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Colorimetric sensing, which provides effective detection of bio-molecular signals with one’s naked eye, is an exceptionally promising sensing technique in that it enables convenient detection and simplification of entire sensing system. Though colorimetric sensors based on all-dielectric nanostructures have potential to exhibit distinct color variations enabling manageable detection due to their trivial intrinsic loss, there is crucial limitation that the sensitivity to environmental changes lags behind their plasmonic counterparts because of relatively small region of near field-analyte interaction of the dielectric Mie-type resonator. To overcome this challenge, we proposed all-dielectric metasurface colorimetric sensor which exhibits dual-resonance in the visible region. Thereafter, we confirmed with simulation that, in the elaborately designed dual-Lorentzian-type spectra, highly perceptible variations of structural color were manifested even in minute change of peripheral refractive index. In addition to verifying physical effectiveness of the superior colorimetric sensing performance appearing in the dual-resonance type sensor, by combining advanced optimization technique utilizing deep neural networks, we attempted to maximize sensing performance while obtaining dramatic improvement of design efficiency. Through well-trained deep neural network that accurately simulates the input target spectrum, we numerically verified that designed colorimetric sensor shows a remarkable sensing resolution distinguishable up to change of refractive index of 0.0086.

Flat nanophotonic devices hold a great potential to process diffractive optical information within ultra-thin submicron thickness. In particular, optical filtering of transmissive angular spectrum in the free space is an essential functionality in diffractive optics. Here, we propose a novel configuration and theoretical study of an ultrathin transmissive angular filtering metamaterial for the first time to the best of our knowledge. Based on the adiabatically tapered plasmonic waveguide metamaterial in the visible regime, full color angle-selective transmission is achieved near the optic axis including the representative blue (473 nm), green (532 nm), and red (633 nm) colors. By providing further analysis on bandwidth extension, we envision that the proposed flat angular filtering mechanism in the visible range promises practical value and potential for a variety of metamaterial-assisted compact diffractive imaging and sensing applications such as augmented or virtual reality displays and biomedical optical sensors.

Effective dynamic modulation of visible light properties has been significantly desired for advanced imaging and sensing technologies. In particular, phase-change materials have attracted much attention as active material platforms owing to their broadband tunability of optical dielectric functions induced by the temperature-dependent phase-changes. However, their uses for visible light modulators are still limited to meet multi-objective high performance owing to the low material quality factor and active tunability in the visible regime. Here, a design strategy of phase-change metafilm absorber is demonstrated by making the use of the material drawbacks and extending design degree of freedom. By engineering tunability of effective anisotropic permittivity tensor of VO2-Ag metafilm around near-unity absorption conditions, strong dynamic modulation of reflection wave is achieved with near-unity modulation depth at desired wavelength regions without sacrificing bandwidth and efficiency. By leveraging effective medium theory of metamaterial and coupled mode theory, the intuitive design rules and theoretical backgrounds are suggested. It is also noteworthy that the dynamic optical applications of intensity modulation, coloring, and polarization rotation are enabled in a single device. By virtue of ultrathin flat configuration of a metafilm absorber, design extensibility of reflection spectrum is also verified. It is envisioned that our simple and powerful strategy would play a robust role in development of miniaturized light modulating pixels and a variety of photonic and optoelectronic applications.

Fano resonance, one of the interesting resonance phenomena in physics, provides versatile applications when combined with a concept of metasurface in nanophotonics. Fano-resonant metasurface (FRM) is attracting a lot of attention due to its superior narrowband characteristics as well as design freedom of metasurfaces in nanoscale. However, only the control of apparent asymmetric spectral nature of Fano resonance has been focused at applications such as optical sensors, as the amplitude feature of Fano resonances is relatively easy to control and can be measured by an experimental setup. Here, a method for modulating the phase information of FRM by both simulation and experiment is demonstrated. As a proof of concept, an optical demultiplexer, which can divide four target wavelengths in different directions of free space, is verified experimentally. It covers a broadband wavelength range of more than 350 nm in the near-infrared region with extremely small full-width at half-maximum. This approach can offer the complete control of FRM for a wide range of applications, including optical multiplexers, routers, filters, and switches, beyond conventional applications that have been limited to the amplitude control of Fano resonance.

