KEYWORDS: Near field optics, Optical components, Control systems, Plasmonics, Luminescence, Digital holography, Microscopy, Antennas, Optical communications, Signal processing
Planar photonic metasurfaces, exhibiting artificial optical effects at the interface, are enabling a broad variety of possibilities as optical elements, communications, and signal processing. The signal we perceive from a metasurface is determined by the phases of the different nanostructures that compose the system. This phase controls the spatial radiation distribution following Huygens’principle and has been utilized in planar optical devices exhibiting negative refraction, cloaking, and holographic elements to name a few.
In this presentation, we will first demonstrate the quantitative direct measurement of the phase front produced by a metasurface using digital holography microscopy. We will then show that by designing and tuning the multipolar components of the nanostructured building blocks, it is possible to also control the spectral response as well as the polarization state of the system. By composing a metasurface with such complex nanostructures fabricated in silver, we are able to control the scattered light and channel different colors into different directions. In the second series of experiments, we specifically study the multipolar radiation of a bianisotropic scatterer and use it for the efficient splitting of circularly polarized light, similar to a photonic spin Hall effect. Since the near-field enhancement and circularly polarized scattering in this case occur at the individual antenna level, this planar surface is capable of extracting the fluorescence and controlling the spin-polarized emission from nearby emitters, as will be demonstrated experimentally. These results have practical implications for controlling the optical activity and can potentially enable new polarization-dependent light-emitting devices for applications in imaging, optical communication, and optical displays.
During the last decade, important attention has been devoted to the observation of nonlinear optical processes in plasmonic nanosystems, giving rise to a new field of research called nonlinear plasmonics. The cornerstone of nonlinear plasmonics is the use of the large field enhancement associated with the excitation of localized surface plasmon resonances to reach high nonlinear conversion yields. Among all the nonlinear optical processes, second harmonic generation (SHG), the process whereby two photons at the fundamental frequency are converted into one photon at the second harmonic frequency, is undoubtedly the most studied one due to the relative simplicity of its experimental observation. However, the physical origin of SHG from plasmonic nanostructures hides a lot of subtleties, which are mainly related to its particular behavior upon inversion symmetry. In order to catch all the peculiarities of SHG, it is mandatory to develop dedicated numerical methods able to accurately describe all the underlying physical processes and the influence of the initial assumptions needs to be well-characterized. In this presentation, we discuss and compare different methods (namely full-wave computations based on the surface integral equations method, mode analysis, the Miller’s rule, and the effective nonlinear susceptibility method) proposed for the evaluation of the SHG from plasmonic nanoparticles emphasizing their limitations and advantages. In particular, the design of double resonant antennas for efficient nonlinear conversion at the nanoscale is addressed in detail.
Holograms, the optical devices to reconstruct pre-designed images, have been evolved dramatically since the advances in today’s nanotechnology [1-4]. Metamaterials, the sub-wavelength artificial structures with tailored refraction index, enable us to design the meta-hologram working in arbitrary frequency region. Here we demonstrated the first reflective type, dual image and high efficient meta-hologram with the incident angle as well as the coherence of incident wave insensitivity in visible region at least from λ = 632.8 nm to λ = 850 nm. The meta-hologram is composed of 50-nm-thick gold cross nano-antenna coupled with 130-nm-thick gold mirror with a 50-nm-thick MgF2 as spacer. It shows different images “RCAS” and “NTU” with high image contract under x- and y-polarized illumination, respectively. Making use of the characteristic of meta-materials, these optical properties of proposed meta-hologram can be transferred to arbitrary electromagnetic region by scale-up the size of the unit cell of meta-hologram, leading to more compact, efficient and promising electromagnetic components.
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