Optical waveguide sheet, optical transmission module, and manufacturing method for an optical waveguide sheet

An optical transmission module, comprising:

• an optical waveguide sheet including:
• a plurality of reflection surfaces;
• a core that extends in a first direction, wherein
• the core includes a plurality of portions that comprises a maximum diameter portion, a minimum diameter portion, and a taper portion,
• a cross-sectional area of the maximum diameter portion is maximum among the plurality of portions of the core,
• the maximum diameter portion is in a plane parallel to a second direction and a third direction,
• the second direction is orthogonal to the first direction,
• the third direction is orthogonal to the second direction,
• a cross-sectional area of the minimum diameter portion is minimum among the plurality of portions of the core,
• the minimum diameter portion is in the plane parallel to the second direction and the third direction,
• the cross-sectional area, in the plane parallel to the second direction and the third direction, of the minimum diameter portion of the core is in a trapezoidal shape having two parallel sides along the second direction and other two non-parallel sides,
• a width of the taper portion gradually changes in the first direction between the maximum diameter portion and the minimum diameter portion,
• the taper portion is continuous with the maximum diameter portion and the minimum diameter portion,
• the maximum diameter portion and the minimum diameter portion are alternately arranged in the first direction with the taper portion between the maximum diameter portion and the minimum diameter portion,
• a reflection surface of the plurality of reflection surfaces is in the core, and
• light enters the core via the plurality of reflection surfaces from the third direction orthogonal to the first direction;
• a cladding structure around the core;
• and
• a sheet-like base material, wherein
• the sheet-like base material is below the core and the cladding structure, and
• the sheet-like base material comprises a synthetic resin;
• a first optical connector that causes the light to enter the maximum diameter portion of the core via the first optical connector;
• and
• a second optical connector, wherein the light is emitted from the minimum diameter portion of the core via the second optical connector.

A manufacturing method for an optical waveguide sheet, comprising:

• applying a core material onto a sheet member, wherein the sheet member comprises a synthetic resin;
• transferring a shape of a groove to the core material by rotating a cylindrical transfer roll, wherein
• the cylindrical transfer roll comprises a cylindrical surface, and
• the groove is formed while pressing the cylindrical transfer roll against the core material;
• forming a core by curing the core material, wherein the core comprises a plurality of portions that includes a maximum diameter portion, a minimum diameter portion, and
• a taper portion;
• applying a cladding material onto the sheet member and the core;
• and
• forming a cladding structure by curing the cladding material, wherein
• the groove has the shape such that the core extends in a first direction,
• a cross-sectional area of the maximum diameter portion is maximum among the plurality of portions of the core,
• the maximum diameter portion is in a plane parallel to a second direction and a third direction,
• the second direction is orthogonal to the first direction,
• the third direction is orthogonal to the second direction,
• a cross-sectional area of the minimum diameter portion is minimum among the plurality of portions of the core,
• the minimum diameter portion is in the plane parallel to the second direction and the third direction,
• the cross-sectional area, in the plane parallel to the second direction and the third direction, of the minimum diameter portion of the core is in a trapezoidal shape having two parallel sides along the second direction and other two non-parallel sides,
• a width of the taper portion gradually changes in the first direction between the maximum diameter portion and the minimum diameter portion,
• the taper portion is continuous with the maximum diameter portion and the minimum diameter portion,
• the maximum diameter portion and the minimum diameter portion are alternately arranged in the first direction with the taper portion between the maximum diameter portion and the minimum diameter portion,
• a reflection surface is in the core, and
• light enters the core via the reflection surface from the third direction orthogonal to the first direction.