Browsing by Author "Hajian, Hodjat"

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Open Access
Active metamaterial nearly perfect light absorbers: A review [Invited]
(Optical Society of America, 2019) Hajian, Hodjat; Ghobadi, Amir; Bütün, Bayram; Özbay, Ekmel
Achieving nearly perfect light absorption from the microwave to optical region utilizing metamaterials has begun to play a significant role in photonics and optoelectronics due to their vital applications in thermal emitters, thermal photovoltaics, photovoltaics, sensing, filtering, and photodetection. However, employing passive components in designing perfect absorbers based on metamaterials and photonic crystals imposes some limits on their spectral operation. In order to overcome those limits, extensive research has been conducted on utilizing different materials and mechanisms to obtain active metamaterial light absorbers. In this review paper, we investigate the recent progress in tunable and reconfigurable metamaterial light absorbers through reviewing different active materials and mechanisms, and we provide a perspective for their future development and applications.
Open Access
Anisotropic absorber and tunable source of MIR radiation based on a black phosphorus-SiC metasurface
(Elsevier BV, 2022-03-28) Hajian, Hodjat; Rukhlenko, I. D.; Hanson, G. W.; Özbay, Ekmel
We propose a black phosphorus-silicon carbide (BP-SiC) metasurface with in-plane structural symmetry that can act as both a nearly perfect anisotropic absorber and tunable polarized source of mid-infrared (MIR) radiation. The metasurface is a periodic array of square SiC patches integrated with a BP flake at the top and separated from a bottom reflector by a BaF2 spacer. We first use analytical calculations and numerical simulations to study the hybridization of the anisotropic plasmons of BP with isotropic phonons of SiC. We also analyze the in-plane characteristics of the resulting hybrid modes of the BP/SiC heterostructure and the BP-SiC metasurface. It is then demonstrated that the proposed metasurface can serve as a nearly perfect anisotropic absorber of MIR radiation with highly selective and omnidirectional features. It is also shown that the metasurface can be used as a polarized MIR source with tunable temperature, which is determined by the thermal equilibrium between the matter and radiation. The suggested design holds promise for artificial coatings that can tune the blackbody thermal signatures, MIR sensing, and highly directional in-plane transportation of the MIR energy.
Open Access
Bismuth-based metamaterials: From narrowband reflective color filter to extremely broadband near perfect absorber
(De Gruyter, 2019) Ghobadi, Amir; Hajian, Hodjat; Gökbayrak, Murat; Bütün, Bayram; Özbay, Ekmel
In recent years, sub-wavelength metamaterials-based light perfect absorbers have been the subject of many studies. The most frequently utilized absorber configuration is based on nanostructured plasmonic metals. However, two main drawbacks were raised for this design architecture. One is the fabrication complexity and large scale incompatibility of these nano units. The other one is the inherent limitation of these common metals which mostly operate in the visible frequency range. Recently, strong interference effects in lithography-free planar multilayer designs have been proposed as a solution for tackling these drawbacks. In this paper, we reveal the extraordinary potential of bismuth (Bi) metal in achieving light perfect absorption in a planar design through a broad wavelength regime. For this aim, we adopted a modeling approach based on the transfer matrix method (TMM) to find the ideal conditions for light perfect absorption. According to the findings of our modeling and numerical simulations, it was demonstrated that the use of Bi in the metal-insulator-metal-insulator (MIMI) configuration can simultaneously provide two distinct functionalities; a narrow near unity reflection response and an ultra-broadband near perfect absorption. The reflection behavior can be employed to realize additive color filters in the visible range, while the ultra-broadband absorption response of the design can fully harvest solar irradiation in the visible and near infrared (NIR) ranges. The findings of this paper demonstrate the extraordinary potential of Bi metal for the design of deep sub-wavelength optical devices.