As an increased demand in high resolution display, the pixel size in the image sensor is reduced to increase the resolution. Although there have been recent studies on metasurface color routers to overcome the limitation of the conventional image sensor, there are still limitations in that the designed devices do not show the advantages of router or are difficult to fabricate. In this study, the fabricable metasurface that distribute three visible wavelengths to each targeted color sensor is proposed numerically. For the distribution like the Bayer pattern, a dual focal phase profile is utilized for green color. The designed metasurface size is 2 μm by 2 μm, and the routing efficiencies are 12 %, 25 %, and 30 % for 473 nm, 532 nm, and 660 nm, respectively, where the performance in red light exceed the fundamental limit of efficiency of the conventional Bayer color filter array.

Transparent heat films (THFs) are attracting increasing attention for their usefulness in various applications, such as vehicle windows, outdoor displays, and biosensors. In this study, the effects of induction power and radio frequency on the welding characteristics of silver nanowires (Ag NWs) and Ag NW-based THFs were investigated. The results showed that higher induction frequency and higher power increased the welding of the Ag NWs through the nano-welding at the junctions of the Ag NWs, which produced lower sheet resistance, and improved the adhesion of the Ag NWs. Using the inductive welding condition of 800 kHz and 6 kW for 60 s, 100 ohm/sq of Ag NW thin film with 95% transmittance at 550 nm after induction heating could be decreased to 56.13 ohm/sq, without decreasing the optical transmittance. In addition, induction welding of the Ag NW-based THFs improved haziness, increased bending resistance, enabled higher operating temperature at a given voltage, and improved stability.

One of the most important research topic in optics and photonics is the design of metasurfaces to substitute conventional optical elements that demonstrate unprecedented merits in terms of performance and form factor. In this context, full-space control of metasurfaces that makes it possible to manipulate scattered light in transmission and reflection spaces simultaneously, is proposed as the next-generation scheme in optics, with a potential for applications such as 360° holographic images and novel optical systems. However, previously designed metasurfaces lacked functionality because the desired operation occurs under preconditioned light; therefore, they are difficult to use in real applications. Here, we present a design method that enables polarization-dependent full-space control, in which two independent and arbitrary phase profiles can be addressed to each space. Upon introducing a phase gradient value to realize the critical angle condition, conversion of transmissive into reflective operation is realized. Then, rectangular nanopillars are utilized to facilitate polarization beam splitting with the desired phase. Three samples were fabricated and measured based on the proposed scheme.

Metasurface color filters (MCFs) have attracted considerable attention thanks to their compactness and functionality as a candidate of an optical element in a miniaturized image sensor. However, conventional dielectric and plasmonic MCFs that have focused on color purity and efficiency cannot avoid reflection in principle, which degrades image quality by optical flare. Here, we introduce absorptive-type MCFs through truncated-cone hyperbolic metamaterial absorbers. By applying a particle swarm optimization method to design multiple parameters simultaneously, the proposed MCF is theoretically and numerically demonstrated in perceptive color on CIELAB and CIEDE2000 with suppressed-reflection. Then, a color filter array is numerically proven in 255 nm of sub-pixel pitch.

Background The conventional scores of the neuropsychological batteries are not fully optimized for diagnosing dementia despite their variety and abundance of information. To achieve low-cost high-accuracy diagnose performance for dementia using a neuropsychological battery, a novel framework is proposed using the response profiles of 2666 cognitively normal elderly individuals and 435 dementia patients who have participated in the Korean Longitudinal Study on Cognitive Aging and Dementia (KLOSCAD). Methods The key idea of the proposed framework is to propose a cost-effective and precise two-stage classification procedure that employed Mini Mental Status Examination (MMSE) as a screening test and the KLOSCAD Neuropsychological Assessment Battery as a diagnostic test using deep learning. In addition, an evaluation procedure of redundant variables is introduced to prevent performance degradation. A missing data imputation method is also presented to increase the robustness by recovering information loss. The proposed deep neural networks (DNNs) architecture for the classification is validated through rigorous evaluation in comparison with various classifiers. Results The k-nearest-neighbor imputation has been induced according to the proposed framework, and the proposed DNNs for two stage classification show the best accuracy compared to the other classifiers. Also, 49 redundant variables were removed, which improved diagnostic performance and suggested the potential of simplifying the assessment. Using this two-stage framework, we could get 8.06% higher diagnostic accuracy of dementia than MMSE alone and 64.13% less cost than KLOSCAD-N alone. Conclusion The proposed framework could be applied to general dementia early detection programs to improve robustness, preciseness, and cost-effectiveness.

