Browsing by Subject "Metasurfaces"

Now showing 1 - 12 of 12

Open Access
Broad-band polarization-insensitive all-dielectric metalens enabled by intentional off-resonance waveguiding at mid-wave infrared
(American Institute of Physics, 2019) Tanrıöver, İbrahim; Demir, Hilmi Volkan
Metasurfaces are promising candidates to take the place of conventional optical components as they enable wavefront engineering at sub- and near-wavelength distances along both lateral and vertical directions. Plasmonic metasurfaces containing sub-wavelength metallic structures constitute initial examples of this concept. However, plasmonic metasurfaces cannot achieve satisfactory efficiencies in the transmission mode due to their intrinsic losses. The low efficiencies of transmissive plasmonic metasurfaces motivated solutions using dielectric ones. Such high-efficiency all dielectric metasurfaces depend on either resonance tuning or Pancharatnam–Berry (geometrical) phase approaches. However, these approaches are limited to either narrow operation bands or suffer polarization dependency. Here, we propose and show high-index dielectric nanopillars operated as cylindrical waveguides deliberately in the off-resonance regime to achieve polarization independent wavefront control over wide spectral bands. As a proof-of-concept structure, we demonstrated a focusing metalens operating at wavelengths from 4.0 to 4.6 μm under both s- and p-polarized illuminations. The designed lens maintains the focusing operation with a maximum of 4% focal distance shift having a relative efficiency of >94% and an absolute efficiency of >67% all over the defined spectral band of 600 nm, which outperforms the previously reported metalenses in terms of wide-band operation with high performance.
Open Access
Disordered and densely packed ITO nanorods as an excellent lithography-free optical solar reflector metasurface
(American Chemical Society, 2019) Yıldırım, Deniz Umut; Ghobadi, Amir; Soydan, Mahmut Can; Ateşal, Okan; Toprak, Ahmet; Çalışkan, Mehmet Deniz; Özbay, Ekmel
Precise control and stabilization of the operating temperature environment of spacecraft and satellites during their life cycle is of paramount importance to increase device reliabilities and reduce the thermomechanical constraints. Optical solar reflectors are the physical interface between the spacecraft and space, and they are broadband mirrors for the solar spectrum, while having strong thermal emission in the mid-infrared part of the electromagnetic spectrum. Strong light–matter interactions in metamaterials and metasurfaces offer significant advantages compared to the conventional methods in performance, weight, launch, and assembly costs. However, the fabrication complexity of these metastructures due to necessitating lithography hinders their upscaling, reproducibility, large-area compatibility, and mass production. In this regard, we propose a facile, lithography-free fabrication route, exploiting oblique deposition to design a metasurface based on disordered and densely packed Indium Tin Oxide (ITO) nanorod forests. The excellent light trapping capability of the nanorod forests, randomness in the geometrical dimensions of these nanorods, combined with the lossy plasmonic nature of ITO in the thermal-infrared range led to strong coupling of thermal radiation to broad plasmonic resonances and, consequently, an experimental emissivity of 0.968, in a very wide range from 2.5 to 25 μm. In the solar spectrum, the low-loss dielectric characteristic of ITO resulted in an experimental solar absorptivity as small as 0.168. Our proposed design with high throughput, robustness, low cost, and high performance, therefore, shows great promise not only for space missions, but also for promoting environmentally friendly passive radiative cooling for our planet and thermal imaging in the field of security labeling.
Open Access
Disordered and densely packed ITO nanorods as an excellent lithography-free optical solar reflector metasurface for the radiative cooling of spacecraft
(SPIE, 2019) Yıldırım, Deniz Umut; Ghobadi, Amir; Soydan, Mahmut Can; Ateşal, Okan; Toprak, Ahmet; Çalışkan, Mehmet Deniz; Özbay, Ekmel
Optical Solar Reflectors (OSRs) form the physical interface between the spacecraft and space and they are essential for the stabilization and uniform distribution of temperature throughout the spacecraft. OSRs need to possess a spectrally selective response of broadband and perfect electromagnetic wave absorption in the thermal-infrared spectral range, while strongly reflecting the solar energy input. In this work, we experimentally show that disordered and densely packed ITO nanorod forests can be used as an excellent top-layer metasurface in a metal-insulator-oxide cavity configuration, and a thermal-emissivity of 0.97 is experimentally realized in the spectral range from 2.5 to 25 μm. The low-loss dielectric response of ITO in the solar spectrum, from 300 nm to 2.5 μm range limited the solar absorptivity to an experimental value of 0.167. These make our proposed design highly promising for its application in space missions due to combining high throughput, robustness, low cost with ultra-high performance.
