THz Technology Research Articles

Temperature-dependent optical and dielectric properties of polyvinyl chloride and polystyrene blends in terahertz regime

Terahertz time-domain spectroscopy (THz-TDS) has been used to study the temperature-dependent refractive index, absorption coefficient and dielectric constant of polyvinyl chloride/polystyrene (PVC/PS) blends in frequency range of 0.2–1.8 THz. Moreover, the Sellmeier and thermo optic coefficients of PVC/PS blends with different weight ratios have been explored in the temperature range of 25–80 °C. These parameters are used to evaluate the dispersion properties of these blends in the observed frequency range. A clear indication of temperature dependence on the values of refractive index and the real dielectric constant of these blends have been observed. Their values decrease linearly with increasing temperature up to 80 °C. Whereas, no noticeable change has been observed in the imaginary dielectric constant and the absorption coefficient. These results provide a database of temperature-dependent optical and dielectric parameters of PVC/PS polymer blends for their efficient utilization for device fabrication in THz technology.

T-generation mobile communication leveraging cutting-edge photonic technologies (Photonic 6G)

t-generation mobile communication leveraging cutting-edge photonic technologies (Photonic 6G) Our aim is to develop ‘Photonic 6G’, an all-photonic THz communication technology, by integrating advanced photonic methods. This includes generating low-phase-noise THz waves with microcombs and converting modulated THz waves into optical carrier signals. By leveraging these advancements, we aim to enable advanced modulation and multiplexing in the optical domain, ultimately achieving the integration for photonic 6G.

Ultrafast Terahertz Superconductor Van der Waals Metamaterial Photonic Switch

The high‐temperature layered superconductor (HTS) BSCCO is one of the key quantum material platforms in THz science and technology. Compact, stable, and reliable BSCCO THz photonic integrated circuit components can be developed to effectively and efficiently control and manipulate THz wave radiation, especially for future communication systems and network applications. Herein, the design, simulation, and modeling of ultrafast THz metamaterial photonic integrated circuits are reported on a few nanometer‐thick HTS BSCCO van der Waals (vdWs), capable of the active modulation of phase with constant transmission coefficient over a narrow‐frequency range. Meanwhile, the metamaterial circuit works as an amplitude modulator without significantly changing the phase in a different frequency band. Under the application of ultrashort optical pulses, the transient modulation dynamics of the THz metamaterial offer a fast‐switching timescale of 50 ps. The dynamics of picosecond light–matter interaction, Cooper pairs breaking, photoinduced quasiparticles generation and recombination, phonon bottleneck effect, and emission and relaxation of bosons in BSCCO vdW metamaterial arrays are discussed for the potential application of multifunctional superconducting photonic integrated circuits in communication and quantum technologies.

Harnessing THz Technology: Biosensor for Highly Accurate Cervical Cancer Cell Detection via Refractive Index.

In order to rapidly identify various species of cancer cells in the tissues of person, a unique diamond shaped hollow-core photonic crystal fiber (PCF)-formed by optical waveform is developed and computationally studied. In this investigation, we found the most prevalent cancers, such as HeLa-derived cervical carcinoma. Since normal and cancer cells differ in their refractive indices (RIs), other significant optical properties can be assessed using this information. With the use of the finite element method, a computational tool for solving simultaneous equations, the defining characteristics the suggested cancer cell sensor are examined using COMSOL-Multiphysics software. Additionally, strict mesh parts are used to preserve the utmost level of modeling realism. At 2.4 THz, the PCF detector attains a Relative Sensitivity of around 97.51% and 96.29%, Confinement Loss of 6.1 × 10 -09db/m and 4.39 × 10-07db/m with respect to cervical carcinoma cell and cervical normal cell. The straightforward PCF structure provides a wide chance of application using the continuing fabrication technique, based on these conventional values of performance indices. This biosensor utilizes the distinctive refractive characteristics of cancer cells, providing a highly accurate and dependable approach for the early identification of cervical cancer. This has the potential to significantly transform the process of cervical cancer screening. The novel method boosts the ability to detect and identify certain conditions, leading to increased diagnostic capabilities for early treatment and better results for patients.

