THz Waveband Research Articles

Designing a broadband terahertz plasmonic field enhancer with a homojunction of semiconductors

We proposed a broadband THz plasmonic field enhancer taking advantage of the spatially varying charge carrier concentration in a homojunction of semiconductors. The theoretical simulation indicates that the structure has a broadband resonance response and shows a field enhancement factor greater than 10 in the majority of the THz waveband. Near 6 THz, a maximum of 30-fold field enhancement is predicted. We believe that the proposed structures are ideal candidates for broadband field enhancement and may help realize more sophisticated THz devices.

Researches on the scattering characteristics in THz band of conductor cylinder coated with parabolic distribution and time-varying plasma media

It is widely acknowledged that inhomogeneous and time-varying plasma can effectively reduce the back scattering radar cross section (RCS) and THz wave has the potential to penetrate the plasma and against the plasma stealth. Therefore, the backscattering and bistatic radar cross section (RCS) of conductor cylinder coated with parabolic distribution and time-varying plasma media in THz wave band are studied by the Runge-Kutta Exponential Time Differencing-Finite Difference Time Domain (RKETD-FDTD) method in this paper. The influences of plasma parameters are analyzed. From both the backscattering and bistatic RCS simulations, it is obviously that inhomogeneous and time-varying plasma cloaking system makes a significant difference on reducing the RCS and improve the plasma stealth while electromagnetic wave in THz region can successfully weaken its influence and contribute to the anti-stealth.

Prototype of KIOSK Data Downloading System at 300 GHz: Design, Technical Feasibility, and Results

Recent advances in semiconductor device technologies and the ever growing worldwide traffic explosion have focused great attention on THz frequencies, which had long been considered a forbidden region in the electromagnetic spectrum. The huge bandwidth, perhaps much larger than the total bandwidth used on Earth for all wireless systems, is now believed to be the only way to handle incredibly large amounts of data instantaneously by wireless means. In this article, we describe the development of a KIOSK data downloading system prototype designed for touch-and-go use. Implementation of the 300 GHz THz front-end components and the performance are briefly summarized. A preliminary investigation of the LoS channel responses and a simple comparison of the forward error correction algorithms in the given THz channel are presented as well. Finally, an experimental demonstration of instant data transfer with the prototype is described to confirm the feasibility of using the THz wave band for future wireless applications.

A scheme to enhance the conversion efficiency of slow‐wave electron cyclotron masers in the large signal approximation

Based on the anomalous Doppler effect, we propose a scheme to improve the practicability of slow‐wave electron cyclotron masers in the large signal approximation. This scheme simultaneously contains the tapered guiding magnetic field and tapered refractive index. Numerical calculations show that this scheme enables the conversion efficiency to reach a higher value within a shorter time than previous schemes. Besides, this scheme also works well in the cases of THz wave band and beam axial‐velocity spread.

A novel millimeter wave super lens using coupling effects in split-ring resonator

We report a millimeter wave super lens based on the left-handed metamaterial using split-ring resonator (SRR). The millimeter wave cannot propagate far away due to short wavelength. Therefore, the system for THz or millimeter wave band demands the lens to obtain strong focused signal from weak waves caused by scattering in atmospheric environment. In metamaterials, coupling effects between individual constituents play a dominant role for the optical and electronic properties. The proposed left-handed metamaterial (LHM) lens based on SRR and coupling effects can be designed by scanning the focal point of flat LHM lens in the region under detection and screening directly the field intensity distribution of backscattered millimeter wave refocused by the flat LHM lens. The simulation results confirm that this lens exhibits a focus with strong E-field distribution.

Diffractive microlens integrated into Nb(5)N(6) microbolometers for THz detection.

We fabricated square diffractive microlens array with five staircases in the THz wave band for Nb5N6 microbolometers. With each microlens intergrated with an Nb5N6 microbolometer on the same substrate, an array chip was fabricated in the 4 inches silicon wafer. The lens exhibits good focusing and improves the coupling efficiency. The voltage response of the microbolometer integrated with diffractive microlens is 16 times higher than that of the microbolometer fabricated on silicon substrate. The microbolometers used as room-temperature detectors yield a good responsivity of 71 V/W and a noise equivalent power of 1.0 × 10-10 W/Hz. The diffractive microlens array features light weight, low absorption loss, and high resolution and can be mass produced using standard micro-fabrication techniques.

