Abstract-Characteristic analysis of a photoexcited tunable metamaterial absorber for terahertz waves

• 
  • Pibin Bing, 
   
  • Xinyue Guo, Hua
   
  •  Wang, 
   
  • Zhongyang Li, J
   
  • ianquan Yao,
   https://link.springer.com/article/10.1007%2Fs12596-019-00533-1

The absorption characteristics of a photoexcited tunable perfect metamaterial absorber (PMA) at terahertz (THz) frequencies are analyzed based on the split-ring resonators (SRRs)-dielectrics-metallic structure, which are caused by different thicknesses and dielectric constants of polyimide, cell sizes and widths of SRRs, and lengths and conductivities of the photosensitive silicon. The results manifest that the resonance frequency and absorption strength of the designed PMA can be tuned by adjusting the shape, size, thickness, and properties of the metallic structure and dielectric spacer. The simple design and wide frequency tuning range of the PMA can find potential applications in terahertz detectors, filters, switchers, and absorbers.

Abstract- Stochastic Polynomial Chaos Expansion Analysis of a Split Ring Resonator at Terahertz Frequencies

Hulusi Acikgoz,  Raj Mittra,

http://ieeexplore.ieee.org/document/8279392/

Polynomial Chaos Expansion technique is applied to a conducting array of Split Ring Resonator to study the effect of the uncertainties of its design parameters on its reflectance at THz frequencies. The uniformly distributed random input design parameters have been considered. The first (average) and second (standard deviation) moments are estimated using the PCE. Strong variation of the output response caused by the uncertainties of the design parameters has been noticed. A sensitivity analysis has been carried out to assess the influence of each input parameters on the reflectance. The results show the effectiveness of the PCE and demonstrate that the PCE can be a useful statistical tool to analyze electromagnetic structures.

Abstract-Electromagnetically induced transparency control in terahertz metasurfaces based on bright-bright mode coupling

Riad Yahiaoui, Joshua A. Burrow, Sirak M. Mekonen, Andrew Sarangan, Jay Mathews, Imad Agha, Thomas A. Searles

http://arxiv-export-lb.library.cornell.edu/abs/1712.08733

We demonstrate a classical analogue of electromagnetically induced transparency (EIT) in a highly flexible planar terahertz metamaterial (MM) comprised of three-gap split ring resonators. The keys to achieve EIT in this system are the frequency detuning and hybridization processes between two bright modes coexisting in the same unit cell as opposed to bright-dark modes. We present experimental verification of two-bright mode coupling for a terahertz EIT-MM in the context of numerical results and theoretical analysis based on a coupled Lorentz oscillator model. In addition, a hybrid variation of the EIT-MM is proposed and implemented numerically in order to dynamically tune the EIT window by incorporating photosensitive silicon pads in the split gap region of the resonators. As a result, this hybrid MM enables the potential active optical control of a transition from the on-state (EIT mode) to the off-state (dipole mode).

Abstract-Colossal Terahertz Field Enhancement using Split-Ring Resonators with a Sub-10 nm Gap

Nayeon Kim, Sungjun In, Dukhyung Lee, Jiyeah Rhie, Jeeyoon Jeong, Dai-Sik Kim, Namkyoo Park


http://pubs.acs.org/doi/abs/10.1021/acsphotonics.7b00627?mi=aayia761&af=R&AllField=nano&target=default&targetTab=std

Terahertz (THz) nanogap structures have emerged as versatile platforms for THz science and applications by virtue of their strong in-gap field enhancements and accompanying high levels of sensitivity to gap environments. However, despite their potential, reliable fabrication methods by which to create THz structures with sub-10 nm gaps remain limited. In this work, we fabricated THz split-ring resonator (SRR) arrays featuring a sub-10 nm split gap. Our fabrication method, involving photolithography, argon ion milling, and atomic layer deposition, is a high-throughput technique which is also applicable to the fabrication of other THz structures with sub-10 nm gaps. Through THz-time domain spectroscopy and a numerical simulation, we identified the fundamental magnetic resonances of the nanogap SRRs, at which the electric field enhancement factor is experimentally estimated to be around 7000. This substantial field enhancement makes SRRs with a sub-10 nm gap suitable for the study of high-field phenomena and related applications.

Abstract-Terahertz spectroscopy of graphene complementary split ring resonators with gate tunability

Satoru Suzuki, Yoshiaki Sekine and Kazuhide Kumakura

http://iopscience.iop.org/article/10.7567/JJAP.56.095102/meta

Polarized transmission and reflection spectra in the terahertz region were obtained from a graphene complementary split ring resonator device. The complementary structure combined with an ion gel gate electrode rendered the optical properties of the device tuneable. The oscillator strength at the intraband plasmon resonance was largely enhanced with the gate-voltage-induced doping, and absorption exceeded 2.3%/layer of the interband transition. The resonance frequency could also be largely increased with the gate voltage. These results suggest the possibility of graphene-based metamaterials with tuneable permeability or permittivity and tuneable resonance frequencies.

