Power splitters including a tunable multimode interference coupler
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.
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 . The structure of claim 1 further comprising:
a second resistive heating element adjacent to the grating lines.
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 . 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 . 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 . The structure of claim 5 wherein the grating lines have a width that varies with position along the longitudinal axis.
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 . 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 . The structure of claim 8 wherein the length of the grating lines varies according to a non-linear function.
10 . The structure of claim 9 wherein the non-linear function is a quadratic function.
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 . The structure of claim 11 wherein the length of the grating lines varies according to a non-linear function.
13 . The structure of claim 12 wherein the non-linear function is a quadratic function.
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 . 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 . The structure of claim 15 further comprising:
a ring resonator disposed adjacent to the first arm.
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 . 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 . 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 . 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.