System and method for low loss waveguide bends
View Patent ↗In one embodiment, there is disclosed a waveguide medium using total internal reflection to create a relatively sharp (approximately 90°) bend for optical signals traversing the waveguide. A discontinuity of the medium (such as air) is used to create a turning mirror within the waveguide path. By curving the discontinuity, the entire input optical signal is focused into the output portion of the waveguide, thereby compensating for the diffraction loss of the optical signal at the bend. In one embodiment in order to facilitate proper alignment of the masks certain portions of the waveguide on a first mask are extended (widened) beyond their optimum physical size. This extended portion is then used to position an edge of a second mask, such that optical signal scatter caused by the extended portions of the waveguide are compensated for by adjusting the curvature.
1. An optical transmission medium for communicating optical signals along an optical path, comprising:
a first solid-core waveguide portion defining a first portion of the optical path, the first solid-core waveguide portion formed in a solid material having a first end and a second end, the first end of the first solid-core waveguide portion having a first wing portion co-formed with a remaining portion of the first solid-core waveguide portion; and
a second solid-core waveguide portion defining a second portion of the optical path, the second solid-core waveguide portion co-formed in the solid material with the first solid-core waveguide portion and aligned at an angle of substantially 90 degrees to the first solid-core waveguide portion, the second solid-core waveguide portion having a first end and a second end, the first end of the second solid-core waveguide portion having a second wing portion co-formed with a remaining portion of the second solid-core waveguide portion, the first end of the first solid-core waveguide portion meeting the first end of the second solid-core waveguide portion at a junction region defined by a cavity in the solid material, the cavity defining a discontinuity between the first solid-core waveguide portion and air in the cavity, the discontinuity having a first end, a second end, and a radius of curvature, the discontinuity forming a total internal reflection interface between the first end of the first solid-core waveguide portion and the first end of the second solid-core waveguide portion, the total internal reflection interface causing a substantial portion of the optical signals communicated along the optical path to traverse a substantially 90-degree bend between the first solid-core waveguide portion and the second solid-core waveguide portion, the first wing portion extending along the first end of the discontinuity in alignment with the discontinuity, the second wing portion extending along the second end of the discontinuity in alignment with the discontinuity.
2. The optical transmission medium of claim 1 wherein a width of said discontinuity is sufficient to capture a substantial portion of said optical signals traversing said bend.
3. The optical transmission medium of claim 1 wherein said radius of curvature is established to compensate for diffraction of the optical signals so as to transmit substantially all of said optical signals around said bend.
4. The optical transmission medium of claim 1 wherein said radius of curvature is between 5 and 1000 micrometers.
5. The optical transmission medium of claim 1 wherein each of the first and second wing portions has a length sufficient to catch an optical mode profile of the optical signals.
6. The optical transmission medium of claim 5 wherein a width each of the first and second wing portions is between one and five times a width of the optical mode profile.
7. The optical transmission medium of claim 5 wherein optical signal scatter caused by said first and second wing portions is compensated for by said radius of curvature.
8. The optical transmission medium of claim 1 wherein each of said first and second solid-core waveguide portions comprises a low index contrast waveguide.
9. The optical transmission medium of claim 8 wherein said low index contrast waveguide is one of: a ridge waveguide or a buried waveguide.
10. The optical transmission medium claimed in claim 1 , wherein the first and second wing portions follow the radius of curvature of the discontinuity.