Optical multiplexer and manufacturing method for the same

1. An optical multiplexer comprising:

a first optical waveguide;

a second optical waveguide; and

at least one multiplexing unit, wherein

the first optical waveguide has a first mode coupling region and the second optical waveguide has a second mode coupling region, and the first mode coupling region and the second mode coupling region have a predetermined length and are proximate to each other with a gap having a predetermined width in between,

the first and second optical waveguides in the first and second mode coupling regions form the multiplexing unit,

light transfers between the first and second optical waveguides in the first and second mode coupling regions in the multiplexing unit,

first light in the first optical waveguide in the first mode coupling region and second light in the first optical waveguide in the first coupling region or the second optical waveguide in the second mode coupling region are multiplexed to one of the first and second optical waveguides in the first and second mode coupling regions in the multiplexing unit,

the first light and the second light have different wavelengths, and

a core cross-section of the first and second optical waveguides at least in the first and second mode coupling regions in the first and second optical waveguides has a top base and a bottom base having different lengths, and ratio of a length of the top base to a length of the bottom base is 0.95 or less.

2. The optical multiplexer according to claim 1 , wherein a shape of the core cross-section of the first and second optical waveguides at least in the first and second mode coupling regions is any of a trapezoid, a pseudo-trapezoid, a shape where a plurality of rectangles having different widths are layered each other and a shape where the gap between adjacent cores is partially filled in with a core material.

3. The optical multiplexer according to claim 2 , wherein the pseudo-trapezoid is either a trapezoid where any of a lateral side, the top base, and the bottom base is a curve or a trapezoid where the inner angle between the top base and a lateral side or the outer angle between a lateral side and the bottom base is rounded.

4. The optical multiplexer according to claim 1 , wherein

the first optical waveguide and the second optical waveguide are waveguides where light propagation in a basic mode is the largest component of light propagation, and

a multimode optical waveguide is arranged between the first optical waveguide in the first mode coupling region and the second optical waveguide in the second mode coupling region.

5. The optical multiplexer according to claim 1 , wherein

a second wavelength of the second light is shorter than a first wavelength of the first light, and

the first light transfers from the first optical waveguide in the first mode coupling region to the second optical waveguide in the second mode coupling region, and the second light propagates straight forward through the second optical waveguide in the second mode coupling region so that the first and second light is multiplexed to the second optical waveguide in the second mode coupling region.

6. The optical multiplexer according to claim 1 , wherein

a second wavelength of the second light is shorter than a first wavelength of the first light, and

the first light transfers from the first optical waveguide in the first mode coupling region to the second optical waveguide in the second mode coupling region and after that, finally returns to the first optical waveguide in the first mode coupling region, and the second light transfers from the second optical waveguide in the second mode coupling region to the first optical waveguide in the first mode coupling region so that the first and second light is multiplexed to the first optical waveguide in the first mode coupling region.

7. The optical multiplexer according to claim 1 , wherein

a second wavelength of the second light is shorter than a first wavelength of the first light, and

the first light transfers from the first optical waveguide in the first mode coupling region to the second optical waveguide in the second mode coupling region, and after that, returns to the first optical waveguide in the first mode coupling region, and then finally transfers to the second optical waveguide in the second mode coupling region, and the second light transfers from the first optical waveguide in the first mode coupling region to the second optical waveguide in the second mode coupling region so that the first and second light is multiplexed to the second optical waveguide in the second mode coupling region.

8. The optical multiplexer according to claim 1 , wherein

the first light is red and the second light is blue.

9. A method for manufacturing the optical multiplexer according to claim 1 , comprising the step of patterning a core layer including a core material into the first optical waveguide and the second optical waveguide.

10. An optical multiplexer, comprising:

a first optical waveguide having a first mode coupling region;

a second optical waveguide having a second mode coupling region that is adjacent to the first optical waveguide;

a third optical waveguide having a third mode coupling region that is adjacent to the second optical waveguide on the opposite side from the first optical waveguide; and

a fourth optical waveguide having a fourth mode coupling region that is adjacent to the first optical waveguide on the opposite side from the second optical waveguide, wherein

the third mode coupling region and the second mode coupling region are arranged to be proximate to each other with a first gap width in between over a first length so as to form a first multiplexing unit,

the second mode coupling region and the first mode coupling region are arranged be proximate to each other with a second gap width in between over a second length so as to form a second multiplexing unit,

the first mode coupling region and the fourth mode coupling region are arranged to be proximate to each other with a third gap width in between over a third length so as to form a third multiplexing unit,

first light having a first wavelength is entered into the first or fourth optical waveguide,

second light having a second wavelength shorter than the first wavelength is entered into the second optical waveguide,

third light having a third wavelength shorter than the first wavelength and different from the second wavelength is entered into the third optical waveguide,

the first through third light is multiplexed to the second mode coupling region in the second optical waveguide or to the third mode coupling region in the third optical waveguide so as to be emitted from an optical waveguide that is connected to the second or the third mode coupling region, and

the first through third multiplexing units are arranged to overlap each other in a light propagating direction from the entrance side to the emission side of the first through third light.

11. The optical multiplexer according to claim 10 , wherein

the first and third gap widths are approximately same, and

the second gap width is greater than the first and third gap widths.

12. An optical multiplexer, comprising:

a first optical waveguide having a first mode coupling region;

a second optical waveguide having a second mode coupling region that is adjacent to the first optical waveguide;

a third optical waveguide having a third mode coupling region that is adjacent to the second optical waveguide on the opposite side from the first optical waveguide; and

a fourth optical waveguide having a fourth mode coupling region that is adjacent to the first optical waveguide on the opposite side from the second optical waveguide, wherein

the third mode coupling region and the second mode coupling region are arranged to be proximate to each other with a first gap width in between over a first length so as to form a first multiplexing unit,

the second mode coupling region and the first mode coupling region are arranged be proximate to each other with a second gap width in between over a second length so as to form a second multiplexing unit,

the first mode coupling region and the fourth mode coupling region are arranged to be proximate to each other with a third gap width in between over a third length so as to form a third multiplexing unit,

first light having a first wavelength is entered into the first or fourth optical waveguide,

second light having a second wavelength shorter than the first wavelength is entered into the second optical waveguide,

third light having a third wavelength shorter than the first wavelength and different from the second wavelength is entered into the third optical waveguide,

the first through third light is multiplexed to the second mode coupling region in the second optical waveguide or to the third mode coupling region in the third optical waveguide so as to be emitted from an optical waveguide that is connected to the second or the third mode coupling region, and

the first through third multiplexing units are arranged to overlap each other in a light propagating direction from the entrance side to the emission side of the first through third light,

wherein heights, widths, and gap widths of the first through fourth optical waveguides are symmetric between left and right in a cross-sectional diagram in a location where the first through third multiplexing units overlap in a direction perpendicular to the light propagating direction.