Research of Beta-Endosulfan Based on THz Time-Domain Spectroscopy

THz spectral properties between 0.2-1.5THz of beta-endosulfan, one of the persistent organic pollutants (POPs), are investigated based on the THz time domain system. Part of the characteristic absorption peaks are theoretically analyzed by Dmol3 modular program. The experimental results show that the average refractive index of beta-endosulfan in the THz waveband is about 1.005 and characteristic absorption peaks exist at 0.67, 0.80, 1.03, 1.14, 1.26 and 1.46THz. The absorption peaks at 0.67THz and 1.03THz have a good match with the theoretic absorption peak positions which appear at 0.72THz and 1.07THz calculated by Dmol3. The peaks at 0.67THz and 1.03THz may be caused by the torsion in B and C direction of beta-endosulfan crystal lattice, along with the translation in A direction. Compared with the experimental results of alpha-endosulfan, it can be seen clearly that these two isomers have completely different absorption peaks. For further it indicates that terahertz time domain spectroscopy (THz-TDS) has great application value in identifying isomers.

Thermally controlled terahertz metamaterial modulator based on phase transition of VO2 thin film

Utilizing insulator-metal phase transition of vanadium dioxide thin film, we propose a thermally controlled terahertz modulator based on metamaterial, and research the transmission characteristics and temperature tunable characteristics of phase transition in metamaterials in THz wave band. While the incident THz wave is of horizontal polarization or vertical polarization, two independent pass bands are generated near 1 THz. The center frequencies of the two pass bands are 1.3 THz and 1.7 THz, the bandwidths of them are 0.2 THz and 0.35 THz. In addition, when temperature rises from 40℃ to 80℃, the transmissions of the two pass bands drop apparently, especially at phase transition temperature of 68℃. For the two polarization states, the modulation depths achieve 60% or more, which is the great function of a modulator.

Sensing Textile Fibers by THz Time-Domain Spectroscopy

Along with the booming development of multi-component blending fabrics, the accurate detection of component of fabrics has become a major goal in textile testing. Terahertz sensing technology provides a new way for detecting the materials. THz time-domain spectroscopy (THz-TDS) is a novel spectroscopic technique which measures the electric field of the radiation through a sample and provides the phase and amplitude changes of the radiation, which can provide information unavailable through conventional methods such as microwave and X-ray techniques. In this investigation, THz-TDS technology was introduced into the textile differentiation. Three kinds of cellulose textile fibers, cotton fiber, bamboo fiber and viscose fiber, were prepared as the sample and detected by THz-TDS at room temperature in the absence of vapor. The temporal and frequency signals of the fibers were obtained. In the THz absorption spectrum, the characteristic absorption peaks of textile fibers in THz wave band were found, which can be used to recognize the fibers. This approach provides a novel non-contact examine method for fiber identification in complicated textiles.

Detection and identification of selected alcohols using terahertz time-domain spectroscopy

The optical property and spectroscopy of selected kinds of alcohols are studied based on the terahertz time-domain spectroscopy (THz-TDS) in the spectral range of 0.5-2.5 THz. The B3LYP method in conjunction with the 6-31G (d) basis set was used to optimize the geometric structure of samples and simulate the alcohols spectrum. No absorption peak occurs in THz wave band based on our simulation, suggesting that the present experimental absorption peaks resulted from the intermolecular interaction.

Theoretical and experimental study on transmission properties of THz wave in metal-coated hollow waveguide

Limited by serious material absorption and dispersion in THz wave band, efficient and long distance delivery of THz signal is one of important problems for constructing a compact THz system. Based on the transmission loss coefficient in metal waveguide obtained by perturbation method, the transmission loss properties of THz wave in metal-coated hollow waveguide varying with different metal materials and waveguide structure parameters are simulated. According to the numerical results, an Ag-coated hollow waveguide with inner diameter of 1.1 mm was designed and fabricated, and the transmission loss of THz wave was 8.6 dB/m at frequency of 2.5 THz as found in experiment, which realizes a short distance transmission with ultralow loss in THz region.