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Vol. 3 ， Issue 4 ， 2014
- Abstract：Metamaterials are artificial structures that are usually described by effective medium parameters on the macroscopic scale, and these metamaterials are referred to as 'analog metamaterials'. Here, we propose 'digital metamaterials' through two steps. First, we present 'coding metamaterials' that are composed of only two types of unit cells, with 0 and π phase responses, which we name '0' and '1' elements, respectively. By coding '0' and '1' elements with controlled sequences (i.e., 1-bit coding), we can manipulate electromagnetic (EM) waves and realize different functionalities. The concept of coding metamaterials can be extended from 1-bit coding to 2-bit coding or higher. In 2-bit coding, four types of unit cells, with phase responses of 0, π/2, π, and 3π/2, are required to mimic the '00', '01', '10' and '11' elements, respectively. The 2-bit coding has greater freedom than 1-bit coding for controlling EM waves. Second, we propose a unique metamaterial particle that has either a '0' or '1' response controlled by a biased diode. Based on this particle, we present 'digital metamaterials' with unit cells that possess either a '0' or '1' state. Using a field-programmable gate array, we realize digital control over the digital metamaterial. By programming different coding sequences, a single digital metamaterial has the ability to manipulate EM waves in different manners, thereby realizing 'programmable metamaterials'. The above concepts and physical phenomena are confirmed through numerical simulations and experiments using metasurfaces.Keywords：coding;digital;metamaterial;metasurface;programmable
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Published：2024-09-26 - Abstract：Noble metal nanoparticles support localized surface plasmon resonances (LSPRs) that are extremely sensitive to the local dielectric properties of the environment within distances up to 10–100 nm from the metal surface. The significant overlap between the sensing volume of the nanoparticles and the size of biological macromolecules has made LSPR biosensing a key field for the application of plasmonics. Recent advancements in evaluating plasmonic refractometric sensors have suggested that the phase detection of light can surpass the sensitivity of standard intensity-based detection techniques. Here, we experimentally confirm that the phase of light can be used to precisely track local refractive index changes induced by biomolecular reactions, even for dilute and layers of short-range-ordered plasmonic nanoparticles. In particular, we demonstrate that the sensitivity can be enhanced by tuning in to a zero reflection condition, in which an abrupt phase flip of the reflected light is achieved. Using a cost-effective interference fringe tracking technique, we demonstrate that phase measurements yield an approximately one order of magnitude larger relative shift compared with traditional LSPR measurements for the model system of NeutrAvidin binding to biotinylated nanodisks.Keywords：biosensors;interferometry;metasurfaces;nanostructures;spectroscopy
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Published：2024-09-26 - Abstract：Herein, we report on surface plasmon (SP)-sensitive semitransparent inverted polymer photovoltaic (PV) devices that are based on multilayered material systems consisting of poly(3-hexylthiophene): fullerene-derivative bulk-heterojunction PV layers and thin gold or silver anodes. We demonstrate that these PV devices allow the simultaneous generation of both electrical power and SPs on their anodes for photoexcitation just above the optical absorption edge of the PV layers, resulting not only in attenuated total reflection, but also in attenuated photocurrent generation (APG) under the SP resonance (SPR) condition. Moreover, we also confirm that the biomolecular interaction of biotin–streptavidin on the PV devices can be precisely detected via apparent SPR angle shifts in the APG spectra, even without the need for complex attenuated total reflection configurations. We highlight our view that APG measurements made using these PV devices show great potential for the development of future generations of compact and highly sensitive SPR-based optical sensors.Keywords：attenuated total reflection;optical sensors;photocurrent generation;polymer photovoltaic devices;surface plasmon
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Published：2024-09-26 - Abstract：Nanomanipulation under scanning electron microscopy (SEM) enables direct interactions of a tool with a sample. We recently developed a nanomanipulation technique for the extraction and identification of DNA contained within sub-nuclear locations of a single cell nucleus. In nanomanipulation of sub-cellular structures, a key step is to identify targets of interest through correlating fluorescence and SEM images. The DNA extraction task must be conducted with low accelerating voltages resulting in low imaging resolutions. This is imposed by the necessity of preserving the biochemical integrity of the sample. Such poor imaging conditions make the identification of nanometer-sized fiducial marks difficult. This paper presents an affine scale-invariant feature transform (ASIFT) based method for correlating SEM images and fluorescence microscopy images. The performance of the image correlation approach under different noise levels and imaging magnifications was quantitatively evaluated. The optimal mean absolute error (MAE) of correlation results is 68±34 nm under standard conditions. Compared with manual correlation by skilled operators, the automated correlation approach demonstrates a speed that is higher by an order of magnitude. With the SEM-fluorescence image correlation approach, targeted DNA was successfully extracted via nanomanipulation under SEM conditions.Keywords：correlative microscopy;fluorescence;image correlation;nanomanipulation;SEM;subcellular structures