Open Access
Correction to: Active tuning from narrowband to broadband absorbers using a sub-wavelength VO2 embedded layer
(Springer, 2021-02-04) Osgouei, Ataollah Kalantari; Hajian, Hodjat; Khalichi, Bahram; Serebryannikov, Andriy E.; Ghobadi, Amir; Özbay, Ekmel
Metamaterial perfect absorbers (MPAs) with dynamic thermal tuning features are able to control the absorption performance of the resonances, providing diverse applications spanning from optical switches and filters to modulators. In this paper, we propose an MPA with diverse functionalities enabled by vanadium dioxide (VO2) embedded in a metal-dielectric plasmonic structure. For the initial design purpose, a silicon (Si) nanograting on a silver (Ag) mirror is proposed to have multiple resonant responses in the near infrared (NIR) region. Then, the insertion of a thin VO2 layer at the right position enables the design to act as an on/off switch and resonance tuner. In the insulator phase of VO2, in which the permittivity data of VO2 is similar to that of Si, a double strong resonant behavior is achieved within the NIR region. By increasing the temperature, the state of VO2 transforms from insulator to metallic so that the absorption bands turn into three distinct resonant peaks with close spectral positions. Upon this transformation, a new resonance emerges and the existing resonance features experience blue/red shifts in the spectral domain. The superposition of these peaks makes the overall absorption bandwidth broad. Although Si has a small thermo-optic coefficient, owing to strong light confinement in the ultrasmall gaps, a substantial tuning can be achieved within the Si nanogratings. Therefore, the proposed hybrid design can provide multi-resonance tunable features to cover a broad range and can be a promising strategy for the design of linearly thermal-tunable and broadband MPAs. Owing to the proposed double tuning feature, the resonance wavelengths exhibits great sensitivity to temperature, covering a broad wavelength range. Overall, the proposed design strategy demonstrates diverse functionalities enabled by the integration of a thin VO2 layer with plasmonic absorbers.
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
Epsilon-near-zero enhancement of near-field radiative heat transfer in BP/hBN and BP/α-MoO3 parallel-plate structures
(AIP Publishing LLC, 2022-03-16) Hajian, Hodjat; Rukhlenko, I.D.; Erçağlar, Veysel; Hanson, G.; Özbay, Ekmel
Black phosphorous (BP) is a well-known two-dimensional van der Waals (vdW) material with in-plane anisotropy and remarkable electronic and optical properties. Here, we comprehensively analyze the near-field radiative heat transfer (NFRHT) between a pair of parallel non-rotated BP flakes that occurs due to the tunneling of the coupled anisotropic surface plasmon polaritons (SPPs) supported by the flakes. It is demonstrated that the covering of the BP flakes with hexagonal boron nitride (hBN) films leads to the hybridization of the BP's SPPs with the hBN's hyperbolic phonon polaritons and to the significant enhancement of the NFRHT at the hBN's epsilon-near-zero frequencies. It is also shown that the NFRHT in the BP/hBN parallel-plate structure can be actively switched between the ON and OFF states by changing the chemical potential of the BPs and that the NFRHT can be modified by altering the number of the BP layers. Finally, we replace hBN with α-MoO3 and explore how the NFRHT is spectrally and strongly modified in the BP/α-MoO3 parallel-plate structure. We believe that the proposed BP/polar-vdW-material parallel-plate structures can prove useful in the thermal management of optoelectronic devices. Following the pioneering work of Polder and Hove,1 the near-field radiative heat transfer (NFRHT) has attracted considerable attention in the last two decades due to its promising applications in thermophotovoltaics,2,3 thermal rectification,4 electroluminescent cooling,5 thermal diodes,6 and transistors.7 While the propagating waves contribute to the far-field radiative heat transfer,8 the evanescent waves are responsible for the heat flux in the NFRHT—also referred to as photon tunneling. It is known that the NFRHT is considerably enhanced due the excitation of surface polaritons.9,10 The efficiency of the NFRHT can exceed the blackbody limit by several orders in magnitude via the resonant coupling of surface plasmon polaritons (SPPs) in structures based on metals,11,12 doped Si,1–14 and surface phonon polaritons in heat transfer devices composed of SiO2,15 Al2O3,16 and SiC.17,18 Moreover, it was shown that due to the thermal excitation of isotropic graphene SPPs, NFRHT between two closely spaced parallel-plates of graphene can be strongly mediated, enhanced, and tuned via the modification of