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The common way to manipulate light consists in using classical optical elements such as lenses and mirrors. Since few years, a new way to manipulate light with two dimensional optical components (metasurfaces) have been exploited to control light propagation using local phase discontinuities. Abrupt modifications of the fields across an interface can be engineered by depositing an array of sub-wavelength resonators specifically tailored to address local amplitude, phase and polarization changes [1]. Metasurfaces have been implemented to obtain various sorts of optical functionalities, ranging from the basic control of the transmission and reflection of light [1-2], to the control of the radiation patterns for comprehensive wavefront engineering and holography[3].
In this work, we will present our recent results on metasurfaces able to deflect and/or focus light at visible wavelength using an ensemble of spatially varying nano-ridges and nanopillars made of GaN semiconductor materials. The objective of our studies is to achieve controllable GaN nano-optoelectronic components. Classical nanofabrication techniques for realizing metasurfaces, such as reactive ion etching, considerably alter the electronic performance of nanostructures by the creation of surface edge states, typically sources for defects that greatly degrade device performances. The important penetration of plasma is critical for devices that become smaller that the electron elastic mean free path, modifying the transport and the luminescence of nanostructured materials. To circumvent this problem, we propose a new metasurface process based on selective area sublimation [4]. We will also discuss recent result on the integration of 2D metasurfaces on bottom emitting VCSELs for in-situ direct laser wavefront shaping.
In the second part of this discussion, we will introduce the concept of conformal boundary optics and present our latest numerical tool to model and design free form optical components [6,7]. Illustrative examples such as absorbing metasurface, beam refractor, and curved lens have been explored, showing consistent results in agreement with fully theoretical predictions. This method turns into a powerful tool for accurately designing and predicting optical functionalities of conformal metasurfaces for new lightweight, small scaled, flexible and wearable optical devices.
References
[1] P. Genevet, F Capasso, F Aieta, M Khorasaninejad, R Devlin., “Recent advances in planar optics: from plasmonic to dielectric metasurfaces” Optica 4 (1), 139-152 (2017).
[2] N. Yu, P. Genevet, M. Kats, J.P. Tetienne, F. Capasso, Z. Gaburro, Science 334,333 (2011)
[3] P. Genevet and F. Capasso, “Reports of Progress in Physics”, 78, 024401 (2015)
[4] Damilano, B., Vézian, S., Brault, J., Alloing, B., & Massies, J. (2016). Selective area sublimation: a simple top-down route for GaN-based nanowire fabrication. Nano letters, 16(3), 1863-1868.
[5] Han, J. T. H., Wong, L.J., Molardi C. and Genevet P., “Controlling Electromagnetic Fields at Boundaries of Arbitrary Geometries”, PRA 94, 023820 (2016).
[6] K. Achouri, M. A. Salem, and C. Caloz, IEEE Transactions on Antennas and Propagation, vol. 63, no. 7, pp. 2977–2991, 2014.
[7] K. Wu, P. Coquet, Q. Wang and P. Genevet, “Free-form conformal Metasurfaces: modeling and design”, Nature Communications (in press, 2018)
Acknowledgments: PG acknowledges support from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement no. 639109).
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