Rapid and non-destructive identification of plastic particles through THz technology and machine learning

For fast and accurate non-destructive differentiation of plastic pellets with similar appearance during import and export inspections, as well as for quality control purposes. Terahertz technology offers a non-destructive analysis approach for samples from diverse fields. By integrating deep learning algorithms with terahertz time-domain spectroscopy (THz-TDS) and linear discriminant analysis (LDA), it is possible to establish a highly accurate terahertz spectroscopy qualitative identification model. Additionally, the incorporation of principal component analysis (PCA) enables the application of this model to higher dimensional data. Notable differences in absorption coefficient, phase difference, and refractive index are observed among different plastic particles. The implementation of this rapid, accurate, and non-destructive detection method can greatly facilitate the testing and identification of plastic particles in customs and quality inspection departments.

Weakly confined silicon nanodiscs as material system for THz absorption: analytical study

A weakly confined silicon based nano structure as a THz absorbing material is introduced. Using an effective mass approximation and 2D hydrogenic solution along with 1st order perturbation correction for truncated potential, we calculated inter-band and intra-band energy spectrum of weakly confined silicon nanodisc system. Variation of inter-band and intra-conduction-band absorption spectrum with the different sizes of the nanodisc are presented for various diameter from 10 nm to 32 nm and constant thickness of 4 nm. Inter-band and intra-band absorption spectrum are simulated using the oscillator strength. These calculation shows that intra-band absorption spectrum of the weakly confined nanodisc can cover a large THz (∼ 0.3–6.5 THz) spectrum range for these set of nanodiscs. The proposed silicon based THz absorbing material can be utilized for CMOS compatible THz technology if design on silicon-on-insulator system.

THz quantum gap: exploring potential approaches for generating and detecting non-classical states of THz light.

Over the past few decades, THz technology has made considerable progress, evidenced by the performance of current THz sources and detectors, as well as the emergence of several THz applications. However, in the realm of quantum technologies, the THz spectral domain is still in its infancy, unlike neighboring spectral domains that have flourished in recent years. Notably, in the microwave domain, superconducting qubits currently serve as the core of quantum computers, while quantum cryptography protocols have been successfully demonstrated in the visible and telecommunications domains through satellite links. The THz domain has lagged behind in these impressive advancements. Today, the current gap in the THz domain clearly concerns quantum technologies. Nonetheless, the emergence of quantum technologies operating at THz frequencies will potentially have a significant impact. Indeed, THz radiation holds significant promise for wireless communications with ultimate security owing to its low sensitivity to atmospheric disturbances. Moreover, it has the potential to raise the operating temperature of solid-state qubits, effectively addressing existing scalability issues. In addition, THz radiation can manipulate the quantum states of molecules, which are recognized as new platforms for quantum computation and simulation with long range interactions. Finally, its ability to penetrate generally opaque materials or its resistance to Rayleigh scattering are very appealing features for quantum sensing. In this perspective, we will discuss potential approaches that offer exciting prospects for generating and detecting non-classical states of THz light, thereby opening doors to significant breakthroughs in THz quantum technologies.

Tunability Dependence of All-Optical Liquid Crystal Delay Line on Laser Polarization and Incidence Angle

This work experimentally investigates the optical manipulation of trans-cis swaps and resultantly their optical/electromagnetic imprints as a driver for realizing the tunable delay lines in the microwave X band (8-12 GHz) regime utilizing the polarization and incident angle dependencies of azo-admixed liquid crystals (LCs). Measurement results confirm that the tuning efficacy of the azo-LCs-based delay line is highly dependent on the polarization of the laser beam concerning the rubbing and filling directions of LCs. When the laser light beam is polarized parallel to the rubbed direction as well as the LCs filling direction, the achievable differential phase shift is maximized. Full Text: PDF References T. Sakamoto, Optoelectronic Circuits for Control of Lightwaves and Microwaves (London, IntechOpen 2011). CrossRef J.F. Li, "All-optically controlled microwave analog phase shifter with insertion losses balancing", Eng. Lett. 28, 3 (2020). DirectLink J.P.F. Lagerwall, G. Scalia, "A new era for liquid crystal research: Applications of liquid crystals in soft matter nano-, bio- and microtechnology", Curr. Appl. Phys. 12, 6 (2012). CrossRef S. Kim, K. Seiji, "Photochemical On–Off Switching of One-Dimensional Photonic Crystals Consisting of Azo-Functionalized Liquid Crystal Polymer and Polyvinyl Alcohol", Crystals 9, 12 (2019). CrossRef J.F. Li, "Micro-LED Mass Transfer Technologies", ICEPT (Guangzhou, IEEE 2020). CrossRef U. Chodorow, J. Parka, O. Chojnowska, "Liquid Crystal Materials in THz Technologies", Phot. Lett. Poland 4, 3 (2012). CrossRef

Super-resolution terahertz synthetic aperture image reconstruction algorithm.