Optical toroidal dipole and electromagnetic field enhancement have attracted much interest owing to their interesting physical features and various potential nanophotonic applications. In this paper, novel antireflective nanofocusing methods to deliver and squeeze toroidal dipole moment with simultaneous enhancement of electric and magnetic fields are suggested. By coupling the two fundamental modes of a metal–insulator–metal waveguide with a partial mirror in a waveguide and a nanocavity, resonant squeezing of longitudinal and perpendicular toroidal dipoles in an ultracompact nanocavity (∼ λ 2 / 190) is achieved at the near-telecom wavelengths. Moreover, electric and magnetic field enhancements occur simultaneously in a designated nanocavity. We expect that the proposed scheme would pave a way to engineer nanophotonic waveguide based light-matter interactions by enhancing both electric and magnetic fields. This study would interest both nanophotonics and quantum optics communities.

Conventional transmission-type color filter metasurfaces have not considered reflection that might cause image quality degradation of practical CMOS image sensors including flare effect. Here, we propose RGB color-optimized tapered hyperbolic metamaterial cavities as absorptive color filters. Since multiple geometry parameters need to be considered for optimization, we design our metasurfaces based on particle swarm optimization through FDTD simulations. Consequently, less than 20 % reflection is achieved over visible wavelength and transmission from each RGB-pixel covers about 78% of sRGB region.

Controlling the polarization state of light has been a significant issue for various integrated optical devices such as optical imaging, sensors, and communications. Recent advances in metamaterials enable the optical elements for controlling light to be miniaturized and to have various multi-functions in subwavelength scale. However, a conventional approach of a circular polarizer has an inherent limitation to eliminate the unwanted circular polarization, which means that the efficiency varies significantly depending on the polarization state of incident light. Here, we propose a novel concept of a circular polarizer by combining two functions of transmission and conversion for orthogonal circular polarizations with a total thickness of 440 nm. The proposed three-layer metasurface composed of rotating silver nanorods transmits the left-handed circularly polarized (LCP) light with maintaining its own polarization state, whereas the right-handed circularly polarized (RCP) light is converted into LCP light. Regardless of the polarization state of incoming light, the polarization of light in the last medium is LCP state in the broadband operating wavelength range from 800 nm to 1100 nm. The converted RCP and the transmitted LCP have efficiencies of up to 48.5% and 42.3%, respectively. Thus the proposed metasurface serves as a stable circular polarizer for a randomly polarized light. In addition, high-efficiency asymmetric transmission of about 0.47 is achieved at the same time due to the conversion characteristic of RCP component. The proposed metasurface has the significance as an ultra-thin optical element applicable to optical switching, sensors, and communications in unidirectional channel as well as a broadband circular polarizer for randomly polarized light.

Recently, nanostructures composed of tapered apertures have been researched for electromagnetic field enhancement. Tapered plasmonic aperture antenna can concentrate transverse electric dipoles and longitudinal magnetic dipoles in tiny volume of plasmonic waveguide or metasurface. It is an important element for efficient nonlinear optics, modification of spontaneous decay rates, and sensitive nanophotonic sensors to simultaneously intensify both of electric and magnetic fields. However, even though their advantages include apparent theory based on constructive interference of surface plasmons and relatively simple fabrication, the enhancement performances are not strong as much as those of conventional bridged bowtie aperture antenna. Here, we propose a novel design with reflection type metasurface patterned by a funnel-shaped waveguide cavity array. This supports longitudinal cavity mode along the direction of incident light in addition to perimeter cavity mode or transverse cavity mode of conventional tapered apertures. Longitudinal cavity mode contributes to electric and magnetic fields on transverse plane and transverse cavity mode with funnel shape induces strong circulating currents around tiny volume that generate magnetic dipoles on longitudinal plane. To demonstrate our proposed design, we carry out three-dimensional finite element method for numerical calculation. It shows resonant average (maximum) enhancements of electric and magnetic intensities reach about 177 (1484) and 91 (274), respectively, at the wavelength of 1120 nm. Furthermore, the enhancement of spontaneous decay rates and Purcell effect are verified numerically. Our design can offer a new approach of various nano-optical applications such as biochemical sensor, nonlinear optics, and photoluminescence application.

