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Nonlinear nanophotonics on-chip

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The MPQ Laboratory has set up a fabrication process of Aluminium Gallium Arsenide (AlGaAs) layers on top of a good-quality optical substrate of Aluminium Oxide (AlOx). This technological breakthrough, resulting in an excellent mechanical stability of the AlGaAs-AlOx interface, has enabled us to fabricate the first AlGaAs monolithic optical nanoantennas and enter the very promising and competitive domain of semiconductor nanophotonics, with the first demonstration of second harmonic generation (SHG) in a nanoantenna within an international collaboration.

Non-plasmonic nanophotonics is raising a strong interest, because the optical response of high-permittivity dielectric nanoparticles in a low refractive-index environment shows negligible dissipative losses and strong multipolar magnetic resonances in the visible and near infrared. Whereas some very interesting results have been demonstrated in the silicon-on-insulator platform in the last two years, the monolithic AlGaAs-on-AlOx system provides an ideal choice for nanophotonics thanks to several strong points of AlGaAs with respect to silicon, among which the nonlinearity and a direct gap that is both larger and variable with the aluminium molar fraction. Under the same excitation conditions, the SHG efficiency of MPQ nanoantennas improves the record of metallic nanoantennas by five orders of magnitude.

Figure :
Sketch of the nonlinear nanoemitter

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Monolithic AlGaAs second-harmonic nanoantennas, F. Gili, L. Carletti, A. Locatelli, D. Rocco, M. Finazzi, L. Ghirardini, I. Favero, C. Gomez, A. Lemaître, M. Celebrano, C. De Angelis, and G. Leo, Optics Express 24, 15965 (2016).