Thermally tunable terahertz metasurface absorber based on all dielectric indium antimonide resonator structure

Highlights

• A thermally tunable terahertz metasurface absorber (MSA) was proposed.

• The absorbance of MSA is 99.9% at 1.43 THz and the Q-factor is about 26.9 when external environment temperature is 285 K.

• Physics origin of MMA is studied by electric field and power loss density distributions.

• The absorption of the MSA can be adjusted by changing environment temperature and the parameters of the unit-cell structure.

Abstract

In this paper, we present a novel design of temperature tunable metasurface absorber (MSA) based on all dielectric indium antimonide (InSb) resonator structure in terahertz (THz) region. The permittivity of the InSb dielectric is dependent on the variation of temperature. Based on the perfect impedance-match (Re(z)≈1) to the free space, the absorbance of the proposed MSA is up to 99.9% at 1.43 THz and the Q-factor is about 26.9 when temperature is 285 K. The perfect absorption of the MSA is mainly from excitation of fundamental dipolar mode. In addition, the MSA is polarization-insensitive for both transverse electric (TE) and transverse magnetic (TM) waves. Furthermore, the absorption properties of the MSA can be adjusted by changing the geometric parameters of the unit-cell structure and temperature. The design offers a new route for control of THz absorption with potential applications in imaging, energy harvesting, sensing, and detecting.

Introduction

Terahertz (THz) technology has attracted research attention increasingly in recent decades since its great potential application in imaging, security, biomedicine, communication, and so on [[1], [2], [3], [4], [5]]. However, the development and practical applications of this technology still faces some challenges since the lack of materials in nature that response for THz waves. Electromagnetic (EM) metamaterials (MMs) or metasurfaces as artificially engineered composite materials/structures with sub-wavelength resonant element arrays have rendered us numerous opportunities to obtain exotic effect and phenomenon in THz region that unavailable easily in natural materials [6,7]. Owing to their extraordinary EM properties, MMs have been applied in lens [8], absorbers [9], sensors [[10], [11], [12], [13]], solar energy [14], filters [15], polarization rotator/convertor [16,17], and modulator [18]. THz metamaterial absorbers (MMAs) are especially attractive since they have great application values in stealth, imaging, sensing/detection, communication and other fields [19]. Since Tao et al. proposed and demonstrated the first THz MMA with absorption rate of 70% at 1.3 THz by independently adjusting the permittivity and permeability to match the impedance of free space [19], which has gradually become one of the research hotspots in THz area. MMAs typically consist of three layers, a patterned metallic resonator structure (eg. patch, ring, split-ring, cut-wire, cross and its variation) layer, a dielectric spacer layer, and a metallic ground-plane [[19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]]. Various THz MMAs with appropriate geometrical parameters and constituent materials can display unique absorption characteristics, such as narrowband [[19], [20], [21]], multiband or broadband [[22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40]], and insensitivity to angles of incidence and polarization [[40], [41], [42], [43], [44], [45], [46]]. Although various desirable absorption properties of THz MMAs have been explored by designing complex geometries, which is hard to meet the requirement of practical integration in modern thin, miniaturized, and planar devices. To overcome these issues, all-dielectric metasurfaces provide another approach, which have been used to construct the THz devices in a relative simple configuration [[47], [48], [49], [50], [51], [52], [53], [54], [55], [56], [57]].

Recently, all-dielectric metasurface absorbers (MSAs) have been developed through special structural designs of dielectric or semiconductor materials [[50], [51], [52], [53], [54], [55], [56], [57], [58]]. The benefits of all-dielectric MSAs are that they allow for perfect absorption while requiring relatively simple geometric structures. For example, Cole, et al. demonstrated an all-dielectric MSA using simple cylinder structure, which can achieve near-perfect absorption (99.5%) in THz region [50]. Padilla et al. proposed and demonstrated experimentally all-dielectric MSAs using boron doped silicon based on hybrid dielectric waveguide resonance, achieving an absorption of 97.5%, which can be applied for uncooled terahertz imaging [51,52]. Gao et al. proposed and demonstrated experimentally an all-dielectric MSA using zirconium dioxide (ZrO₂) microspheres based on the Mie-resonance by self-assembly method, yielding near-unity absorption around 0.4 THz [53]. We recently demonstrated an all-dielectric MSA using bilayer polydimethylsiloxane (PDMS) resonator structure based on surface plasmonic polaritons (SPPs) and guided mode resonance, which can achieve dual-band perfect absorption in THz region [54]. However, in these all-dielectric MSAs, the absorption characteristics have been fixed once the designed structures are fabricated, which will limit their practical applications. Thus, it is urgently needed to the development of MSAs with active regulation and control by means of electricity, light, and heat [32,[56], [57], [58], [59]].

In this paper, we proposed and demonstrated a thermally tunable MSA based on an indium antimonide (InSb) dielectric resonator structure in THz region. The unit-cell of the MSA consists of periodic array of InSb star shaped structure adhered on a continuous gold film. The dielectric property of the InSb can be actively adjusted through the external environment heat with different temperature. Simulation results exhibit that the MSA can achieve an absorbance of over 99% with the high Q-factor of about 26.9 at 1.43 THz when the temperature is 285 K. In addition, the performance of the designed MSA can be kept stable under normal incidence with different polarization angle for both TE and TM modes. The absorption mechanism of the MSA was illustrated by analyzing the distributions of the electric field and power loss density of the unit-cell structure. Finally, we also study systematically the absorption properties of the MSA by changing the geometric parameters of the InSb resonator structure and external environment temperature. The temperature sensitivity of the MSA is about 9.6 GHz/K. Thus, our design has some potential applications in communication, sensing, and imaging in THz region.