the chemical potential of graphene in the infrared range.19–22 Black phosphorous (BP) is often used as an anisotropic plasmonic van der Waals (vdW) material for the realization of enhanced NFRHT.23,24 It has a tunable bandgap, ranging from 1.51 eV for a monolayer BP to 0.59 eV for a five-layer BP, and a thickness-dependent anisotropic absorption coefficient.25 The latter feature implies that, unlike graphene, the SPPs of BP exhibit anisotropic behavior.26 Moreover, it has been reported that the thermal conductivities of BP along the zigzag and armchair directions are three orders of magnitude lower than that of graphene at 300 K.27 This makes BP a better candidate than graphene for the heat management via NFRHT. Recent studies have revealed that the NFRHT is greatly enhanced by the out-of-plane hyperbolic plasmon polaritons or phonon polaritons (HPPs) of metamaterials28–32 as well as by the in-plane modes of the graphene-based33,34 or BP-based35 metasurfaces. However, the dependence of the maximum wavenumber of HPPs on the size of the unit cell and the associated fabrication complexity (due to electron beam lithography or several film deposition processes) of the hyperbolic metamaterials or metasurfaces challenge their practical realization for the NFRHT purposes. Natural hyperbolic vdW materials, such as hexagonal boron nitride (hBN)36–38 and α-MoO3,39,40 have also been used to enhance the NFRHT. It has been demonstrated that the NFRHT can be mechanically tuned in twisted hBN films37 or actively modulated in graphene-hBN heterostructures.41–43 Because α-MoO3 has different optical responses along its three crystallographic directions, a similar mechanical modulation of the NFRHT is observed for the twisted films of α-MoO3 with differently aligned surfaces.40 Despite a great deal of recent studies on this topic, the active modulation of enhanced NFRHT in non-rotated epsilon-near-zero BP/hBN and BP/α-MoO3 parallel-plate structures has not been analyzed so far to the best of our knowledge. In the present paper, we comprehensively analyze the NFRHT between two parallel non-rotated BP flakes covered with hBN films [Fig. 1(b)]. It is found that the coupling of the anisotropic plasmons of BP with the hyperbolic phonons of hBN considerably enhances the NFRHT near the edges of the Reststrahlen bands (RBs) of hBN, where hBN exhibits the epsilon-near-zero (ENZ) feature. We demonstrate the possibilities of the active and passive tunings of the NFRHT through changing the chemical potential and altering the number of layers of the BP flakes. It is also shown that the replacement of hBN with α-MoO3 allows one to strongly manipulate the spectrum of the NFRHT in the structure.
Open Access
Erratum: α -MoO3-SiC metasurface for mid-IR directional propagation of phonon polaritons and passive daytime radiative cooling (Applied Physics Letters (2022) 121 (182201) DOI: 10.1063/5.0128110)
(AIP Publishing LLC, 2022-11-21) Erçağlar, Veysel; Hajian, Hodjat; Rukhlenko, I.D.; Özbay, Ekmel
This article was originally published online on 31 October 2022 with errors in the Author Contributions section and Refs. 24 and 41. The Author Contributions section and references are shown correctly below. All online and printed versions of the article were corrected on 1 November 2022. AIP Publishing apologizes for this error. © 2022 Author(s).
Open Access
Graphene-based metasurface absorber for the active and broadband manipulation of terahertz radiation
(Optica, 2021-09) Boşdurmaz, Ekin Bircan; Hajian, Hodjat; Erçağlar, Veysel; Özbay, Ekmel
Graphene-based metasurface nearly perfect absorbers (MPAs) can be used as an efficient tool for the active control and manipulation of waves in the terahertz (THz) gap. Here, we propose a novel, to the best of our knowledge, graphene-based MPA that is designed based on a simple configuration and is capable of absorbing THz radiation within a broad bandwidth of almost 3 THz with polarization-insensitive and omnidirectional characteristics. The MPA comprises a periodic array of graphene patches with two different dimensions that are separated from a gold bottom reflector with an SiO2 spacer layer. The broadband spectral response of the MPA, which is also verified by analytical calculations, is due to the support of propagating surface plasmon excitations and can be either actively tuned via changes in the chemical potential of graphene or passively adjusted by the modification of the geometrical parameters of the patches and thickness of the spacer layer. As a complement to the previous studies in the literature, due to the simplicity of its design and broad spectral response, it is believed that the suggested graphene-based MPA will find potential applications in THz spectroscopy and communications.
