Ball-lens coupling efficiency for laser-diode to single-mode fiber: comparison of independent studies by distinct...

Results of two recent studies representing distinct approaches to optimizing laser-diode to single-mode fiber ball-lens coupling efficiency are compared and revealed to be in close agreement. One method is based on a conventional optical analysis-design program combining geometrical and diffraction methods, merged with calculated coupling efficiency in terms of balanced spherical aberration. The other is based on exact solution of Maxwell's equations for scattering of a beam from a dielectric sphere. The results suggest that optimum coupling efficiency may depend critically on sufficiently fine discretization of the distances of source and fiber from the lens. The studies compared here are synergistic with several other recently reported studies on coupling efficiency, and those studies are appropriately cross referenced. A graphic relationship is developed between coupling efficiency and Strehl ratio as an optical tolerance for the coupling system based on balanced spherical aberration.