Semiderivative real filter for microoptical elements quality control

The article presents a proposal for a new method of automatic quality control of microlenses arrays, which is based on a semiderivative real filter. The use of the semiderivative filter for examining pure-phase objects involves modifying the spatial frequency. The basis of the proposed setup is a 4f correlator setup with coherent light. The phase object examined is placed in the input plane of the correlator. Next, the light passes through a filter located in the frequency plane, which gives an intensity signal. In the output plane a charge-coupled device (CCD) camera registers the light intensity, the range of which informs the shape of the phase object. The proposed method is shift invariant, so it allows for examination of single elements or a set of micro-optical elements simultaneously. Additionally, the same setup allows for measuring the phase of objects whose thickness is either considerably smaller or much bigger than 2π.