Waveguide structure and method for forming the same

An optical attenuating structure, comprising:

• a first protrusion of a substrate extending along a first direction, wherein the first protrusion includes a first portion and a second portion coupled with the first portion;
• and
• a second protrusion of the substrate, disposed opposite to the first protrusion and extending along the first direction,
• wherein a first distance between the first portion and the second protrusion along a second direction orthogonal to the first direction is substantially greater than a second distance between the second portion and the second protrusion along the second direction, and a first height of the first portion along a third direction orthogonal to the first direction and the second direction is substantially less than a second height of the second portion along the third direction.

An optical attenuating structure, comprising:

• a first protrusion and a second protrusion of a substrate, wherein the first protrusion and the second protrusion extend along a first direction;
• and
• a third protrusion of the substrate, disposed between the first protrusion and the second protrusion, contacted with the first protrusion and extending along the first direction,
• wherein the third protrusion includes a first portion and a second portion coupled to the first portion and disposed between the first protrusion and the first portion, a first distance between the first portion and the second protrusion along a second direction orthogonal to the first direction is substantially less than a second distance between the second portion and the second protrusion along the second direction, and a first height of the first portion along a third direction orthogonal to the first direction and the second direction is substantially less than a second height of the second portion along the third direction.