Abstract: Ball lenses are frequently used in low to mid-cost laser packages where coupling efficiency is not a major concern. As a single element, the low cost, high precision, and high symmetry of ball lenses offer considerable advantages in packaging. When moderately higher coupling efficiencies are necessary, two-lens designs (in which the first lens is spherical) are often used successfully. Since the aberrations scale with lens diameter, the coupling efficiency generally increases as the diameter of the ball lens decreases. However, placement tolerances become more critical as the lens diameter is reduced and can limit the minimum practical ball diameter. A compromise between higher coupling efficiency and workable tolerances is often encountered when the ball lens diameter is on the order of 500 micrometers. As a result, higher coupling packaging schemes often abandon ball lenses in favor of high NA molded aspheric elements which eliminate spherical aberrations altogether. However, high NA molded aspheres are relatively expensive, and since aberrations are only corrected for a small region on axis, the alignment and bonding of these lenses become critical. We analyze the problem of pupil distortion and spherical aberrations produced by ball lenses and propose potentially cost- effective designs for downstream aberration compensation. !10
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