||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 Hence, the fabrication time was reduced and the yield was promoted due to the withdrawn step of tip elimination.|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 0.6μm with the curvature radii in the minor axis ranged from 2.4 to 2.9μm (with tolerance of 0.5μm). Alternatively, the offsets were ought to be controlled in less than 0.3μm though the curvature radii in the minor axis ranged from 2.4 to 3.7μm (with larger tolerance of 1.3μm). 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 0.6μm with 2.4 to 2.9μm curvature radius. As a result, the coupling efficiencies were all higher than 80%.