J. Sebastian Gomez-Diaz

Gradient Nonlinear Pancharatnam-Berry Metasurfaces

We apply the Pancharatnam-Berry phase approach to plasmonic metasurfaces loaded by highly nonlinear multiquantum-well substrates, establishing a platform to control the nonlinear wave front at will based on giant localized nonlinear effects. We apply this approach to design flat nonlinear metasurfaces for efficient second-harmonic radiation, including beam steering, focusing, and polarization manipulation. Our findings open a new direction for nonlinear optics, in which phase matching issues are relaxed, and an unprecedented level of local wave front control is achieved over thin devices with giant nonlinear responses.

Ultrathin gradient nonlinear metasurface with a giant nonlinear response

Gradient metasurfaces have recently been demonstrated to provide control of the phase of scattered fields over subwavelength scales, enabling a broad range of linear optical components in a flat, ultrathin, integrable platform. Additionally, the development of nonlinearmetasurfaces has disrupted conventional nonlinear optical device design by relaxing phase matching constraints, reducing size and dimensionality, and providing record values of localized nonlinear responses. However, extending the “flat optics” paradigm to the nonlinear case faces important challenges, since we are required to simultaneously achieve efficient frequency conversion and sub-diffractive phase control. Here, we experimentally demonstrate continuous phase control of the giant nonlinear second harmonic optical response from metasurfaces tied to intersubband transitions in semiconductor multi-quantum wells, establishing an exciting path toward realizing the vision of flat, nonlinear optics.

Flat nonlinear optics: metasurfaces for efficient frequency mixing

Gradient metasurfaces, or ultrathin optical components with engineered transverse impedance gradients along the surface, are able to locally control the phase and amplitude of the scattered fields over subwavelength scales, enabling a broad range of linear components in a flat, integrable platform1–4. On the contrary, due to the weakness of their nonlinear optical responses, conventional nonlinear optical components are inherently bulky, with stringent requirements associated with phase matching and poor control over the phase and amplitude of the generated beam. Nonlinear metasurfaces have been recently proposed to enable frequency conversion in thin films without phase-matching constraints and subwavelength control of the local nonlinear phase5–8. However, the associated optical nonlinearities are far too small to produce significant nonlinear conversion efficiency and compete with conventional nonlinear components for pump intensities below the materials damage threshold. Here, we report multi-quantum-well based gradient nonlinear metasurfaces with second-order nonlinear susceptibility over 106 pm/V for second harmonic generation at a fundamental pump wavelength of 10 μm, 5-6 orders of magnitude larger than traditional crystals. Further, we demonstrate the efficacy of this approach to designing metasurfaces optimized for frequency conversion over a large range of wavelengths, by reporting multi-quantum-well and metasurface structures optimized for a pump wavelength of 6.7 μm. Finally, we demonstrate how the phase of this nonlinearly generated light can be locally controlled well below the diffraction limit using the Pancharatnam-Berry phase approach5,7,9, opening a new paradigm for ultrathin, flat nonlinear optical components.

Magnetically-biased graphene-based hyperbolic metasurfaces

We explore the unusual electromagnetic response of magnetically-biased densely-packed graphene ribbons. Applying an effective medium approach, we show how the presence of a magnetostatic bias induces resonances on all components of the effective conductivity tensor, significantly enriching the features of the supported surface plasmons polaritons (SPPs). Specifically, we demonstrate magnetically-induced non-resonant topological transitions at terahertz (THz) frequencies, enabling planar canalization without the influence of large dissipative losses, and we predict the presence of weakly-confined transverse electric SPPs in a narrow band below resonance. Our findings may pave the way towards the development of planar, ultra-sensitive sensors, lenses, non-reciprocal components and imaging systems at THz.

Ultrathin nonlinear metasurfaces

We present a novel class of ultrathin metasurfaces operating in a nonlinear regime, simultaneously providing generation efficiencies that are many orders of magnitude larger than in other nonlinear setups, and, at the same time, capable of controlling the local phase of the nonlinear signal with high precision and subwavelength resolution. The key to achieving such outstanding performance is combining a strong local field enhancement and polarization selectivity of plasmonic nano-antennas with extremely high nonlinearity of multi-quantum well semiconductor stacks. In this work, we discuss the operation principles of such metasurfaces and provide experimental and numerical results. We also show how a savvy application of Lorentz reciprocity principle allows for fast and efficient analysis and modeling of such metasurfaces consisting of thousands of elements.

Graphene plasmonics: Theory and experiments

The pioneering theoretical and experimental research in terahertz graphene plasmonics developed by Prof. Julien Perruisseau-Carrier and his group is reviewed. From the experimental point of view, Prof. Perruisseau-Carrier determined the reconfigurable EM properties of graphene in different frequency bands and introduced self-biased graphene-based structures with enhanced performance and unprecedented recon-figuration capabilities. Theoretically, Prof. Perruisseau-Carrier proposed novel miniaturized and reconfigurable plasmonic devices at terahertz, including resonant and leaky-wave antennas, reflectarrays, filters, modulators, non-reciprocal structures, Faraday-rotators, and frequency selective surfaces, forecasting the required technology for developing tunable communication, imaging, biomedical, and sensing systems in the terahertz band.