Focusing Characteristics of Convex-Shaped Distributed-Index Microlens

Abstract
We have investigated the structure and performance of novel convex-shaped distributed-index microlenses. The surface curvature of its convex shape and the index distribution formed in the ion exchange process were measured precisely. Based on the measured structural parameters, focusing characteristics were evaluated by the ray tracing simulation. It was confirmed that 93% of its large numerical aperture (∼0.5) is attributed to the convex shape. The focusing characteristics show that laser light is directly focused to a 10 µmφ circular spot with 4 dB coupling loss, which is compatible with single-mode fibers.