Integrated multistage taper coupler for waveguide to fiber coupling
A waveguide coupler has a compression region and an expansion region for coupling light between a silicon waveguide and an optical fiber. The compression region receives light from the silicon waveguide and compresses an optical mode of the light. Light is transmitted from the compression region to an expansion region. The expansion region expands the light to have a larger cross section. Light is then transmitted to the optical fiber.
1. A waveguide coupler for transmitting light between a silicon waveguide and an optical fiber, the coupler comprising:
a compression region, the compression region operable to:
receive an optical beam from a semiconductor waveguide,
compress the optical beam to have a smaller cross section compared to light confined in the semiconductor waveguide; and
transmit optical beam to an expansion region;
the expansion region, wherein:
the expansion region comprises a first part;
the first part overlaps, and is directly adjacent to, at least a portion of the compression region; and
the expansion region is operable to:
receive the optical beam from the compression region;
expand the optical beam to have a larger cross section compared to light confined in the semiconductor waveguide; and
transmit the optical beam to the optical fiber.
2. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 1 , wherein the compression region comprises a shoulder and a ridge, and the shoulder and the ridge both compress the optical beam.
3. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 2 , wherein the ridge terminates at a first tip having a width equal to or less than 225 nanometers and the shoulder terminates at a second tip having a width less than or equal to 225 nanometers.
4. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 3 , wherein the second tip has a width less than or equal to 175 nanometers.
5. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 1 , wherein the first part and the at least a portion of the compression region are made of different materials.
6. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 1 , wherein the first part has a cross section between 2.5 microns and 3.5 microns and has a height between 2.5 microns and 3.5 microns.
7. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 1 , wherein the expansion region adiabatically expands the optical beam received from the compression region as the optical beam is guided to the optical fiber.
8. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 1 , wherein the compression region adiabatically compresses the optical beam received from the semiconductor waveguide.
9. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 1 , wherein:
the compression region comprises a first material having a first index of refraction;
the expansion region comprises a second material having a second index of refraction; and
the first index of refraction is greater than the second index of refraction.
10. The coupler for transmitting light between the silicon waveguide and the optical fiber of claim 1 , wherein the expansion region comprises:
a shoulder, the shoulder having:
a first part, wherein the first part is not tapered;
a second part, wherein the second part is tapered to laterally expand or compress the optical beam; and
a third part, wherein:
the second part is disposed between the third part and the first part; and
the shoulder in the first part is not tapered;
a ridge, wherein:
the ridge extends over top of the second part and the third part; and
the ridge tapers to laterally expand or compress the optical beam.
11. An expansion region for use in a coupler for guiding light between a silicon waveguide and an optical fiber, expansion region comprising:
a first waveguide portion having:
a first part, wherein the first part is not tapered;
a second part, wherein the second part is tapered to laterally expand or compress light; and
a third part, wherein:
the second part is disposed between the third part and the first part; and
the first waveguide portion in the third part is not tapered;
a second waveguide portion, wherein:
the second waveguide portion extends over top of the second part and the third part;
the second waveguide portion is directly adjacent to the second part and the third part of the first waveguide portion; and
the second waveguide portion tapers to laterally expand or compress light.
12. The expansion region for use in the coupler for guiding light between the silicon waveguide and the optical fiber of claim 11 , wherein:
the third part has a first end and a second end;
the second end is connected to the second part;
the first end is used as an input/output of the coupler;
the second waveguide portion has a width at the first end;
the first waveguide portion has a width at the first end; and
the width of the first waveguide portion at the first end is wider than the width of the second waveguide portion at the first end.
13. The expansion region for use in the coupler for guiding light between the silicon waveguide and the optical fiber of claim 12 , wherein the width of the first waveguide portion at the first end is 0.6 to 3.0 microns wider than the width of the second waveguide portion at the first end.
14. The expansion region for use in the coupler for guiding light between the silicon waveguide and the optical fiber of claim 11 , the expansion region comprises SiON or SiN.
15. The expansion region for use in the coupler for guiding light between the silicon waveguide and the optical fiber of claim 11 , the expansion region has refractive index that matches a refractive index, or effective refractive index, of the optical fiber.
16. The expansion region for use in the coupler for guiding light between the silicon waveguide and the optical fiber of claim 11 , the expansion region comprises SiON or SiN.
17. The expansion region for use in the coupler for guiding light between the silicon waveguide and the optical fiber of claim 11 , wherein the first part of the first waveguide portion overlaps a portion of a compression region of the coupler.
18. A method for coupling a semiconductor waveguide to an optical fiber, the method comprising:
transmitting a beam of light from a waveguide into an optical coupler;
compressing the beam of light received from the waveguide in a first region of the optical coupler;
expanding the beam of light in a second region of the optical coupler after compressing the beam of light in the first region, wherein the first region and the second region are adjacent; and
transmitting the beam of light from the optical coupler to an optical fiber after expanding the beam of light in the second region of the optical coupler.
19. The method for coupling the semiconductor waveguide to the optical fiber of claim 18 , wherein:
the second region overlaps at least a portion of the first region;
the first region comprises a first material having a first index of refraction;
the second region comprises a second material having a second index of refraction; and
the first index of refraction is greater than the second index of refraction.