Search

Terahertz high-data communication creates numerous demands for terahertz wave amplitude modulation. Here, we experimentally demonstrate a high-speed terahertz wave modulator based on 4-N,N-dimethylamino-4'-N'-methyl-stilbazolium tosylate (DAST)/Si hybrid structure. An externally modulated 808-nm pumping laser is utilized to generate photoexcited free carriers at the DAST medium. With the increase of illumination laser intensity, the modulation depth continues to increase in the frequency range from 0.23 to 0.35 THz. A dynamic amplitude modulation at 0.25-THz carrier wave shows that the our modulator provides a modulation speed of 1.26 MHz with a depth of up to 53% at an external pump laser irradiance of 3.5 W/cm2. Our present DAST/Si hybrid structure provides a practicable route to achieve effective signal modulation for terahertz communication system.

Abstract Background As a significant terahertz functional device, terahertz beam splitters with high performance are highly required to meet the need for terahertz communication, terahertz image, and terahertz sensor systems. Results The proposed 1×6 power splitter becomes 1×4 power splitter with the aid of the localized temperature change at the frequency of 1.0THz. The total output power is equivalent to 97.8% of the input power for the six-channel splitter and 95.4% for the four-channel splitter. The dimension of the device is of 35a×27a. Conclusions A temperature-controlled terahertz power divider based on photonic crystal multimode interference structure and Y-junction photonic crystal waveguides is an efficient mechanism for the power divider of terahertz waves. The proposed device paves a promising way for the realization of terahertz wave integrated device.

We investigate the giant tunable Goos-Hänchen shifts in prism/graphene structure. It is found that large positive and negative lateral Goos-Hänchen shifts can be easily controlled by adjusting the chemical potential of the graphene, which is modulated by the external applied electric field. By using the stationary-phase method, we theoretically analyze the effect of the external applied electric field on Goos-Hänchen shifts of the proposed prism/graphene structure. Our theoretical study shows that the magnitude of the Goos-Hänchen shift is more than 200 times that of the operating terahertz wavelength. Numerical calculation results further indicate that the present structure has the potential application for the terahertz-wave switch.

Vortex beams carry orbital angular momentum (OAM), which can increase channel capacity in communication systems. In 2019, the International Telecommunication Union designated the terahertz band as the sixth generation wireless communication carrier, so it is very meaningful to study the OAM of terahertz waves. In this letter, we demonstrated a reflective metasurface terahertz vortex beam generator with a wide operating bandwidth (1.6 ∼ 2.4 THz), which consists of a gold metasurface array and a gold ground plane separated by a polyimide layer. Under illumination of circularly-polarized waves, the proposed metasurface produces vortex beams with topological charges of l = ±1, l = ±2, and l = ±3 with the mode purity larger than 0.6. Simulation results are in good agreement with the theoretical predictions. Our approach provides a new idea for the design of terahertz vortex wave generators. [ABSTRACT FROM AUTHOR]

How to improve the sensitivity of terahertz wave metasurface biosensors has always been a research hotspot in the field of biosensors. In this article, we propose a well-shaped all dielectric metasurface, which can simultaneously excite electromagnetic induced transparency (EIT) and bound states in the continuum (BIC) effects, achieving high sensitivity sensing at three frequency points. The maximum Q value of refractive index sensing is 69238, with a sensitivity of 535 GHz/RIU and the figure of merits (FoM) of 85468. Moreover, the structure exhibits EIT group delay effect, with a maximum group delay of 5.57ps. The results indicate that the well-shaped all dielectric metasurface enhances the interaction between terahertz waves and matter, which can not only achieve multi frequency terahertz high sensitivity sensing, but also be used for the design of new slow light devices. • We propose a well-shaped all dielectric metasurface. • The maximum Q value of refractive index sensing is 69238, with a sensitivity of 535 GHz/RIU. • The structure exhibits EIT group delay effect, with a maximum group delay of 5.57ps. [ABSTRACT FROM AUTHOR]

