Toraldo filters enable super-resolution imaging

Toraldo filters are named after Giuliano Toraldo di Francia, an Italian scientist who investigated pupil-plane filtering as a way to increase the resolution of an imaging system beyond the diffraction limit by using a set of concentric amplitude and/or phase filters at the pupil of an image-forming system. Half a century later, researchers at the University of Calcutta (Calcutta, India) have developed evolutionary algorithms to optimize the design for simple, low-cost Toraldo filters that achieve super-resolution imaging.

By using evolutionary algorithms based on genetics including binary coding of design variables and evolution of a population through selection, crossover, and mutation, the point-spread function of an image can be altered through an optimized phase-filter design. The optimization algorithms were applied to the fabrication of multizone, equal-area phase filters (four-zone and eight-zone) to provide both axial and transverse super-resolution; that is, the filters narrow down the axial and transverse spread, respectively, of the diffraction spot. Further experiments on unequal area phase filters are in progress. Contact Lakshminarayan Hazra at [email protected].