Browsing by Subject "Metasurface"

Now showing 1 - 12 of 12

Open Access
Adaptive metasurface designs for thermal camouflage, radiative cooling, and photodetector applications
(2022-01) Buhara, Ebru
Metamaterials, described as artificial sub-wavelength nanostructures, refer to a class of manufactured materials that possess distinctive electromagnetic features which cannot be found with natural materials. Thermal tunability, negative re-fractive index, perfect absorption, and invisible cloaking are examples of these attributes. Here, we design and implement metamaterials in four important ap-plication areas, namely 1) Multi-spectral infrared camouflage through excitation of plasmon-phonon polaritons in a visible-transparent hBN-ITO nanoantenna emitter, 2) Adaptive visible and short-wave infrared camouflage using a dynami-cally tunable metasurface, 3) Mid-infrared adaptive thermal camouflage using a phase-change material coupled dielectric nanoantenna, 4) An All-Dielectric Meta-surface Coupled with Two-Dimensional Semiconductors for Thermally Tunable Ultra-narrowband Light Absorption. In the first work, a metasurface design is developed to provide adaptive camou-flage in both visible and SWIR ranges. The proposed metasurface is made of an indium tin oxide (ITO) grating on a metal-insulator-metal (MIM, Ag-Sb2S3-Ag) nanocavity. In the amorphous state, the design operates as a colored transmis-sive window while, in the crystalline phase, it switches into a reflective mirror. In the meantime, the cavity acts as a thermally tunable host for the ITO nanoan-tenna providing tunable SWIR absorption to cover two transmissive regions at 1150-1350 nm (Region I) and 1400-1700 nm (Region II). It is found that the excitation of extended surface plasmons (ESPs) and guided mode resonances (GMRs) are responsible for light absorption in the SWIR range. Our theoretical calculations show that, besides the design’s ability for color adoption, the SWIR reflectance in Region I/Region II are reduced to 0.37/0.53 and 0.75/0.25 in the amorphous/crystalline phases. In the second work, a hybrid nanoantenna architecture made of ITO-hBN grating is proposed to satisfy all multi-spectral camouflage requirements. In this design, simultaneous excitation of plasmon-phonon polaritons in ITO and hBN leads to broadband absorption in the NTIR range and reflection in MWIR and LWIR ranges. Moreover, the bulk absorption in ITO film provides SWIR mode camouflage. Moreover, to highlight the importance of this hybrid design, the ITO-hBN design is compared with ITO-TiO2 heterostructure(TiO2 is a lossless dielectric in our desired ranges). Finally, the camouflage performance of the meta-surface is evaluated as the outgoing emission suppression when the metasurface design is on top of the blackbody object. In the third work, a PCM-dielectric based metasurface nanoantenna emitter design is proposed to achieve low observability at the MIR region by tailoring the spectral emissivity of the design. The proposed thermal nanoantenna emitter is composed of a high index dielectric (silicon (Si) in our case) nanograting on top of a thick silver (Ag) mirror. An ultrathin VO2 interlayer is embedded within the grating to actively tune its absorption response. The design geometries are adopted to place the resonance wavelengths in the atmospheric absorption win-dows for thermal camouflage applications. Based on the position of the VO2 layer, the optical response of the design in the metal phase can be diversely tuned from a narrowband to a broadband thermal emitter. Therefore, upon increase in the surface temperature, the proposed metasurface based thermal nanoantenna emitter turns into a broadband emitter with a stronger radiative thermal emission while it compatibly releases its heat based on the camouflage technology require-ment. The proposed design has perfect matching with atmospheric absorption windows so that it can efficiently release its heat without being observed by ther-mal camera systems. The detectability of the structure by a possible IR sensor is calculated using power calculations over the selected spectra. In addition, due to the hysteresis behavior of VO2, the calculations are done separately for cooling and heating conditions. In the fourth and final work, a dielectric based metasurface platform is pro-posed to achieve ultra-narrowband light absorption within a monolayer thick TMDC layer. For this purpose, the metasurface design is optimized. Then, this design is coupled with mono and multilayer TMDCs to observe better absorption results. For this purpose, MoS2, and WS2 are chosen as the most commonly used TMDCs. The coupling of light into Mie resonances, supported by dielec-tric nanograting, provides narrowband absorption within the TMDC layer. To reach further enhancement, a cavity design is integrated into this dielectric-based metasurface. For the best optimized design, the absorptance efficiency reaches to 0.85 and FWHM stays as narrow as 3.1 nm. Finally, the thermal tunability char-acteristic of the design is shown, without use of any phase change material. This is achieved due to strong light confinement within the design. Due to this con-finement, any small change in the refractive index is seen by the resonant design. Thus, the resonance frequency shifts and thermal tunability is acquired. The thermal sensitivity of the above-mentioned optimized design reaches to 0.0096 nm/◦C.