Coding metasurface offers a promising way for manipulating electromagnetic waves using several structural metaparticles or changing the metaparticle geometry parameters. It leads to time-consuming optimization in multibit coding designs. Different from the previous conventional coding metasurface, both Pancharatnam–Berry (PB) phase and the predesigned coding sequences in the coding elements are used to manipulate terahertz wave, which becomes more flexible. In this paper, a multibit digital coding metasurface is constructed using the PB phase based on a same size metaparticle with various orientations. Both theoretically calculated and numerically simulated scattering patterns of the designed coding PB phase metasurfaces demonstrate the expected manipulations. The designed coding metasurfaces having polarization dependance for left circularly, right circularly, and linearly polarized waves are confirmed. The maximum bandwidth of a radar cross section reduction of approaching –10 B is 0.8 THz (range from 0.8 to 1.6 THz). [ABSTRACT FROM AUTHOR]

In terahertz system, controlling terahertz wave propagation is a very important issue. In this letter, we have proposed and demonstrated a terahertz wave Set-Reset latch based on two-dimensional photonic crystal. The present device consists of two photonic crystal NOR gates and two photonic crystal multimode-interfere structures. Finite-difference time-domain method is used to analyze and confirm the propagation properties of the device. The total size of our proposed Set-Reset latch is equal to 85 a × 40 a . The response time of the Set-Reset latch is 3.25 ps. Our study suggests that the Set-Reset latch has great potential in future terahertz wave information processing integrated circuit. [ABSTRACT FROM AUTHOR]

Generally, one of the disadvantages of the reported metasurface is single-channel, which affects its practical application in multiplexing system. To overcome this shortage, a reflected shared-aperture metasurface is proposed to produce multi-channel and multifunction. The unit cell consists of a square metal strip silicon dioxide substrate and a metal plate bottom layer. Based on geometrical phase theory, 0 ∼ 2 π phase shift can be covered by rotating orientation angles of the top metal strip. The designed metasurface realizes multi-channel and multi-function including four-channel deflected beams with different angles, dual-channel vortex beams with different topological charges, and dual-channel vortex focusing beams under right-handed circularly polarized (RCP) wave incidents. Our investigation offers a simple and effective approach to design high-efficiency terahertz wavefront manipulation devices. • We propose a multi-channel and multi-function terahertz metasurface. • Our structure realizes four-channel deflected beams with different angles, dual-channel vortex beams with different topological charges, and dual-channel vortex focusing beams. • The metasurface offers a simple and effective approach to design high-efficiency terahertz wavefront manipulation devices. [ABSTRACT FROM AUTHOR]

We propose a bi-directional multi-function terahertz metasurface, which consists of photosensitive silicon and metal composite pattern, F4B-metal layer-Si 3 N 4 , photosensitive silicon and split metal ring composite pattern from top to bottom layer. When terahertz wave is incident along +Z direction and the conductivity of the photosensitive silicon is 0 S/m, the metasurface behaves as y -polarization wave to x -polarization wave converter with a bandwidth of 3.82 THz. As the conductivity of the photosensitive silicon changes as 1 × 105 S/m, the proposed structure achieves linear-to-circular polarization converter. When terahertz wave is incident along - Z direction and the conductivity of the photosensitive silicon is 0 S/m, the structure exhibits as a band-stop filter with a stopband bandwidth of 20 GHz. Furthermore, the metasurface becomes a broadband tunable terahertz absorber when the conductivity of the photosensitive silicon changes as 1 × 105 S/m. Our proposed structure behaves bidirectional, switchable and multi-functional terahertz manipulation characteristics, providing a new perspective for multi-function terahertz device design. • We propose a bi-directional multi-function terahertz metasurface. • The proposed structure exhibits a polarization waves converter, band-stop filter and broadband tunable terahertz absorber. • The metasurface provides bidirectional, switchable and multi-functional terahertz manipulation characteristics. [ABSTRACT FROM AUTHOR]

To extend the usage of the terahertz wave, we present a simple method for variable focus length terahertz wave lens based on graphene. The focus length of the graphene-based terahertz lens can be tunable by changing the applied electric field without change the configuration. To demonstrate the feasibility of the approach, numerical simulation performed with the aid of the finite element method is used to evaluate the terahertz performance of the proposed device. With an appropriate design, the focal length of the proposed device can be tuned from 7.3 μm to 15.2 μm. The total size of the present graphene lens is only 3.5 μm×13 μm. It is believed to be applicable for future communication, imaging and sensing in terahertz range. [ABSTRACT FROM AUTHOR]

An all-rod terahertz wave air-core photonic crystal fiber is designed and fabricated. Transmission spectra through the sample are measured by using terahertz time-domain spectroscopy system. Periodic transmission band and low loss of the fiber are experimentally proved. Measurement results show that the power loss of the present terahertz wave photonic crystal fiber is less than 1.9 dB/cm in transmission bands. The wave confinement ability of the fiber is also demonstrated. [ABSTRACT FROM AUTHOR]

