Abstract
We report the simultaneous increase of both nonlinear Kerr coefficient n2 and third-order nonlinear susceptibility χ(3) in aluminum zinc oxide (AZO) attained by pump-probe spectroscopy in a frequency degenerate configuration. Our experiments demonstrate a 6-fold enhancement in the third-order nonlinear susceptibility and over one order of magnitude increase in the nonlinear Kerr coefficient, while also determining two distinct operational wavelengths for optimal modulation of either the real or the imaginary part of the complex refractive index. These results, besides providing a broader spectral characterization of the third-order nonlinearity in AZO thin films, also show the fundamental advantages of performing nonlinear optics via degenerate excitation near the ENZ wavelength.
Highlights
Over the past decade, nanophotonics research has been heavily focusing on developing and advancing material platforms for practical nanophotonic devices that are low-loss, tailorable and can be integrated with existing semiconductor technologies
On the direction of low-loss CMOS compatible technologies and metal-free nanophotonics, the scientific community is moving towards all-dielectric components [1], where dielectric materials replace the metallic inclusions in high refractive index contrast systems [2]
Among the most exploited Transparent Conductive Oxides (TCOs) we find Indium Tin Oxide (ITO), Aluminum Zinc Oxide (AZO), Gallium Zinc Oxide (GZO) and Indium Cadmium Oxide (ICO)
Summary
Nanophotonics research has been heavily focusing on developing and advancing material platforms for practical nanophotonic devices that are low-loss, tailorable and can be integrated with existing semiconductor technologies. For high pump intensity, the optically induced change in the complex refractive index can be fitted to a semi-empirical model accounting for the standard Taylor series expansion of the dielectric polarization density inclusive of higher-order nonlinear susceptibility terms up to χ(7) [12,13,14] These results are of fundamental interest because they might be key to overcome the typical nonlinear trade-off between magnitude and speed which has hampered the development of practical integrated nonlinear devices for decades already. Because of the hybrid nature of TCOs being in the middle between semiconductors and metals, both interband and intraband optical nonlinearities can be efficiently excited [17,18] These nonlinearities can be judiciously combined to increase the material bandwidth up to few THz, perform all-optical three-state logic operations, and attain ultra-fast signal routing [19]. By means of a pump/probe set-up, where the operational wavelength is set within the ENZ material window, we proceeded with the quantitative evaluation of the predicted nonlinear enhancement
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