Embargo
Hybrid biosensing systems for the detection of biomolecules and disease biomarkers
(2023-08) Aslan, Yusuf
Optical metasurfaces are configurations of artificially structured surfaces designed to obtain unusual electromagnetic properties. The ability to manipulate a confined electromagnetic field enables metasurfaces to be utilized as optical point-of-care (POC) biosensors for the detection of low concentrations of biomarkers. Moreover, the integration of fluorescent molecules and plasmonic metasurfaces is utilized to enhance both plasmonic and fluorescent signals; however, the nanoscale distance and spectral overlap between the fluorescent emitter and plasmonic metasurface are crucial for the separation of the fluorescence-coupled plasmonic radiation and non-radiative induced plasmon surface entrapment. In this study, fluorescently labeled (FITC) proteins are integrated over a plasmonic metasurface via three different surface modifications for obtaining a hybrid biosensing system that boosts the device’s plasmonic sensitivity and lowers the detection limit. The metasurface is fabricated via physical vapor deposition of titanium (10 nm), silver (30 nm), and gold (15 nm), respectively over polycarbonate nanograting substrates of optical disks (DVDs). Additionally, the surface modifications are arranged via short-distance, medium-distance, and long-distance modifications for fluorescently labeled molecule binding. After the evaluations, the highest plasmonic wavelength shift over the FITC labeled protein binding is obtained from the medium-distance modification with ~4.4 times signal enhancement over the short-distance modification. The medium-distance modification is further combined with an immunoassay for the detection of Alzheimer’s disease. Consequently, this study paves the way for designing new arrangements on a metasurface to couple with fluorescence molecules while enhancing the analytical performance of the plasmonic biosensor.
Open Access
Metasurface microlens focal plane arrays and mirrors
(2017-01) Akın, Onur
Lenses, mirrors and focal plane arrays (FPAs) are among the key components a ecting the functionality, performance and cost of electro-optical (EO) systems. Conventional lenses rely on phase accumulation mechanism for bending wavefront of light. This mechanism and the scarcity of transparent materials result in high-complexity, high-cost and bulky EO systems. Conventional mirrors, on the other hand, are limited by the electromagnetic properties of metals and cannot be used in certain EO systems. Also, conventional FPAs su er the fundamental tradeo between the optical resolution and optical crosstalk. Metasurfaces, relying on the concept of abrupt phase shifts, can be used to build a new class of optical components. However, for realizing metasurfaces, optical resonators should cover a full 0-to-2 phase shift response with close to uniform amplitude response. In this thesis, to develop these metasurface optical components, nanoantennas that act as unit cell optical resonators were designed and modeled. A design methodology for building and optimizing these metasurfaces using the designed nanoantennas was developed. After obtaining the metasurfaces, we successfully addressed the problems of optical crosstalk in mid-wavelength infrared (MWIR) FPAs and weak eld localization in mirror contacts. Full-wave simulations con rmed major crosstalk suppression of the microlens arrays to achieve 1% optical crosstalk in the proposed metasurface FPAs, which outperforms all other types of MWIR FPAs reported to date. However, due to intrinsic absorption losses in metals, the resulting device e ciency was low ( 10%). To solve this problem, metallic nanoantennas were replaced by dielectric nanoantennas and the focusing e ciency was dramatically increased to 80%. This is the rst account of high-e ciency low-crosstalk metasurface MWIR FPAs. Full-wave simulations also con rmed the strong eld localization of metasurface mirrors that can impose a phase shift response close to 0 . The ndings of this thesis indicate that metasurface FPAs and mirrors are highly promising for future EO systems.
Open Access
Microheater-integrated spectrally selective multiband mid-infrared nanoemitter for on-chip optical multigas sensing
(American Chemical Society, 2023-11-10) Rahimian Omam, Zahra; Ghobadi, Amir; Khalichi, Bahram; Güneş, Burak; Özbay, Ekmel
Traditional optical gas sensors often require multiple components such as broadband infrared sources, detectors, and band-pass filters to detect various target gases, resulting in bulky and expensive sensor designs. A streamlined optical gas-sensing platform utilizing a narrowband thermal emitter with a spectrally selective response, capable of accommodating various target gases, has the potential to supplant current bulky designs. Through the on-chip integration of a narrowband metamaterial perfect absorber with a microelectromechanical system (MEMS) heater, a selective infrared source emitter could be designed. In this paper, a multiband metamaterial absorber with resonance modes located at different gas absorption signatures is developed for optical multi-gas-sensing applications. The proposed nanoemitter supports penta-band light absorption through the simultaneous excitation of phononic modes (within the hexagonal boron nitride (hBN) topmost layer) and plasmonic modes (with the spectrally selective underlying metal-insulator-metal (MIM) absorber stack). It achieves five near-perfect sharp absorption resonance peaks compatible with the H2S, CH4, CO2, NO, and SO2 gas absorption signatures in the mid-infrared (MIR) spectral range. This spectrally engineered multiwavelength absorption behavior is achieved by simultaneously coupling the optical phonons (OPhs) and the plasmonic modes in the vicinity of the OPh region of hBN and by exciting plasmonic modes with the help of the spacer (ZnTe: zinc telluride) and the metallic nanogratings. Finally, this low-cost and efficient penta-band absorber is combined with a MEMS-based microheater. The microheater uses a Peano-shaped configuration to provide a highly uniform surface temperature, which is crucial for accurate and reliable gas sensing. The proposed platform demonstrates excellent potential in terms of cost-effectiveness, source-free operation, and suitability for multi-gas-sensing platforms.
