Patent ID: 7664352

Claim:
A spot size converter comprising: a clad disposed on a major surface of a substrate; a first core extending straight through the clad, the first core having a main core region and an optical input-output region, the main core region having a rectilinear solid shape with four sides and an end, the four sides including a first side, a second side parallel to the first side, a third side orthogonal to the first and second sides, and a fourth side parallel to the third side, the optical input-output region extending from the end of the main core region, the optical input-output region having a sloping surface orthogonal to the third and fourth sides of the main core region, the sloping surface extending from the second side of the main core region to an extension of the first side of the main core region, the first core being surrounded by the clad except for the sloping surface of the optical input-output region, the sloping surface being left exposed by the clad; and a second core disposed on the clad and covering the sloping surface of the optical input-output region of the first core; wherein the first core, the second core, and the clad have respective refractive indexes; the refractive index of the first core is at least forty percent greater than the refractive index of the clad; and the refractive index of the second core is greater than the refractive index of the clad and less than the refractive index of the first core.