In this paper, a broadband and high-efficient tri-layered chiral structure metasurface (CSM) for linear polarization conversion and multi-functional wavefront manipulation was proposed and ...investigated numerically in terahertz region. The unit-cell of the proposed CSM consist of two orthogonal metal wires sandwiched with square split-ring resonator (SRR) structure, which can manipulate the polarization and wavefront of the transmitted wave simultaneously. Based on the Fabry-Perot-like cavity-enhanced effect of proposed CSM, broadband and high-efficiency cross-polarization conversion can be achieved. Numerical simulation results indicate that the cross-polarization transmission coefficient is higher than 0.9 from 0.4 THz to 1.0 THz, with a fractional bandwidth of 85.7%. The proposed CSM can achieve complete 2π phase coverage by adjusting the geometric parameters of the unit-cell structure. Anomalous refraction with a wide angle, two kinds of focusing metalenses and vortex beam generation are investigated to verify the multi-functional wavefront manipulation performance of the proposed CSM. Our work provides an effective method of enhancing the performance of transmission-type metasurface and the proposed devices show endless potential in wavefront control and communication applications in terahertz region.
A simple design of triple-band perfect light absorber (PLA) based on hybrid metasurface in visible region has been presented in this work, which turns out to be applicable for refractive index (RI) ...sensing. Distinct from previous designs, the proposed hybrid metasurface for visible PLA is only consisted of periodic silicon cross nanostructure arrays and gold substrate. The periodic silicon cross arrays deposited on the gold substrate contribute to excite the guided modes under the normal incident light illumination. According to the simulation results, it can be found that three perfect absorption peaks of 98.1%, 98.7%, and 99.6% which are located at 402.5 THz, 429.5 THz, and 471.5 THz, respectively, have been clearly observed in PLA. This triple-band perfect absorption effect could be attributed to the intrinsic loss of silicon material originated from the guided mode excitations caused by the standing waves of different orders. It has been confirmed that the perfect absorption properties of the PLA can be easily regulated by changing the geometric parameters of the unit-cell nanostructure. Furthermore, the designed PLA served as a RI sensor can achieve sensitivity of about 25.3, 41.3, and 31.9 THz /refractive index unit (RIU). It can be believed that the proposed design of PLA for RI sensing would provide great potential applications in sensing, detecting, the enhanced visible spectroscopy, etc.
In this paper, we present a plasmonic chiral metasurface absorber (CMSA), which can achieve high selective absorption for right-handed and left-handed circular polarization (RCP, “+”, and LCP, “−”) ...lights at optical frequency. The CMSA is composed of a dielectric substrate sandwiched with bi-layer fourfold twisted semicircle metal nanostructure. The proposed CMSA has a strong selective absorption band, where absorption peaks for LCP and RCP lights occur at different resonance frequencies, reflecting the existence of a significant circular dichroism (CD) effect. It is shown that the absorbance of the CMSA can reach to 93.2% for LCP light and 91.6% for RCP light, and the maximum CD magnitude is up to 0.85 and 0.91 around 288.5 THz and 404 THz, respectively. The mechanism of the strong chiroptical response of the CMSA is illustrated by electric fields distributions of the unit-cell nanostructure. Furthermore, the influence of the geometry of the proposed CMSA on the circular polarization selective absorption characterization is studied systematically.
In this paper, we present an effective design of a tri-band high-efficiency circular polarization (CP) convertor based on double-split-ring resonator (DSRR) structures in the microwave region. The ...proposed CP convertor is composed of a periodic array of sub-wavelength tri-layered DSRR structures separated by a dielectric spacer, which can convert the normal incident CP wave to its orthogonal one at the three different resonance frequencies. Numerical simulation results indicate that the cross-polarization transmission coefficients of CP wave can achieve maximum values of 0.81 at 6.95 GHz, 0.65 at 10.55 GHz, and 0.81 at 12.85 GHz, respectively, which is in reasonable agreement with experiment. In addition, the corresponding CP conversion efficiency is over 90% at three different resonance frequencies. The simulated surface current distributions indicate that the high-efficient CP conversion properties are mainly attributed to the near field electric and magnetic dipole coupling between the adjacent DSRR layers. Due to its excellent tri-band CP properties, the proposed structure would find potential applications in the fields of remote sensing, radar, and satellite communication.
It has been demonstrated that metasurfaces have the ability to manipulate the wavefront. However, most multifunctional metasurfaces reported to date only operate in either reflection or transmission ...mode. In this paper, a bilayer metasurface based on geometric phase is proposed to independently tailor the wavefronts of transmitted and reflected circularly polarized (CP) waves at two different terahertz frequencies. More specifically, the metasurface can transform the incident CP wave to its cross-polarization component with a high conversion coefficient of about 0.87 (0.92) after refraction (reflection) at 0.6 (1.67) THz. The full 2π phase shift can be obtained independently by varying the geometrical parameters of the unit-cell structure at two different operation modes. As proofs of concept, anomalous refraction and reflection, dual-band full-space cylindrical focusing metalens and vortex beam generation with different modes are numerically demonstrated. Our work provides an effective method to integrate two or more different functionalities into a simple metasurface-based device, and the independent phase modulation characteristic of our proposed metasurface also shows infinite potential in wavefront control of full space.