A compact terahertz polarization beam splitter by combining line defects and two photonic crystal cavities is designed and numerically demonstrated. Both plane wave expansion method and finite-difference time-domain method are used to calculate and analyze the characteristics of the proposed device. The simulation results show that the designed polarization beam splitter can split TE and TM polarized terahertz wave into different propagation directions with high efficiency over the terahertz wave frequency range from 1.16 THz to 1.19 THz. The extinction ratios are found to be larger than 20 dB for both TE and TM polarized terahertz wave. By using such a polarization beam splitter, the device size could be reduced significantly. This enables the polarization beam splitter to be used in terahertz wave system and terahertz wave integrated circuit fields. [ABSTRACT FROM AUTHOR]

We propose a scheme to manipulate the Goos–Hänchen shift of a terahertz wave reflected from the prism–metal–polymer–metal interface via external voltage bias. By adjusting the external voltage bias, the refractive index of the nonlinear polymer can be changed, so the lateral Goos–Hänchen shift is dynamically tuned. The relation among the Goos–Hänchen shift, prism and the nonlinear polymer is investigated in theory analysis and simulation. Using this scheme, the Goos–Hänchen shift can be tuned without changing the original structure of the proposed device. Numerical calculation results further indicate that the proposed structure has the potential application for the integrated terahertz wave switch. [ABSTRACT FROM AUTHOR]

We propose a new scheme to manipulate a terahertz wave beam. By adjusting an external ambient temperature, the refractive index of the temperature-sensitive material can be changed, so the giant lateral Goos–Hänchen shift is dynamically tuned. Using this scheme, the terahertz wave can be controlled without changing the original device structure. The relations among the Goos–Hänchen shift, external ambient temperature, incidence angle, and operation frequency are investigated in theory analysis. The finite-element method is used to verify and analyze the characteristics of the tunable terahertz wave Goos–Hänchen shift. The present device exhibited an extinction ratio of 24.3 dB at terahertz wave wireless communication frequency of 0.857 THz. [ABSTRACT FROM PUBLISHER]

ABSTRACT An equivalent circuit model is proposed to estimate the absorbance characteristics of the proposed terahertz wave absorber based on metamaterial. The component can be optimized to achieve high absorption of different frequency of the incident electromagnetic wave by adjusting physical dimensions and material parameters. The fabricated device was characterized by using a Fourier transform infrared spectrometer. The designed absorber demonstrated excellent absorbance compared with previously reported metamaterial-based terahertz wave absorbers, which exhibited 99.3% absorbance at 0.575 THz. The simulation and measurement results show that the absorber is an excellent terahertz wave collector. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2195-2198, 2013 [ABSTRACT FROM AUTHOR]

Abstract: A novel terahertz wave modulator based on guided wave resonance structure is demonstrated. The terahertz wave modulator consists of a prism–metal–polymer–metal multilayer structure. An external pump laser across the large third-order nonlinear susceptibility polymer layer modulates the energy coupling efficiency of incoming terahertz wave into guided wave resonance at fixed input angles. The reflection intensity of the terahertz-beam in the proposed structure can be flexibly tuned from near unity to zero, which is very fast on the order of ten picoseconds. This provides a strategy for constructing and studying ultrafast low-power integrated terahertz wave devices. [Copyright &y& Elsevier]

Abstract: We theoretically investigate the modulation efficiency, response time, and pump power of a terahertz-beam intensity modulator by using an organic photonic crystal slab structure with high quality factor “defect” cavity. The basic operation of an ultrafast low-power terahertz wave modulator actuated by the dynamical shifts of the defect mode induced by pump intensity is discussed in detail. The finite-difference time-domain method is used to verify and analyze the characteristics of the terahertz wave modulator. The device exhibited extinction ratio of 47.15dB and insertion loss of 3.2dB at frequency of 1.062THz with ultrafast response times on the order of several picoseconds. [Copyright &y& Elsevier]

Abstract: We design terahertz wave reflective polarizer that operates over a wide terahertz wavelength range and is based on a periodic bilayer structure. The structure is characterized by transfer matrix calculations. Results of simulations show that the mirror is highly reflecting for incidence angle θ ≤60°and TE as well as TM polarization in the wavelength range between 541.6μm and 574.2μm (i.e. frequency band between 522.5GHZ and 533.9GHZ). As the incidence angle increases this reflection band blueshifts for both TM and TE polarizations. [ABSTRACT FROM AUTHOR]