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Published：2024-09-26 - Abstract：Plasmonic hybrid nanomaterials are highly desirable in advanced sensing applications. Different components in these materials undertake distinct roles and work collectively. One material component may act as an efficient light concentrator and optical probe, whereas another provides specific chemical or biological functionality. In this work, we present DNA-assembled bimetallic plasmonic nanostructures and demonstrate their application for the all-optical detection of hydrogen. Gold (Au) nanorods are functionalized with DNA strands, which serve both as linkers and seeding sites for the growth of palladium (Pd) nanocrystals and facilitate reliable positioning of Pd satellites around an Au nanorod at an ultrashort spacing in the nanometer range. Dark-field scattering spectra of single Au–DNA–Pd nanorods were recorded during controlled cycles of hydrogen gas exposure, and an unambiguous concentration-dependent optical response was observed. Our method enables, for the first time, the all-optical detection of hydrogen-induced phase-change processes in sub-5-nm Pd nanocrystals at the single-antenna level. By substituting the Pd satellites with other functional materials, our sensor platform can be extended to plasmonic sensing of a multitude of chemical and biological reagents, both in liquid and gaseous phases.Keywords：DNA self-assembly;hydrogen sensing;palladium;plasmonics
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Published：2024-09-26 - Abstract：We demonstrate a new concept for reconfigurable nanophotonic devices exploiting ultrafast nonlinear control of shaped wavefronts in a multimode nanomaterial consisting of semiconductor nanowires. Femtosecond pulsed laser excitation of the nanowire mat is shown to provide an efficient nonlinear mechanism to control both destructive and constructive interference in a shaped wavefront. Modulations of up to 63% are induced by optical pumping, due to a combination of multimode dephasing and induced transient absorption. We show that part of the nonlinear phase dynamics can be inverted to provide a dynamical revival of the wavefront into an optimized spot with up to 18% increase of the peak to background ratio caused by pulsed laser excitation. The concepts of multimode nonlinear switching demonstrated here are generally extendable to other photonic and plasmonic systems and enable new avenues for ultrafast and reconfigurable nanophotonic devices.Keywords：nanophotonics;nanowires;nonlinear optics;reconfigurable;ultrafast;wavefront shaping
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Published：2024-09-26 - Abstract：The orientation and shifting of individual carbon nanotubes are extremely important in the assembly of building blocks of nanodevices and in the development of one-dimensional materials for interdisciplinary applications. Here, we report an optical method that is capable of producing the controlled orientation and targeted shifting of single multiwalled carbon nanotubes (MWCNTs) using an optical-fiber nanotip. In a demonstration of this technique, a single MWCNT with an outer diameter of 50 nm and a length of 0.9 µm was first trapped by the nanotip using a laser beam with a wavelength of 980 nm and was then oriented and shifted along the nanotip axis as a result of the interaction of the MWCNT with the optical field output by the nanotip. Various optical powers were applied to characterize the orientation and shifting performance. The orientation and shifting of MWCNTs of various sizes were also demonstrated.Keywords：carbon nanotube;nanomanipulation;optical orientation;optical shifting
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Published：2024-09-26 - Abstract：Computer-generated planar holograms are a powerful approach for designing planar lightwave circuits with unique properties. Digital planar holograms in particular can encode any optical transfer function with high customizability and is compatible with semiconductor lithography techniques and nanoimprint lithography. Here, we demonstrate that the integration of multiple holograms on a single device increases the overall spectral range of the spectrometer and offsets any performance decrement resulting from miniaturization. The validation of a high-resolution spectrometer-on-chip based on digital planar holograms shows performance comparable with that of a macrospectrometer. While maintaining the total device footprint below 2 cm2, the newly developed spectrometer achieved a spectral resolution of 0.15 nm in the red and near infrared range, over a 148 nm spectral range and 926 channels. This approach lays the groundwork for future on-chip spectroscopy and lab-on-chip sensing.Keywords：digital planar holograms;integrated optics;nanofabrication;nanophotonics;spectrometer
