Browsing by Author "Vandenbosch, G. A. E."

Now showing 1 - 12 of 12

Open Access
Connection of collimation, asymmetric beaming, and independent transmission-reflection processes in concentric-groove gratings supporting spoof surface plasmons
(Springer, 2019) Habib, Mohsin; Serebryannikov, A. E.; Çağlayan, H.; Vandenbosch, G. A. E.; Özbay, Ekmel
Transmission through subwavelength apertures enables separation of the incidence half-space and the exit half-space, which leads to that the spatial distribution of the field in the latter is not affected by the distribution in the former. The distribution in the exit half-space is mainly determined by the properties of surface plasmons (SPs) at the exit-side interface. In this paper, for the microwave structures with one-side concentric corrugations around a single annular hole, we demonstrate the possible connections between asymmetric transmission in the beaming regime and collimation of the waves incident at different angles, which can be considered as two sides of the same phenomenon occurring due to the common effect of such a separation and the radiation shaping effect being possible due to the spoof SPs at the corrugated exit interface. Collimation manifests itself in that the waves incident at different angles from a wide range contribute to the single outgoing beam so that a far-zone observer cannot distinguish between the contributions of different angles of arrival. Asymmetry in transmission manifests itself in that the spatial shaping of radiation (beaming) in the exit half-space appears only for one of the two opposite incidence directions. Moreover, even in the structures with the same corrugations on both sides, i.e., without asymmetric transmission, spatial separation of two wave processes, e.g., two symmetric or asymmetric collimation processes, can be obtained for a wide range of nonzero angles of incidence.
Open Access
Embedded arrays of annular apertures with multiband near-zero-index behavior and demultiplexing capability at near-infrared
(OSA - The Optical Society, 2019-07-27) Hajian, Hodjat; Serebryannikov, A. E.; Krawczyk, M.; Vandenbosch, G. A. E.; Özbay, Ekmel
In this paper, we study transmission through the embedded arrays of subwavelength annular apertures at near-infrared. Single, i.e. non-embedded arrays of annular holes are known for their capability for high-efficiency transmission even through rather thick apertures in a wide frequency range, extending from microwaves to the visible. In the suggested structures, which contain up to four embedded arrays, multiband operation can be obtained, so that each array is mainly responsible for one of four transmission bands. In such a way, a demultiplexing-like functionality can be realized, i.e. the desired parts of the incident-wave spectrum are distributed between several transmission channels. In the studied structures, we obtain (nearly) zero phase advancement and that indicates near-zero-index behavior at the expected propagation thresholds of plasmonic modes in the frequency domain. Therefore, the earlier developed concept of supercoupling and squeezing into very narrow waveguide channels is applicable to the studied structures. The number of near-zero-index bands is determined by the number of the embedded arrays. The effects of thickness, width of the slits, and permittivity of the filling material are numerically studied and discussed in detail. It is shown that multiband transmission may exist in the near-zero-index regime in a very wide range of parameter variations.
Open Access
A route to unusually broadband plasmonic absorption spanning from visible to mid-infrared
(Springer, 2019) Aalizadeh, Majid; Khavasi, A.; Serebryannikov, A. E.; Vandenbosch, G. A. E.; Özbay, Ekmel
In this paper, a route to ultra-broadband absorption is suggested and demonstrated by a feasible design. The high absorption regime (absorption above 90%) for the suggested structure ranges from visible to mid-infrared (MIR), i.e., for the wavelength varying from 478 to 3278 nm that yields an ultra-wide band with the width of 2800 nm. The structure consists of a top-layer-patterned metal-insulator-metal (MIM) configuration, into the insulator layer of which, an ultra-thin 5 nm layer of manganese (Mn) is embedded. The MIM configuration represents a Ti-Al2O3-Ti tri-layer. It is shown that, without the ultra-thin layer of Mn, the absorption bandwidth is reduced to 274 nm. Therefore, adding only a 5 nm layer of Mn leads to a more than tenfold increase in the width of the absorption band. It is explained in detail that the physical mechanism yielding this ultra-broadband result is a combination of plasmonic and non-plasmonic resonance modes, along with the appropriate optical properties of Mn. This structure has the relative bandwidth (RBW) of 149%, while only one step of lithography is required for its fabrication, so it is relatively simple. This makes it rather promising for practical applications.
