Apparatuses and methods for an optical coupler

An optical coupler, comprising:

• a low confinement (LC) optical waveguide comprising a first LC end, a second LC end opposite the first LC end, and a first portion (FP) of LC optical waveguide comprising a first FP end, a second FP end opposite the first FP end, and a first port that at least one of is at and extends from the first LC end, wherein low confinement optical waveguide means an optical waveguide having a first confinement factor less than 0.25, wherein the first port is configured to receive or emit a first optical signal consisting of a fundamental transverse electrical mode or a fundamental transverse magnetic mode, and wherein the
• first confinement factor=(Neff−Ncladding)/(Ncore1−Ncladding),
• wherein Neff means an effective index of a fundamental mode of an optical signal in a waveguide, Ncladding means an index of refraction of cladding material of the waveguide, and Ncore1 means an index of refraction of core material of the low confinement optical waveguide;
• a first high confinement (HC) optical waveguide comprising a first HC end, a second HC end opposite the first HC end, and a second portion (SP) and a third portion of first HC optical waveguide, wherein the second portion comprises a first SP end, and a second SP end opposite the first SP end, wherein the third portion comprises a first TP end and a second TP end, wherein a high confinement optical waveguide means an optical waveguide having a second confinement factor greater than 0.75, wherein a first distance between the first HC end and a point, closest to the first HC end, on the low confinement optical waveguide is greater than one wavelength of the first optical signal;
• wherein a first tapered distance between the low confinement optical waveguide and a closest point on the first high confinement optical waveguide is adiabatically tapered smaller away from the first HC end so that a second distance between the first portion and a closest point on the second portion is less than the one wavelength of the first optical signal, wherein the first portion is substantially parallel to the second portion so that an optical signal insertion loss between the first and the second portions is less than 0.1 decibels, wherein a first width of the first high confinement optical waveguide is adiabatically tapered narrower from the first HC end through the first SP end, wherein a width of the first SP end is less than Lambda/Ncore, where Lambda is a wavelength of the first optical signal, wherein a width of the second SP end is greater than Lambda/Ncore, wherein the
• second confinement factor=(Neff−Ncladding)/(Ncore2−Ncladding),
• wherein Ncore2 means an index of refraction of core material of a high confinement optical waveguide, and wherein a second tapered distance between the low confinement optical waveguide and a closest point on the first high confinement optical waveguide is adiabatically tapered larger toward the second LC end so that a third distance between the second LC end and a closest point on the first high confinement optical waveguide is greater than the one wavelength of the first optical signal;
• a second high confinement optical waveguide comprising a third HC end, a fourth HC end opposite the third HC end, and a fourth portion (FthP) of second HC optical waveguide comprising a first FthP end, and a second FthP end opposite the first FthP end, wherein the fourth portion is substantially parallel to the third portion so that an optical signal insertion loss between the second and the third portions is less than 0.1 decibels, wherein a second width of the second high confinement optical waveguide is adiabatically tapered wider from the first FthP end through the second FthP end, wherein a width of the first FthP end is less than Lambda/K*Ncore, wherein a width of the second FthP end is greater than Lambda/K*Ncore, and wherein K is a constant greater than one, wherein a fourth distance between the third HC end and a closest point on the first high confinement optical waveguide is greater than one wavelength of the first optical signal;
• wherein a third tapered distance between the second high confinement optical waveguide and a closest point on the first high confinement optical waveguide is adiabatically tapered smaller away from the third HC end so that a fifth distance between the third portion and the fourth portion is less than the one wavelength of the first optical signal, and wherein a fourth tapered distance between the first high confinement optical waveguide and the second high confinement optical waveguide is adiabatically tapered larger toward the second HC end so that a sixth distance between the second HC end and a closest point on the second high confinement optical waveguide is greater than the one wavelength of the first optical signal;
• a substrate, wherein the LC optical waveguide, the first HC optical waveguide, and the second HC optical waveguide are over the substrate;
• and
• wherein the fourth HC end is configured to respectively emit or receive the first optical signal consisting of respectively the fundamental transverse electrical mode or the fundamental transverse magnetic mode;
• wherein the LC optical waveguide, the first HC optical waveguide, and the second HC optical waveguide are planar optical waveguide.