Large scale three-dimensional inverse design of discrete scatterer optics

In recent years, diffractive, discrete scatterer based optics such as metasurfaces have shown considerable promise in the realization of arbitrary optical functions. However, these optical elements are systems large numbers of tunable degrees of freedom that are impractical to tune using forward design methods. In parallel, there has been great progress in using computational inverse design methods to produce high quality nanophotonic elements. We show that this inverse design method is capable of handling the large scale of the three-dimensional electromagnetic scattering problem, and leads to a realistic path towards the computational design and optimization of these discrete scatterer based optics capable of performing arbitrary optical functions in the far field. Then, we present an experimental demonstration of an optical element at 1.55 μm that focuses light into a discrete helical pattern that is designed using an inverse method based on generalized Lorenz-Mie scattering theory. This optical function is realized by specifying a suitable figure of merit that encapsulates the performance of the optical element. The fabrication of these optical elements with such small length scales is done using the Nanoscribe GT two-photon lithography system.

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