Open Access
Hybrid indium tin oxide-Au metamaterial as a multiband bi-functional light absorber in the visible and near-infrared ranges
(2021-04-23) Osgouei, Ataollah Kalantari; Hajian, Hodjat; Serebryannikov, Andriy E.; Özbay, Ekmel
Metamaterial nearly perfect light absorbers (MPAs) with dual-narrowband functionality—that absorb light in two narrowband adjacent wavelength regions—have attracted considerable attention due to their intriguing applications, such as sensing, photovoltaic, and thermal emission. Here, we propose a multi-band MPA with two narrowband absorption responses that are centered on the visible and near-infrared (NIR) wavelengths (773 nm and 900 nm, respectively) and a broadband absorptive characteristic in another window in the NIR region (ranging from 1530 nm to 2700 nm with a bandwidth of 1170 nm). The MPA comprises a periodic array of self-aligned hybrid indium tin oxide (ITO)-Au split-ring-resonators that are separated from an optically thick bottom reflector with a SiO2 layer. Based on numerical calculations, which are accompanied with a semi-analytical examination, we find that the dual narrowband and broadband responses are attributed to the hybridization of the optical responses of gold as a plasmonic material with the ones of ITO. Note that ITO acts as a low-loss dielectric in the visible range and a lossy plasmonic material in the NIR region. Moreover, due to the applied symmetry in the unit cell of the metamaterial, the proposed MPA represents polarization insensitive and omnidirectional absorptive features. The proposed metastructure can find potential applications in selective thermophotovoltaic devices, thermal emitters, and sensors.
Open Access
Hybrid surface plasmon polaritons in graphene coupled anisotropic van der Waals material waveguides
(Institute of Physics Publishing Ltd., 2021-08-23) Hajian, Hodjat; Rukhlenko, I. D.; Hanson, G. W.; Özbay, Ekmel
Polaritons in anisotropic van der Waals materials (AvdWMs), with either hyperbolic or elliptical topologies, have garnered significant attention due to their ability of field confinement and many useful applications in in-plane polariton nanophotonics, including directional guiding, canalization, and hyperlensing. Here, we obtain the dispersion relation of hybrid surface plasmon polaritons (SPPs) supported by a parallel-plate waveguide composed of an AvdWM, as an example tungsten ditelluride, that is coupled with a graphene layer. Through analytical calculations and numerical simulations, we first investigate the impact of losses on the modal characteristics of SPPs supported by the AvdWM. We then show that the coupling of the anisotropic layer to a graphene sheet in a parallel-plate waveguide heterostructure allows one to control the in-plane propagation and dispersion topology of the hybrid SPPs by changing the spacer thickness and the graphene chemical potential. Moreover, it is found that owing to the different coupling regimes, this anisotropic-isotropic SPPs hybridization can enhance the propagation length and spatial localization of the guided modes. We believe this approach can lead to the realization of vdW heterostructures with improved functionalities for in-plane and out-of-plane infrared nanophotonics.
Open Access
Lithography-free planar band-pass reflective color filter using a series connection of cavities
(Nature Publishing Group, 2019-01) Ghobadi, Amir; Hajian, Hodjat; Soydan, Mahmut Can; Bütün, Bayram; Özbay, Ekmel
In this article, a lithography-free multilayer based color flter is realized using a proper series connection of two cavities that shows relatively high efciency, high color purity, and a wide view angle. The proposed structure is a metal-insulator-metal-insulator-semiconductor (MIMIS) design. To optimize the device performance, at the frst step, transfer matrix method (TMM) modeling is utilized to fnd the right choices of materials for each layer. Simulations are carried out later on to optimize the geometries of the layers to obtain our desired colors. Finally, the optimized devices are fabricated and experimentally characterized to evaluate our modelling fndings. The characterization results of the fabricated samples prove the successful formation of efcient and wide view angle color flters. Unlike previously reported FP based designs that act as a band-stop flter in refection mode (absorbing a narrow frequency range and refecting the rest of the spectrum), this design generates a specifc color by refecting a narrow spectral range and absorbing the rest of the spectrum. The fndings of this work can be extended to other multilayer structures where an efcient connection of cavities in a tandem scheme can propose functionalities that cannot be realized with conventional FP resonators.
