Terahertz Wave Communication Research Articles

Frequency down-conversion of terahertz waves at optically induced temporal boundaries in GaAs waveguides

Abstract In this study, the frequency down-conversion of terahertz waves is analytically and experimentally demonstrated at the temporal boundaries within a GaAs waveguide. The temporal boundary is established by photoexciting the top surface of the waveguide, thereby instantaneously increasing its electrical conductivity. This photoexcited waveguide supports a transverse electromagnetic (TEM) mode with a frequency lower than those of the transverse magnetic (TM) modes present in the original waveguide. At the temporal boundary, the incident TM mode couples with the TEM mode, resulting in frequency down-conversion. Subtracting the propagation loss from the frequency-converted components indicates that the frequency conversion occurs with an efficiency consistent with the analytical predictions. The propagation loss is primarily due to ohmic loss, caused by the finite electrical conductivity of the photoexcited region. Given that the frequency of transverse electric modes is up-converted at the temporal boundary, our findings suggest that the direction of frequency conversion (upward or downward) can be controlled by manipulating the incident polarization. The polarization-dependent frequency conversion in waveguides holds significant potential for applications in devices designed for the interconversion of terahertz signals across various frequency channels. This capability is instrumental in the development of frequency-division-multiplexed terahertz wave communication systems, thereby enabling high data transfer rates.

Anti-resonant hollow-core terahertz fiber based on Bragg structure elements

An anti-resonant hollow-core terahertz fiber applying Bragg structure as the basic unit is presented, the basic unit is composed of two or three concentric tubes which is cut and connected by an outer ring. Simulations results show that the proposed fiber has the transmission characteristics of both conventional anti-resonant structure and Bragg fiber, and its confinement loss could be 2–3 orders of magnitude lower than that of an anti-resonant hollow-core terahertz fiber composed of only a single semi-tube as the anti-resonant unit, and the total transmission loss is one order of magnitude lower, which can achieve a low transmission loss of 0.5 dB/m or less with the bandwidth of 0.15 THz. In addition, the appropriated choice of the outer ring diameter can effectively suppress the mode coupling between the core and cladding, thereby reducing its confinement loss and bending loss. The proposed fibers show great potential for applications in terahertz wave communication and the fabrication of terahertz sensors.

Graphene-metasurface for wide-incident-angle terahertz absorption

We demonstrate a graphene-metasurface structure for tunable wide-incident-angle terahertz wave absorption, which involves depositing planar arrays of Omega-shaped graphene patterns on a silicon dioxide substrate. We also discuss how the graphene Fermi-level layer and various substrates affect the absorption characteristics. The absorption of the proposed terahertz absorber is above 80% at an incident angle of 0°–60° in frequencies ranging from 0.82 to 2.0 THz. Our results will be very beneficial in the application of terahertz wave communications and biomedical imaging/sensing systems.

Light-control splitting ratio tunable Y-type Terahertz waves to beam splitter based on two-dimensional photonic crystal

Light-control splitting ratio tunable Y-type Terahertz waves to beam splitter based on two-dimensional photonic crystal is proposed.In this scenario,the feature that coupling with line defects and the point defects of nonlinear polymer materials which have the third-order nonlinear Kerr effect is utilized.The performance of Terahertz waves splitter with tunable splitting ratio is studied by Plane Wave Method(PWM)and Finite-Difference Time-Domain(FDTD).The research results show that the Ytype Terahertz wave splitter with tunable splitting ratio of two output ports by changing the light intensity of the control light can be realized.This beam splitter which the transmittance reaches over 98%can achieve Terahertz waves splitting with a specific wavelength.At the same time,the additional loss is less than 0.087dB and the response time reaches the order for ps.The splitter with tunable splitting ratio will have broad application prospects in future Terahertz wave communication.

Photonic crystal terahertz wave logic AND-XOR gate

Terahertz wave logic gates are one of the key devices required in terahertz wave communication systems and signal processing systems. In this paper, we design a logic gate to realize the function of AND gate and XOR gate. The logic AND-XOR gate is based on two large photonic crystal ring resonators, one small ring resonator and photonic crystal branch waveguides. The structure is analyzed and simulated by treating the plane wave expansion and finite difference time domain methods. The steady-state field distributions and output power characteristics of the gate are analyzed. The simulation results show that the designed device with the feasibility can be used in terahertz wave integrated digital circuit.

Design for realizing an all-optical terahertz wave half adder based on photonic crystals

Terahertz wave half adders are one of the key logic devices required in terahertz wave communication systems and signal processing systems. In this paper, we aim to design an optical structure for realizing half-adder operation based on the multiple-mode interference effect. The central frequency of the logic device is 1.05 THz. By injecting terahertz wave signal into the input ports of the structure, the desired logic states are achieved and the resulting truth table verifies the functionality of the designed half adder. The simulation results based on the finite difference time domain and plane wave expansion methods show that the designed structure with the feasibility can be used in terahertz wave integrated digital circuits.

