Super-Oscillating Diffractive Optical Spot Generators

The prior discrete Fourier transform (PDFT) is applied to the design of super-oscillating diffractive optical elements with rotational symmetry. Numerical simulations of the filter response are used to demonstrate the potential of the PDFT-based approach, which includes a regularization method for improved numerical and functional stability of the filter design. For coherent monochromatic illumination, the Strehl ratio of spot generators as a function of the spot radius is compared to the theoretical upper bound. It is shown that the performance of the PDFT design varies significantly depending on the aperture function and the encoding as a phase-only diffractive element. Experimental results are in good agreement with simulations and demonstrate the moderate demands to implement super-oscillating diffractive optical elements.