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Published：2024-09-26 - Abstract：Ru complexes ([Ru(dpp)3]Cl2) were spin coated on poly(methyl methacrylate) (PMMA) opal photonic crystals (PhCs), and a ~320-fold luminescence enhancement was observed compared to that on glass, which is the largest luminescence enhancement of dye molecules by the modulation of three-dimensional (3D) PhCs reported until now. The enhancement mechanism was carefully examined and it was shown that the luminescence of [Ru(dpp)3]Cl2 depended on the molecule concentration and temperature. It can be concluded that the suppressed non-radiative relaxation among the molecules and the field enhancement both contribute significantly to the luminescence enhancement. The PMMA PhC/Ru complex composites were then tested for their intracellular oxygen sensing and cell imaging properties; these composites effectively improved the limit of detection (LOD) and the brightness of the cell images.Keywords：cell imaging;fluorescence enhancement;oxygen sensing;photonic crystals
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Published：2024-09-26 - Abstract：Since the advent of femtosecond lasers, performance improvements have constantly impacted on existing applications and enabled novel applications. However, one performance feature bearing the potential of a quantum leap for high-field applications is still not available: the simultaneous emission of extremely high peak and average powers. Emerging applications such as laser particle acceleration require exactly this performance regime and, therefore, challenge laser technology at large. On the one hand, canonical bulk systems can provide pulse peak powers in the multi-terawatt to petawatt range, while on the other hand, advanced solid-state-laser concepts such as the thin disk, slab or fibre are well known for their high efficiency and their ability to emit high average powers in the kilowatt range with excellent beam quality. In this contribution, a compact laser system capable of simultaneously providing high peak and average powers with high wall-plug efficiency is proposed and analysed. The concept is based on the temporal coherent combination (pulse stacking) of a pulse train emitted from a high-repetition-rate femtosecond laser system in a passive enhancement cavity. Thus, the pulse energy is increased at the cost of the repetition rate while almost preserving the average power. The concept relies on a fast switching element for dumping the enhanced pulse out of the cavity. The switch constitutes the key challenge of our proposal. Addressing this challenge could, for the first time, allow the highly efficient dumping of joule-class pulses at megawatt average power levels and lead to unprecedented laser parameters.Keywords：cavity dumping;cavity enhancement;coherent pulse addition;high average power and high peak power;ultrafast lasers
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Published：2024-09-26 - Abstract：Most current solar panels are fabricated via complex processes using expensive semiconductor materials, and they are rigid and heavy with a dull, black appearance. As a result of their non-aesthetic appearance and weight, they are primarily installed on rooftops to minimize their negative impact on building appearance. The large surfaces and interiors of modern buildings are not efficiently utilized for potential electric power generation. Here, we introduce dual-function solar cells based on ultrathin dopant-free amorphous silicon embedded in an optical cavity that not only efficiently extract the photogenerated carriers but also display distinctive colors with the desired angle-insensitive appearances. Light-energy-harvesting colored signage is demonstrated. Furthermore, a cascaded photovoltaics scheme based on tunable spectrum splitting can be employed to increase power efficiency by absorbing a broader band of light energy. This study pioneers a new approach to architecturally compatible and decorative thin-film photovoltaics.Keywords：color filters;nanocavities;organic–inorganic nanostructures;photovoltaics;spectrum splitting
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Published：2024-09-26
Original Articles
- Abstract：This paper describes the fundamentals of phase-only liquid crystal on silicon (LCOS) technology, which have not been previously discussed in detail. This technology is widely utilized in high efficiency applications for real-time holography and diffractive optics. The paper begins with a brief introduction on the developmental trajectory of phase-only LCOS technology, followed by the correct selection of liquid crystal (LC) materials and corresponding electro-optic effects in such devices. Attention is focused on the essential requirements of the physical aspects of the LC layer as well as the indispensable parameters for the response time of the device. Furthermore, the basic functionalities embedded in the complementary metal oxide semiconductor (CMOS) silicon backplane for phase-only LCOS devices are illustrated, including two typical addressing schemes. Finally, the application of phase-only LCOS devices in real-time holography will be introduced in association with the use of cutting-edge computer-generated holograms.Keywords：electro-optic effect;liquid crystal material;liquid crystal on silicon device;real-time holography
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Published：2024-09-26
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