Cobalt-Based Ferrites Characterization Using Two Different Terahertz Time-Domain Spectrometers

We report an experimental study of the electrical properties of manganese cobalt (MnCo) and nickel cobalt (NiCo) ferrites in the terahertz (THz) frequency band. The study is motivated by the potential of MnCo, NiCo, and other magnetic ceramics for the fabrication of active and passive devices for THz wave communications. Using two different terahertz (THz) time-domain spectroscopy systems, we characterized the optical constants of cobalt ferrites doped with manganese and nickel in the technologically important 0.2–1 THz frequency band. The MnCo and NiCo ferrites investigated in our study exhibit a lower refractive index and absorption coefficient in the 0.2–1 THz frequency band than commercial strontium ferrite. We observed that using different valency ion oxide leads to a sudden change of the refractive index as a function of sample stoichiometries. Our experimental results provide evidence that microwave ferrite technology can be extended to the THz frequency band.

Compact and Tunable-Multichannel Terahertz Wave Filter

A compact terahertz tunable multichannel filter based on two cascaded photonic crystal waveguide directional couplers, formed by two closely spaced line defect waveguides in a two-dimensional photonic crystal of silicon rods in the air, is numerically studied using plane wave expansion and finite difference time domain methods. The filtering properties of the present terahertz wave filter, including channel number and frequency, can be tuned by adjusting excitation of external applied magnetic field. The dynamical shift of channels with external applied magnetic field intensity is studied in detail. The transmittances of the present filter are higher than 95% for each terahertz wave frequency with a compact size of 3.8 mm $\times$ 10 mm. The designed device can possess both multichannel and tuning features, which could be of technical use in the terahertz wave communications system applications.

Realization of band-pass and low-pass filters on a single chip in terahertz regime

In this paper, we present the design, simulation, fabrication and characterization of a terahertz (THz) filter based on metamaterial consisting of the periodical double symmetric splits ring resonator (DS-SRR) array. We can observe that the metamaterial-based filter possesses a band-pass transmission when the electrical field is along y direction, and it possesses a low-pass transmission when the electrical field is along x direction. Our results demonstrate that the proposed filter can realize the switching between band-pass effect and low-pass effect by only changing the polarization direction of the incident electromagnetic wave. Moreover, the calculated surface current distributions are also used to analyze the switchable mechanism of the THz metamatrial filter. Therefore, the proposed THz wave filter has a potential application in THz wave communication systems.

Scattering of terahertz wave by charged spherical particles

The scattering characteristics of terahertz wave by a spherical particle are studied in this paper. A model, which can uniformly describe the expansion coefficients of uncharged, evenly charged and partially charged conditions, is developed and verified. The results of numerical calculation manifest that the scattering of terahertz wave is enhanced, whenever the particle is evenly or partially charged in the given frequency range, particle radius and the surface charge densities, compared with the uncharged case. Moreover, it is also found that the scattering of terahertz wave is basically monotonously enhanced if the particle is negatively charged; and it is basically non-monotonously enhanced if the particle is positively charged. Besides, the terahertz wave’s 3-D scattering field intensity distributions of uncharged, evenly charged and partially charged conditions are compared. In a word, this study is crucial to discuss the feasibility of terahertz wave communication technology in the complicated environment with charged particles. In addition, the potential application of this study in biomedical field is also proposed.

Studies of terahertz wave propagation in non-magnetized plasma

The space crafts, such as spaceship, space shuttle and so on, will face a famous blackout problem when they re-enter the earth's atmosphere at high velocity. The plasma sheath severely affects the propagation of the incident electromagnetic wave and causes severe electromagnetic wave attenuation, which results in the communication failures between the space crafts and the ground control center. It is important to study the properties of terahertz wave propagation in non-magnetized plasma, for using the terahertz wave communication is an alternative method to solve the reentry blackout problem. The terahertz wave propagation characteristics in non-magnetized plasma are studied in this paper. The variations of the terahertz wave propagation properties with the terahertz wave frequency, plasma density, plasma collision frequency and the thickness of the plasma are acquired. Some new phenomena are found i.e., there appears periodic oscillation on the reflectivity curve with the increase of terahertz wave frequency, and the period of oscillation is 0.03THz. The oscillation amplitude increases with the increase of terahertz frequency, decreases with the increase of plasma density, and increases with the increase of plasma collision frequency. The oscillation is attributed to the multiple reflections of the electromagnetic wave at the interfaces at z=0 and z=-d. The terahertz wave propagation properties in plasma are studied experimentally with the shock tube, and the experimental results match well with the theoretical ones. Both the theoretical and experimental results indicate that using terahertz wave communication is an effective way to solve the reentry blackout problem.

A novel terahertz wave switch based on metamaterial

AbstractIn this letter, a novel terahertz (THz) wave switch based on metamaterial is proposed and measured.On–off switching is based on a controllable resonance of the metamaterial by applying an external semiconductor laser to illuminate substrate. Experimentally, we demonstrate on–off response time speed and extinction ratio of the proposed THz wave switch is of 1 ms and 19.4 dB at 0.32 THz, respectively. The presented THz wave switch has a potential application to THz wave communication systems. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:276–278, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25751

Controllable terahertz wave attenuator

AbstractA new type of optically controllable terahertz wave attenuator using high‐resistivity silicon wafer is developed and tested. Without optical excitation, the high‐resistivity silicon is a lossless dielectric material at terahertz wave region. When the high‐resistivity silicon wafer is optically excited, free carriers are generated, and the silicon wafer becomes a lossy dielectric. We study theoretically and demonstrate experimentally light‐controllable terahertz wave of the high‐resistivity silicon wafer. The results show that more than 10‐dB attenuation of the novel terahertz wave attenuator is obtained at frequency of 0.3 THz. The proposed device can be used in future terahertz wave communication systems. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1810–1812, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23528