Open Access
Multifunctional tunable gradient metasurfaces for terahertz beam splitting and light absorption
(Optica, 2021-08-15) Erçağlar, Veysel; Hajian, Hodjat; Serebryannikov, Andriy E.; Özbay, Ekmel
Obtaining functional devices with tunable features is benefi cial to advance terahertz (THz) science and technology. Here, we propose multifunctional gradient metasur faces that are composed of a periodic array of binary Si microcylinders integrated with VO2 and graphene. The metasurfaces act as transmittive (reflective) beamsplitters for the dielectric (metallic) phase of VO2 with a switchable characteristic. Moreover, by integrating the metasurfaces with graphene and modifying its chemical potential, one can tune the intensity of the split beam as well as obtain nearly perfect resonant absorptions. Consequently, the proposed metasurfaces can find potential applications in THz interferometers, multiplexers, and light absorbers.
Open Access
Plasmon and phonon polaritons in planar van der Waals heterostructures
(Elsevier, 2023) Hajian, Hodjat; Erçağlar, Veysel; Özbay, Ekmel
The investigation of the characteristics of plasmon polaritons and phonon polaritons in planar systems is one of the key tools in understanding the optical response of plasmonic and phononic waveguides, metamaterials, and metasurfaces. Due to the considerable research interest in the polaritonics of van der Waals (vdW) materials in recent years, we conducted a detailed study on the infrared isotropic/anisotropic polaritons in plasmonic and phononic van der Waals heterostructures.
Open Access
Quasi-bound states in the continuum for electromagnetic induced transparency and strong excitonic coupling
(Optica, 2024-05-20) Hajian, Hodjat; Zhang, Xia; Mccormack, Oisin; Zhang, Yongliang; Dobie, Jack; Rukhlenko, Ivan d.; Ozbay, Ekmel; Bradley, A. Louise
Advancing on previous reports, we utilize quasi-bound states in the continuum (q-BICs) supported by a metasurface of TiO₂ meta-atoms with broken inversion symmetry on an SiO₂ substrate, for two possible applications. Firstly, we demonstrate that by tuning the metasurface's asymmetric parameter, a spectral overlap between a broad q-BIC and a narrow magnetic dipole resonance is achieved, yielding an electromagnetic induced transparency analogue with a 50 μs group delay. Secondly, we have found that, due to the strong coupling between the q-BIC and WS₂ exciton at room temperature and normal incidence, by integrating a single layer of WS₂ to the metasurface, a 37.9 meV Rabi splitting in the absorptance spectrum with 50% absorption efficiency is obtained. These findings promise feasible two-port devices for visible range slow-light characteristics or nanoscale excitonic coupling.
Open Access
Reprogrammable metasurface design for NIR beam steering and active filtering
(Institute of Physics Publishing Ltd., 2024-07-24) Hajian, Hodjat; Proffit, Matthieu; Özbay, Ekmel; Landais, Pascal; Bradley, A. Louise
Reprogrammable metasurfaces enable active modulation of light at subwavelength scales. Operating in the microwave, terahertz, and mid-infrared ranges, these metasurfaces find applications in communications, sensing, and imaging. Electrically tunable metasurfaces operating in the near-infrared (NIR) range are crucial for light detection and ranging (LiDAR) applications. Achieving a NIR reprogrammable metasurface requires individual gating of nano-antennas, emphasizing effective heat management to preserve device performance. To this end, here we propose an electrically tunable Au-vanadium dioxide (VO2) metasurface design on top of a one-dimensional Si-Al2O3 photonic crystal (PC), positioned on a SiC substrate. Each individual Au-VO2 nano-antenna is switched from an Off to ON state via Joule heating, enabling the programming of the metasurface using 1-bit (binary) control. While operating as a nearly perfect reflector at lambda(0)=1.55 mu m, the materials, thickness, and number of the layers in the PC are carefully chosen to ensure it acts as a thermal metamaterial. Moreover, with high optical efficiency (R similar to 40% at lambda(0)), appropriate thermal performance, and feasibility, the metasurface also enables broadband programmable beam steering in the 1.4-1.7 mu m range for a wide steering angle range. This metasurface design also offers active control over NIR light transmittance, reflectance and absorptance in the wavelength range of 0.75-3 mu m. These characteristics render the device practical for LiDAR and active filtering.
