We proposed recently that the building blocks of metal optics (encompassing plasmonics, metasurfaces, and metamaterials) can be fabricated in existing CMOS foundry processes by repurposing the back-end-of-the-line (BEOL) of the CMOS chip in. We demonstrated a metal-optic liquid crystal modulator using a chip that is fully fabricated in the conventional 65-nm CMOS process. In this talk, we provide an in-depth presentation on the design constrains and post-processing steps required to convert CMOS chips to nano-photonic devices. We will also present recent developments and prospects of CMOS meta-optics and optoelectronics.
Here, we propose an experiment, based on levitation optomechanics, to measure gravitational forces from nanoscale objects. In the experiment, two optically trapped particles in ultrahigh vacuum conditions represent the source and test masses. Importantly, the source mass is a rotating Janus nanoparticle such that the test mass (sensor) experiences a periodic gravitational potential. Using realistic experimental parameters, a signal-to-noise ratio ≥ 1 is obtained for a Janus particle with radius ≥ 100 nm and a mass ≥ 10 fg. The proposed experiment enables first steps towards table-top tests of quantum gravity.
We show that metallic wires in CMOS chips can provide dual functionalities as electronic interconnects and as plasmonic/metamaterial devices. We demonstrate plasmonic resonances in a chip fabricated in a bulk Si CMOS foundry (TSMC, 65 nm node). Through minimal post processing, we integrate the designed nanophotonic CMOS chip with liquid crystals and demonstrate a high-speed liquid crystal-based electro-optic modulator.
High-speed SLMs are necessary for various classical and quantum applications, including massively parallel remote sensing, high-repetition-rate pulsed laser shaping, and scalable control of quantum objects at timescales faster than their decoherence time. Here, we demonstrate a high-speed SLM by two-dimensional electric field patterning of a lithium niobate thin film. A high-quality factor guided mode resonance enhances the amplitude and phase modulation from the induced index variation. Our approach offers fast (> GHz), low power, and high diffraction efficiency tuning.
We show that the recombination rate from excitons in Lead Halide Perovskite (LHP) polycrystalline thin films is suppressed, rather than enhanced, when they are placed on hyperbolic metamaterials and a plasmonic substrate by 30% and 50%, respectively. We reveal that these LHP films enjoy a dominant in-plane transition dipole, which is responsible for the decrease in the recombination rate. In triple cation LHPs we observe a 10-fold decrease in the recombination rate, comparable to recombination rate suppression obtained by Photonic Crystal cavities. By controlling the recombination rate of LHPs, we demonstrate a 250% increase in photoresponsivity of LHP-based photodetectors.
We analyze the impact of angular selectivity on the radiative cooling performance of thermal emitters. We show that combining angular and spectral selectivity enables realizing deep subfreezing temperatures. While angularly selective thermal emitters are robust to environmental effects, they require management of non-radiative heat transfer processes. We introduce a general scheme to realize angularly and spectrally selective absorption/emission using a thin film stack consisting with a total thickness of ~ 9 μm; an order of magnitude less than previously proposed angular selective thermal emitters. We finally discuss the prospects of angular selectivity based on conic mirrors.
Perfect light absorption (PLA) in nanophotonics has a wide range of applications from solar-thermal based applications to radiative cooling. However, most of the proposed platforms require intense lithography which makes them of minor practical relevance. On the other hand, thin-film light absorbers are lithographically free and can be deposited cheaply on large area based on matured technologies. However, thin-film light absorbers were thought to have major limitation and cannot be tailored compared to metamaterials. Here, we show how to design PLA using thin-films in terms of wavelength range, bandwidth, spatial profile of optical losses, directionality and iridescence. We also show that iridescent free, PLA can occur by simply heating metallic thin-films when the metal is of low reflectance and its oxide is of high refractive index. We theoretically and experimentally demonstrate Generalized Brewster angle effect in thin film light absorbers. In addition, we demonstrate hydrogen sensing using three different PLA strategies showing record sensitivity and figure of merit. Furthermore, we show various strategies to create ultra-pure structural colors. Finally, we demonstrate different solar-thermal applications for novel thin-film PLA designs.
We present a new class of thin-film based metamaterials that exhibits Fano resonance with wide range of potential applications. We realize Fano resonance via thin-film interference between a broadband (continuum) and a narrowband (discrete) light absorbers. Fano resonant optical coatings (FROCs) exhibit selective light reflection, similar to distributed bragg reflectors, with narrower bandwidth and overall significantly less thickness for a given wavelength range. Accordingly, FROCs produce vibrant colors superior to structural coloring via selective light absorption that has been demonstrated using metamaterials and thin-film cavities. We control the iridescence of the produced colors and can produce iridescent free, ultra-pure colors spanning the entire visible spectrum. Furthermore, we show that FROCs can be used as narrowband beam splitters, as opposed to being simple color filter similar to metal-dielectric cavities. Finally, we utilize the absorption/reflection properties of FROCs in energy applications and show that by selectively reflecting light within the absorption band of Si photovoltaic cell, while absorbing the rest of the solar spectrum, we obtain higher power from PV cells as opposed to a normal silver mirror, while increasing the FROC temperature significantly. Accordingly, FROCs can play a crucial role in hybrid, solar-PV and solar-thermal power generation which is of major importance in recent years due to limitation on electric energy storage. By coating an Aluminum sheet with FROC, while processing its back side to be superwicking, we demonstrate single-element spectral splitting that generate electricity from a PV cell while using the generated heat for water desalination.
