A research team from the Universität Mannheim in Germany has produced micro-objectives with a large numerical aperture by stacking gradient-index microlenses. The results, which were published in the Dec. 1, 1999, issue of Applied Optics, suggest that the technique may bring the corrective advantages of ion-exchanged microlenses to optical storage and confocal microscopy.

The researchers designed the micro-objectives with a ray-trace program they developed. The resolution of the 0.45-NA three-lens stacked objective was tested with a circular 2-µm-linewidth test pattern and a Ronchi grating with 2- to 1-µm linewidths.