Sajjad Abdollahramezani1 Hossein Taghinejad1 Yashar Kiarashinejad1 Omid Hemmatyar1 Mohammadreza Zandehshahvar1 Ali Eftekhar1 Ali Adibi1

1, Georgia Institute of Technology, Atlanta, Georgia, United States

To spectrally, spatially, and/or even temporally manipulating optical wavefronts in the subwavelengthscale, plasmonic metasurfaces consisting of a planar array of patterned metallic nanostructures havegained extensive attention [1]. However, their low coupling efficiency as well as inherent ohmic lossescoming with significant heat generation hinder many practical on-demand applications. The advent ofall-dielectric metasurfaces, which employ optically induced electric and magnetic Mie resonances ofsubwavelength high-index nanoparticles, expedited the realization of miniaturized CMOS-compatiblemetadevices addressing the challenges associated with plasmonic counterparts [2, 3]. Nevertheless, thefunctionality of the implemented metadevices cannot be tuned postfabrication. To dynamically engineerthe amplitude, phase, polarization, and/or dispersion of light for a wider range of applications, exploit-ing active functional materials is indispensable [4]. Here, we present a non-volatile active platform byhybridizing a high-index metasurface with phase-change alloy Ge2Sb2Te5(GST). The intrinsic high in-dex and drastic optical contrast of GST (upon conversion from amorphous to the crystalline in multiplestates) make multipolar Mie resonances of all-dielectric nanoresonators optically tunable. As a proof-of-concept, we demonstrate a small footprint, multi-wavelength, and multi-level optical modulator capableof modulating the light with high modulation depth in extreme states of GST. We also experimentallyshow how the structure takes advantage of the interplay of electric and magnetic resonance modes, dueto the induced intermediate states of GST, leading to a considerable phase shift of the transmitted lightnecessary for beaming applications. We leverage a new deep learning architecture to effectively de-sign optimized metadevices considering the fabrication imperfections while the underlying physics oflight-matter interactions is explained through a sheer mathematical platform [5, 6]. Our findings furthersubstantiate active dielectric metasurfaces as promising candidates for the development of miniaturizedenergy harvesting modules, optical sensors, phased array antennas, and holograms.

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[4] Abdollahramezani, Sajjad, Hossein Taghinejad, Tianren Fan, Yashar Kiarashinejad, Ali A. Eftekhar,
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architecture.” arXiv preprint arXiv:1809.08907 (2018).
[5] Kiarashinejad, Yashar, Sajjad Abdollahramezani, and Ali Adibi. ”Deep learning approach
based on dimensionality reduction for designing electromagnetic nanostructures.” arXiv preprint
arXiv:1902.03865 (2019).
[6] Kiarashinejad, Yashar, Sajjad Abdollahramezani, Mohammadreza Zandehshahvar, Omid Hem-
matyar, and Ali Adibi. ”Deep Learning Reveals Underlying Physics of Light-matter Interactions in
Nanophotonic Devices.” arXiv preprint arXiv:1905.06889 (2019).