An optical subassembly for low-feedback coupling of light from a light source into an optical waveguide such as an optical fiber is described. The optical subassembly has an aspherical lens with surface sag having a rotationally symmetrical sag component without having a cone sag component, and a rotationally asymmetrical helical component for reducing coupling of light reflected from the optical fiber tip back into the laser aperture by causing a significant portion of the reflected light to encircle the laser aperture. The lens shape and the height of the helix are selected so that tight focusing onto the fiber tip is preserved, while the optical feedback is reduced.