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Register a new userPlasmonic nanoantenna design and fabrication based on evolutionary optimization
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Nanoantennas for light enhance light-matter interaction at the nanoscale making them useful in optical communication, sensing, and spectroscopy. So far nanoantenna engineering has been largely based on rules derived from the radio frequency domain which neglect the inertia of free metal electrons at optical frequencies causing phenomena such as complete field penetration, ohmic losses and plasmon resonances. Here we introduce a general and scalable evolutionary algorithm that accounts for topological constrains of the fabrication method and therefore yields unexpected nanoantenna designs exhibiting strong light localization and enhancement which can directly be printed by focused-ion beam milling. The fitness ranking in a hierarchy of such antennas is validated experimentally by two-photon photoluminescence. Analysis of the best antennas operation principle shows that it deviates fundamentally from that of classical radio wave-inspired designs. Our work sets the stage for a widespread application of evolutionary optimization to a wide range of problems in nano photonics.
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The design of nano-antennas is so far mainly inspired by radio-frequency technology. However, material properties and experimental settings need to be reconsidered at optical frequencies, which entails the need for alternative optimal antenna designs. Here a checkerboard-type, initially random array of gold cubes is subjected to evolutionary optimization. To illustrate the power of the approach we demonstrate that by optimizing the near-field intensity enhancement the evolutionary algorithm finds a new antenna geometry, essentially a split-ring/two-wire antenna hybrid which surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime.
Plasmonic nano-optical tweezers enable the non-invasive manipulation of nano-objects under low illumination intensities, and have become a powerful tool for nanotechnology and biophysics. However, measuring the trap stiffness of nanotweezers remains a complicated task, which hinders the development of plasmonic trapping. Here, we describe an experimental method to measure the trap stiffness based on the temporal correlation of the fluorescence from the trapped object. The method is applied to characterize the trap stiffness in different double nanohole apertures and explore the influence of their design parameters in relationship with numerical simulations. Optimizing the double nanohole design achieves a trap stiffness 10x larger than the previous state-of-the-art. The experimental method and the design guidelines discussed here offer a simple and efficient way to improve the performance of nano-optical tweezers.
We optimize multilayered anti-reflective coatings for photovoltaic devices, using modern evolutionary algorithms. We apply a rigorous methodology to show that a given structure, which is particularly regular, emerge spontaneously in a very systematical way for a very broad range of conditions. The very regularity of the structure allows for a thorough physical analysis of how the designs operate. This allows to understand that the central part is a photonic crystal utilized as a buffer for light, and that the external layers have the purpose of reducing the impedance mismatch between the outer media and the Bloch mode supported by the photonic crystal. This shows how optimization can suggest new design rules and be considered as a source of inspiration. Finally, we fabricate these structures with easily deployable techniques.
We suggest a broadband optical unidirectional arrayed nanoantenna consisting of equally spaced nanorods of gradually varying length. Each nanorod can be driven by near-field quantum emitters radiating at different frequencies or, according to the reciprocity principle, by an incident light at the same frequency. Broadband unidirectional emission and reception characteristics of the nano-antenna open up novel opportunities for subwavelength light manipulation and quantum communication, as well as for enhancing the performance of photoactive devices such as photovoltaic detectors, light-emitting diodes, and solar cells.
In this article, we propose a programmable plasmonic waveguide system (PPWS) to achieve several different functions based on metal coding metamaterials (MCMs) and inverse design technology. There is no need to spend much time on considering the relation between the function and the structure because the MCMs in the PPWS are reprogrammable. In order to demonstrate the effectiveness of the PPWS, we utilize it to achieve several filtering functions, including bandstop and bandpass filters. The simulation results exhibit that the performance of filters is improved based on genetic algorithm, particle swarm optimization, multi-traversal direct-binary search and simulated annealing. Especially, the bandwidth and quality factor for the narrow-band filter can reach 6.5 nm and 200.5. In addition to the simple filtering functions, some relatively complex transmission characteristics can be obtained by using the PPWS, such as plasmon-induced transparency-like effects. In conclusion, genetic algorithm is considered as the most efficient inverse design method for our system due to its less optimization time and stable performance. In comparison with the previous works, our proposed PPWS not only provides a general framework for obtaining an effective, flexible and compact plasmonic device but also shows the applications of inverse design on photonics devices.
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