Open Access
A simple mie-resonator based meta-array with diverse deflection scenarios enabling multifunctional operation at near-infrared
(De Gruyter Open, 2020) Aalizadeh, Majid; Serebryannikov, A. E.; Özbay, Ekmel; Vandenbosch, G. A. E.
Deflection, a basic functionality of wavefront manipulation is usually associated with the phase-gradient metasurfaces and the classical blazed gratings. We numerically and experimentally demonstrate an unusually wideband and simultaneously wide-angle deflection achieved at near-infrared in reflection mode for a periodic (nongradient), ultrathin meta-array comprising only one silicon nanorod (Mie resonator) per period. It occurs in the range where only the first negative diffraction order and zero order may propagate. Deflection serves as the enabler for multifunctional operation. Being designed with the main goal to obtain ultra-wideband and wide-angle deflection, the proposed meta-array is also capable in spatial filtering and wide-angle splitting. Spatial filtering of various types can be obtained in one structure by exploiting either deflection in nonzero diffraction orders, or the specular-reflection (zero-order) regime. Thus, the role of different diffraction orders is clarified. Moreover, on–off switching of deflection and related functionalities is possible by changing polarization state of the incident wave. The suggested device is simple to fabricate and only requires cost-effective materials, so it is particularly appropriate for the large-area fabrication using nanoprint lithography. Ultra-wideband wide-angle and other deflection scenarios, along with the other functionalities, are promising for applications in optical communications, laser optics, sensing, detection, and imaging.
Open Access
Tailoring far-infrared surface plasmon polaritons of a single-layer graphene using plasmon-phonon hybridization in graphene-LiF heterostructures
(Nature Publishing Group, 2018) Hajian, Hodjat; Serebryannikov, A. E.; Ghobadi, Amir; Demirağ, Yiğit; Bütün, Bayram; Vandenbosch, G. A. E.; Özbay, Ekmel
Being one-atom thick and tunable simultaneously, graphene plays the revolutionizing role in many areas. The focus of this paper is to investigate the modal characteristics of surface waves in structures with graphene in the far-infrared (far-IR) region. We discuss the effects exerted by substrate permittivity on propagation and localization characteristics of surface-plasmon-polaritons (SPPs) in single-layer graphene and theoretically investigate characteristics of the hybridized surface-phonon-plasmon-polaritons (SPPPs) in graphene/LiF/glass heterostructures. First, it is shown how high permittivity of substrate may improve characteristics of graphene SPPs. Next, the possibility of optimization for surface-phonon-polaritons (SPhPs) in waveguides based on LiF, a polar dielectric with a wide polaritonic gap (Reststrahlen band) and a wide range of permittivity variation, is demonstrated. Combining graphene and LiF in one heterostructure allows to keep the advantages of both, yielding tunable hybridized SPPPs which can be either forwardly or backwardly propagating. Owing to high permittivity of LiF below the gap, an almost 3.2-fold enhancement in the figure of merit (FoM), ratio of normalized propagation length to localization length of the modes, can be obtained for SPPPs at 5-9 THz, as compared with SPPs of graphene on conventional glass substrate. The enhancement is efficiently tunable by varying the chemical potential of graphene. SPPPs with characteristics which strongly differ inside and around the polaritonic gap are found.
Open Access
Temperature-mediated invocation of the vacuum state for switchable ultrawide-angle and broadband deflection
(Nature Publishing Group, 2018) Serebryannikov, A. E.; Lakhtakia, A.; Aalizadeh, Majid; Özbay, Ekmel; Vandenbosch, G. A. E.
