Patent ID: 8208772
Filing Date: 2012-06-26
Classification: G02B

Abstract:
1. A directional coupler for coupling a mixed light signal including first light with a wavelength of 1.31 micrometers and second light with a wavelength of 1.49 micrometers without polarization dependence, the directional coupler comprising: a clad; and a first optical waveguide made of monocrystalline silicon embedded in the clad, for receiving input of the mixed light signal, the first optical waveguide having a first central axis along which the mixed light signal propagates; and a second optical waveguide made of monocrystalline silicon embedded in the clad at a distance from the first optical waveguide permitting optical coupling of the second light from the first optical waveguide into the second optical waveguide, the first optical waveguide having a second central axis along which the second light propagates, the first and second central axes being mutually parallel; wherein the clad has a refractive index n with a value in a first range from 1.46 to 2.0; the first and second central axes are mutually separated by a distance G, the distance G having a value in a second range from 0.6 micrometers to 0.9 micrometers; and in a first plane orthogonal to the first and second central axes, the first and second optical waveguides have square cross sectional shapes, the square shapes having sides of a length s with a value in a third range from 0.21 micrometers to 0.35 micrometers, the value of the length s being determined from the distance G and the refractive index n.