Multistage spot size converter in silicon photonics

• US 10,649,148 B2
• Filed: 10/25/2018
• Issued: 05/12/2020
• Est. Priority Date: 10/25/2017
• Status: Active Grant

• Current Assignee: Skorpios Technologies Inc.
• Original Assignee: Skorpios Technologies Inc.
• Inventors: Sodagar, Majid, Krasulick, Stephen B., Zyskind, John, Apiratikul, Paveen, Cafiero, Luca
• Primary Examiner(s): Peace, Rhonda S
• Application Number:
  US16/171,132
• Publication Number:
  US 20190170944A1
• Time in Patent Office: 565 Days
• CPC Class Codes: G02B 2006/12061 Silicon
• CPC Class Codes: G02B 6/305 and having an integrated mode-size expanding section, e.g. tapered waveguide

Abstract

A device is provided for optical mode spot size conversion to optically couple a semiconductor waveguide with an optical fiber. The device includes a waveguide comprising a waveguide taper region, which comprises a shoulder portion and a ridge portion above the shoulder portion. The ridge portion has a width that tapers to meet a width of the shoulder portion. The waveguide taper region comprises a first material. The device also has a mode converter coupled to the waveguide. The mode converter includes a plurality of stages, and each of the plurality of stages tapers in a direction similar to a direction of taper of the waveguide taper region. The mode converter is made of a second material different from the first material.

Claims

1. A device for optical mode spot size conversion to optically couple a semiconductor waveguide with an optical fiber, the device comprising:

a waveguide comprising a waveguide taper region, wherein;

the waveguide taper region comprises a shoulder portion and a ridge portion, the ridge portion disposed directly above the shoulder portion and oriented along a direction of beam propagation, the ridge portion having a width that tapers to meet a width of the shoulder portion; and

the waveguide taper region comprises a first material; and

a mode converter coupled to the waveguide, wherein;

the mode converter comprises a plurality of stages;

each of the plurality of stages tapers in a direction similar to a direction of taper of the waveguide taper region; and

the mode converter is made of a second material different from the first material.

2. The device of claim 1, wherein:

the mode converter comprises a first stage and a second stage of the plurality of stages, the second stage overlying the first stage;

the first stage comprises a first portion that does not taper and a second portion that tapers; and

the second stage extends over the first portion and the second portion of the first stage.

3. The device of claim 2, wherein the first portion of the first stage of the mode converter and the shoulder portion of the waveguide have a common width.

4. The device of claim 1, wherein the waveguide further comprises a waveguide extension region coupled between the waveguide taper region and the mode converter, wherein:

the waveguide extension region is made of the first material;

the waveguide extension region has a thickness equal to a combined thickness of the shoulder portion and the ridge portion of the waveguide taper region; and

the waveguide extension region and the shoulder portion of the waveguide taper region have a common width.

5. The device of claim 4, wherein the waveguide extension region has a common thickness as the waveguide taper region and a first stage of the mode converter.

6. The device of claim 4, wherein the waveguide extension region has a common width as an output end of the waveguide taper region and an input end of a first stage of the mode converter.

7. The device of claim 1, wherein the number of stages in the mode converter is greater than three and less than eleven.

8. The device of claim 1, wherein the number of stages in the mode converter is seven.

9. The device of claim 1, wherein the ridge portion tapers from a narrower width of 0.75-2.75 μ

m near an input end to a wider width of 2.0-4.5 μ

m near an output end.

10. The device of claim 1, wherein, at an output end of the mode converter, the mode converter has a rectangular cross-section, and the plurality of stages has a common maximum width.

11. The device of claim 1, wherein:

the mode converter comprises a first stage and a second stage of the number of stages,

the first stage has a first maximum width,

the second stage has a second maximum width, and

the first maximum width of the first stage is greater than the second maximum width of the second stage.

12. The device of claim 1, wherein:

at a cross section of the mode converter at an output end of the device, each stage of the plurality of stages has a different width; and

a first stage of the plurality of stages, which is closer to the shoulder portion, has a wider width than a second stage of the plurality of stages, which is farther from the shoulder portion than the first stage.

13. The device of claim 12, wherein:

the first stage of the mode converter has a first length,

the second stage of the mode converter has a second length, and

the first length is equal to the second length.

14. The device of claim 1, wherein:

the waveguide taper region comprises crystalline silicon in a device layer disposed on a buried-oxide layer of an SOI (silicon-on-insulator) substrate; and

the mode converter comprises non-crystalline silicon formed on the buried-oxide layer of the SOI substrate.

15. A method, for converting optical mode spot size between a semiconductor waveguide and an optical fiber, the method comprising:

receiving a light beam at a waveguide comprising a waveguide taper region, the waveguide taper region comprising a shoulder portion and a ridge portion, the ridge portion disposed directly above the shoulder portion and oriented along a direction of beam propagation, the ridge portion having a width that tapers to meet a width of the shoulder portion, the waveguide taper region comprising a first material;

expanding an optical mode of the light beam in the waveguide taper region;

coupling the light beam from the waveguide taper region to a mode converter, wherein;

the mode converter comprises a plurality of stages;

each of the plurality of stages tapers in a direction similar to a direction of taper of the waveguide taper region; and

the mode converter is made of a second material different from the first material;

expanding the light beam through each of the plurality of stages in the mode converter; and

coupling the light beam to the optical fiber.

16. The method of claim 15, further comprising transmitting the light beam through a first stage of the mode converter to a second stage, wherein:

the first stage comprises a first portion that does not taper and a second portion that tapers; and

the second stage extends over the first portion and the second portion of the first stage.

17. The method of claim 15, further comprising transmitting the light beam through a waveguide extension region coupled between the waveguide taper region and the mode converter, wherein:

the waveguide extension region is made of the first material;

the waveguide extension region has a thickness equal to a combined thickness of the shoulder portion and the ridge portion of the waveguide taper region; and

the waveguide extension region and the shoulder portion of the waveguide taper region have a common width.

18. A device for optical mode spot size conversion to optically couple a semiconductor waveguide with an optical fiber, the device comprising:

a waveguide comprising a waveguide taper region and a waveguide extension region coupled to the waveguide taper region, wherein;

the waveguide taper region comprises a shoulder portion and a ridge portion above the shoulder portion, the ridge portion having a width that tapers to meet a width of the shoulder portion; and

the waveguide taper region is made of a first material;

the waveguide extension region is made of the first material;

the waveguide extension region has a thickness equal to a combined thickness of the shoulder portion and the ridge portion of the waveguide taper region; and

the waveguide extension region and the shoulder portion of the waveguide taper region have a common width; and

a mode converter coupled to the waveguide extension region, wherein;

the mode converter comprises a plurality of stages;

each of the plurality of stages tapers in a direction similar to a direction of taper of the waveguide taper region;

the mode converter comprises a first stage and a second stage of the plurality of stages, the first stage comprising a first portion that does not taper and a second portion that tapers; and

the second stage extends over the first portion and the second portion of the first stage; and

the mode converter is made of a second material different from the first material.

19. The device of claim 18, wherein the ridge portion tapers from a narrower width of 0.75-2.75 μ

m near an input end to a wider width of 2.0-4.5 μ

m near an output end.

20. The device of claim 18, wherein the waveguide extension region has a common thickness as the waveguide taper region and the first stage of the mode converter.