Patent ID: 8064741

Claim:
An optical mode converter comprising: a coupling waveguide having at an input end a first effective refractive index, the coupling waveguide comprising a tapered core of a substantially constant refractive index with a substantially square cross section at the input end having a size that tapers down moving away form the input end, the coupling waveguide having a cladding at least partially surrounding the tapered core; and a receiving waveguide having a second effective refractive index at an output end, comprising a core of a substantially constant refractive index greater than the refractive index of the tapered core of the coupling waveguide, and a cladding at least partially surrounding the core, a side surface of the tapered core of the coupling waveguide being optically in contact, in a coupling portion thereof, with the receiving waveguide so as to allow optical coupling between the coupling waveguide and the receiving waveguide, wherein the refractive index of the tapered core of the coupling waveguide is selected so that the first effective refractive index and the second effective refractive index differ from each other in absolute value less than 30% of the difference between the core refractive index and the effective refractive index of the receiving waveguide.