Fabrication and testing of planar microlens arrays by ion exchange technique in glass

The mask structured ion exchange in glass (MSI) is a powerful tool for realizing general planar phase distributions and in particular custom designed planar GRIN micro lenses with diffraction limited performance and high fill factor. For lens characterization the numerical aperture is a key parameter. However the classical geometrical definition of the N.A. disregards aberrations. Here we suggest an addition to this classical definition, which is based on diffraction limited performance. For a testing of micro lens arrays, global process parameters are assessed by interferometric measurements of a subset of the lenses. Local process variations typically result in small non-symmetric aberrations. These aberrations mainly lead to a lateral shift of the focus. Thus, for rapid quality control of micro lens arrays we analyze all focal positions in parallel. From the lateral deviations of the focal positions a quality criterion for each individual micro lens can be derived.