We present a simple design of a broadband tunable metamaterial absorber (MMA) in the terahertz (THz) region, which consists of a single layer complementary gammadion-shaped (CGS) graphene sheet and a ...polydimethylsiloxane (PDMS) dielectric substrate placed on a continuous metal film. The Fermi energy level (
) of the graphene can be modulated dynamically by the applied DC bias voltage, which enables us to electrically control the absorption performance of the proposed MMA flexibly. When
= 0.8 eV, the relative bandwidth of the proposed MMA, which represents the frequency region of absorption beyond 90%, can reaches its maximal value of 72.1%. Simulated electric field distributions reveal that the broadband absorption mainly originates from the excitation of surface plasmon polaritons (SPPs) on the CGS graphene sheet. Furthermore, the proposed MMA is polarization-insensitive and has wide angles for both transverse-electric (TE) and transverse-magnetic (TM) waves in the broadband frequency range. The broadband absorption capacity of the designed MMA can be effectively adjusted by varying the Fermi energy level of graphene. Lastly, the absorbance of the MMA can be adjusted from 42% to 99.1% by changing the
from 0 eV to 0.8 eV, which is in agreement with the theoretical calculation by using the interference 41theory. Due to its simple structure and flexible tunability, the proposed MMA has potential application prospects in tunable filtering, modulators, sensing, and other multispectral devices.
We present a broadband plasmonic absorber (PA) based on all silicon nanostructure resonators in visible region, which can be functioned as metamaterial (MM) blackbody for nearly all light radiation. ...Distinct from previous designs, the proposed PA is only consisted of periodic all silicon circular-split-ring (CSR) nanostructure resonators array adhered on a continuous gold substrate. Simulation results indicate that the absorbance of the proposed PA is greater 98% from 514 THz to 638 THz, and the absorption peak is up to 99.9% at 520 THz and 626.5 THz, respectively. The proposed PA is polarization-insensitive and toleration of wide incident angles for both transverse electric (TE) and transverse magnetic (TM) modes. In addition, the designed PA can tolerate some geometric parameters errors in fabrication. Thus, the proposed PA for MM blackbody can be potential application in the photodetectors, thermal imaging, photoelectrochemical, and solar energy harvesting devices.
•A broadband visible plasmonic absorber (PA) was proposed.•The absorbance of PA is greater 98% from 514 THz to 638 THz•Physics origin of PA is studied by field and power loss density distributions.•The absorption performance PA can remain stable with small changes of the geometric parameter.
In this paper, a dual-band and high-efficiency circular polarization (CP) convertor based on anisotropic metamaterial (AMM) was proposed and investigated in microwave region. The proposed AMM based ...CP convertor is composed of a sub-wavelength metal grating sandwiched with bi-layered disk-split-ring (DSR) structure array, which can convert the normal incident CP wave to its orthogonal one around two adjacent frequency ranges. Based on the intrinsic anisotropic and Fabry-Perot-like cavity-enhanced effect, a high CP conversion efficiency can be achieved by applying the proposed AMM. Numerical simulation results indicate that the cross-polarization transmission coefficients can achieve maximum values of 0.84 at 4.5 GHz, and 0.92 at 7.9 GHz, respectively, which is in well agreement with experiment. In addition, the measured CP conversion efficiency is beyond 99% at resonance frequencies. The mechanism of the CP conversion properties can be explained by the electromagnetic (EM) interference model and the simulated electrical field distribution. Due to its excellent polarization conversion properties, the proposed CP convertor based on AMM structure shows potential application in such as radar, remote sensing, and satellite communication.
A narrow-band metasurface absorber (MSA) based on InSb micro-cylinder arrays has been proposed and investigated numerically, which could be believed to be applicable for both temperature and ...refractive index (RI) sensing in terahertz (THz) region. Distinct from previous designs, the proposed narrow-band MSA is only consisted of a sub-wavelength periodic micro-cylinder array based on the InSb material possessing an extremely thermosensitive relative permittivity which varies with the external environment temperature, and a gold ground-plane deposited on a glass substrate. Numerical simulation results indicate that the proposed MSA can achieve an absorbance of 99.9% at 1.8985 THz and the corresponding Q-factor is about 120.9 at room temperature (300 K). It is inferred that the narrow-band perfect absorption of the MSA could be contributed to the surface plasmon polariton (SPP) resonance mode excitation. Furthermore, the absorption property of the designed MSA is found to be highly sensitive to the RI value variations of the surrounding mediums and fluctuations of external environment temperature. Thus, the proposed MSA can be not only operated as a temperature sensor with a sensitivity of 2.13 GHz/K, but also a RI sensor with a sensitivity of 960 GHz/RIU (refractive index unit). Due to its high sensing performance, it can be believed that the narrow-band MSA has great potential applications in chemical, biological or other optoelectronic related areas.
A compact microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures based on substrate integrated plasmonic waveguide (SIPW) and spoof surface plasmon polariton (SSPP) is ...proposed and investigated. The dispersion and transmission characteristics of the proposed unit-cell structures of SSPP and SIPW were analyzed numerically, respectively. Numerical results indicate that the high and low cut-off frequencies of the bandpass filter can be independently adjusted by changing geometric parameters of unit-cell structures of SSPP and SIPW, respectively. The proposed microwave bandpass filter has a smaller electrical size because of its better electromagnetic (EM) field constraints than the traditional SIW ones with combed groove lines SSPPs. To verify the design method and concept, a microwave bandpass filter with fishbone-shaped and hourglass-shaped groove structures has been designed, fabricated, and measured. The results demonstrate that the proposed passband is in the range of 7.3–10.1 GHz, the return loss is higher than 10 dB and the insertion loss is less than 2 dB. The microwave bandpass filter is very compact in size, only about 0.99 λ
0
× 0.35 λ
0
, where λ
0
is the wavelength at the center frequency.
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