Waveguide couplers for multi-mode waveguides

1. A generalized Mach-Zehnder interferometer, comprising:

a first multi-channel optical coupler that includes four or more output ports;

a second multi-channel optical coupler that includes four or more input ports;

four or more optical waveguides, including:

a first optical waveguide of the four or more optical waveguides that is connected to a first output port of the four or more output ports and a first input port of the four or more input ports; and

a second optical waveguide of the four or more optical waveguides that is connected to a second output port of the four or more output ports and a second input port of the four or more input ports; and

one or more phase shifters coupled with at least a subset of the four or more optical waveguides,

wherein:

at least one of the first multi-channel optical coupler or the second multi-channel optical coupler includes two or more multi-mode optical couplers, including a first multi-mode optical coupler that includes:

a first waveguide including a first multi-mode waveguide section, the first waveguide being located in a first layer of material; and

a second waveguide that is distinct and separate from the first waveguide, the second waveguide including a second multi-mode waveguide section, the second waveguide being located in a second layer of material that is distinct and separate from the first layer of material, wherein the first multi-mode waveguide section is positioned adjacent to the second multi-mode waveguide section;

the first optical waveguide includes a first portion in the first layer of material and a second portion in the second layer of material and a first interlayer optical coupler coupling the first portion of the first optical waveguide to the second portion of the first optical waveguide; and

the second optical waveguide includes a third portion in the second layer of material and a fourth portion in the first layer of material and a second interlayer optical coupler coupling the third portion of the second optical waveguide to the fourth portion of the second optical waveguide.

2. The generalized Mach-Zehnder interferometer of claim 1 , wherein

the first multi-mode optical coupler includes:

the first multi-mode waveguide section of the first waveguide of the first multi-mode optical coupler has a cross-section characterized by a first height and a first width that is greater than the first height; and

the second multi-mode waveguide section of the second waveguide of the first multi-mode optical coupler has a cross-section characterized by a second height and a second width that is greater than the second height,

wherein the first multi-mode waveguide section is positioned adjacent to the second multi-mode waveguide section at least partially above or below the second multi-mode waveguide section so that light entering the first multi-mode waveguide section is coupled from the first multi-mode waveguide section to the second multi-mode waveguide section.

3. The generalized Mach-Zehnder interferometer of claim 2 , wherein:

the first width is at least three times the first height; and

the second width is at least three times the second height.

4. The generalized Mach-Zehnder interferometer of claim 1 , wherein:

the first multi-mode waveguide section and the second multi-mode waveguide section are configured to allow light entering the first multi-mode waveguide section in a fundamental mode is coupled from the first multi-mode waveguide section to the second multi-mode waveguide section while remaining in the fundamental mode.

5. The generalized Mach-Zehnder interferometer of claim 1 , wherein:

the first waveguide of the first multi-mode optical coupler includes a third multi-mode waveguide section that is distinct from, and mutually exclusive to, the first multi-mode waveguide section so that light propagating in the third multi-mode waveguide section propagates toward the first multi-mode waveguide section; and

the second waveguide of the first multi-mode optical coupler includes a fourth multi-mode waveguide section that is distinct from, and mutually exclusive to, the second multi-mode waveguide section so that light propagating in the fourth multi-mode waveguide section propagates toward the second multi-mode waveguide section.

6. The generalized Mach-Zehnder interferometer of claim 5 , wherein:

the first waveguide of the first multi-mode optical coupler includes a fifth multi-mode waveguide section that is coupled to the first multi-mode waveguide section on a first end and to the third multi-mode waveguide section on a second end that is opposite to the first end; and

the second waveguide of the first multi-mode optical coupler includes a sixth multi-mode waveguide section that is coupled to the second multi-mode waveguide section on a first end and to the fourth multi-mode waveguide section on a second end that is opposite to the first end,

wherein at least one of the fifth multi-mode waveguide section and the sixth multi-mode waveguide section is curved.

7. The generalized Mach-Zehnder interferometer of claim 6 , wherein:

the first waveguide of the first multi-mode optical coupler includes a seventh multi-mode waveguide section that is distinct from, and mutually exclusive to, the first multi-mode waveguide section so that light propagating in the first multi-mode waveguide section propagates toward the seventh multi-mode waveguide section; and

the second waveguide of the first multi-mode optical coupler includes an eighth multi-mode waveguide section that is distinct from, and mutually exclusive to, the second multi-mode waveguide section so that light propagating in the second multi-mode waveguide section propagates toward the eighth multi-mode waveguide section.