The resolution of terahertz images based on the near-field synthetic aperture radar (NSAR) imaging mode is low due to the narrow antenna beamwidth and the electromagnetic wave loss that was ignored by previous algorithms. We propose a super-resolution terahertz NSAR imaging algorithm. There are two algorithm steps: First, we use the forward mathematical model of the NSAR imaging system and the back-projection algorithm (BPA) to calculate the point spread function (PSF). The next step is to deconvolve the NSAR image reconstructed by BPA to enhance its lateral resolution. To evaluate the effectiveness of our proposed method, we conducted both simulations and experiments. The experiment results show that the proposed method achieves a resolution of 0.67λ, which is a significant improvement. Overall, the proposed method has great potential to enhance the resolution of THz images and advance the use of THz technology in various fields.

Design and performance analysis of PCF-based octagonal chemical sensor to detect benzene, ethanol, and water in terahertz spectrum

An octagonal cladding with a hexahedron core PCF sensor is designed to detect chemical compounds at terahertz frequency. The proposed sensor contains circular air holes (CAHs) in the vestibule area. To measure the performance of the sensor effective material loss, confinement loss, and a large frequency area have been used in terms of relative sensitivity (RS). For the design and analysis of our proposed hexahedron PCF sensors, the finite element (FEM) utilizes numerally the optic parameters. The diameter and core size of the proposed air whole were checked to optimize the production tolerance and sensing performance. At the area of 1 THz spectrum Ethanol, Benzene, and Water are used for numerical examination The fiber appears to be a high Relative sensitivity which is 91.25 %, 93.80 %, and 89.95 % respectively for Ethanol (n = 1.354), Benzene (n = 1.366) and Water (n = 1.330). The sensor provides low confinement losses with 5.95 × 10−08 dB/m, 6.25 × 10−08 dB/m, and 5.94 × 10−08 dB/m corresponding for those three chemicals. The geometric construction of the projected sensor can be used in chemical sensing in biomedical, industrial quality control, material research, clinics, gas sensors, micro-optics, and many communication applications in THz technology.

Take Terahertz for a spin

Despite important developments in photo-conductive switches and quantum cascade lasers for THz generation, THz technologies are used in only a few relatively niche applications. We spoke to Dr. Romain Lebrun, the project coordinator from Thales Research Center, about the work of the s-Nebula project in developing a new approach based on spintronics and exploring the potential applications of this emerging technology.

Y-shaped tunable monolithic dual colour lasers for THz technology

Abstract. THz generation by difference frequency generation can be accomplished by many different laser systems. The most cost efficient and compact solution will be monolithic dual-colour lasers. Application of these lasers in THz metrology can suffer from several drawbacks like coupling between the modes, strong amplitude variations, low tuning capabilities, or a complicated growth process. We discuss the impact of these points for THz measurements and present a simple monolithic dual colour laser which can be used for material characterisations.

Next-generation mobile communication leveraging cutting-edge photonic technologies (Photonic 6G)

Next-generation mobile communication leveraging cutting-edge photonic technologies (Photonic 6G) Our aim is to develop ‘Photonic 6G’, an all-photonic THz communication technology, by integrating advanced photonic methods. This includes generating low-phase-noise THz waves with microcombs and converting modulated THz waves into optical carrier signals. By leveraging these advancements, we aim to enable advanced modulation and multiplexing in the optical domain, ultimately achieving the integration for photonic 6G.

Experimental study on evolution and mechanism for dielectric response of different rank coals in terahertz band

Terahertz technology holds the potential for applications in identifying risks and development stages of coal spontaneous combustion (CSC). However, one critical factor influencing the precision of THz technology in CSC applications is the coal rank. In light of these, this study aimed to investigate the permittivity (0.4–1.6 THz) of different rank coals. Additionally, its underlying mechanism was analyzed utilizing Fourier-transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy. Results indicate that increased coal rank leads to a decrease in both real permittivity (from 2.462 to 2.327) and imaginary permittivity (from 0.0447 to 0.0250), primarily due to diminished moisture (from 12.82 % to 1.35 %). After moisture removal, increased coal rank results in an increased real permittivity (from 2.292 to 2.315), primarily due to the carbon crystallite (interlayer spacing changed from 3.553 to 3.529, and stacking height shifted from 14.805 to 19.743) and microstructure profiles. Moreover, minerals are identified as another primary factor affecting real permittivity. For imaginary permittivity, increased coal rank leads to a decrease (from 0.0411 to 0.0245), primarily due to oxygen-containing functional groups (from 42.96 % to 31.71 %). The conclusion advances the fundamental theoretical research on coal permittivity, providing a solid theoretical foundation for THz technology in CSC applications.

