Simple Terahertz Research Articles

Design and error analysis of simple terahertz high birefringence microstructured fiber

Abstract High birefringence fibers are significant in the terahertz technology field, serving as waveguides for terahertz transmission. They are applicable in various fields such as communication, imaging. Integrating metal microstructures into polymer microstructured optical fibers can effectively modulate the transmission characteristics of the fiber, enhancing birefringence and reducing loss, thereby achieving better performance compared to traditional single-material fibers. This paper presents a structurally simple terahertz high birefringence microstructured fiber, where the introduction of gold microstructures enhances the birefringence of fiber, with a maximum birefringence of up to 1.089 × 10−2. We also discuss several manufacturing errors that may occur during the fiber fabrication process. The results indicate that the designed fiber exhibits significant manufacturing tolerance. Variations in the thickness and angle of the gold microstructures, as well as the angular offset of the elliptical cladding wall, peak-to-valley errors, and changes in the aspect ratio of the elliptical tube, have relatively minor effects on the overall transmission performance. The research findings provide insights for designing subsequent high birefringence terahertz fibers, thereby propelling advancements in this field. They offer a theoretical basis for the preparation of related microstructured fiber structures and provide valuable understanding for optimizing fiber manufacturing processes.

Vanadium dioxide-based terahertz metasurface device with switchable broadband absorption and beam steering functions

A simple terahertz (THz) metasurface device with dual functionalities of broadband absorption and beam steering is proposed in this paper. The device exploits the phase change properties of vanadium dioxide (VO2), transitioning between its insulating state and metallic states to achieve functional switching. In the metallic state, the device exhibits broadband absorption, surpassing 90% absorption in the 1.03–2.07 THz range. The absorption function maintains exceptional performance across a wide range of incident angles and possesses polarization insensitive properties. In the insulating state of VO2, the metasurface converts into a THz reflective beam steering device. By employing phase coding, 1-bit coding metasurfaces based on phase gradients are designed, enabling dual-beam and four-beam reflection. Building upon this foundation, 2-bit coding metasurfaces facilitate anomalous reflection of a single beam in distinct directions. Consequently, the device not only toggles between broadband absorption and beam steering but also satisfies the design criteria for 3-bit coding metasurfaces. The modulation characteristics of this device serve as a valuable design reference for multifunctional THz devices in diverse scenarios.

Generation of Terahertz Radiation via the Transverse Thermoelectric Effect.

Terahertz (THz) radiation is a powerful tool with widespread applications ranging from imaging, sensing, and broadband communications to spectroscopy and nonlinear control of materials. Future progress in THz technology depends on the development of efficient, structurally simple THz emitters that can be implemented in advanced miniaturized devices. Here, it is shown how the natural electronic anisotropy of layered conducting transition metal oxides enables the generation of intense terahertz radiation via the transverse thermoelectric effect. In thin films grown on off-cut substrates, femtosecond laser pulses generate ultrafast out-of-plane temperature gradients, which in turn launch in-plane thermoelectric currents, thus allowing efficient emission of the resulting THz field out of the film structure. This scheme is demonstrated in experiments on thin films of the layered metals PdCoO2 and La1.84 Sr0.16 CuO4 , and model calculations that elucidate the influence of the material parameters on the intensity and spectral characteristics of the emitted THz field are presented. Due to its simplicity, the method opens up a promising avenue for the development of highly versatile THz sources and integrable emitter elements.

Simple terahertz metasurface with broadband and efficient functionality.

Pancharatnam-Berry (PB) metasurfaces have demonstrated mighty capability to manipulate electromagnetic (EM) waves, and exhibited potential applications for devices with broadband and efficient functionality. However, it remains a challenge to simultaneously achieve broadband and efficient wavefront manipulation for terahertz (THz) components with simple profiles. Herein, we introduce a simple ultra-thin PB metasurface with superior properties in the THz region. The structure is composed of a simple metallic C-Shaped Split Ring Resonator (CSRR) patterned on a flexible polyimide support layer. It is verified that the circular transmission efficiency is close to the theoretical limit of the single-layer metasurface in the range of 0.6 - 1.2 THz. Furthermore, we design metasurfaces based on the PB meta-atoms with spatially rotated orientation to achieve beam steering and superposition of vortex waves. The results are basically in line with expectations, validating the good performances of our proposal. This simple and easily deployable metasurface will give rise to more possibilities for the design of THz functional devices.

Improvement of a Terahertz Detector Performance Using the Terajet Effect in a Mesoscale Dielectric Cube: Proof of Concept

Herein, a simple terahertz (THz) receiver that uses subwavelength focusing of the THz beam on the detector area is proposed. As a proof of concept, a THz detection system with an original optical coupling scheme is implemented, where the signal to be detected is coupled to a THz detector through a mesoscale dielectric particle lens. Coherent detection is successfully demonstrated with an enhancement of the detector sensitivity of about 4.3 dB, compared with that of a direct detection system with the slight decreasing (≈1.67 times) of noise equivalent power value. The results show that the proposed method can reduce the size and increase the sensitivity of various THz systems, including imaging, sensing, and ranging, which would enable significant progress in different fields such as physics, medicine, biology, astronomy, security, etc.