In order to effectively improve the information carrying capacity of modern wireless communication systems, vortex beams with orbital angular momentum (OAM) have attracted extensive attention due to extending communication capacity through orthogonal channels with different OAM modes carrying different information. However, the reported studies are only concentrated on single-function vortex beam. Here, we propose a notched concave metasurface to generate for multifunctional vortex beams such as four vortex beams, focusing vortex beams, deviation focusing vortex beams, and multi-beam vortex beam under different polarization. The theoretical results show good agreements with the full-wave simulations. The designed metasurface enables diversified promising applications for flexible manipulation OAM and terahertz wave polarization detection in future terahertz wireless communication. • We propose a notched concave metasurface to generate for multifunctional vortex beams. • The multifunctional vortex beams includes four vortex beams, focusing vortex beams, deviation focusing vortex beams, and multi-beam vortex beam under different polarization. • The simple metasurface structure provide a flexible control approach of terahertz vortex beam. [ABSTRACT FROM AUTHOR]

Abstract: We study theoretically and demonstrate experimentally light controllable terahertz wave switch. When the modulated optical excitation source is used to irradiate a high resistivity silicon wafer, a novel controllable terahertz wave switch is achieved. The results show that the ON–OFF response time is less than 150ms and the attenuation of the novel terahertz wave switch is more than 20dB at frequency of 0.315THz. [Copyright &y& Elsevier]

Abstract: We design an ultra-fast terahertz wave switch based on T-shape photonic crystal waveguide. The polymer rod is added in the junction as a point defect, the refractive index of which can be varied by adjusting the external pump laser intensity. The transmission spectrum is calculated by finite-difference time-domain method, which shows that the output energy of the two output ports is closely related to the refractive index of the polymer rod. By continuous wave excitation of the guided mode, the simulation results show that the T-shaped photonic crystal waveguide can flexibly tune the power in two output ports. The tuning rate of the device is about 0.3ns. These results provide a useful guide and a theoretical basis for the developments of terahertz wave functional components. [Copyright &y& Elsevier]

We propose an anisotropic terahertz metasurface based on silicon Mie resonance for achieving terahertz wave beam deflection manipulation. The presented coding metasurface can achieve various functions for two orthogonal linear polarized terahertz waves incidence. By elaborately designing 1-bit and 2-bit anisotropic coding metasurface with different coding matrix, we verify the anisotropic coding metasurface having excellent performance on manipulation reflection beam numbers and beam deflection angles under different polarization waves incidence. The proposed anisotropic terahertz metasurface provides an efficient and flexible method for regulation terahertz wave and has the potential for the promising applications of terahertz MIMO communication systems. • The coding metasurface achieve various functions for terahertz waves incidence. • We designed 1-bit and 2-bit anisotropic coding metasurfaces by utilizing dielectric silicon Mie resonance. • Due to the charming characteristic of anisotropic metasurface with simple structure, it has the potential applications in terahertz MIMO communication system. [ABSTRACT FROM AUTHOR]

Abstract: We design an omnidirectional dielectric mirror that operates over a wide terahertz wavelength range and is based on a periodic bilayer (tellurium and polystyrene) structure. The structure is characterized by using transfer matrix calculation. Results of simulation show that the presented dielectric mirror is highly reflecting for all incidence angles and TE as well as TM polarization in the frequency band from 0.451 to 0.821THz (i.e. wavelength ranges from 365.5 to 665.5μm), when the incidence angle is less than 45°. Tolerance analysis reveals a large tolerance to fabrication errors. [Copyright &y& Elsevier]

With the rapid development of terahertz wave technology and application systems, the dynamic manipulation of terahertz radiation is highly needed. We have investigated the performances of a graphene-embedded coding metasurface that can dynamically control the terahertz wave transmission. The coding element consists of gold substrate, silicon-polyimide interlayer and the top graphene-embedded metallic pattern that can realize abrupt reflection phase shift by adjusting the graphene Fermi level. Especially, by changing the Fermi energy of the graphene through bias voltage and pre-designed coding sequence, the new coding metasurface structure can control the reflected terahertz wave beams to various directions. The method brings us much freedom in design of terahertz wave manipulation device. [ABSTRACT FROM AUTHOR]