Optical waveguide directional coupler and method for making same

1. An optical waveguide directional coupler comprising:

a base comprising a planar member and a raised elongated ridge member, the ridge member extending upwardly from the planar member and having a planar upper surface, a material of the ridge member being the same as a material of the planar member; and

an optical waveguide formed in the base and exposed at the upper surface, the optical waveguide extending through the ridge member along a lengthwise direction of the ridge member, distal ends of the optical waveguide exposed at opposite end surfaces of the ridge member, the optical waveguide comprising a first flat side surface, a second flat side surface, a third flat side surface, a fourth flat side surface, and a first flat connection side surface, the first flat side surface adjoining the third flat side surface, the first flat connection side surface interconnected between the second flat side surface and the fourth flat side surface, the first flat side surface being parallel to the second flat side surface, the third flat side surface being parallel to the fourth flat side surface, an included angle θ1 between the first flat side surface and the third flat side surface being an obtuse angle, an included acute angle α1 being formed between a main plane of the first flat connection side surface and a main plane of the second flat side surface, and the included angle θ1 and the included angle α1 satisfying the following formula: α1<(180°−θ1).

2. The optical waveguide directional coupler as claimed in claim 1 , wherein the optical waveguide further comprises a fifth flat side surface, a sixth flat side surface parallel to the fifth flat side surface and a second flat connection side surface, the third flat side surface adjoins the fifth flat side surface, the second flat connection side surface is interconnected between the fourth flat side surface and the sixth flat side surface, an included angle θ3 between the third flat side surface and the fifth flat side surface is an obtuse angle, an included acute angle α3 is formed between a main plane of the second flat connection side surface and a main plane of the fourth flat side surface, and the included angle θ3 and the included angle α3 satisfy the following formula: α3<(180°−θ3).

3. The optical waveguide directional coupler as claimed in claim 2 , wherein the included angle θ3 is equal to the included angle θ1, and the included angle α3 is equal to the included angle α1.

4. The optical waveguide directional coupler as claimed in claim 1 , wherein the shape of the ridge member conforms to the shape of the optical waveguide.

5. The optical waveguide directional coupler as claimed in claim 2 , wherein the ridge member comprises a first sidewall, a second sidewall, a third sidewall, a fourth sidewall, and a first connection sidewall, the first sidewall adjoins the third sidewall, the first connection sidewall is interconnected between the second sidewall and the fourth sidewall, the first sidewall is parallel to the second sidewall and the first flat side surface, the third sidewall is parallel to the fourth sidewall and the third flat side surface, an included angle θ2 between the first sidewall and the third sidewall is an obtuse angle, an included acute angle α2 is formed between a main plane of the first connection sidewall and a main plane of the second sidewall, and the included angle θ2 and the included angle α2 satisfy the following formula: α2<(180°−θ2).

6. The optical waveguide directional coupler as claimed in claim 5 , wherein the included angle θ2 is equal to the included angle θ1, and the included angle α2 is equal to the included angle α1.

7. The optical waveguide directional coupler as claimed in claim 5 , wherein the ridge member further comprises a fifth sidewall, a sixth sidewall and a second connection sidewall, the third sidewall adjoins the fifth sidewall, the second connection sidewall is interconnected between the fourth sidewall and the sixth sidewall, the fifth sidewall is parallel to the fifth flat side surface, the sixth sidewall is parallel to the sixth flat side surface, and the second connection sidewall is parallel to the second flat connection side surface.

8. An optical waveguide directional coupler comprising:

a base comprising a planar member and a raised elongated ridge member, the ridge member extending upwardly from the planar member and having a planar upper surface; and

an optical waveguide formed in the base and exposed at the upper surface, the optical waveguide extending through the ridge member along a lengthwise direction of the ridge member, distal ends of the optical waveguide exposed at opposite end surfaces of the ridge member, the optical waveguide comprising a first flat side surface, a second flat side surface, a third flat side surface, a fourth flat side surface, and a first flat connection side surface, the first flat side surface adjoining the third flat side surface, the first flat connection side surface interconnected between the second flat side surface and the fourth flat side surface, the first flat side surface being parallel to the second flat side surface, the third flat side surface being parallel to the fourth flat side surface, an included angle θ1 between the first flat side surface and the third flat side surface being an obtuse angle, an included acute angle α1 being formed between a main plane of the first flat connection side surface and a main plane of the second flat side surface, and the included angle θ1 and the included angle α1 satisfying the following formula: α1<(180°−θ1), wherein the optical waveguide further comprises a fifth flat side surface, a sixth flat side surface parallel to the fifth flat side surface and a second flat connection side surface, the third flat side surface adjoins the fifth flat side surface, the second flat connection side surface is interconnected between the fourth flat side surface and the sixth flat side surface, an included angle θ3 between the third flat side surface and the fifth flat side surface is an obtuse angle, an included acute angle α3 is formed between a main plane of the second flat connection side surface and a main plane of the fourth flat side surface, and the included angle θ3 and the included angle α3 satisfy the following formula: α3<(180°−θ3).

9. The optical waveguide directional coupler as claimed in claim 8 , wherein the ridge member comprises a first sidewall, a second sidewall, a third sidewall, a fourth sidewall, and a first connection sidewall, the first sidewall adjoins the third sidewall, the first connection sidewall is interconnected between the second sidewall and the fourth sidewall, the first sidewall is parallel to the second sidewall and the first flat side surface, the third sidewall is parallel to the fourth sidewall and the third flat side surface, an included angle θ2 between the first sidewall and the third sidewall is an obtuse angle, an included acute angle α2 is formed between a main plane of the first connection sidewall and a main plane of the second sidewall, and the included angle θ2 and the included angle α2 satisfy the following formula: α2<(180°−θ2).

10. The optical waveguide directional coupler as claimed in claim 9 , wherein the included angle θ2 is equal to the included angle θ1, and the included angle α2 is equal to the included angle α1.

11. The optical waveguide directional coupler as claimed in claim 9 , wherein the ridge member further comprises a fifth sidewall, a sixth sidewall and a second connection sidewall, the third sidewall adjoins the fifth sidewall, the second connection sidewall is interconnected between the fourth sidewall and the sixth sidewall, the fifth sidewall is parallel to the fifth flat side surface, the sixth sidewall is parallel to the sixth flat side surface, and the second connection sidewall is parallel to the second flat connection side surface.

12. The optical waveguide directional coupler as claimed in claim 8 , wherein the included angle θ3 is equal to the included angle θ1, and the included angle α3 is equal to the included angle α1.

13. The optical waveguide directional coupler as claimed in claim 8 , wherein the shape of the ridge member conforms to the shape of the optical waveguide.