Open Access
Adaptive thermal camouflage using sub-wavelength phase-change metasurfaces
(Institute of Physics Publishing Ltd., 2022-12-09) Omam, Zahra Rahimian; Ghobadi, Amir; Özbay, Ekmel; Khalichi, Bahram
Sub-wavelength metasurface designs can be used to artificially engineer the spectral thermal signature of an object. The real-time control of this emission can provide the opportunity to switch between radiative cooling (RC) and thermal camouflage functionalities. This performance could be achieved by using phase-change materials (PCMs). This paper presents a sub-wavelength dynamic metasurface design with the adaptive property. The proposed metasurface is made of vanadium dioxide (VO2) nanogratings on a silver (Ag) substrate. The design geometries are optimized in a way that both narrowband and broadband mid-infrared (MIR) emitters can be realized. At low temperatures, insulating VO2 nanogratings trigger the excitation of Fabry–Perot mode inside the grating and surface plasmon polaritons at the metal–dielectric interface with an emission peak located in the MIR region to maximize the RC performance of the design. As temperature rises, the PCM transforms into a metallic phase material and supports excitation of Wood's anomaly and localized surface plasmon resonance modes. Accordingly, the thermal signature is adaptively suppressed.
Open Access
Adaptive thermally tunable radiative cooling with angle insensitivity using phase-change-material-based metasurface
(Institute of Physics Publishing Ltd., 2023-11-17) Boşdurmaz, Ekin Bircan; Ghobadi, Amir; Özbay, Ekmel
Radiative cooling is the passive cooling of a material with the help of a specific spectral response to emit thermal energy into space through atmospheric transparency windows. However, most of the proposed designs have no dynamically tunable emission response. In this paper, we present a feasible inverse pyramid structure made of a phase change material (PCM) on top of a metallic mirror to realize an adaptive radiative cooler with almost angle-independent emission response. The design uses the thermally controlled PCM called Samarium nickelate (SmNiO3) to actively tune the spectral response of the design, which, in turn, allows the design to radiatively cool itself. The emission response of the design is compatible with atmospheric transmissive windows. As the design heated up to higher temperatures, the peak of the emission spectrum red-shifts and moves toward the atmospheric transparency window.
Open Access
An all-dielectric metasurface coupled with two-dimensional semiconductors for thermally tunable ultra-narrowband light absorption
(Springer, 2020) Buhara, Ebru; Ghobadi, Amir; Özbay, Ekmel
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted tremendous attention over the past decades. Due to their unique features such as high mobility and direct bandgap, they are suitable candidate for the optoelectronic devices. However, due to their ultrathin thickness, their optical absorption is quite weak, and therefore, a trapping scheme for strong light- matter interaction is essential to overcome this deficiency. To accomplish strong light absorption, loss-less dielectric-based metasurfaces with ideally no parasitic absorption are excellent choices. Herein, we report an ultra-narrowband thermally tunable all-dielectric metasurface coupled absorber with TMD monolayer. In this proposed structure, high absorption with ultra-narrow full-width-at-half-maximum (FWHM) is achieved. Different design configurations are studied to find the most suitable structure. In the optimized design, an absorptance as high as 0.85 with a FWHM of 3.1 nm is achieved. This structure also shows thermal sensitivity of 0.0096 nm/°C, without the use of any phase change material component. This architecture can be used as a 2D and highly efficient tunable single-color photodetector. The proposed dielectric metasurface can be adopted for other types of 2D and ultrathin semiconductor-based optoelectronics.
