US-12619121-B2 - Power splitters including a tunable multimode interference coupler

Abstract

Structures for a power splitter that include a multimode interference coupler and methods of forming such structures. The structure comprises a multimode interference coupler including a grating having a plurality of grating lines, an input waveguide core, and an output waveguide core. The grating lines are disposed between the input waveguide core and the output waveguide core. The structure further comprises a resistive heating element adjacent to the grating lines.

Inventors

• Michal RAKOWSKI
• Yusheng Bian
• Roderick A. Augur
• Ayat M. Taha
• Marios Papadovasilakis
• Yonas Hadush Gebregiorgis
• Jaime Viegas

Assignees

• GLOBALFOUNDRIES U.S. INC.
• Khalifa University of Science and Technology

Dates

Publication Date

20260505

Application Date

20230926

Claims (20)

1. 1 . A structure for a power splitter, the structure comprising: a multimode interference coupler including a grating having a plurality of grating lines, a first input waveguide core, and a first output waveguide core, the grating lines disposed between the first input waveguide core and the first output waveguide core; and a first resistive heating element adjacent to the grating lines, wherein the grating lines have a first duty cycle that decreases with a first variable rate from the first input waveguide core toward a center of the grating, and the grating lines have a second duty cycle that increases with a second variable rate from the center of the grating toward the first output waveguide core.
2. 2 . The structure of claim 1 further comprising: a second resistive heating element adjacent to the grating lines.
3. 3 . The structure of claim 2 wherein the grating lines are laterally disposed between the first resistive heating element and the second resistive heating element.
4. 4 . The structure of claim 3 wherein the grating has a length given by a distance between the grating lines respectively closest to the first input waveguide core and the first output waveguide core, and the first resistive heating element and the second resistive heating element each extend over an entirety of the length of the grating.
5. 5 . The structure of claim 1 wherein the grating includes a longitudinal axis and a plurality of gaps that alternate with the grating lines along the longitudinal axis, and the gaps have a width dimension that varies with position along the longitudinal axis.
6. 6 . The structure of claim 5 wherein the grating lines have a width that varies with position along the longitudinal axis.
7. 7 . The structure of claim 6 wherein the grating has a length given by a distance between the grating lines respectively closest to the first input waveguide core and the first output waveguide core, the grating has a period given by a sum of the width dimension of the gaps and the width of the grating lines, and the period is constant along the length of the grating.
8. 8 . The structure of claim 5 wherein the grating lines have a length in a direction transverse to the longitudinal axis, and the length of the grating lines varies with position along the longitudinal axis.
9. 9 . The structure of claim 8 wherein the length of the grating lines varies according to a non-linear function.
10. 10 . The structure of claim 9 wherein the non-linear function is a quadratic function.
11. 11 . The structure of claim 1 wherein the grating includes a longitudinal axis, the grating lines have a length in a direction transverse to the longitudinal axis, and the length of the grating lines varies with position along the longitudinal axis.
12. 12 . The structure of claim 11 wherein the length of the grating lines varies according to a non-linear function.
13. 13 . The structure of claim 12 wherein the non-linear function is a quadratic function.
14. 14 . The structure of claim 1 wherein the multimode interference coupler includes a second input waveguide core, a second output waveguide core, and the grating lines of the grating are disposed between the second input waveguide core and the second output waveguide core.
15. 15 . The structure of claim 14 further comprising: an optical coupler; a first arm routed from the first output waveguide core to the optical coupler; and a second arm routed from the second output waveguide core to the optical coupler.
16. 16 . The structure of claim 15 further comprising: a ring resonator disposed adjacent to the first arm.
17. 17 . The structure of claim 1 further comprising: a first dielectric layer over the multimode interference coupler and the first resistive heating element; and a contact in the first dielectric layer, the contact coupled to the first resistive heating element.
18. 18 . The structure of claim 17 further comprising: a semiconductor substrate; and a second dielectric layer on the semiconductor substrate, wherein the multimode interference coupler and the first resistive heating element overlie the second dielectric layer.
19. 19 . The structure of claim 1 wherein the first resistive heating element comprises a strip including a semiconductor material and a silicide layer on the strip.
20. 20 . A method of forming a structure for a power splitter, the method comprising: forming a multimode interference coupler including a grating having a plurality of grating lines, an input waveguide core, and an output waveguide core, wherein the grating lines are disposed between the input waveguide core and the output waveguide core; and forming a resistive heating element adjacent to the grating lines, wherein the grating lines have a first duty cycle that decreases with a first variable rate from the input waveguide core toward a center of the grating, and the grating lines have a second duty cycle that increases with a second variable rate from the center of the grating toward the output waveguide core.

