Implementation of multilens micro-optical systems with large numerical aperture by stacking of microlenses.

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Abstract
In the field of micro-optics there is a demand for objectives with large numerical aperture (NA). One example is optical storage in which a NA greater than 0.5 is required. For planar microlenses the NA is determined by means of the maximal index difference and the degree of exchange and reaches typical values of 0.13-0.2. Thus stacking is needed to build high NA objectives from planar microlenses. An additional benefit of stacking lenses is the possibility to correct for different types of aberrations. We realized two stacked systems: an array of micro-objectives with a NA of 0.45 from three microlens arrays and a confocal sensor head from four microlens arrays and one pinhole array mask.