A robust adaptive-thresholding primal-dual sparse recovery for THz imaging

Terahertz time-domain spectroscopy (THz-TDS) system is a powerful tool in material spectral analysis and non-destructive testing (NDT). However, the data acquisition is time-consuming due to the point-by-point scanning process, which leads to limitations in THz imaging applications. In this paper, a robust adaptive-thresholding primal-dual sparse recovery (APSR) method is proposed to reconstruct high-resolution THz images and reduce the acquisition time. A sparsity averaging dictionary, which is a concatenate of multiple bases, is applied to improve the robustness and generalization. A reweighted scheme is also adopted to enhance the sparse solution. As a crucial consideration in the sparse recovery method, we propose a robust adaptive threshold estimator based on the median absolute deviation in the sense that the final threshold determines the reconstruction quality and the convergence rate. Meanwhile, together with the Nesterov acceleration technique, a large threshold can be applied at the beginning of the iteration to help accelerate the convergence. Numerical experiments demonstrate that the APSR method can reconstruct THz images with robustness even with low SNR (of 30 dB) and low sampling rate (of 30%) compared to conventional methods. In the real THz-TDS system, our proposed sparse imaging method can successfully recover a composite object with much fewer THz spectra and reduces the acquisition time to 30% at the cost of a relative error of 2.5%, demonstrating the efficiency of our proposed method and the penetrating ability of THz technology in the NDT applications.

Prospects Of Terahertz Technology – A Comprehensive Review

Prospects Of Terahertz Technology – A Comprehensive Review

Optical materials for IR fiber optics based on solid solutions of AgCl0.25Br0.75 – TlCl0.74Br0.26, AgCl0.25Br0.75 – TlBr0.46I0.54 systems

The development of optical materials, that are transparent from the visible to the far IR without absorption windows, including fiber optics materials, continues to be an urgent scientific problem, which is associated with high prospects for their application in wide-spectrum systems, IR and THz technology. This article is devoted to the development of materials based on the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems from constructing phase diagrams to synthesis of single crystals and optical ceramics and their transmission properties investigation. According to the results of studying the phase diagram of the AgCl0.25Br0.75 – TlCl0.74Br0.26 system, homogeneity regions of 0–7 mol. % and 95–100 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75, in which there are single-phase solid solutions with the structure Fm3m and Pm3 m, respectively, were obtained. In this diagram, regions of heterogeneity with a composition of 7–79 mol. % and 79–95 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 and a mixture of two phases in the first region Fm3m and R-3, and in the second region Pm3 m and R-3 were found. Within the AgCl0.25Br0.75 – TlBr0.46I0.54 system's phase diagram, homogeneity regions with compositions of 0–15 mol. % and 92–100 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 and similar structures Fm3m and Pm3 m, respectively, were determined. This system also contains regions of heterogeneity with compositions of 15–36 mol. %. and 69–92 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 with phase composition Fm3m and R-3, and Pm3 m and R-3. In each system, compositions were selected from the homogeneity and heterogeneity regions, and samples of single crystals and two-phase ceramics were synthesized. For the AgCl0.25Br0.75 – TlCl0.74Br0.26 system, a single crystal with a composition of 3 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 and two-phase ceramics of 7, 31, 86, 92 mol. % TlCl0.74Br0.26 in AgCl0.25Br0.75 were obtained. Single crystals 3, 6, 9, 92 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 and ceramics 32, 76 mol. % TlBr0.46I0.54 in AgCl0.25Br0.75 were synthesized in AgCl0.25Br0.75 – TlBr0.46I0.54 system. The samples are 35 ± 5 mm high and 10 ± 0.1 mm in diameter, and their color varies from yellow to orange depending on the composition. The transmittance ranges of all synthesized samples were investigated. The study was carried out on polycrystalline plates with a diameter of 15 ± 5 mm, thickness of 400 ± 5 μm, and surface roughness Ra = 0.2 μm. The crystallite size of the alloying phase R-3 in the optical ceramics was less than 100 nm. For AgCl0.25Br0.75 – TlCl0.74Br0.26 system materials, the transmission spectra covered the region from 0.4 to 55.0 μm. Materials based on the AgCl0.25Br0.75 – TlBr0.46I0.54 system showed transmission in the wavelength range of 0.49–60.0 μm. All materials are transparent in the wide region without absorption windows with a transparency level up to 79%. Thus, new optical materials based on the AgCl0.25Br0.75 – TlCl0.74Br0.26 and AgCl0.25Br0.75 – TlBr0.46I0.54 systems have been developed, which have a wide transmission range from the visible to the IR. This opens broad prospects for their use as an optical material for wide-spectrum devices, as well as IR fiber optics.