Open Access
Spectrally selective ultrathin photodetectors using strong interference in nanocavity design
(Institute of Electrical and Electronics Engineers Inc., 2019) Ghobadi, Amir; Demirağ, Yiğit; Hajian, Hodjat; Toprak, Ahmet; Bütün, Bayram; Özbay, Ekmel
Thinning the active layer's thickness of the semiconductor down to a level comparable with the carriers' diffusion length while keeping its absorption high is an ultimate goal to boost the performance of optoelectronic devices. Strong interference in multilayer structures is one of the promising and practical solutions owing to their simple and large-scale compatible fabrication route. These nanocavity designs not only provide near unity absorption, but they can also be designed in a way that a spectrally selective absorption response can be achieved. In this letter, we will demonstrate the functionality of a metal- insulator-semiconductor (MIS) cavity to obtain spectrally selective ultrathin photodetectors. To prove our theoretical and numerical findings, a 4-nm-thick amorphous silicon (aSi)-based MIS cavity is designed, fabricated, and characterized. The experimental results show that the optimized cavity design can act as an efficient visible blind ultraviolet (UV) photodetector. The proposed design shows the responsivity values of 120 and 2.5 mA/W in the UV (λ = 350 nm) and visible (λ = 500 nm) regions, respectively.
Open Access
Strong interference in planar, multilayer perfect absorbers: achieving high-operational performances in visible and near-infrared regimes
(Institute of Electrical and Electronics Engineers Inc., 2019) Ghobadi, Amir; Hajian, Hodjat; Bütün, Bayram; Özbay, Ekmel
Light-Matter Interactions at subwavelength-designed nanostructures have been the subject of intensive study in recent years. The realization of an ideal "blackbody" absorber is an emerging topic in nanophotonics and nanoplasmonics. An ideal black absorber is an object that harvests incoming light with near-unity efficiency. Based on their absorption spectral coverage, they are classified as narrow-band or broadband absorbers. This requirement can be achieved in bulky designs that have a thickness much larger than its light penetration depth as well as antireflective surface texturing.
Open Access
Strong light-matter interaction in lithography-free planar metamaterial perfect absorbers
(American Chemical Society, 2018) Ghobadi, Amir; Hajian, Hodjat; Bütün, Bayram; Özbay, Ekmel
The efficient harvesting of electromagnetic (EM) waves by subwavelength nanostructures can result in perfect light absorption in the narrow or broad frequency range. These metamaterial-based perfect light absorbers are of particular interest in many applications, including thermal photovoltaics, photovoltaics, sensing, filtering, and photodetection applications. Although advances in nanofabrication have provided the opportunity to observe strong light-matter interaction in various optical nanostructures, the repeatability and upscaling of these nano units have remained a challenge for their use in large scale applications. Thus, in recent years, the concept of lithography-free planar light perfect absorbers has attracted much attention in different parts of the EM spectrum, owing to their ease of fabrication and high functionality. This Perspective explores the material and architecture requirements for the realization of light perfect absorption using these multilayer metamaterial designs from ultraviolet (UV) to far-infrared (FIR) wavelength regimes. We provide a general theoretical formulation to find the ideal condition for achieving near unity light absorption. Later, these theoretical estimations are coupled with findings of recent studies on perfect light absorbers to explore the physical phenomena and the limits of different materials and design architectures. These studies are categorized in three main class of materials; metals, semiconductors, and other types of materials. We show that, by the use of proper material and design configuration, it is possible to realize these lithography-free light perfect absorbers in every portion of the EM spectrum. This, in turn, opens up the opportunity of the practical application of these perfect absorbers in large scale dimensions. In the last section, we discuss the progress, challenges, and outlook of this field to outline its future direction.
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
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.