Reducing loss at intersection in optical waveguides

An optical waveguide comprising:

• a plurality of linear cores arranged in a plane in a form of a monolayer core, including a combination of cores not parallel to one another in the plane, and made of a material having a refractive index n2;
• a clad surrounding the plurality of cores, arranged to form interfaces in accordance with the relationship with the plurality of cores, and made of a material having a refractive index n3;
• and
• core intersection spaces formed by the plurality of cores intersecting each other and made of the material having the refractive index n2,
• wherein a difference between the refractive indices is set as follows:
• n2 (core)>n3 (clad),
• each of the core intersection spaces is separated from four intersecting cores at four side planes of the core intersection space,
• four gaps each of which has a spacing δ are formed between the four separated cores and the core intersection space, and
• the four separated gaps, each of which has the spacing δ, are filled with the material having the refractive index n3,
• wherein the gap spacing δ is 1 to 6 μm under conditions that the dimensions of the intersection space are H (height)=W1 (width)=W2 (width)=30 to 50 μm and a relative difference in refractive index Δ, calculated by ((n2)2−(n3)2/2(n3)2, =2 to 5%.

An optical waveguide comprising:

• a plurality of linear cores arranged in a plane in a form of a monolayer core, including a combination of cores not parallel to one another in the plane, and made of a material having a refractive index n2;
• a clad surrounding the plurality of cores, arranged to form interfaces in accordance with the relationship with the plurality of cores, and made of a material having a refractive index n3;
• and
• core intersection spaces formed by the plurality of cores intersecting each other and made of the material having the refractive index n2,
• wherein a difference between the refractive indices is set as follows:
• n2 (core)>n3 (clad),
• each of the core intersection spaces is separated from four intersecting cores at four side planes of the core intersection space,
• four gaps each of which has a spacing δ are formed between the four separated cores and the core intersection space, and
• the four separated gaps, each of which has the spacing δ, are filled with the material having the refractive index n3,
• wherein the gap spacing 8 is 2 μm under conditions that the dimensions of the intersection space are H (height)=W1 (width)=W2 (width)=35 μm and a relative difference in refractive index Δ, calculated by ((n2)2−(n3)2)/2(n3)2, =5%.