Graphene-Based Composite Right/Left-Handed Leaky-Wave Antenna at Terahertz

In this paper, a simple terahertz (THz) leaky-wave antenna (LWA) composed of periodic gapped graphene ribbons and a silicon substrate is presented. The graphene sheets of the antenna operate in an electric field with a resonance distribution of transverse electric (TE) surface plasmon polaritons (SPPs). The THz LWA has both negative and positive propagation constant with the variation of frequencies. Thus, the LWA performs as a composite right/left-handed (CRLH) LWA with backfire-to-endfire beam steering capability in the THz band. The working principle of the THz LWA is analyzed in detail using the theory of dispersion relation formulae and the equivalent CRLH circuit model. The THz LWA is verified by numerical simulations, and the frequency scannable capability of the THz LWA is confirmed. The proposed antenna has great potential applications for the THz LWA of the radiation capability in the entire upper quadrants.

Huge field enhancement and high transmittance enabled by terahertz bow-tie aperture arrays: a simulation study.

Sub-wavelength aperture arrays featuring small gaps have an extraordinary significance in enhancing the interactions of terahertz (THz) waves with matters. But it is difficult to obtain large light-substance interaction enhancement and high optical response signal detection capabilities at the same time. Here, we propose a simple terahertz bow-tie aperture arrays structure with a large electric field enhancement factor and high transmittance at the same time. The field enhancement factor can reach a high value of 1.9×104 and the transmission coefficient of around 0.8 (the corresponding normalized-to-area transmittance is about 14.3) at 0.04 µm feature gap simultaneously. The systematic simulation results show that the designed structure can enhance the intensity of electromagnetic hotspot by continuously reducing the feature gap size without affecting the intensity of the transmittance. We also visually displayed the significant advantages of extremely strong electromagnetic hot spots in local terahertz refractive index detection, which provides a potential platform and simple strategy for enhanced THz spectral detection.

A simple terahertz time-domain signal reconstruction algorithm for thickness measurement in real-world applications

We propose a simple signal reconstruction algorithm for terahertz time-domain spectroscopy in ambient atmosphere for application to time-of-flight thickness measurement. Time-of-flight measurement method is a very basic method of measuring thickness, but it has the advantage of being very fast. Therefore, it is often used for rapid measurement in industrial environment. The echo signal is buried in the spurious oscillations of the ambient atmosphere because of water vapor. We successfully found the echo signal and measured the thickness of the sample, silicon wafers and various type of explosive materials, without any prior information in humid air.

Tunable multiple plasmon-induced transparency in a simple terahertz Dirac semimetal based metamaterial

We proposed a bulk Dirac semimetal (BDS) based metamaterial that consists of two identical vertical BDS rods and two horizontal BDS rods with different lengths. Numerical simulation results show that the proposed structure can realize the tunable multiple plasmon-induced transparency (multi-PIT) effect. The multi-PIT effect is mainly attributed to the introduction of the bonding mode simply by manipulating the lengths of horizontal rods. By changing the Fermi energy of the BDS, the tunable multi-PIT spectrum and tunable multi-band group delay can be achieved. The multi-PIT peaks are also sensitive to the background refractive index and can lead high FOM values of 16, 50.9 and 10.6, respectively. The proposed structure is desirable for designing tunable THz sensors, modulators and slow light devices.

Dielectric Properties of DMSO‐Doped‐PEDOT:PSS at THz Frequencies

Poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) is a promising candidate for terahertz (THz) metamaterial devices. Its dielectric properties can be changed by the dopant dimethylsulfoxide (DMSO). In this study, the dielectric properties of DMSO‐doped‐PEDOT:PSS films are investigated using terahertz time‐domain spectroscopy (THz‐TDS) measurements. The values of the carrier density and mobility are also determined by fitting the dielectric permittivity to the Drude–Smith model. A simple THz frequency selective surface (FSS) is designed based on these DMSO‐doped‐PEDOT:SS films. Strong band rejection can be achieved at resonant frequencies. These results may inspire the development of new materials for manipulating THz waves in future studies.

High-Sensitivity and Broadband, Real-Time Terahertz Camera Incorporating a Micro-Bolometer ArrayWith Resonant Cavity Structure

Terahertz (THz) cameras comprising an uncooled micro-bolometer array have been developed for simple THz imaging, and the improvement of their sensitivity is one of the important issues. We fabricated a new micro-bolometer array with a resonant cavity structure for a real-time THz camera, alongside a new method for evaluating the sensitivity across a wide range of the THz frequency region. The frequency dependence of the sensitivity of the THz camera is measured in the 0.5–2.0-THz frequency range taking the polarization dependence into account. It was found that the resonant cavity structure effectively increased the sensitivity of the THz camera, and, actually, the improvement by one order of magnitude was achieved in the frequency range below 1 THz. The THz camera with much enhanced sensitivity will expand the frontiers of real-time THz imaging such as molecular imaging and nondestructive inspection.