Description

BACKGROUND The disclosure relates to photonics chips and, more specifically, to structures for a power splitter that include a multimode interference coupler and methods of forming such structures. Photonics chips are used in many applications and systems including, but not limited to, data communication systems and data computation systems. A photonics chip includes a photonic integrated circuit comprised of photonic components, such as modulators, polarizers, and optical couplers, that are used to manipulate light received from a light source, such as a laser or an optical fiber. A power splitter is a photonic component that is commonly used in photonics chips to divide optical power between multiple waveguides with a desired coupling ratio. Conventional power splitters have a fixed power splitting ratio, which prevents designers from compensating for fabrication imperfections and dynamically balancing the interferometer for high-extinction and high signal-to-noise ratio performance. Improved structures for a power splitter that include a multimode interference coupler and methods of forming such structures are needed. SUMMARY In an embodiment of the invention, a structure for a power splitter is provided. The structure comprises a multimode interference coupler including a grating having a plurality of grating lines, an input waveguide core, and an output waveguide core. The grating lines are disposed between the input waveguide core and the output waveguide core. The structure further comprises a resistive heating element adjacent to the grating lines. In an embodiment of the invention, a method of forming a structure for a power splitter is provided. The method comprises forming a multimode interference coupler including a grating having a plurality of grating lines, an input waveguide core, and an output waveguide core. The grating lines are disposed between the input waveguide core and the output waveguide core. The method further comprises forming a resistive heating element adjacent to the grating lines. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments of the invention and, together with a general description of the invention given above and the detailed description of the embodiments given below, serve to explain the embodiments of the invention. In the drawings, like reference numerals refer to like features in the various views. FIG. 1 is a top view of a structure at an initial fabrication stage of a processing method in accordance with embodiments of the invention. FIG. 2 is a cross-sectional view taken generally along line 2-2 in FIG. 1. FIG. 2A is a cross-sectional view taken generally along line 2A-2A in FIG. 1. FIG. 2B is a cross-sectional view taken generally along line 2B-2B in FIG. 1. FIG. 3 is a graphical view depicting an exemplary apodized distribution for the gaps between the grating lines in FIG. 1. FIGS. 4, 4A, 4B are cross-sectional views at a fabrication stage subsequent to FIGS. 1, 2, 2A, 2B. FIG. 5 is a top view of a structure in accordance with alternative embodiments of the invention. DETAILED DESCRIPTION With reference to FIGS. 1, 2, 2A, 2B and in accordance with embodiments of the invention, a structure 10 for a power splitter includes a multimode interference coupler 12 that is disposed on, and over, a dielectric layer 14 and a substrate 16. In an embodiment, the dielectric layer 14 may be comprised of a dielectric material, such as silicon dioxide, and the substrate 16 may be comprised of a semiconductor material, such as single-crystal silicon. In an embodiment, the dielectric layer 14 may be a buried oxide layer of a silicon-on-insulator substrate. The multimode interference coupler 12 is separated from the substrate 16 by the dielectric material of the intervening dielectric layer 14. In an alternative embodiment, one or more additional dielectric layers comprised of, for example, silicon dioxide may be disposed between the multimode interference coupler 12 and the upper surface of the dielectric layer 14. In an embodiment, the multimode interference coupler 12 may be comprised of a material having a refractive index that is greater than the refractive index of silicon dioxide. In an embodiment, the multimode interference coupler 12 may be comprised of a semiconductor material, such as single-crystal silicon, amorphous silicon, or polysilicon. In an alternative embodiment, the multimode interference coupler 12 may be comprised of a dielectric material, such as silicon nitride, silicon oxynitride, or aluminum nitride. In alternative embodiments, other materials, such as a III-V compound semiconductor, may be used to form the multimode interference coupler 12. In an embodiment, the multimode interference coupler 12 may be formed by patterning a layer with lithography and etching processes. In an embodiment, an etch mask may be formed with a lithography proces