Michal Eitan

Highly Efficient and Broadband Wide-Angle Holography Using Patch-Dipole Nanoantenna Reflectarrays

We demonstrate wide-angle, broadband, and efficient reflection holography by utilizing coupled dipole-patch nanoantenna cells to impose an arbitrary phase profile on the reflected light. High-fidelity images were projected at angles of 45 and 20° with respect to the impinging light with efficiencies ranging between 40-50% over an optical bandwidth exceeding 180 nm. Excellent agreement with the theoretical predictions was found at a wide spectral range. The demonstration of such reflectarrays opens new avenues toward expanding the limits of large-angle holography.

Quantifying the radiation efficiency of nano antennas

The radiation efficiency of nano antennas is a critical parameter determining their suitability for various applications. To that end, the radiation efficiency of a single antenna is directly quantified using far-field measurements of the reflectance of an array comprising identical nano-antennas. Excellent agreement in terms of resonance frequencies, optical bandwidth, and scattering efficiency is found between the results of experimental measurements and finite element-based numerical analysis of scattering from Au nano-antenna arrays. Extremely high overall radiation efficiencies, exceeding 82%, are obtained. The high efficiency can facilitate the employment of such nano-antennas for applications in imaging, spectroscopy, and solar energy harvesting.

High load sensitivity in wideband infrared dual-Vivaldi nanoantennas.

Dual-Vivaldi nanoantenna (DVA) arrays were designed, fabricated, and optically characterized in the infrared (IR) and visible regimes. The antenna arrays were characterized by measuring the scattered light at IR (1450-1640 nm) and visible (780 nm) spectral ranges. The radiation efficiency and the spectral response of the antennas were found to be in good agreement with numerical simulations. The results presented here demonstrate the extremely wideband nature of the DVAs and the strong impact of load at the antenna terminals on its scattering response. These properties, as well as their many degrees of freedom for design, render the DVAs excellent candidates for optical sensing applications.

Genetically optimized all-dielectric metasurfaces

We present and study theoretically a new design approach for obtaining wide angle, highly efficient, all-dielectric metasurfaces. As a concrete example we focus on optimizing flat beam deflector for both the infra-red and visible spectral regions. Transmission efficiencies of up to 87.2% are obtained theoretically for deflection angle of 65° in visible (580nm) spectrum and up to 82% for deflection angle of 30.5° at telecom wavelength (1550nm). The enhanced efficiencies at wide deflection angles are obtained by genetic optimization of the nano-structures comprising the metasurface. Compared to previously employed design approaches, our approach enhances the transmission efficiency substantially without sacrificing rectangular grid arrangement and facilitates the realization of wide angle flat deflectors and holograms/lenses.

Nano slot-antenna array refractive index sensors: approaching the conventional theoretical limit of the figure of merit

We demonstrate a refractive index (RI) detection technique based on an array of nanometer scale slot-antennas milled in a thin gold layer using a single lithographic step. Our experimental Figures of merit (FOMs) of 140-210 in the telecom wavelength range approach the fundamental limit for standard propagating SPR sensors (~250). The underlying mechanism enabling such high FOMs is the combination of a narrowband resonance of the slot-antennas with degeneracy breaking of Wood’s anomaly under slightly non-perpendicular illumination. In addition, we study the sensitivity of the thickness of the analyte layer. This concept can be easily tuned to any desired wavelength and RI range by modifying the slot dimensions and the array spacing, thus rendering it highly attractive for numerous sensing applications.

Ultra-sensitive refractive index sensor utilizing plasmonic resonance splitting

We demonstrate experimentally an ultra-sensitive RI sensor based on plasmonic slot nano-antenna arrays utilizing a novel resonance splitting phenomenon observed at small incidence angles. Sensitivities exceeding 1000nm/RIU and high FOM exceeding 50 are demonstrated.

Nano-antenna elements for controlling optical phase

We demonstrate the use of nano-antenna unit cells composed of coupled dipole and patch elements over a reflective back plane, which are designed to control the phase of a reflected optical beam. The antennas were studied both numerically and experimentally and allow exact control over the output phase in the range of 00-3600. Several diffractive optical applications are shown numerically and experimentally: Blazed gratings which allow deflection of the output beam to high reflection angles show very high diffraction efficiency, and arbitrary wave shapes such as computer generated holograms can be formed with very high efficiency and large angles relative to the incident beam. The optical conversion efficiency was measured to be above 40% for all applications.

UWB Dual-Vivaldi nano-antenna and load effect on the reflection properties

Dual-Vivaldi nanoantenna arrays were designed, fabricated and optically characterized in the infrared (IR) and visible regimes. The antenna arrays were characterized by measuring the scattered light at IR (1450-1640 nm) and visible (780 nm) spectral ranges. The radiation efficiency and the spectral response of the antennas were found to be in good agreement with numerical simulations. The results presented here demonstrate the extremely wide-band nature of the dual-Vivaldi antennas and the strong dependence of the scattering response on the load at the antenna terminals. These properties, as well as their many degrees of freedom for design, render the dual-Vivaldi antennas excellent candidates for optical sensing applications.

Nano-particle trapping by optically induced Dielectrophoresis enhanced by nano-antennas

We demonstrate experimentally trapping and manipulation of 50nm gold nanoparticles suspended in Isopropanol using dielectrophoretic (DEP) forces induced by illuminating arrays of nano--antennas with IR laser light. The trapping experiments are compared to numerical models.

Optical nano-antennas: a new approach for optical imaging and detection

We study theoretically and experimentally the IR emission properties from gold nano-antenna arrays. A new characterization method based on far field measurements only is developed and presented. Excellent agreement in terms of resonance frequencies, optical bandwidth, and emission efficiency is found between the experimental results and a theoretical analysis based on finite element modeling of the arrays. Extremely high overall emission efficiencies, exceeding 95%, are obtained experimentally. The high efficiency and the simple far-field characterization scheme presented here can facilitate the employment of such nano-antennas for numerous applications in imaging, spectroscopy, and solar energy harvesting.