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Register a new userLight enhancement on thin and ultra-thin high-index dielectric slabs with rectangular nano-pits
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Authors
Jerome Le Perchec
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We closely study the local amplifications of visible light on a thin dielectric slab presenting a sub-wavelength array of small, rectangular, bottom-closed holes. The high-quality Fabry-Perot resonances of eigen modes which vertically oscillate, and their corresponding near-field maps, especially inside the voids, are numerically quantified with RCWA and analytically interpreted through a quasi-exact modal expansion. This last method gives explicit opto-geometrical rules allowing to finely understand the general trends in 1D and 2D. In more advanced examples, we show that multi-cavity and/or slightly thicker two-dimensional gratings may generate anomalously frequency-susceptible surfaces over a broad spectral range. Also, dielectric membranes a few nanometers thick only, can catch light, with tremendous enhancements of the electric field intensity ($>10^6$) that largely extends in the surrounding space.
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Besides purely academic interest, giant field enhancement within subwavelength particles at light scattering of a plane electromagnetic wave is important for numerous applications ranging from telecommunications to medicine and biology. In this paper, we experimentally demonstrate the enhancement of the intensity of the magnetic field in a high-index dielectric cylinder at the proximity of the dipolar Mie resonances by more than two orders of magnitude for both the TE and TM polarizations of the incident wave. We present a complete theoretical explanation of the effect and show that the phenomenon is very general - it should be observed for any high-index particles. The results explain the huge enhancement of nonlinear effects observed recently in optics, suggesting a new landscape for all-dielectric nonlinear nanoscale photonics.
We report the possibility to generate tremendous light-field enhancements within shallow nano-trenches made in a high index dielectric material, because of resonant behaviours reminiscent of what we get with sub-wavelength plasmonic cavities. The high quality factors are explained through a modal analysis and can be tuned with appropriate design rules. The thin dielectric void gratings here simulated could be a relevant alternative to plasmon-based devices for chemical sensing, or could be used as efficient wavelength-selective photo-absorbers by taking weakly absorbing materials.
Nano-optic imagers that modulate light at sub-wavelength scales could unlock unprecedented applications in diverse domains ranging from robotics to medicine. Although metasurface optics offer a path to such ultra-small imagers, existing methods have achieved image quality far worse than bulky refractive alternatives, fundamentally limited by aberrations at large apertures and low f-numbers. In this work, we close this performance gap by presenting the first neural nano-optics. We devise a fully differentiable learning method that learns a metasurface physical structure in conjunction with a novel, neural feature-based image reconstruction algorithm. Experimentally validating the proposed method, we achieve an order of magnitude lower reconstruction error. As such, we present the first high-quality, nano-optic imager that combines the widest field of view for full-color metasurface operation while simultaneously achieving the largest demonstrated 0.5 mm, f/2 aperture.
We report on the observation of metallic behavior in thin films of oxygen-deficient SrTiO$_3$ - down to 9 unit cells - when coherently strained on (001) SrTiO$_3$ or DyScO$_3$-buffered (001) SrTiO$_3$ substrates. These films have carrier concentrations of up to 2$times10^{22}$ cm$^{-3}$ and mobilities of up to 19,000 cm$^2$/V-s at 2 K. There exists a non-conducting layer in our SrTiO$_{3-delta}$ films that is larger in films with lower carrier concentrations. This non-conducting layer can be attributed to a surface depletion layer due to a Fermi level pinning potential. The depletion width, transport, and structural properties are not greatly affected by the insertion of a DyScO$_3$ buffer between the SrTiO$_3$ film and SrTiO$_3$ substrate.
Waveguide characterization of dielectric materials is a convenient and broadband approach for measuring dielectric constant. In conventional microwave measurements, material samples are usually mechanically shaped to fit the waveguide opening and measured in closed waveguides. This method is not practical for millimeter-wave and sub-millimeter-wave measurements where the waveguide openings become tiny, and it is rather difficult to shape the sample to exactly the same dimensions as the waveguide cross-section. In this paper, we present a method that allows one to measure arbitrarily shaped dielectric slabs that extend outside waveguides. In this method, the measured sample is placed between two waveguide flanges, creating a discontinuity. The measurement system is characterized as an equivalent Pi-circuit, and the circuit elements of the Pi-circuit are extracted from the scattering parameters. We have found that the equivalent shunt impedance of the measured sample is only determined by the material permittivity and is rather insensitive to the sample shape, position, sizes, and other structural details of the discontinuity. This feature can be leveraged for accurate measurements of permittivity. The proposed method is very useful for measuring the permittivity of medium-loss and high-loss dielectrics from microwave to sub-terahertz frequencies.
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