Design and demonstration of fan-out elements generating an array of subdiffraction spots

We present a design method for diffractive fan-out elements generating an array of subdiffraction spots in a predetermined area using propagating light. A specific constraint is introduced to the Gerchberg-Saxton algorithm to control the dispersion of light energy and the phase of spots. In our demonstration, an element generating a 3 × 3 spot array achieves the spot size reduced to 70% comparing to the diffraction limited spot in simulation and about 80% in the experiment. Various layouts of subdiffraction spots can be made with a high signal to noise ratio using our design method. The relationship between the spot size and the power efficiency is also shown based on the simulation.