Open Access
Multi-band light-matter interaction in hBN-based metasurface absorber
(Institute of Electrical and Electronics Engineers, 2022-09-28) Omam, Zahra Rahimian; Khalichi, Bahram; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, Ekmel
This paper presents a multi-band metamaterial-based absorber using phononic two-dimensional (2D) material. The structure consists of a top hexagonal boron nitride (hBN) layer on an aluminum nanograting structure deposited on a dielectric slab waveguide and a thick metallic reflector forming an MIM (metal-insulator-metal) configuration. The proposed absorber exhibits a hyperbolic phonon polariton (HPPs) in hBN, surface plasmon (SP) modes in the spacer (ZnTe: zinc telluride), and Fabry-Perot resonances in the MIM configuration, resulting in five sharp, high absorption peaks in the mid-infrared (MIR) spectral range. The proposed multi-band absorber can be utilized in various applications, ranging from optical detection devices to multispectral thermoelectric volt.
Open Access
Semiconductor thin film based metasurfaces and metamaterials for photovoltaic and photoelectrochemical water splitting applications
(WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Ghobadi, Amir; Ghobadi, Türkan Gamze Ulusoy; Karadaş, Ferdi; Özbay, Ekmel
In both photovoltaic (PV) and photoelectrochemical water splitting (PEC‐WS) solar conversion devices, the ultimate aim is to design highly efficient, low cost, and large‐scale compatible cells. To achieve this goal, the main step is the efficient coupling of light into active layer. This can be obtained in bulky semiconductor‐based designs where the active layer thickness is larger than light penetration depth. However, most low‐bandgap semiconductors have a carrier diffusion length much smaller than the light penetration depth. Thus, photogenerated electron–hole pairs will recombine within the semiconductor bulk. Therefore, an efficient design should fully harvest light in dimensions in the order of the carriers' diffusion length to maximize their collection probability. For this aim, in recent years, many studies based on metasurfaces and metamaterials were conducted to obtain broadband and near‐unity light absorption in subwavelength ultrathin semiconductor thicknesses. This review summarizes these strategies in five main categories: light trapping based on i) strong interference in planar multilayer cavities, ii) metal nanounits, iii) dielectric units, iv) designed semiconductor units, and v) trapping scaffolds. The review highlights recent studies in which an ultrathin active layer has been coupled to the above‐mentioned trapping schemes to maximize the cell optical performance.
Unknown
Single and cascaded, magnetically controllable metasurfaces as terahertz filters
(Optical Society of America OSA, 2016) Serebryannikov, A. E.; Lakhtakia, A.; Özbay, Ekmel
Transmission of a normally incident, linearly polarized, plane wave through either a single electrically thin metasurface comprising H-shaped subwavelength resonating elements made of magnetostatically controllable InAs or a cascade of several such metasurfaces was simulated in the terahertz regime. Stop bands that are either weakly or strongly controllable can be exhibited by a single metasurface by proper choice of the orientation of the magnetostatic field, and a ∼19%downshift of stop bands in the 0.1-5.5 THz spectral regime is possible on increasing the magnetostatic field strength from 0 to 1 T. Better controllability and wider bandwidths are possible by increasing the number of metasurfaces in a cascade, although increase of the total losses can lead to some restrictions. ON/OFF switching regimes, realizable either by applying/removing the magnetostatic field or just by changing its orientation, exist.
