LOSS ANALYSIS OF LASER DIODE TO SINGLE-MODE FIBER COUPLERS WITH GLASS SPHERES OR SILICON PLANOCONVEX LENSES

The single-mode laser diode to single-mode fiber coupling efficiency is analyzed for couplers with glass ball lenses and silicon plano-convex lenses, respectively. The contributions of the different origins of loss are given. It is found that in nearly all cases, most of the total loss is determined by the spherical aberration of that lens, which collects the divergent laser diode light (lens 1). This loss is calculated for a variety of glass ball lenses and silicon plano-convex lenses and shown to be dependent on the laser diode spot size (or divergence angle). It is shown that the minimum loss of a coupling configuration is determined with good accuracy by the parameters of lens 1 and a single additional parameter, the effective laser diode spot size (or effective divergence angle, which is simply the sum of the divergence angles at the input and output side of the lens) for the laser diode, and the coupling arrangement. The calculated losses are compared with both our own measurements and with published experimental values. In most cases, theory and measurement agree very well. Differences are discussed. © 1990 IEEE