Design of Quasi-Shaped spectroscopy based optical sensor for the detection of alcohol

In this research, an entirely novel optical sensor for alcohol detection based on quasi-shaped spectroscopy is offered. A quasi shape with a tightly bonded structure in the cladding region and a hexahedron core region makes up the recommended design, which has a remarkable sensitivity of about 91.35%, 92.55%, and 90.40%and low confinement losses (CLs) of 5.44 × 10−08 dB/m, 6.75 × 10−08 dB/m, and 5.85 × 10−08 dB/m for detecting alcohol like ethanol (n = 1.354), butanol (n = 1.3993), and propanol(n = 1.384), at 1 THz. The numerical aperture, the effective area, and the V-parameter have all been identified and assessed. The 0.8THz to 3 THz operational wavelength range is stated. In the COMSOL Multiphysics (Version 5.6) environment, the properties of these suggested alcohol sensors are numerically examined utilizing the FEM (finite element method) with full vectors. In contrast to other efforts, the proposed sensor, which consists of a quasi-lattice PCF with a perfectly matched layer (PML) of a circular air hole shape and TOPAS as the background material, aims to improve sensitivity response. The proposed sensor might be crucial in the alcohol detection process due to its superior sensitivity response, a single mode of operation across the entire operational terahertz range, and shallow confinement loss. So, this PCF can proficiently be pragmatic in many biological sensing and other THz technology domains.

Terahertz cancer imaging and sensing: open research challenges and opportunities

There has been a rapid development of THz technology—sources, detectors and various THz imaging and sensing techniques. The THz technology demonstrates great potential as a modality for early, label free, non-ionizing and non-invasive detection of cancer. Some progressive technological development milestones have been achieved in this regard, however, to become clinically competitive and to provide the sought after real operational convenience, there is need for further research and development to overcome the existing challenges. This paper provides recent trends and perspectives through identification of existing challenges for the development of THz imaging and sensing systems that can evolve into actual medical modalities. We provide an overview of various aspects of THz technology, including techniques for imaging and sensing, mechanisms for THz image contrast and models for tissue dielectric responses to THz waves. The THz imaging application for detection of various cancers is briefed. The advantages of THz cancer imaging and sensing as well as the existing challenges are identified, with recommendations provided in contribution to future research. Further, some recent THz imaging and sensing developments such as the near-field methods to break the diffraction limit including waveguides, resonance and plasmonic metasurfaces are discussed. We emphasize the contribution of analytical algorithms that are based on machine learning, in particular, deep learning for the development of THz technology.Graphical abstract

THz Bragg structures fabricated with additive manufacturing.

The advancement of THz science and technology is desirable to facilitate the application of THz technologies in many sectors. Specialized THz photonic elements for these applications require desirable absorption and refractive characteristics in the THz regime. THz photonic elements can be created with additive manufacturing, and specifically 3D printing, forgoing the need for complex fabrication procedures and methodologies. Such THz photonic elements include periodic Bragg structures, which are capable of filtering specific THz frequencies. The authors present a THz Bragg structure fabricated with 3D printing via fused filament fabrication. The THz Bragg structure is made from high-impact polystyrene filament material, which is characterized in this paper with THz time-domain spectroscopy. The geometry and theoretical operation of the THz Bragg structure is investigated with finite-difference time-domain electromagnetic simulations. The THz Bragg structure is evaluated using a THz experimental test bed. There is agreement between the theoretical and the experimental filtering placement within the frequency domain for the THz Bragg structure. The capability of tunable frequency filtering of the presented THz Bragg structure, fabricated with 3D printing, is established and facilitates future advancements in applications of THz science and technology.