Open Access
Subwavelength densely packed disordered semiconductor metasurface units for photoelectrochemical hydrogen generation
(American Chemical Society, 2022-03-10) Ulusoy Ghobadi, T. Gamze; Ghobadi, Amir; Odabaşı, Oğuz; Karadaş, Ferdi; Özbay, Ekmel
For most semiconductors, especially the visible-light-absorbing ones, the carrier diffusion length is significantly shorter than the light penetration depth, limiting their photoactivities. This limitation could be mitigated through the use of subwavelength semiconductor-based metasurfaces and metamaterials. In this paper, a large-scale compatible metasurface photocathode, made of densely packed disordered p-type chromium oxide (CrOX), is developed to be utilized in photoelectrochemical (PEC) hydrogen generation. For this purpose, first, tightly packed random Cr nanorods are fabricated using an oblique angle deposition technique. Afterward, an annealing step is applied to the sample to transform these metallic units into a semiconducting p-type CrOX-based metasurface. Based on the experimental characterization results and numerical simulations, the proposed design can provide strong light-matter interactions in an ultra-broadband-wavelength range, mainly due to its multidimensional random geometry and ultrasmall gap sizes. Finally, to substantiate the activity of the CrOXnanorods, a core-crown geometry is developed where the NiOXcapping layer catalyzes the hydrogen evolution reaction (HER). The proposed heterostructure metasurface absorber can impose photocurrent values as large as 50 μA cm-2with a photocurrent spectral response extended up to 500 nm. Moreover, the electrode shows outstanding operation under light irradiation for 9 hours. This work demonstrates a simple, scalable design strategy to fabricate low-cost and stable photocathodes for PEC hydrogen evolution. © 2022 American Chemical Society. All rights reserved.
Open Access
Tunable fano‐resonant metasurfaces on a disposable plastic‐template for multimodal and multiplex biosensing
(Wiley-VCH Verlag, 2020) Ahmed, R.; Özen, M. Ö.; Karaaslan, M. G.; Prator, C. A.; Thanh, C.; Kumar, S.; Torres, L.; Iyer, N.; Munter, S.; Southern, S.; Henrich, T. J.; İnci, Fatih; Demirci, U.
Metasurfaces are engineered nanostructured interfaces that extend the photonic behavior of natural materials, and they spur many breakthroughs in multiple fields, including quantum optics, optoelectronics, and biosensing. Recent advances in metasurface nanofabrication enable precise manipulation of light–matter interactions at subwavelength scales. However, current fabrication methods are costly and time‐consuming and have a small active area with low reproducibility due to limitations in lithography, where sensing nanosized rare biotargets requires a wide active surface area for efficient binding and detection. Here, a plastic‐templated tunable metasurface with a large active area and periodic metal–dielectric layers to excite plasmonic Fano resonance transitions providing multimodal and multiplex sensing of small biotargets, such as proteins and viruses, is introduced. The tunable Fano resonance feature of the metasurface is enabled via chemical etching steps to manage nanoperiodicity of the plastic template decorated with plasmonic layers and surrounding dielectric medium. This metasurface integrated with microfluidics further enhances the light–matter interactions over a wide sensing area, extending data collection from 3D to 4D by tracking real‐time biomolecular binding events. Overall, this work resolves cost‐ and complexity‐related large‐scale fabrication challenges and improves multilayer sensitivity of detection in biosensing applications.
Open Access
Universally polarization-insensitive achromatic metasurfaces
(2019-07) Tanrıöver, İbrahim
Transparent optical components constitute the key elements of modern electro-optical systems including optical sensors, displays and imaging systems. The working principle of conventional transparent components rely on gradual phase accumulation. As a direct result of their working principle, these components suffer from fundamental limitations on size. Metasurfaces, enabling full wavefront engineering in subwavelength thicknesses, are promising candidates to replace conventional optics and overcome the size limitations. Early examples of this concept include plasmonic metasurfaces containing sub-wavelength metallic structures. However, these plasmonic structures cannot reach practically sufficient efficiency levels in transmission mode due to fundamental ohmic losses. This strongly motivates highefficiency all-dielectric alternatives. These dielectric solutions have thus far been reported to rely on either the resonance tuning or the geometrical (Pancharatnam– Berry) phase. Though remedying the efficiency limitation, unfortunately, these approaches either are impaired with ultra-narrow operation bands or suffer polarization dependency. In this thesis, we propose and demonstrate two new approaches to address these problems. In the first approach of ours, universally polarization-insensitive achromatic wavefront control is achieved using dielectric nanopillars operated as stepindex cylindrical waveguides intentionally away from the scattering resonances. A metalens operating in the mid-wave infrared region of electromagnetic spectrum is shown using these off-resonance waveguiding unit cells as a proof-of-concept demonstration. Polarization-insensitive diffraction-limited focusing over a broad spectral band of operation is verified by full electromagnetic simulations. In our second approach, to further increase the performance and bandwidth of dielectric metasurfaces, a novel architecture of these phase elements is proposed. Full phase control of wavefront is achieved using these unit cells. Such metalenses operating in the mid-wave infrared and visible regions are designed as proof-of-concept demonstrations. Full electromagnetic solutions confirmed entirely polarizationinsensitive achromatic focusing of the proposed metasurfaces with significantly increased operation bandwidth.