Large elliptical nanostructured gradient-index microlens.

We demonstrate the feasibility of the development of a gradient-index elliptical microlens with a size of 75×125  μm using nanostructured glass technology. The gradient index is obtained by means of a discrete internal structure composed of two glasses with feature sizes much smaller than the wavelength of the incident light. A modified photonic crystal fiber-drawing technique is used for the lens fabrication. The elliptical shape of the lens is obtained by a novel final drawing stage where the spherically symmetric lens preform is drawn into an elliptical form by collapsing two large air holes placed in the preform during assembly. The effective focal lengths of 160 and 260 μm for the orthogonal axes are obtained experimentally for the fabricated lens, and show good agreement with those predicted by the effective medium theory and the full-wave beam propagation simulations.