Spot-size converter for optical mode conversion and coupling between two waveguides

Patent metadata

Field	Value
Publication number	US-9703047-B2
Application number	US-201514635602-A
Country	US
Kind code	B2
Filing date	Mar 2, 2015
Priority date	Feb 28, 2014
Publication date	Jul 11, 2017
Grant date	Jul 11, 2017

Abstract

A spot-size converter for coupling light between first and second waveguides respectively supporting first and second propagation modes having substantially different dimensions is provided. The spot-size converter includes a lower and an upper waveguiding structure each characterized by an effective refractive index. The lower waveguiding structure is coupled to the first waveguide to receive light therefrom or transmit light thereto in the first propagation mode. The upper waveguiding structure is coupled to the second waveguide to transmit light thereto or receive light therefrom in the second propagation mode. The upper waveguiding structure includes a plurality of longitudinally extending high-index elements arranged in multiple vertically spaced rows. At least part of the upper waveguiding structure extends at least partially over the lower waveguiding structure so as to define a coupling region wherein an effective refractive index crossing occurs, thereby enabling evanescent coupling of light between the lower and upper waveguiding structures.

First claim

The invention claimed is:

1. A spot-size converter for coupling light between a first waveguide and a second waveguide respectively supporting a first propogation mode and a second propagation mode having substantially different dimensions, the spot-size converter extending along a longitudinal waveguiding axis and comprising:
a lower waveguiding structure having a first end and a second end opposed to the first end of the lower waveguiding structure, the first end of the lower waveguiding structure being coupled to the first waveguide to receive light therefrom or transmit light thereto in the first propagation mode, the lower waveguiding structure being characterized by a first effective refractive index;
an upper waveguiding structure having a first end and a second end opposed to the first end of the upper waveguiding structure, wherein the first end of the upper waveguiding structure is coupled to the second waveguide and configured to transmit light thereto or receive light therefrom in the second propagation mode, and wherein the upper waveguiding structure is characterized by a second effective refractive index; and
a first plurality of high-index elements disposed within a cladding structure and extending substantially along the waveguiding axis,
wherein the first plurality of high-index elements comprise a first array of high-index elements arranged in a first row that is vertically spaced above the first end of the upper waveguiding structure so as to define a coupling region, wherein a crossing of the first effective refractive index and the second effective refractive index occurs, thereby enabling evanescent coupling of light between the lower waveguiding structure and the upper waveguiding structure.

2. The spot-size converter according to claim 1 , wherein at least one of the lower waveguiding structure and the upper waveguiding structure tapers longitudinally in the coupling region.

3. The spot-size converter according to claim 1 , wherein at least one of the first plurality of high-index elements tapers longitudinally in the coupling region.

4. The spot-size converter according to claim 1 , wherein the lower waveguiding structure comprises a second plurality of high-index elements lying in a common horizontal plane.

5. The spot-size converter according to claim 1 , wherein the lower waveguiding structure comprises a single waveguide element extending along the longitudinal waveguiding axis.

6. The spot-size converter according to claim 5 , wherein the single waveguide element comprises a longitudinally tapered portion tapering down toward the second end of the upper waveguiding structure.

7. The spot-size converter according to claim 6 , wherein the longitudinally tapered portion forms an adiabatic taper.

8. The spot-size converter according to claim 5 , wherein the single waveguide comprises a subwavelength composite portion that defines a subwavelength pattern having a characteristic size which is less than half an effective wavelength of light when propagating therein.

9. The spot-size converter according to claim 5 , wherein the single waveguide element has a bottom layer extending along the waveguiding axis from the first end of the lower waveguiding structure to the second end of the lower waveguiding structure and a top layer superposed on and coextensive with the bottom layer, the top layer extending from the first end to an end tip located between the first end of the lower waveguiding structure and the second end of the lower waveguiding structure.

10. The spot-size converter according to claim 9 , wherein at least one of the top layer and the bottom layer of the single waveguide element comprises a subwavelength composite portion that defines a subwavelength pattern having a characteristic size which is less than half an effective wavelength of light when propagating therein.

11. The spot-size converter according to claim 9 , wherein at least one of the top and bottom layers comprises a longitudinally tapered portion tapering down toward the second end of the lower waveguiding structure.

12. The spot-size converter according to claim 9 , wherein the single waveguide element has a first height corresponding to the bottom layer and a second height corresponding to a superposition of the bottom and top layers, a width of the single waveguide element at the first end of the lower waveguiding structure being equal to the second height and the width of the single waveguide element at the end tip of the top layer being equal to the first height.

13. The spot-size converter according to claim 1 , wherein the lower waveguiding structure is part of a silicon-on-insulator (SOI) arrangement comprising a silicon substrate, an insulating layer formed on the silicon substrate, and a silicon layer formed on the insulating layer and patterned to form the lower waveguiding structure.

14. The spot-size converter according to claim 1 , wherein the lower waveguiding structure and the upper waveguiding structure are made of silicon, silicon nitride, silicon carbide, silicon oxynitride, silicon oxide, indium phosphide, gallium arsenide, a polymer or a combination thereof.

15. The spot-size converter according to claim 1 , wherein a lowest-lying row of the first plurality of high-index elements lies in a same horizontal plane and is made of a same material as the lower waveguiding structure.

16. The spot-size converter according to claim 1 , wherein the second waveguide is an optical fiber.

17. The spot-size converter according to claim 1 , wherein the plurality of high-index elements further compromise:
a second array of high-index elements arranged in a second row;
a third array of high-index elements arranged in a third row,
wherein the second array of high-index elements and the third array of high-index elements are vertically spaced above the first end of the upper waveguiding structure, and
wherein each of the first array of high-index elements, the second array of high-index elements, and the third array of high-index elements comprise two or more high-index elements.

18. The spot-size converter according to claim 1 , further comprising:
an insulating layer,
wherein the first plurality of high-index elements further comprise a second array of high-index elements arranged in a second row,
wherein the second array of high-index elements and the upper waveguiding structure are disposed on the insulator layer.

19. A spot-size converter for coupling light between a first waveguide and a second waveguide respectively supporting a first and a second propagation mode having substantially different dimensions, the spot-size converter extending along a longitudinal waveguiding axis and comprising:
a single lower waveguide element having a first and a second end opposed to the first end, the first end being coupled to the first waveguide to receive light therefrom or transmit light thereto in the first propagation mode, the lower waveguide element being characterized by a longitudinally varying first effective refractive index that decreases toward the second end; and
an upper waveguiding structure having a first and a second end opposed to the first end, the first end being coupled to the second waveguide to transmit light thereto or receive light therefrom in the second propagation mode, the upper waveguiding structure being characterized by a second effective refractive index and comprising a plurality of high-index elements extending substantially along the waveguiding axis and forming an array of rows and columns in a plane transv

Assignees

• Ciena Corp

Inventors

• Painchaud Yves
• Picard Marie-Josée
• Latrasse Christine
• Poulin Michel

Classifications

• G02B6/305 Primary

  and having an integrated mode-size expanding section, e.g. tapered waveguide · CPC title

• G02B6/14

  Mode converters · CPC title

• G02B6/1228 Primary

  Tapered waveguides, e.g. integrated spot-size transformers (for coupling with fibres G02B6/305) · CPC title

• G02B6/124

  Geodesic lenses or integrated gratings · CPC title

• G02B2006/12152

  Mode converter · CPC title