The Transmission Properties of Coated THz Teflon Tube

The S parameters, attenuation characteristics and group delay characteristics of the Teflon tube have analyzed in the paper. Firstly, the S parameters of metal and polymer tube with the same structure are compared. Then the transmission properties of the simple terahertz Teflon tubes and terahertz Teflon tubes which are coated metal film by three different ways are simulated, and the advantages and disadvantages are contrasted. The S parameters of Teflon tube are more ideal, but it is not plain, the attenuation within the working frequency is less than 10.77dB/m, the group delay is less than 10 -10 s, coating Teflon tube with film can make S parameters plain. Teflon tube can transmit THz wave effectively, and if the Teflon tube is coated with films, the transmission characteristics can be improved in conclusion.

A simple nested metamaterial structure with enhanced bandwidth performance

We demonstrate a simple terahertz metamaterial design to increase the fundamental resonance bandwidth by embedding a metal strip inside a nested structure composed of two rings. The bandwidth of the fundamental resonance is 443 GHz which is 4.2 times larger than the bandwidth of the nested structure. And the increase in fundamental resonance broadening is attributed to the reduced effective inductance.This proposed structure provides a meaningful way toward expanding the fundamental mode operating range from narrowband to broadband with a tunable behavior.

A Fast Terahertz Spectrometer Based on Frequency Selective Surface Filters

We present a fast spectrometer working in the 0.7–4.8 THz range. Broadband radiation from a blackbody source is focused first on a rotating silicon wafer, whose surface was patterned with 18 metal band-pass filters, then on the sample under test and finally is detected by a superconducting microbolometer with microsecond time constant. The bolometer sensor is coupled to a spiral antenna whose frequency band matches the spectral range of the filters. The spectral resolution is set by the filters quality factor of about 3. A dynamic range of 100 and a S/N ratio of 20 are achieved by integrating for less than 10 second. The detector can operate up to 6 K in a closed-cycle cooler, hence making the present apparatus suitable for building up a simple terahertz video-rate spectrometer.

Pulsed CH3OH terahertz laser radiation pumped by 9P(36) CO2 lasers

An efficient pulsed CH3OH terahertz (THz) laser pumped by a TEA CO2 laser was investigated experimentally. A simple terahertz cavity and a TEA CO2 laser for the optically pumped THz radiation were studied experimentally. To improve THz laser energy and photon conversion efficiency, two different TEA CO2 lasers were developed to pump CH3OH. When CH3OH was pumped by the 9P(36) line with different powers of the CO2 laser, the generation of terahertz radiation with energy as high as 0.307mJ and 23.75mJ were obtained, respectively. The corresponding photon conversion efficiencies were 0.29% and 2.4%. The photon conversion efficiency increases by a factor of about 8. Meanwhile, higher peak power of pump laser effectively improves the photon conversion efficiency. And the optimum THz laser pressure increases with narrower pulse width of pump laser because of increasing absorptive gases molecules of CH3OH with higher peak power of pump laser.

Pulsed CH3OH Terahertz Laser Emission Pumped by a TEA CO2 Laser

A simple terahertz (THz) cavity and a TEA CO2 laser for the optically pumped THz emission is studied experimentally. To obtain high peak power of pump laser, pressure ratios of gas mixture in the cavity of the TEA CO2 laser are discussed. When CH3OH are pumped by the 9P(16) and 9P(36) CO2 laser lines, the generation of terahertz radiation with energy as high as 353 µJ and 307 µJ are obtained, respectively. The corresponding photon conversion efficiencies are 0.705% and 0.29%. Meanwhile, higher peak power of pump laser effectively improves the photon conversion efficiency. And the optimum THz laser pressure increases with narrower pulse width of pump laser.

Quasi-near field terahertz generation and detection

We describe a simple terahertz (THz) time domain spectrometer with a bandwidth extending up to 7.5 THz. We show that by keeping the generation and detection crystals close to each other a high signal-to-noise ratio (SNR) can be achieved without using lock-in detection and dry nitrogen flushing. The observed spectra show very good agreement with the spectra calculated based on a simple model which includes phase matching and absorption in the generation and detection crystals. Using this set-up we have measured the absorption lines in D-tartaric acid from 0.5 THz up to 7 THz. We show that the high frequency region > 3 THz is the better choice to measure small changes in the water content of a hygroscopic sample compared to the low frequency region.

A simple terahertz spectrometer based on a low-reflectivity Fabry-Perot interferometer using Fourier transform spectroscopy

A simple terahertz (THz) Fourier transform spectrometer is theoretically and experimentally demonstrated with a low-reflectivity Fabry-Perot interferometer. Composed with only two parallel low reflectivity surfaces, this simple spectrometer has the ability to measure the spectrum over more than one octave with a controllable resolution. The emission spectra of a wavelength-tunable photonic transmitter excited by an optical coherent control system are determined by the spectrometer. With a simple algorithm for the spectral reconstruction and a compact structure with easy alignment, the demonstrated spectrometer will meet the needs of many important applications where a compact and convenient spectrometer is required in the frequency range from sub-THz wave up to even visible light.