Abstract-Sensing viruses using terahertz nano-gap metamaterials

S. J. Park, S. H. Cha, G. A. Shin, and Y. H. Ahn

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-8-8-3551

We demonstrate highly sensitive detection of viruses using terahertz split-ring resonators with various capacitive gap widths. Two types of viruses, with sizes ranging from 60 nm (PRD1) to 30 nm (MS2), were detected at low densities on the metamaterial surface. The dielectric constants of the virus layers in the THz frequency range were first measured using thick films, and the large values found identified them as efficient target substances for dielectric sensing. We observed the resonance-frequency shift of the THz metamaterial following deposition of the viruses on the surface at low-density. The resonance shift was higher for the MS2 virus, which has a relatively large dielectric constant. The frequency shift increases with surface density until saturation and the sensitivity is then obtained from the initial slope. Significantly, the sensitivity increases by about 13 times as the gap width in the metamaterials is decreased from 3 µm to 200 nm. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization.

© 2017 Optical Society of America

Abstract-Angle- and Polarization-Insensitive Metamaterial Absorber using Via Array

Daecheon Lim

, Dongju Lee

 & Sungjoon Lim

http://www.nature.com/articles/srep39686

In this paper, we propose an angle- and polarization-insensitive metamaterial absorber. We design a metamaterial unit cell that is based on a split ring cross resonator (SRCR). We observe that the absorption frequency and absorption ratio are insensitive to incident angles when a via array surrounds the SRR. We demonstrate the effect of the via array using full-wave simulations by comparing the absorptivity of the SRCR with and without the via array. Because of the symmetric geometry, we also realize polarization insensitivity. We build the proposed absorber on a printed-circuit-board with 30 × 30 unit cells, and we demonstrate its performance experimentally in free space. Under normal incidence, the fabricated absorber shows 99.6% absorptivity at 11.3 GHz for all polarization angles, while for oblique incidence, the fabricated absorber maintains an absorptivity higher than 90% for incident angles up to 70° and 60° for transverse magnetic (TM) and transverse electric (TE) modes, respectively.

Abstract-Metamaterial terahertz switch based on split-ring resonator embedded with photoconductive silicon

Metamaterial terahertz switch based on split-ring resonator embedded with photoconductive silicon Xinwang Liu, Hongjun Liu, Qibing Sun, and Nan Huang  »View Author Affiliations

Applied Optics, Vol. 54, Issue 11, pp. 3478-3483 (2015)
http://dx.doi.org/10.1364/AO.54.003478

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-54-11-3478

View Full Text Article

Enhanced HTML    Acrobat PDF (929 KB)

In this paper, a metamaterial terahertz (THz) switch based on a split-ring resonator embedded with photoconductive silicon is presented and numerically investigated. Simulation results show that the switch works at two different resonant modes with different pump light powers and that the response time of the switch is less than 1 ps. By defining the switching window as the frequency range where the transmission magnitude of the ON state is one order of magnitude higher than the OFF state, a switching window ranging from 1.26 to 1.49 THz is obtained. The large modulation depth of the switch is due to the large separations of the maximum and minimum transmissions, which are 0.89 and 0.01, respectively. Particularly, the switch is frequency tunable by changing the thickness and permittivity of the dielectric layer.

© 2015 Optical Society of America

Abstract-Enhanced spin-precession dynamics in a spin-metamaterial coupled resonator observed in terahertz time-domain measurements

T. Kurihara, K. Nakamura, K. Yamaguchi, Y. Sekine, Y. Saito, M. Nakajima, K. Oto, H. Watanabe, and T. Suemoto

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.144408

We demonstrate enhancement of the spin precession of orthoferrite ErFeO3 using the magnetic near-field produced by a split-ring resonator (SRR), using the terahertz pump-optical Faraday probe measurement. The precession amplitude was enhanced by ∼8 times when the resonance frequency of spin precession was close to the magnetic resonance of SRR. The time evolution of spin precession was successfully reproduced by a coupled spin- and SRR-resonance model mediated by the magnetic near-field. It is suggested that optimization of the metamaterial structure would further increase the enhancement factor, leading to the nonlinear control of spin dynamics using terahertz radiation.

DOI: http://dx.doi.org/10.1103/PhysRevB.90.144408

• 
• 
• 
• 

• 
  

Highly efficient broadband terahertz radiation from metamaterials

A THz spectrometer driven by femtosecond laser pulses was used to demonstrate THz emission from a split-ring resonator metamaterial of single nanometer thickness
 http://phys.org/news/2014-01-highly-efficient-broadband-terahertz-metamaterials.html#jCp

by Breehan Gerleman Lucchesi

(Phys.org) —Scientists at the U.S. Department of Energy's Ames Laboratory have demonstrated broadband terahertz (THz) wave generation using metamaterials. The discovery may help develop noninvasive imaging and sensing, and make possible THz-speed information communication, processing and storage. The results appeared in the Jan. 8 issue of Nature Communications.

