Patent ID: 7020367

Claim:
An optical coupler comprising: a tapered waveguide formed so that a waveguide width of said tapered waveguide is narrower toward an emission end of a light signal than at a predetermined starting position, wherein a difference between a first coupling factor and a second coupling factor is set to be lower than a third value, wherein the first coupling factor is a coupling factor to a waveguide having a same width as said tapered waveguide in a first position in an inherent mode, where said tapered waveguide is cut in said first position, wherein the second coupling factor is a coupling factor to a waveguide having a same width as said tapered waveguide in a second position in an inherent mode, where said tapered waveguide is cut in said second position, wherein, said second position is separated at a predetermined distance from said first position along a direction of said tapered waveguide toward said emission end.