Patent ID: 8442365

Claim:
An optical subassembly comprising a light source having an aperture for emitting light, an optical waveguide having an aperture for receiving light, and a lens for coupling light emitted from the light source aperture into the optical waveguide aperture, wherein the lens has a surface having a sag consisting of a superposition of a rotationally symmetrical sag component and a rotationally asymmetrical sag component, wherein in operation, the rotationally asymmetrical sag component results in lessening of coupling of light reflected from the optical waveguide back into the light source aperture, due the light reflected from the optical waveguide forming a donut-shaped spot at the light source, whereby at least a fraction of the reflected light encircles the light source aperture, and wherein the rotationally symmetrical sag component is one of spherical sag component or aspherical sag component not having a cone sag component.