Giant nonlinear response from plasmonic metasurfaces coupled to intersubband transitions

Structuring optical materials on a nanometer scale can lead to artificial effective media, or metamaterials, with strongly altered optical behavior. Metamaterials can provide a wide range of linear optical properties such as negative refractive index 1,2 , hyperbolic dispersion 3 , or magnetic behavior at optical frequencies 4 . Nonlinear optical properties, however, have only been demonstrated for patterned metallic films 5-10 which suffer from high optical losses 11 . Here we show that second-order nonlinear metamaterials can also be obtained from non-metallic centrosymmetric constituents with inherently low optical absorption.In our proof-of-principle experiments, we have iterated atomic-layer deposition (ALD) of three different constituents, A = Al 2 O 3 , B = TiO 2 and C = HfO 2 . The centrosymmetry of the resulting ABC stack is broken since the ABC and the inverted CBA sequences are not equivalent -a necessary condition for non-zero second-order nonlinearity. To the best of our knowledge, this is the first realization of a bulk nonlinear optical metamaterial.The basic idea of metamaterials is simple, yet powerful: Using ordinary constituents shaped on a sufficiently small spatial scale, effective material properties that go qualitatively beyond those of the ingredients become possible 12,13 . Early examples are stacks of isotropic layers leading to nanolaminates with an effective anisotropic electromagnetic response 14 . Metamaterials may also lead to properties that are typically not present in nature, such as hyperbolic dispersion observed in layered metal-dielectric structures 3 or negative refractive indices which can be exploited to create superlenses 2 .However, while these examples refer to linear optical properties only, nonlinear phenomena are of fundamental technological importance as well. For example, optical nonlinearities are utilized for generating frequencies otherwise hardly accessible 7 , for modulating light at hundreds of GHz 15 , or for creating optical gates 16 . Nonlinear optics additionally enables fundamental components for quantum applications, such as sources of entangled photons by spontaneous down-conversion 17 .Second-order nonlinear optical crystals, such as potassium dihydrogen phosphate (KDP), lithium niobate (LiNbO 3 ) or superlattices grown by molecular-beam epitaxy (MBE) 18 are readily available, but these materials are difficult to incorporate in most photonic platforms. Nonlinear optical metamaterials are therefore interesting not only for answering general physical questions, but also because they may offer a method of incorporating second-order nonlinear materials on photonic platforms.Current research on nonlinear optical metamaterials has shown interesting results already such as high-harmonic generation 9 or giant surface nonlinearities 5 . However, most results available so far report on enhancements of pre-existing nonlinearities which originate at metal-dielectric interfaces 5,[8][9][10]19 . Furthermore, nonlinear metamaterials available so far consist of met...

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confidence: 99%

“…Current research on nonlinear optical metamaterials has shown interesting results already such as high-harmonic generation 9 or giant surface nonlinearities 5 . However, most results available so far report on enhancements of pre-existing nonlinearities which originate at metal-dielectric interfaces 5,[8][9][10]19 .…”

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confidence: 99%

Second-order nonlinear optical metamaterials: ABC-type nanolaminates

Alloatti

Kieninger

Froelich

et al. 2015

“…However, harmonic generation using the sub-wavelength structures reported thus far relies on field enhancements associated with localized surface plasmon resonances or collective resonances and requires exquisite fabrication techniques 1,[4][5][6][7] .…”

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confidence: 99%

Enhanced third harmonic generation from the epsilon-near-zero modes of ultrathin films

Luk

Ceglia

Liu

et al. 2015

152

118

We experimentally demonstrate efficient third harmonic generation from an indium tin oxide (ITO) nanofilm (λ/42 thick) on a glass substrate for a pump wavelength of 1.4 µm.A conversion efficiency of 3.3x10 -6 is achieved by exploiting the field enhancement properties of the epsilon-near-zero (ENZ) mode with an enhancement factor of 200. This nanoscale frequency conversion method is applicable to other plasmonic materials and reststrahlen materials in proximity of the longitudinal optical phonon frequencies.

“…The combination of metasurfaces and ISB transitions has been exploited for the demonstration of the strong coupling regime in the mid and far-IR ranges of the electromagnetic spectrum, [6][7][8] as well as for second harmonic generation, and in photodetectors. [9][10][11] When relying on a planar approach to create polaritonic meta-devices, however, the tuning of the resonator frequency inherently modifies the interaction volume and therefore the number of underlying interacting dipoles. More generally, for an optoelectronic meta-device, one can envisage a well-defined semiconductor spatial region in which an appropriate physical phenomenon takes place (e.g., photoluminescence, detection, and lasing), and which is combined with an external tuning circuit to adjust the resonant frequency.…”

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confidence: 99%

Room temperature strong light-matter coupling in three dimensional terahertz meta-atoms

Paulillo¹,

Manceau²,

et al. 2016

We demonstrate strong light-matter coupling in three dimensional terahertz meta-atoms at room temperature. The intersubband transition of semiconductor quantum wells with a parabolic energy potential is strongly coupled to the confined circuital mode of three-dimensional split-ring metal-semiconductor-metal resonators that have an extreme sub-wavelength volume (λ/10). The frequency of these lumped-element resonators is controlled by the size and shape of the external antenna, while the interaction volume remains constant. This allows the resonance frequency to be swept across the intersubband transition and the anti-crossing characteristic of the strong light-matter coupling regime to be observed. The Rabi splitting, which is twice the Rabi frequency (2ΩRabi), amounts to 20% of the bare transition at room temperature, and it increases to 28% at low-temperature.