T1.4 Ultrathin Metasurfaces for the Visible Light Based on Dielectric Resonators
Haogang Cai (Argonne National Laboratory)
Metasurface-based optical elements enable abrupt wavefront engineering by locally controlling the properties (amplitude, phase, etc.) of the incident illumination. They hold great potential to promote a new generation of wearable devices and thin optical systems for imaging and sensing. To date, most of the existing metasurface designs rely on high-aspect-ratio nanostructures, with a thickness close to or even higher than the wavelength. There has been an increasing demand to reduce the metasurface thickness and nanostructure aspect-ratio, in order to facilitate the fabrication compatibility and integration with electronics and dynamic tunable platforms.
In this talk, I will present ultrathin (~ 1/5 of the wavelength) transmissive metalenses for the visible light, using two different approaches of either amplitude or phase modulation. For amplitude modulation, we developed a digital transmission coding scheme that allows manipulation of multiple wavelengths without increasing the thickness or complexity of the structural elements. Phase modulation is necessary in order to improve the optical efficiency. But the design is more challenging, because ultrathin nanoresonators are electromagnetically coupled with each other, compared with high-aspect-ratio nanostructures with wave-guiding confinement. To solve this problem, we developed an inverse design strategy using evolutionary optimization. We employed genetic algorithms interfaced with Finite-Difference Time-Domain solvers, which mimic natural selection in order to determine the optimal arrangement of nanoresonators to achieve the desired target optical functions. The inverse designs significantly improved the focusing efficiency, approximately double of the conventional designs by library search, which was demonstrated experimentally.
Event Timeslots (1)
SYMPOSIUM T1 – MATERIALS FOR OPTOELECTRONICS
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Haogang Cai
Location: Technological Institute LR4