Open Access
Design of metamaterial-based nanostructures for 5G applications & thermal radiation management
(2023-06) Boşdurmaz, Ekin Bircan;
The properties of natural materials can be the only limiting factor in today’s technologies. For this, researchers in the last decades found that engineering the features of naturally occurring materials in the subwavelength scales can drasti-cally change their properties. These materials beyond the natural ones are called “metamaterials”, where “meta” means “beyond” in Greek. Although the fabrica-tion of these materials can be quite challenging, clever designs and exploitation of physical phenomena can lead to tunable responses, eliminating the need for multi-ple structures. Here, diﬀerent strategies for designing tunable meta-surfaces for a wide range of applications will be presented by giving two examples. These appli-cations are namely: 1. Graphene-based Metasurface Absorber for the Active and Broadband Manipulation of Terahertz Radiation, 2. Adaptive Thermally Tunable Radiative Cooling with Angle Insensitivity Using Phase-Change Material-Based Metasurface.
Open Access
Dielectric metasurfaces as passive radiative coolers, colorimetric refractive index sensors, color filters, and one-way perfect absorber/reflectors with transparent sidebands
(2020-07) Yıldırım, Deniz Umut
Metamaterials deﬁne the class of synthetic, man-made materials with exotic properties that cannot be observed with natural materials. Their sub-wavelength counterparts are called metasurfaces. In particular, dielectric metasurfaces are extensively studied due to the advantages they oﬀer in comparison to metamaterials, which are mainly their reduced thickness and not suﬀering from ohmic losses that are present in metals. Here, we design and implement dielectric metasurfaces in four important application areas, namely 1. Passive radiative coolers for spacecraft, 2. Colorimetric refractive index sensors, and 3. Color ﬁlters based on monolayer graphene. 4. A metasurface with a resonant one-way absorption/reﬂection with transmissive sidebands functionality In the ﬁrst work, we propose a facile, lithography-free fabrication route, exploiting oblique deposition to design an optical solar reﬂector, which constitutes the physical interface between the spacecraft and space. Our proposed metasurface is 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 µm to 25 µm. In the solar spectrum, low-loss dielectric characteristic of ITO resulted in an experimental solar absorptivity as small as 0.168. This 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. In the second work, we propose a highly-sensitive refractive index sensor, utilizing the excitation of guided-modes of a novel, 2-dimensional periodically modulated dielectric grating-waveguide structure. The optimized nanosensor can numerically excite guided-mode resonances with an ultra-narrow linewidth (fullwidth at half-maximum) of 0.58 nm. Sensitivity is numerically investigated by considering the deposition of dielectric layers on the structure. For a layer thickness of 30 nm, the maximum sensitivity reached as high as 110 nm/refractive index unit (RIU), resulting in a very high Figure of Merit of 190. The fabricated devices with 30 nm Aluminum Oxide and Zinc Oxide coatings achieved a maximum sensitivity of 235.2 nm/RIU with a linewidth of 19 nm. Colorimetric detection with polarization-insensitivity is conﬁrmed practically by a simple optical microscope. Samples with diﬀerent coatings have been observed to have clearly distinct colors, while the color of each sample is nearly identical upon azimuthal rotation. Excellent agreement is obtained between the numerical and experimental results regarding the spectral position of the resonances and sensitivity. The proposed device is, therefore, highly promising in eﬃcient, highlysensitive, almost lossless, and compact molecular diagnostics platform in the ﬁelds of biomedicine with personalized, label-free, early point-of-care diagnosis and ﬁeld analysis, drug detection, and environmental monitoring. In the third work, we numerically propose a graphene perfect absorber that can be utilized as a color ﬁlter, utilizing the excitation of guided-modes of a dielectric slab