We investigate Huygens’ optical vector wave field synthesis scheme for electric dipole metasurfaces with the capability of modulating in-plane polarization and complex amplitude and discuss the practical issues involved in realizing multi-modulation metasurfaces. The proposed Huygens’ vector wave field synthesis scheme identifies the vector Airy disk as a synthetic unit element and creates a designed vector optical field by integrating polarization-controlled and complex-modulated Airy disks. The metasurface structure for the proposed vector field synthesis is analyzed in terms of the signal-to-noise ratio of the synthesized field distribution. The design of practical metasurface structures with true vector modulation capability is possible through the analysis of the light field modulation characteristics of various complex modulated geometric phase metasurfaces. It is shown that the regularization of meta-atoms is a key factor that needs to be considered in field synthesis, given that it is essential for a wide range of optical field synthetic applications, including holographic displays, microscopy, and optical lithography.

Since the surface plasmon polariton (SPP) has received a great deal of attention because of its capability of guiding light within the subwavelength scale, finding methods for arbitrary SPP field generation has been a significant issue in the area of integrated optics. To achieve such a goal, it will be necessary to generate a plasmonic complex field. In this paper, we propose a novel method for generating a plasmonic complex field propagating with arbitrary curvatures by using double-lined distributed nanoslits. As a unit cell, two facing nanoslits are used for tuning both the amplitude and the phase of excited SPPs as a function of their tilted angles. For verification of the proposed design rule, the authors experimentally demonstrate some plasmonic caustic curves and Airy plasmons.

We propose a novel scheme to realize broadband polarization conversion in optical spectral range. A polarization conversion metamaterial is designed using anisotropic metal rods placed on top of a metal film with a dielectric spacer between them. As the fourfold symmetry is broken, the coupling of plasmon resonances generates orthogonal polarization component in the reflection. Especially, resonant frequencies of magnetic and toroidal resonances are close together, which leads to bandwidth expansion of polarization conversion. The polarization conversion ratio is above 0.9 over the 100 nm bandwidth in optical spectral range.

We proposed a refractive index sensor using a phase-compensated cavity whose resonant wavelength can be tuned by the alignment between layers. The structures are composed of double-layered nanoslit array, which has total thickness of 100 nm while the cavity length is 30 nm thick. Using nanoslit array as a reflector has made it possible to design the phase shift carefully so that the subwavelength Fabry-Perot cavity can be obtained. When the cavity is filled with sensing medium, where the field enhancement is achieved by Fabry-Perot (FP) resonance, the proposed structure is found to achieve sensitivity ranging from 337 nm/RIU to 1250 nm/RIU at each different alignment. The resonant wavelength ranges from 1100 nm to 2500 nm, which contains biological windows and telecommunication wavelength range, so the structure is expected to be used in various purposes.

Active switching of near-field directivity, which is an essential functionality for compact integrated photonics and small optoelectronic elements, has been challenging due to small modulation depth and complicated fabrication methods for devices including active optical materials. Here, we theoretically and experimentally realize a nanoscale active directional switching of surface plasmon polaritons (SPPs) using a phase transition material for the first time. The SPP switching device with noticeable distinction is demonstrated based on the phase transition of vanadium dioxide (VO2) at the telecom wavelength. As the insulator-to-metal phase transition (IMT) of VO2 induces the large change of VO2 permittivity at telecom wavelengths, the plasmonic response of a nanoantenna made of VO2 can be largely tuned by external thermal stimuli. The VO2-insulator-metal (VIM) nanoantenna and its periodic array, the VIM metagrating, are suggested as optical switches. The directional power distinction ratio is designed to change from 8.13:1 to 1:10.56 by the IMT and it is experimentally verified that the ratio changes from 3.725:1 to 1:3.132 as the VIM metagratings are heated up to 90 °C. With an electro-thermally controllable configuration and an optimized resonant design, we expect potential applications of the active switching mechanism for integrable active plasmonic elements and reconfigurable imaging.

It has been hard to achieve simultaneous plasmonic enhancement of nanoscale light-matter interactions in terms of both electric and magnetic manners with easily reproducible fabrication method and systematic theoretical design rule. In this paper, a novel concept of a flat nanofocusing device is proposed for simultaneously squeezing both electric and magnetic fields in deep-subwavelength volume (~λ3/538) in a large area. Based on the funneled unit cell structures and surface plasmon-assisted coherent interactions between them, the array of rectangular nanocavity connected to a tapered nanoantenna, plasmonic metasurface cavity, is constructed by periodic arrangement of the unit cell. The average enhancement factors of electric and magnetic field intensities reach about 60 and 22 in nanocavities, respectively. The proposed outstanding performance of the device is verified numerically and experimentally. We expect that this work would expand methodologies involving optical near-field manipulations in large areas and related potential applications including nanophotonic sensors, nonlinear responses, and quantum interactions.

