Apparatuses and methods for an optical coupler

An optical coupler, comprising:

• a low confinement optical waveguide comprising a first low confinement end, a second low confinement end opposite the first low confinement end, and a first portion (FP) comprising a first FP end, a second FP end opposite the first FP end, and a first port, wherein at least one of the first FP end, the second FP end and the first port is at and extends from the first low confinement end, wherein the low confinement optical waveguide comprises a first core covered by cladding and has a first standardized refractive index 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 standardized refractive index=(Neff1−Ncladding)/(Ncore1−Ncladding),
• wherein Neff1 means an effective index of an optical signal fundamental mode in the low confinement optical waveguide, Ncladding means an index of refraction of the cladding, and Ncore1 means an index of refraction of the first core;
• a first high confinement optical waveguide comprising a first high confinement end, a second high confinement end opposite the first high confinement end, and a second portion (SP) and a third portion (TP), 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 the first high confinement optical waveguide comprises a second core covered by the cladding and has a second standardized refractive index greater than 0.75, wherein a first distance between the first high confinement end and a point, closest to the first high confinement 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 high confinement 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 of the low confinement optical waveguide is substantially parallel to the second portion of the first high confinement optical waveguide 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 high confinement end through the first SP end, wherein a width of the first SP end is less than Lambda/Ncore2, where Lambda is a wavelength of the first optical signal, wherein a width of the second SP end is greater than Lambda/Ncore2, wherein the
• second standardized refractive index=(Neffh−Ncladding)/(Ncore2−Ncladding),
• wherein Neffh means an effective index of an optical signal fundamental mode in each of the first and a second high confinement optical waveguides, wherein Ncore2 means an index of refraction of the second core, 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 low confinement end so that a third distance between the second low confinement end and a closest point on the first high confinement optical waveguide is greater than the one wavelength of the first optical signal;
• the second high confinement optical waveguide comprising a third high confinement end, a fourth high confinement end opposite the third high confinement end, and a fourth portion (FthP) comprising a first FthP end, and a second FthP end opposite the first FthP end, wherein the second high confinement optical waveguide comprises the second core covered by the cladding and has the second standardized refractive index greater than 0.75, wherein the fourth portion of the second high confinement optical waveguide is substantially parallel to the third portion of the first high confinement optical waveguide so that an optical signal insertion loss between the third and the fourth 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 fourth distance between the third high confinement 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 high confinement 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 high confinement end so that a sixth distance between the second high confinement 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 low confinement optical waveguide, the first high confinement optical waveguide, and the second high confinement optical waveguide are over the substrate;
• and
• wherein the fourth high confinement end is configured to emit when the first port is configured to receive, or receive when the first port is configured to emit, the first optical signal;
• wherein the low confinement optical waveguide, the first high confinement optical waveguide, and the second high confinement optical waveguide are planar optical waveguides.