waveguide by a novel sub-wavelength dielectric grating structure. When the guided-mode resonance is critically coupled to the graphene, we obtain perfect absorption with an ultra-narrow bandwidth (full-width at half-maximum) of 0.8 nm. The proposed design not only preserves the spectral position of the resonance, but also maintains > 98% absorption at all polarization angles. The spectral position of the resonance can be tuned as much as 400 nm in visible and near-infrared regimes by tailoring geometrical parameters. The proposed device has great potential in eﬃcient, tunable, ultra-sensitive, compact and easyto-fabricate advanced photodetectors and color selective notch ﬁlters. In the fourth and ﬁnal work, we numerically propose the one-way perfect absorption of near-infrared (NIR) radiation in a tunable spectral range with high transmission in the neighboring spectral ranges. This functionality is obtained by using a 2-dimensional, guided-mode resonance based grating-waveguide metasurface that acts as a frequency-selective reﬂector, a spacer dielectric, and an absorbing oxide layer. Within the bandwidth of the excited guided-mode resonance excited at 1.82µm with a full-width at half-maximum of 19 nm), we conﬁrmed perfect absorption when light is incident from one of the two opposite directions, whereas in the other direction, perfect reﬂection is observed. The forward-to-backward absorption ratio reached as high as 60, while the thickness of the entire structure is in the order of the operating wavelength. In addition to the spectral tunability of the excited resonances and their bandwidths, our proposed device supports transparency windows with 65% transmission in the adjacent frequency bands. Our 2D grating is also veriﬁed to enable near-absolute insensitivity to the polarization state of incident light. Geometrical parameter modiﬁcation also gives our design great tunability, as we also designed a device with 300 nm absorption/reﬂection linewidth.
Embargo
Giant ultrafast all-optical modulation based on exceptional points in exciton–polariton perovskite metasurfaces
(American Chemical Society, 2024-01-22) Masharin, Mikhail A.; Oskolkova, Tatiana; Işık, Furkan; Demir, Hilmi Volkan; Samusev, A. K.; Makarov, S .V.
Ultrafast all-optical modulation with optically resonant nanostructures is an essential technology for high-speed signal processing on a compact optical chip. Key challenges that exist in this field are relatively low and slow modulations in the visible range as well as the use of expensive materials. Here we develop an ultrafast all-optical modulator based on MAPbBr3 perovskite metasurface supporting exciton–polariton states with exceptional points. The additional angular and spectral filtering of the modulated light transmitted through the designed metasurface allows us to achieve 2500% optical signal modulation with the shortest modulation time of 440 fs at the pump fluence of ∼40 μJ/cm2. Such a value of the modulation depth is record-high among the existing modulators in the visible range, while the main physical effect behind it is polariton condensation. Scalable and cheap metasurface fabrication via nanoimprint lithography along with the simplicity of perovskite synthesis and deposition make the developed approach promising for real-life applications.
Open Access
Highly one-way electromagnetic wave transmission based on outcoupling of surface plasmon polaritons to radiation modes
(Institute of Electrical and Electronics Engineers, 2022-09-21) Khalichi, Bahram; Omam, Zahra Rahimian; Osgouei, Ataollah Kalantari; Ghobadi, Amir; Özbay, Ekmel
Unidirectional transmission of electromagnetic waves has attracted great interest due to its wide modern optical applications. This study theoretically demonstrates a one-way transmissive optical device with a high-contrast forward-to-backward ratio at the near-infrared region. The polarization-independent optical diode-like mechanism is designed using a metasurface diffraction grating configuration with symmetry breaking property along the wave propagation in which the working principle is based on the excitation of surface plasmon modes at the interfaces of thin metallic interlayer and their coupling to the radiation modes.
