initial mode size;

bonding the chiplet in the mounting region; and

selectively removing portions of the chiplet to form tapered stages that successively increase in number and lateral size from a proximal end of the chiplet adjacent the waveguide, to a distal end of the chiplet, each tapered stage being formed of a portion of a respective layer of the multi-layer chiplet,

such that the first layer and the tapered stages form a waveguide mode expander that adiabatically expands an optical mode of light traversing the chiplet, from the initial optical mode size entering the proximal end, to the output optical mode size at the distal end.

2. The method of claim 1 wherein the SOI substrate comprises a silicon substrate and the mounting region extends into the silicon substrate.

3. The method of claim 1 wherein the waveguide comprises at least one of crystalline silicon, polycrystalline silicon and amorphous silicon.

4. The method of claim 1 wherein a lower layer of the chiplet comprises a metal layer, and bonding the chiplet comprises forming a metal to semiconductor bond with the SOI substrate.

5. The method of claim 1 wherein the first layer thickness is equal to the waveguide thickness.

6. The method of claim 1 wherein providing the multilayer chiplet comprises:

successively depositing the first layer and the one or more overlying layers on a substrate; and

singulating the substrate to form multiple ones of the chiplet.

7. The method of claim 6 wherein the substrate comprises a compound semiconductor.

8. The method of claim 7 wherein the compound semiconductor is characterized by a substrate lattice constant, and wherein the first layer and the one or more overlying layers are characterized by lattice constants that match the substrate lattice constant.

9. The method of claim 6 wherein providing the multilayer chiplet comprises:

forming the first layer and alternating ones of the one or more overlying layers of a first one of the one or more optical materials; and

forming etch stop layers, that are interspersed between the first layer and the alternating ones of the one or more overlying layers, of a different material than the first one of the one or more optical materials.

10. The method of claim 9 wherein selectively removing portions of the chiplet comprises:

applying a photoresist mask to protect a tapered portion of the chiplet; and

etching a layer of the chiplet that is not protected by photoresist until an underlying etch stop layer is exposed.

11. The method of claim 10 wherein applying a photoresist mask and etching a layer of the chiplet are repeated for each of the one or more overlying layers and for the first layer.

12. A waveguide mode expander comprising:

a tapered shoulder portion formed of a first layer of a high bandgap semiconductor material, wherein;

the first layer defines a thickness;

the shoulder portion forms;

a length from an input end to an output end,

a first width at the input end, and

a second width that is larger than the first width, at the output end; and

a tapered ridge portion, overlying the shoulder portion and formed of one or more additional tapered portions of high bandgap semiconductor materials, wherein;

each of the additional portions is formed of an additional layer having an individual layer thickness;

each of the additional portions forms;

a sequentially shorter length than the length of the shoulder portion and the length of any underlying additional portions;

a first additional portion width at an end of the additional portion that is closest to the input end, and

a second additional portion width that is larger than the first additional portion width, at the output end;

such that the tapered ridge portion and the tapered shoulder portion are configured to expand an optical beam propagating through the waveguide mode expander from the input end to the output end.

13. The waveguide mode expander of claim 12, wherein:

the additional tapered portions form a plurality of stages stacked vertically on top of one other;

a first one of the stages is disposed atop the shoulder portion;

sequentially higher ones of the stages are stacked atop lower ones of the stages; and

at any given cross section of the waveguide mode expander;

the first one of the stages forms a narrower width than the shoulder portion; and

each higher stage of the plurality of stages forms a narrower width than lower ones of the stages.

14. The waveguide mode expander of claim 13, wherein:

the individual layer thicknesses of the stages increase sequentially from the first one of the stages through the sequentially higher ones of the stages.

15. The waveguide mode expander of claim 13, wherein the number of stages is three.

16. The waveguide mode expander of claim 13, wherein the number of stages is at least five.

17. The waveguide mode expander of claim 12, further comprising a cladding deposited over the shoulder portion and the ridge portion.

18. The waveguide mode expander of claim 17, wherein the cladding comprises SiO₂.

19. The waveguide mode expander of claim 12, wherein the ridge portion expands the optical beam by tapering from a narrower width at the input end to a wider width at the output end.

20. The waveguide mode expander of claim 12, further comprising SiO₂ forming a cladding layer under the shoulder portion.

21. The waveguide mode expander of claim 12, wherein at least one of the shoulder portion and the one or more additional tapered portions comprises a compound semiconductor.

22. The waveguide mode expander of claim 12, wherein the ridge portion comprises one or more etch stop layers interspersed with the additional tapered portions.

23. The waveguide mode expander of claim 12, wherein the tapered ridge portion and the tapered shoulder portion expand the optical beam propagating through the waveguide mode expander both horizontally and vertically from the input end to the output end.