Temperature-mediated appearance and disappearance of a deflection grating in a diffracting structure is possible by employing InSb as the grating material. InSb transits from the dielectric state to the plasmonic state in the terahertz regime as the temperature increases, this transition being reversible. An intermediate state is the vacuum state in which the real part of the relative permittivity of InSb equals unity while the imaginary part is much smaller. Then the grating virtually disappears, deflection being impossible as only specular reflection can occur. This ON/OFF switching of deflection and relevant angular filtering are realizable over wide ranges of frequency and incidence angle by a temperature change of as low as 20 K. The vacuum state of InSb invoked for ON/OFF switching of deflection and relevant angular filtering can also be obtained for thermally tunable materials other than InSb as well as by using non-thermal mechanisms.
Open Access
Toward electrically tunable, lithography-free, ultra-thin color filters covering the whole visible spectrum
(Nature Publishing Group, 2018) Aalizadeh, Majid; Serebryannikov, A. E.; Khavasi, A.; Vandenbosch, G. A. E.; Özbay, Ekmel
The possibility of real-time tuning of optical devices has attracted a lot of interest over the last decade. At the same time, coming up with simple lithography-free structures has always been a challenge in the design of large-area compatible devices. In this work, we present the concept and the sample design of an electrically tunable, lithography-free, ultra-thin transmission-mode color filter, the spectrum of which continuously covers the whole visible region. A simple Metal-Insulator-Metal (MIM) cavity configuration is used. It is shown that using the electro-optic dielectric material of 4-dimethyl-amino-N-methyl-4-stilbazoliumtosylate (DAST) as the dielectric layer in this configuration enables efficient electrical tuning of the color filter. The total thickness of the structure is 120 nm, so it is ultra-thin. The output color gets tuned from violet to red by sweeping the applied voltage from −12 to +12 Volts (V). We present an in-detail optimization procedure along with a simple calculation method for the resonance wavelength of the MIM cavity that is based on circuit theory. Such power-efficient structures have a large variety of potential applications ranging from optical communication and switching to displays and color-tunable windows.
Open Access
Tunable deflection and asymmetric transmission of THz waves using a thin slab of graphene-dielectric metamaterial, with and without ENZ components
(Optical Society of America, 2018) Serebryannikov, A. E.; Hajian, Hodjat; Beruete, M.; Özbay, Ekmel; Vandenbosch, G. A. E.
Tunable deflection of obliquely incident, linearly polarized terahertz waves is theoretically studied in a wide frequency range around 20 THz, by combining a thin slab of graphene-dielectric metamaterial (with ten layers of graphene), a dielectric grating, and a uniform polar-dielectric slab operating in the epsilon-near-zero (ENZ) regime. The modulation of the deflection intensity and deflection angle is done by varying the chemical potential of graphene, and is realized with or without connection to the asymmetric transmission. It is shown to depend on the location of the graphene-dielectric metamaterial slab, as well as on the incidence angle. Four scenarios of tunable deflection are found, including the ones realizable in two-component structures without an ENZ slab.
Open Access
Tunable infrared asymmetric light transmission and absorption via graphene-hBN metamaterials
(American Institute of Physics, 2019) Hajian, Hodjat; Ghobadi, Amir; Serebryannikov, A. E.; Bütün, Bayram; Vandenbosch, G. A. E.; Özbay, Ekmel
We theoretically prove in this paper that using planar multilayer graphene-hexagonal boron nitride (hBN) metamaterials (GhMMs) can yield ultrabroadband and high-contrast asymmetric transmission (AT) and asymmetric absorption (AA) of light. The AA and AT features are obtained in the far-infrared (FIR) and mid-infrared (MIR) regions for normally incident light with transverse magnetic polarization. Here, the GhMMs are integrated with two asymmetric gratings of Ge and are composed of alternating multilayers of graphene (11 multilayers) and hBN layers (10 layers). Moreover, the total subwavelength thickness of the hybrid structures is about 3 μm, being less than half of the free-space wavelength up to nearly 50 THz. This approach—which is similar to the one introduced by Xu and Lezec [Nat. Commun. 5, 4141 (2014)] for a passive hyperbolic metamaterial operating in the visible range—is based on the excitation of high-ββ modes of the GhMM with different transmission characteristics. In addition to being ultrabroadband and high-contrast, AT and AA features of the proposed GhMMs can be actively tuned by varying the chemical potential of graphene. Furthermore, it is shown that an on-off switching of AT factor at FIR and selective tunability at MIR frequencies can be obtained via varying μμ. Due to its subwavelength and planar configuration and active operation, these multilayer graphene-hBN metamaterials with AT and AA characteristics hold promise for integration with compact optical systems operating in the MIR and FIR ranges and are suitable for applications such as optical diodes, sensors, and thermal emitters.