Surface plasmon polaritons (SPPs) are surface-bounded electromagnetic waves, propagating along a metal-dielectric interface. Due to larger wavenumber of SPPs compared with propagating light in free-space, additional couplers are required to excite SPPs. Dielectric prisms, gratings, apertures, and optical antennas are widely used. Recently, controlling excitation property of SPPs with coherent characteristics of incident lights, such as polarization and interference has been demonstrated. In this work, we propose a coherent plasmon cavity whose energy density can be tuned by polarization of the incident light. With polarization-sensitive aperture array, it is possible to launch counter-propagating SPPs with phase difference controlled by an angle of polarization. By rotating the polarization angle by 90 degrees, the energy density inside the cavity is enhanced 45 times larger compared with the minimum case.

BACKGROUND: Data on outcomes of suicidality in the community-dwelling elderly are scarce. We investigated the association of suicidality with the suicide attempts in a community-dwelling elderly cohort. METHODS: In the Osan Mental Health Survey, 848 randomly sampled elderly Koreans participated in the baseline evaluation, 623 completed 2-year follow-up evaluation and 32 died during the follow-up period. The survey was conducted between February 2010 and January 2013. We evaluated suicidality using the Mini-International Neuropsychiatric Interview suicidality module that includes both suicidal ideation and attempts. RESULTS: The incidences of suicidality and suicide attempts were 70.7 and 13.1 per 1000 persons per year, respectively. Suicidality was associated with increased risk of suicide attempts (odds ratio (OR)=3.84, 95% CI=1.06-13.87). Two men with suicidality committed suicide by self-poisoning. Moderate to high intensity daily exercise decreased the risk of suicidality to become persistent or recurrent (OR=0.32, 95% CI=0.12-0.81). Low education level (OR=2.41, 95% CI=1.21-4.77) and depression (OR=3.02, 95% CI=1.65-5.53) were associated with risk of incident suicidality. LIMITATIONS: Study sample was enrolled from a single city of Korea, and the size of the study sample was small. CONCLUSIONS: We may reduce suicide attempts by screening for suicidality and implementing exercise programs in community-dwelling elderly people. Language: en

A novel method to launch finite power Airy beams based on a metasurface is presented. By tailoring the amplitude and phase of the transmitted fields from a metallic C-aperture array, launching Airy beams is achieved in free space. The amplitude and phase of the Airy beam profile can be mapped and tailored by tuning only the tilt angles of the aperture. This structure has multifrequency characteristics, which facilitates Airy beam steering because the trajectory of Airy beams is dependent on the wavelength. In addition, the design method can generate Airy beams which have a very compact main lobe (≈2 µm). Computational and experimental results show that proposed metasurface can overcome some limitations of the traditional methods to generate Airy beams. The results can be used for potential applications in integrated optics, beam shaping, biosensing, and next-generation holography.

subjects diagnosed with mild cognitive impairment (MCI). PET volumes were registered to a customized MRI template in MNI stereotaxic space, and standardized uptake value ratio (SUVR) images were generated using Biospective’s fully-automated PIANO TM image processing software. The amyloid burden for each subject was determined from a composite region-of-interest (ROI) on [18F]florbetapir images, and subjects were categorized into Amyloid-Low (Ab L) and Amyloid-High (Ab H) groups. We generated a set of hierarchical likelihood ratio tests to assess betweengroups differences in metabolic connectivity patterns arising from (1) alterations in seed-based correlations and (2) alterations in seed-based covariances and variances with stable seed-based correlations. Results: We observed statistically significant differences in metabolic correlations between the Ab L and Ab H groups for multiple cortical seeds regions, including the angular gyrus and the inferior temporal gyrus. The seed-based covariance analysis identified connectivity patterns in particular brain regions (e.g. precuneus) that were not detected by classical seed-based correlation analysis. Conclusions: We have introduced a new, multivariate metabolic connectivity analysis technique to examine disruptions of the cortical correlation architecture as a function of b-amyloid burden. The novel approach employed in this study may be generalized to other connectivity measures, such as functional connectivity derived from BOLD fMRI, and may provide unique insights into disease-related alterations of the connectome.

A light-folded projection three-dimensional (3D) display system with a single projection lens and a rectangular light tunnel which is composed of four folding mirrors on its inside walls is proposed. It is theoretically shown through the Wigner distribution function analysis that the proposed system can generate the same light field effectively as that of the conventional projection-type multiview 3D display system with plural projection lenses. Multiview 3D imaging of the proposed system configuration is experimentally demonstrated.