Compact optical coupler
Configurations for an optical coupler that includes waveguides that provide asymmetric mode confinement. The optical coupler may include first and second rib waveguides, and the width of the shoulder of at least one rib waveguide may taper to provide the asymmetric mode confinement. In some instances the shoulders of one or both rib waveguides may have different heights in a central region of the optical coupler.
1. An optical coupler, comprising:
a slab waveguide defining a first shoulder region, a second shoulder region, and a third shoulder region;
a first rib waveguide including a first strip positioned on the slab waveguide; and
a second rib waveguide including a second strip positioned on the slab waveguide, wherein:
the slab waveguide comprises a lower slab region having a first height and an upper slab region having a second height higher than the first height;
the upper slab region defines the first shoulder region, the second shoulder region, and the third shoulder region;
the first rib waveguide is optically coupled to the second rib waveguide in a central region;
the first shoulder region is adjacent to a first side of the first strip;
the third shoulder region is adjacent to a first side of the second strip;
the second shoulder region is adjacent to a second side of the first strip and a second side of the second strip; and
a width of the first shoulder region tapers to provide asymmetrical mode confinement of light that passes through the first rib waveguide.
2. The optical coupler of claim 1 , wherein:
the width of the first shoulder region tapers to zero in a first portion of the first rib waveguide;
the first shoulder region defines a first shoulder of the first rib waveguide in the first portion of the first rib waveguide; and
the lower slab region defines the first shoulder of the first rib waveguide in a second portion of the first rib waveguide.
3. The optical coupler of claim 2 , further comprising:
a fourth shoulder region, wherein:
the upper slab region defines the fourth shoulder region;
the fourth shoulder region defines the first shoulder of the first rib waveguide in a third portion of the first rib waveguide; and
a width of the fourth shoulder region tapers in the third portion of the first rib waveguide.
4. The optical coupler of claim 1 , wherein:
a width of the third shoulder region tapers to provide asymmetrical mode confinement of light that passes through the second rib waveguide.
5. The optical coupler of claim 1 , wherein:
a width of the first strip tapers in the central region.
6. The optical coupler of claim 1 , wherein:
a width of the first strip is constant in the central region; and
a width of the second strip is constant in the central region.
7. The optical coupler of claim 1 , wherein:
the width of the first shoulder region tapers to a minimum width;
the first shoulder region defines a first shoulder of the first rib waveguide in the central region; and
the first shoulder region has the minimum width across the central region.
8. An optical coupler, comprising:
a first rib waveguide having a first strip, a first shoulder, and a second shoulder; and
a second rib waveguide having a second strip, a first shoulder, and a second shoulder; wherein:
the first rib waveguide is optically coupled to the second rib waveguide in a central region;
the first shoulder of the first rib waveguide has a first height in the central region;
the second shoulder of the first rib waveguide has a second height higher than the first height in the central region;
the first strip and the second strip are disposed on a slab waveguide, the slab waveguide having a lower slab region and an upper slab region;
the slab waveguide defines the second shoulder of the first rib waveguide in the central region;
the slab waveguide defines the second shoulder of the second rib waveguide in the central region
the lower slab region defines the first shoulder of the first rib waveguide in the central region; and
the upper slab region defines the second shoulder of the first rib waveguide in the central region.
9. The optical coupler of claim 8 , wherein:
the first shoulder of the second rib waveguide has the first height in the central region; and
the second shoulder of the second rib waveguide has the second height in the central region.
10. An optical system, comprising:
one or more light sources configured to generate light; and
an optical coupler, comprising:
a slab waveguide comprising a lower slab region having a first height and an upper slab region having a second height higher than the first height;
a first rib waveguide optically coupled to the one or more light sources to receive a first portion of light therefrom; and
a second rib waveguide optically coupled to the one or more light sources to receive a second portion of light therefrom, wherein:
the first rib waveguide has a first strip and a first shoulder adjacent to a first side of the first strip;
a width of the first shoulder of the first rib waveguide tapers in a first portion of the first rib waveguide to apply asymmetric mode confinement to the first portion of light;
the second rib waveguide has a second strip and a first shoulder adjacent to a first side of the second strip;
a width of the first shoulder of the second rib waveguide tapers in a first portion of the second rib waveguide to apply asymmetric mode confinement to the second portion of light;
the upper slab region defines the first shoulder of the first rib waveguide in the first portion of the first rib waveguide; and
the upper slab region defines the first shoulder of the second rib waveguide in the first portion of the second rib waveguide.
11. The optical system of claim 10 , further comprising a photonic integrated circuit, wherein the photonic integrated circuit incorporates the one or more light sources and the optical coupler.
12. The optical system of claim 10 , wherein:
the first rib waveguide is optically coupled to the second rib waveguide in a central region of the optical coupler.
13. The optical system of claim 12 , wherein:
the first shoulder of the first rib waveguide has the first height in the first portion of the first rib waveguide and the first height in the central region.
14. The optical system of claim 13 , wherein:
the first shoulder of the first rib waveguide tapers to a minimum width in the first portion of the first rib waveguide; and
the first shoulder has the minimum width in the central region.