Open Access
Near-field inter-coupled cell-less metasurface fabrics and their applications
(2021-07) Yağcı, Hüseyin Bilge
Metasurfaces are subwavelength-thick artiﬁcial structures with engineered re-sponses, designed to provide functionalities that do not exist in the natural do-main. Their application areas are broad and vary in both functionality and operation regime. Across all functionalities and regimes, the fundamental pur-pose behind the metasurfaces is to manipulate the surrounding electromagnetic landscape to form devices with superior sensitivity and eﬃciency. With conven-tional design routines and available high-index materials, this was achieved across longer wavelengths in the past decade. However, the lack of suitable materials in the higher frequencies limit the design space for the mainstream approaches that discretize the phase surface with the help of independent nanostructures, dubbed as “meta-cells” or alternatively “meta-atoms”. With increasing frequencies, the discrepancy between a smoothly-changing eﬀective index surface and a discretized step-index surface increase, resulting in unwanted scattering. Additionally, the methodology behind the uncoupled scatterers break up as the meta-atoms act collectively in suﬃciently small scales, resulting in topology-induced errors in the generated phase response. In this thesis, a new class of highly eﬃcient meta-surfaces relying on the near-ﬁeld coupling of identical scatterers in a continuous fabric is proposed. Contrary to the conventional approach, which sees the inter-cell coupling as phase distortions, our proposed methodology utilizes near-ﬁeld coupling between the nearest neighbors, enabling lattice generation schemes ap-plicable at broad scales that are insusceptible to topological errors. Owing to these, this methodology oﬀers opportunities in further miniaturization of optical consumer products. One of the functionalities high in demand from metasurfaces is eﬃcient and achromatic focusing with compact devices in the visible range, core to contact lenses and smartphone cameras. However, the examples in the litera-ture are not suﬃcient in terms of either broadband performance or eﬃciency. Our proposed phase acquisition scheme eﬀectively eliminates inhomogeneous scatter-ing while reducing the design procedure to the tiling of the phase surface, subject to a function of the nearest-neighbor distances. Here, with this methodology, one cylindrical and one circular achromatic metasurface lenses (metalenses) with near-diﬀraction-limit focusing operating across the whole visible spectrum are demonstrated as a proof of concept. The validity of the utilized approach is con-ﬁrmed via both waveguide solutions and full electromagnetic computations. Both structures proved to be highly eﬃcient, with the cylindrical one having superior eﬃciency in its preferred polarization, whereas the circular one is highly eﬃcient while operating independent of polarization. These ﬁndings prove the applicabil-ity of our near-ﬁeld inter-coupled cell-less metasurface fabrics as a compact and eﬃcient optical device generation framework.
Open Access
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
Single and coupled metasurfaces for tunable polarization-sensitive terahertz filters
(IEEE, 2016) Serebryannikov A.E.; Lakhtakia A.; Özbay, Ekmel
We simulated the transmission of terahertz waves through a single metasurface and two coupled metasurfaces that comprise H-shaped subwavelength resonators made of InAs, a magnetically tunable material. The magnetostatic field was varied from 0 to 1 T. The obtained results demonstrate that the substrate permittivity and the coupling of metasurfaces can significantly affect filtering performance as well as the possibility of tuning for different orientations of the magnetostatic field. ï¿½ 2016 IEEE.
Open Access
VO2–graphene-integrated hBN-based metasurface for bi-tunable phonon-induced transparency and nearly perfect resonant absorption
(Institute of Physics Publishing Ltd., 2021-03-23) Erçağlar, Veysel; Hajian, Hodjat; Özbay, Ekmel
A bi-tunable hexagonal boron nitride (hBN)-based metasurface with bi-functional phonon-induced transparency (PIT) and nearly perfect resonant absorption features in the mid-infrared (MIR) range is proposed. The metasurface, that is composed of axially symmetric hBN rings, is separated from a uniform thin vanadium dioxide (VO2) film with a SiO2 spacing layer and is integrated with a top graphene sheet. For the insulating phase of VO2 (i-VO2), PIT with an 80% transmission contrast ratio is observed inside the reststrahlen (RS) band of hBN due to the support of hyperbolic phonon polaritons. A considerably large group delay of 9.5 ps and up to 1.8 THz RIU−1 frequency shift per refractive index unit is also achieved for the i-VO2 case. On the other hand, it is found that for the metallic phase of VO2 (m-VO2), light transmission is prohibited and nearly perfect resonant absorption peaks are appeared inside the RS band of hBN. Finally, by integrating the hBN-based metasurface into the graphene sheet on the top, a tunable PIT-like effect and nearly perfect light absorption is achieved duo to the hybridization of graphene plasmons and hBN phonons. This leads to a modulation depth as high as 87% in the transmission (i-VO2) and 62% in the absorption (m-VO2) responses. Our findings offer a tunable and bi-functional device that is practical for MIR slow-light, sensing, and thermal emission applications.