Terahertz electromagnetic waves occupy a middle ground between electronics waves, like microwave and radio waves, and photonics waves, such as infrared and UV waves. Potentially, THz waves may accelerate telecom technologies and break new ground in understanding the fundamental properties of photonics. Challenges related to efficiently generating and detecting THz waves has primarily limited their use.

Traditional methods seek to either compress oscillating waves from the electronic range or stretch waves from the optical range. But when compressing waves, the THz frequency becomes too high to be generated and detected by conventional electronic devices. So, this approach normally requires either a large-scale electron accelerator facility or highly electrically-biased photoconductive antennas that produce only a narrow range of waves.

To stretch optical waves, most techniques include mixing two laser frequencies inside an inorganic or organic crystal. However, the natural properties of these crystals result in low efficiency.

So, to address these challenges, the Ames Laboratory team looked outside natural materials for a possible solution. They used man-made materials called metamaterials, which exhibit optical and magnetic properties not found in nature.

Costas Soukoulis, an Ames Laboratory physicist and expert in designing metamaterials, along with collaborators at Karlsruhe Institute of Technology in Germany, created a metamaterial made up of a special type of meta-atom called split-ring resonators. Split-ring resonators, because of their u-shaped design, display a strong magnetic response to any desired frequency waves in the THz to infrared spectrum.

A team led by Ames Laboratory physicists demonstrated broadband, gapless terahertz emission (red line) from split-ring resonator metamaterials (background) in the telecomm wavelength. The THz emission spectra exhibit significant enhancement at magnetic-dipole resonance of the metamaterials emitter (shown in inset image). This approach has potential to generate gapless spectrum covering the entire THz band, which is key to developing practical THz technologies and to exploring fundamental understanding of optics.

Ames Laboratory physicist Jigang Wang, who specializes in ultra-fast laser spectroscopy, designed the femto-second laser experiment to demonstrate THz emission from the metamaterial of a single nanometer thickness.

"The combination of ultra-short laser pulses with the unique and unusual properties of the metamaterial generates efficient and broadband THz waves from emitters of significantly reduced thickness," says Wang, who is also an associate professor of Physics and Astronomy at Iowa State University.

The team demonstrated their technique using the wavelength used by telecommunications (1.5 microns), but Wang says that the THz generation can be tailored simply by tuning the size of the meta-atoms in the metamaterial.

"In principle, we can expand this technique to cover the entire THz range," said Soukoulis, who is also a Distinguished Professor of physics and astronomy at Iowa State University.

What's more, the team's metamaterial THz emitter measured only 40 nanometers and performed as well as traditional emitters that are thousands of times thicker.

"Our approach provides a potential solution to bridge the 'THz technology gap' by solving the four key challenges in the THz emitter technology: efficiency; broadband spectrum; compact size; and tunability," said Wang.

Soukoulis, Wang, Liang Luo and Thomas Koschny's work at Ames Laboratory was supported by the U.S. Department of Energy's Office of Science. Wang's work is partially supported by Ames Laboratory's Laboratory Directed Research and Development (LDRD) funding.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.

Ames Laboratory is a U.S. Department of Energy Office of Science national laboratory operated by Iowa State University. Ames Laboratory creates innovative materials, technologies and energy solutions. We use our expertise, unique capabilities and interdisciplinary collaborations to solve global problems.

 Explore further: Laser guided codes advance single pixel terahertz imaging

More information: "Broadband terahertz generation from metamaterials." Liang Luo, Ioannis Chatzakis, Jigang Wang, Fabian B. P. Niesler, Martin Wegener, Thomas Koschny, Costas M. Soukoulis. Nature Communications 5, Article number: 3055 DOI: 10.1038/ncomms4055. Received 05 August 2013 Accepted 03 December 2013 Published 08 January 2014

Abstract-The ratio of the kinetic inductance to the geometric inductance: a key parameter for the frequency tuning of the THz semiconductor split-ring resonator

Jiawei Cong, Binfeng Yun, and Yiping Cui  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-21-17-20363

By introducing the frequency tuning sensitivity, an analytical model based on equivalent LC circuit is developed for the relative frequency tuning range of THz semiconductor split-ring resonator (SRR). And the model reveals that the relative tuning range is determined by the ratio of the kinetic inductance to the geometric inductance (RKG). The results show that under the same carrier density variation, a larger RKG results in a larger relative tuning range. Based on this model, a stacked SRR-dimer structure with larger RKG compared to the single SRR due to the inductive coupling is proposed, which improves the relative tuning range effectively. And the results obtained by the simple analytical model agree well with the numerical FDTD results. The presented analytical model is robust and can be used to analyze the relative frequency tuning of other tunable THz devices.