Managing evanescent optical coupling in photonic integrated circuits
A first waveguide core structure (WCS) is configured to confine an optical wave (OW) at a first wavelength to a first mode and a second wavelength to a second mode, each over a coupling region (CR). A second WCS is configured to confine an OW at the first wavelength to a third mode and the second wavelength to a fourth mode, each over the CR. The CR comprises a structure in which portions of the first and second WCS are in proximity over a coupling distance and provides a first coupling between the first and third mode, at a first location, that is greater than a second coupling between the second and fourth mode at the first location, and a third coupling between the second and fourth mode, at a second location, that is greater than a fourth coupling between the first and third mode at the second location.
1 . An article of manufacture comprising:
a first waveguide core structure configured to
confine an optical wave at a first wavelength to a first mode over a coupling region, and
confine an optical wave at a second wavelength to a second mode over the coupling region; and
a second waveguide core structure configured to
confine an optical wave at the first wavelength to a third mode over the coupling region, and
confine an optical wave at the second wavelength to a fourth mode over the coupling region;
wherein the coupling region comprises a structure in which a portion of the first waveguide core structure is in proximity to a portion of the second waveguide core structure over a coupling distance and is configured to
provide a first coupling between the first mode and the third mode, at a first location along the coupling distance, that is greater than a second coupling between the second mode and the fourth mode at the first location, and
provide a third coupling between the second mode and the fourth mode, at a second location along the coupling distance different from the first location, that is greater than a fourth coupling between the first mode and the third mode at the second location.
2 . The article of manufacture of claim 1 , wherein the first waveguide core structure comprises a semi-rib waveguide core structure comprising a guiding portion characterized by a thickness that is larger than a thickness of a non-guiding region extending from only one side of the guiding portion of the semi-rib waveguide core structure.
3 . The article of manufacture of claim 2 , wherein the second waveguide core structure comprises a rib waveguide core structure comprising a guiding portion characterized by a thickness that is larger than a thickness of non-guiding regions extending from both sides of the guiding portion of the rib waveguide core structure.
4 . The article of manufacture of claim 1 , wherein the first waveguide core structure is configured to define transverse intensity profiles of the first mode and the second mode that spatially vary along the first waveguide core structure.
5 . The article of manufacture of claim 4 , wherein the second waveguide core structure is configured to define transverse intensity profiles of the third mode and the fourth mode that spatially vary along the second waveguide core structure.
6 . The article of manufacture of claim 1 , wherein the portion of the first waveguide core structure is separated from the portion of the second waveguide core structure by less than five times a mode field diameter of a guided mode of the first or second waveguide core structure.
7 . The article of manufacture of claim 1 , wherein an edge of the portion of the first waveguide core structure is separated from an edge of the portion of the second waveguide core structure by a first distance at the first location and by a second distance larger than the first distance at the second location.
8 . The article of manufacture of claim 7 , wherein the second wavelength is larger than the first wavelength.
9 . The article of manufacture of claim 1 , wherein the first waveguide core structure is characterized by at least one of a width or a thickness that varies along the first waveguide core structure.
10 . The article of manufacture of claim 9 , wherein the second waveguide core structure is characterized by at least one of a width or a thickness that varies along the second waveguide core structure.
11 . The article of manufacture of claim 1 , wherein at least one of a width or a thickness of the first waveguide core structure is not equal to a width or a thickness of the second waveguide core structure, respectively, at the first location.
12 . The article of manufacture of claim 1 , wherein the first waveguide core structure is composed of a first material and the second waveguide core structure is composed of a second material different from the first material.
13 . The article of manufacture of claim 1 , wherein the first waveguide core structure is in contact with a first cladding composed of a first material and the second waveguide core structure is in contact with a second cladding composed of a second material different from the first material.
14 . The article of manufacture of claim 1 , further comprising at least one stress-modifying formation located closer to the first waveguide core structure than to the second waveguide core structure, where the stress-modifying formation modifies a stress within a portion of a cladding in contact with the first waveguide core structure.
15 . The article of manufacture of claim 14 , where the modified stress within the portion of the cladding modifies an index of refraction associated with the cladding.
16 . A method comprising:
forming a first waveguide core structure configured to
confine an optical wave at a first wavelength to a first mode over a coupling region, and
confine an optical wave at a second wavelength to a second mode over the coupling region; and
forming a second waveguide core structure configured to
confine an optical wave at the first wavelength to a third mode over the coupling region, and
confine an optical wave at the second wavelength to a fourth mode over the coupling region;
wherein the coupling region comprises a structure in which a portion of the first waveguide core structure is in proximity to a portion of the second waveguide core structure over a coupling distance and is configured to
provide a first coupling between the first mode and the third mode, at a first location along the coupling distance, that is greater than a second coupling between the second mode and the fourth mode at the first location, and
provide a third coupling between the second mode and the fourth mode, at a second location along the coupling distance different from the first location, that is greater than a fourth coupling between the first mode and the third mode at the second location.