Open Access
Ultra-miniature dual-band antenna based on subwavelength resonators on LiNbO3 substrate
(IET, 2018) Serebryannikov, A. E.; Gokkavas, M.; Gundogdu, F. T.; Vandenbosch, G. A. E.; Vasylchenko, A.; Özbay, Ekmel
The common effect of subwavelength resonators and a high-permittivity lithium niobate substrate is used for deep-subwavelength miniaturization of a dual-band S/C-band monopole antenna. The resulting size is just about 1/18th of a wavelength for the lower band.
Open Access
Ultraminiature antennas combining subwavelength resonators and a very-high-ε uniform substrate: the case of lithium niobate
(IEEE, 2020) Serebryannikov, A. E.; Gökkavas, Mutlu; Gündoğdu, Tamara Funda; Volski, V.; Vandenbosch, G. A. E.; Vasylchenko, A.; Özbay, Ekmel
Combining the effects of subwavelength resonators and very-high-permittivity substrates enables a high extent of miniaturization, even for very simple, split-loop resonators. Here, we demonstrate how requirements to the substrate's permittivity are connected with the desired extent of miniaturization and why materials with a relative permittivity of 30 <; ε <; 100, like lithium niobate, may offer a real possibility to miniaturize. For demonstration purposes, we designed, in line with this approach, an ultraminiature dual-band antenna to operate at 2.8 and 4.2 GHz. The antenna is fabricated using microfabrication techniques and studied experimentally. There is good agreement between the measurement and simulation results. The realized gain is about -5 dB for the first resonance, at which the size of the substrate-resonator block is λ/24. The obtained results demonstrate the potential of the suggested approach, which is expected to be applicable to a very wide class of subwavelength resonators and a wide variety of substrates with high permittivity.
Open Access
VO2-hBN-graphene-based bi-functional metamaterial for mid-infrared bi-tunable asymmetric transmission and nearly perfect resonant absorption
(OSA - The Optical Society, 2019) Hajian, Hodjat; Ghobadi, Amir; Serebryannikov, A. E.; Bütün, Bayram; Vandenbosch, G. A. E.; Özbay, Ekmel
Bi-tunable asymmetric light transmission (AT) and nearly perfect resonant absorption functionalities are achieved by a Lorentz-reciprocal metamaterial for the operation at the mid-infrared (MIR) wavelengths and transverse magnetic polarization. The bi-tunable metamaterial with bi-functional features and a total thickness of 1.8 μm is based on an hBN/graphene/hBN heterostructure that is bounded by a Ge grating on the upper side and a hybrid VO2/AuVO2/Au grating on the lower side. Through analytical calculations, we first investigate how the dispersion characteristics of the high-𝛽β hyperbolic phonon polaritons of hBN can be controlled and hybridized through the insulator (i-VO2i-VO2) to metal (m-VO2m-VO2) transition of VO2VO2 in a bare hBN/VO2hBN/VO2 heterostructure. Then, at the absence of graphene and owing to the support of the hybridized high-𝛽β modes, a broad and efficient AT with forward-to-backward contrast exceeding 40% is obtained by numerical calculations for the i-VO2i-VO2 case, as the first functionality of the structure. Moreover, it is found that for the m-VO2m-VO2 case, the device is no longer transmittive and a nearly perfect resonant absorption response, as the second functionality, is observed for backward illumination. Finally, by introducing multilayer graphene into the structure and considering the intermediate states of VO2VO2 in the calculations, the bi-tunable transmission and absorption characteristics of the device are investigated. We believe the designed metamaterial is well-suited for MIR optical diodes, sensors, and thermal emitters.