KEYWORDS: Solar energy, Thin films, Thin film coatings, Optical coatings, Energy efficiency, Solar cells, Photovoltaics, Energy conversion efficiency, Beam splitters, Optical components
Increasing the efficiency and cost effectiveness of solar energy generation allowed them to compete with traditional carbon-based energy sources in many energy markets worldwide. However, a major problem facing the proliferation of solar energy generation is energy storage. Photovoltaic (PV) generators enjoy relatively high efficiency but suffer from high electric energy storage costs. On the other hand, solar-thermal energy conversion enables storing heat and dispatch electricity at lower storage costs but with less efficiency compared to photovoltaics. Hybridizing both solar energy conversion can address the energy storage problem. Furthermore, single junction PVs are unable to convert a large portion of the solar spectrum to energy which eventually lead to PV thermalization. Spectral beam splitting is a promising method to achieve high efficiency solar energy conversion while hybridizing electric and thermal solar energy generation.
Here, we use novel thin-film based optical coatings to develop single element selective light reflector/absorber that reflects within the wavelength range corresponding to a PV cell absorption band, while absorbing the remaining solar spectrum. We show that reflecting solar light on a PV cell using a silver mirror is less efficient and has higher temperature compared to using selective light reflector/absorber when using optical concentration exceeding 2 suns. We demonstrate hybrid PV generation and water sanitation/desalination using an Aluminum sheet with thin-film selective light reflector /absorber deposited on one side, while the other side is treated with femtosecond laser to become superwicking.
Imaging transient dynamics of materials and light-matter interaction at the nanoscale is of great interest to the study of condensed phase dynamics and to the field of nano-photonics. However, optical interrogation of the ultrafast dynamics of nanostructures has not been demonstrated as they are diffraction limited. Furthermore, optical methods are limited due to the low scattering of nanostructures and the strong background reflection. Accordingly, The ultrafast imaging of laser induced nanostructure melting was demonstrated via femtosecond x-ray diffraction imaging which provided relatively high temporal (~10 ps) and high spatial (~10 nm) resolution. However, this technique suffers from the inherent difficulty of using a femtosecond X-ray laser source and the damaging nature of the femtosecond X-ray laser probe required for single-shot imaging. Consequently, X-ray pump-probe imaging was never used to image the re-solidification dynamics of surface structures. On the other hand, cryo-electron microscopy achieved sub-nanometer resolution for single particles, however, it requires experiments to be performed in vacuum with highly specialized and costly instrumentation. Here, we we employ a time-resolved variant of ultramicroscopy that we recently developed to study the ultrafast dynamics of laser ablated surfaces. The technique is non-destructive and allows us to compare the transient image with the initial/final image. Accordingly, we determine the characteristic times for melting and re-solidification of nanostructures using optical wavelengths. We also study the formation and melting of Si nanostructures and image, for the first time, the process of non-thermal melting which occurs on the sub-picosecond time scale.
Transmissive-type metasurfaces represent an ultrathin alternative to traditional optical elements, e.g., lenses and waveplates. However, transmissive-type plasmonic metasurfaces (PMs) have significantly low efficiency compared to dielectric metasurfaces and reflective type PMs particularly in the visible range. For example, the state-of-the-art geometric PMs transmission efficiency is ≤10% with extinction ratios ~ 0 dB. The low transmission efficiency is mainly due to three loss channels (i) absorption losses in metals, (ii) diffraction to undesired high-orders, and most importantly (iii) symmetric forward-backward scattering which puts a 25% theoretical limit on cross-polarization conversion for ultrathin metasurfaces. We use tunable, multipole-interference-based meta-atoms to address all loss channels simultaneously. The experimentally demonstrated transmission efficiency and extinction ratio of our geometric PM are 42.3% and 7.8dB, respectively. As for dielectric metasurfaces, we demonstrate a new class of metasurfaces where the meta-atoms consist of a simple anti-reflective coating (ARC). ARCs enable the control over the entire 2 pi phase range by varying the dielectric films thicknesses while realizing ~ 99% transmission efficiency even in the visible range. The metasurface consists of patches of ARC meta-atoms with dielectric optical thicknesses much lower than that required in Fresnel optics to control the entire phase range.
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