A study of double-variable-curvature microlenses (DVCM) for promoting coupling efficiency between the high-power 980-nm pumping laser diodes and the single-mode fibers has been proposed. In comparison with the previous works on asymmetric fiber microlenses fabricated by the multi-step processes with complicated fabrication, the advantages of the DVCM structure for achieving high coupling are a single-step fabrication, a reproducible process, and a high-yield output. In the fusing procedure, the slight arc fusion was mainly applied for fine polishing merely instead of reshaping for the reason that the fabricated double-variable-curvature fiber endface (DVCFE) was very close to the ideal shape. Hence, the fabrication time was reduced and the yield was promoted due to the withdrawn step of tip elimination. In this study, the geometric center of the fiber was defined through, the cladding diameter and the core diameter, for comparison to measure the offset. The offset measured by the core diameter was more accurate and coincidence with the coupling efficiency in the experiment. In the fabricated 45 DVCMs, to achieve the average coupling efficiencies higher than 84%, the offsets were ought to be controlled in merely less than 0.6£gm with the curvature radii in the minor axis ranged from 2.4 to 2.9£gm (with tolerance of 0.5£gm). Alternatively, the offsets were ought to be controlled in less than 0.3£gm though the curvature radii in the minor axis ranged from 2.4 to 3.7£gm (with larger tolerance of 1.3£gm). However, it was more difficult to control over the offsets than the curvature radii in the minor axis while fabricating the DVCMs. In conclusion, to achieve higher yield, it was relatively practical to control the offsets of fiber microlenses to be less than 0.6£gm with 2.4 to 2.9£gm curvature radius. As a result, the coupling efficiencies were all higher than 80%.

A study of double-variable-curvature microlenses (DVCM) for promoting coupling efficiency between the high-power 980-nm laser diodes and the single-mode fibers has been proposed. The purpose of the fiber microlens fabrication was to make the mode field match between the laser beam and the fiber as the beam propagating through the fiber microlens. To make the mode match, the shapes of the fiber microlens demanded nothing else but the offset and the curvature radii in minor and major axes. The double-variable-curvature fiber endface (DVCFE) was manufactured through a single-step fully automation grinding process and had less average offset of 0.3£gm, consequently. The radii of curvature in minor and major axis were controlled as an average of 1.2£gm and 33.6£gm, respectively. In the fusing procedure, the slight arc fusion was mainly applied for fine polishing merely instead of reshaping for the reason that the fabricated DVCFE was very close to the ideal shape. Hence, the fabrication time was reduced and the yield was promoted due to the withdrawn step of tip elimination. Furthermore, while the fusion parameters were set to be: fusing distance: 10£gm, arc intensity: 3bits, and fusing time: 200ms in the slight fusion process, the offset was reduced to 0.2£gm due to the shape constraint and surface tension of the DVCFE. And the radii of curvature increased 1.7£gm to 2.9£gm in the minor axis and increased 4.5£gm to 38.1£gm in the major axis, respectively. Owing to the controls of the fully automated grinding procedure and the omission of the tip elimination, the coupling efficiency and yield were improved. As a result, in the experiment, the average and maximum coupling efficiency of 83% and 88% were demonstrated, respectively. And the coupling efficiencies of the 20 samples were higher than 80%. In other words, the proposed DVCM structure of this study was a high coupling efficiency, a high yield output, and reproducible and fully automated single-step grinding process.