Design of low insertion loss, single-mode polymeric waveguides

A method for forming a single-mode optical waveguide on a substrate, the substrate defining a surface, the method comprising the steps of:

• depositing a polymeric buffer layer onto the surface of the substrate, the buffer layer defining a surface and having an index of refraction nb;
• depositing a polymeric undercladding layer onto the surface of the buffer layer, the undercladding layer defining a surface and having an index of refraction nu;
• depositing a pattern of a light-transmissive, polymeric core onto the surface of the undercladding layer such that the undercladding layer has a thickness of from about 10 percent to about 50 percent of a thickness of the core, the core having a top surface and a pair of sidewalls and an index of refraction nc;
• and
• depositing a polymeric overcladding layer onto the top surface core and onto the sidewalls of the core having an index of refraction no;
• wherein the core index of refraction nc is greater than the index of refraction of the overcladding layer no and also greater than an index of refraction of the undercladding layer nu;
• wherein Δn=nc−no, and wherein the difference between nc and the index of refraction of buffer nb is at least about 1.5 times Δn, and wherein the value of Δn produces a single-mode waveguide at optical communication wavelengths.

A method for forming a single-mode optical waveguide on a substrate, the substrate defining a surface, the method comprising the steps of:

• depositing a polymeric buffer layer onto a surface of a substrate, the buffer layer defining a surface and having an index of refraction nb;
• depositing a polymeric undercladding layer onto the surface of the buffer layer, the undercladding layer defining a surface and having an index of refraction nu;
• depositing a photosensitive core layer onto the surface of the undercladding layer such that the undercladding layer has a thickness of from about 10 percent to about 50 percent of a thickness of the core, the photosensitive core layer having an index of refraction nc;
• imagewise exposing the photosensitive core layer to actinic radiation;
• and
• developing the core layer, thereby removing non-image areas of the core layer and not removing image areas of the core layer thus forming a patterned light-transmissive core on the undercladding layer and partially revealing a portion of the undercladding layer, which core has a top surface and a pair of side walls, and
• depositing a polymeric overcladding layer onto the top surface of the core, onto the pair of sidewalls of the core and onto the revealed portions of the undercladding layer;
• wherein the core index of refraction nc is greater than the index of refraction of the overcladding layer no and also greater than the index of refraction of the undercladding layer nu;
• wherein Δn=nc−no, and wherein the difference between nc and the index of refraction of buffer nb is at least about 1.5 times Δn, wherein the value of Δn produces a single-mode waveguide at optical communication wavelengths.