8. The generalized Mach-Zehnder interferometer of claim 7 , wherein:

the first waveguide of the first multi-mode optical coupler includes a ninth multi-mode waveguide section that is coupled to the first multi-mode waveguide section on a first end and to the seventh multi-mode waveguide section on a second end that is opposite to the first end; and

the second waveguide of the first multi-mode optical coupler includes a tenth multi-mode waveguide section that is coupled to the second multi-mode waveguide section on a first end and to the eighth multi-mode waveguide section on a second end that is opposite to the first end,

wherein at least one of the ninth multi-mode waveguide section and the tenth multi-mode waveguide section is curved.

9. The generalized Mach-Zehnder interferometer of claim 1 , wherein:

the first waveguide of the first multi-mode optical coupler includes a first single-mode input waveguide section adiabatically coupled to the first multi-mode waveguide section so that the first multi-mode waveguide section receives light from the first single-mode input waveguide section; and

the second waveguide of the first multi-mode optical coupler includes a second single-mode input waveguide section adiabatically coupled to the second multi-mode waveguide section so that the second multi-mode waveguide section receives light from the second single-mode input waveguide section.

10. The generalized Mach-Zehnder interferometer of claim 9 , wherein the first multi-mode optical coupler of claim 9 includes:

a first tapered waveguide section, in the first waveguide of the first multi-mode optical coupler, configured to enable the adiabatic coupling of the first single-mode input waveguide section to the first multi-mode waveguide section; and

a second tapered waveguide section, in the second waveguide of the first multi-mode optical coupler, configured to enable the adiabatic coupling of the second single-mode input waveguide section to the second multi-mode waveguide section.

11. The generalized Mach-Zehnder interferometer of claim 10 , wherein

the first multi-mode optical coupler further includes

in the first waveguide of the first multi-mode optical coupler:

a first single-mode output waveguide section adiabatically coupled to the first multi-mode waveguide section so that the first single-mode output waveguide section receives light from the first multi-mode waveguide section; and

a third tapered waveguide section configured to enable the adiabatic coupling of the first multi-mode waveguide section to the first single-mode output waveguide section; and

in the second waveguide of the first multi-mode optical coupler:

a second single-mode output waveguide section adiabatically coupled to the second multi-mode waveguide section so that the second single-mode output waveguide section receives light from the second multi-mode waveguide section; and

a fourth tapered waveguide section configured to enable the adiabatic coupling of the second multi-mode waveguide section to the second single-mode output waveguide section.

12. The generalized Mach-Zehnder interferometer of claim 1 , wherein

the first multi-mode waveguide section and the second multi-mode waveguide section are parallel to each other; and

the first multi-mode waveguide section and the second multi-mode waveguide section are separated from each other.

13. The generalized Mach-Zehnder interferometer of claim 1 , wherein:

the two or more multi-mode optical couplers also include a second multi-mode optical coupler that includes:

a third waveguide including a third multi-mode waveguide section, the third waveguide being located in the first layer of material; and

a fourth waveguide that is distinct and separate from the third waveguide, the fourth waveguide including a fourth multi-mode waveguide section and being located in the second layer of material;

the third multi-mode waveguide section is positioned adjacent to the fourth multi-mode waveguide section; and

a portion of the second waveguide of the first multi-mode optical coupler is positioned adjacent to a portion of the third waveguide for coupling light from the second waveguide to the third waveguide.

14. The generalized Mach-Zehnder interferometer of claim 13 ,

wherein:

the two or more multi-mode optical couplers also include a third multi-mode optical coupler and a fourth multi-mode optical coupler;

the third multi-mode optical coupler includes:

a fifth waveguide including a fifth multi-mode waveguide section, the fifth waveguide being located in the first layer of material; and

the fourth waveguide that is distinct and separate from the fifth waveguide, the fourth waveguide including a sixth multi-mode waveguide section that is different from the fourth multi-mode waveguide section;

the fifth multi-mode waveguide section is positioned adjacent to the sixth multi-mode waveguide section;

the fourth multi-mode optical coupler includes:

the first waveguide of the first multi-mode optical coupler including a seventh multi-mode waveguide section that is different from the first multi-mode waveguide section; and

a sixth waveguide including an eighth multi-mode waveguide section, the sixth waveguide being located in the second layer of material;

the seventh multi-mode waveguide section is positioned adjacent to the eighth multi-mode waveguide section; and

a portion of the fifth waveguide is positioned adjacent to a portion of the sixth waveguide for coupling light from the fifth waveguide to the sixth waveguide.

15. The generalized Mach-Zehnder interferometer of claim 1 , wherein:

the other of the first multi-channel optical coupler and the second multi-channel optical coupler includes two or more multi-mode optical couplers.