Terahertz Waveguide Research Articles

Spiral shaped highly sensitive rectangular PCF-based cancer cells detector in terahertz regime

Abstract The increasing fatality rate of cancer in the modern world has become a global concern. To address this issue, early detection of cancer cells in human blood is essential. In this article, a rectangular spiral shaped photonic crystal fiber has been proposed for sensing cancer cells in terahertz regime. The proposed PCF based sensor features a square shaped core surrounded by rectangular air holes of different sizes in a spiral manner. Finite element method based COMSOL Multiphysics software has been used for the design and analysis of the model. The model is sensitive to refractive index variation for the identification of cancer cells. The values of effective refractive index, effective mode area, relative sensitivity, non-linearity, and confinement loss are obtained for MCF-7, MDA-MB-231, Jurkat, HeLa, Basal and PC-12. The PCF based sensor resulted in excellent results of relative sensitivity and Confinement loss as good as 99.377% and 8.59 × 10−12 dBm−1 respectively. Furthermore, the present PCF based sensor model is fabrication feasible, and we hope that it can be utilized at industrial level for biosensing applications in terahertz waveguide regime.

High birefringent slotted core slotted cladding porous core PCF for THz waveguide

A novel design featuring a porous core photonic crystal fiber (PC-PCF) is proposed in this paper for terahertz (THz) waveguide application. This work uses finite element method (FEM) and a boundary condition related to perfectly matched layer (PML) for analyzing the guiding properties. This methodology is supported by a fiber type featuring a slotted core and slotted cladding, utilizing Zeonex as the material. It offers high birefringence valued at 0.0978, small confinement loss of 10−14 dB/cm, a meager amount of effective material loss (EML) valued at 0.011697 dB/cm and a very high core power fraction (CPF) of 67.156%. Additionally, it shows a flattened pattern of dispersion measuring 0.4 ± 0.2 ps/THz/cm at an extensive frequency range of 0.5 THz to 2 THz. Other significant waveguide properties: effective refractive index, numerical aperture (NA), V-parameter, effective area, spot size, and beam divergence of the suggested fiber are numerically analyzed and conferred thoroughly. Regarding its mode of operation, the proposed fiber primarily functions in multimode, but it can also operate in single mode for higher porosity levels and lower core diameters. This unique characteristic renders the proposed PC-PCF structure well-suited for a broad range of applications, offering versatility as to its mode of operation.

Robust flexible hollow racetrack-shaped terahertz waveguide with single-polarization single-mode and low-loss by plasma aided hot-pressing method

A flexible single-polarization single-mode (SPSM) polymer/Ag-coated hollow waveguide with a racetrack-shaped cross-section was designed and prepared using a simple hot-pressing method and plasma treatment. The waveguide structural parameters were numerically optimized using the finite element method and the SPSM transmission can be achieved in a high birefringent (>0.8) hollow racetrack-shaped waveguide (HRW). The racetrack-like waveguides were facilely prepared by hot-pressing commercially available circular acrylonitrile butadiene styrene (ABS) and poly-ether-ether-ketone (PEEK) tubing, followed by plasma treatment and silver-plating. The HRW samples with a length of 40 cm were prepared, with a straight transmission loss of 1.74 and 1.68 dB/m at 0.1 THz, respectively, and the polarization degree is 99.9 %. When bent for 120° at a 10 cm radius or twisted by 90°, the waveguide samples have additional losses less than 0.22 and 0.14 dB/m, respectively, while the polarization degrees keep almost unchanged. After 200 h hydrothermal aging (85 RH%, 85 ℃) and 20 times high (85 ℃)/low (−40 ℃) temperature tests, the loss increase is less than 0.14 dB/m and the polarization degree remains unaffected. The HRW could be used in practice as a competitive substitute for traditional rectangular metal waveguides due to its high SPSM performance, lightweight, robustness, flexibility, and easy fabrication.

Highly efficient hybrid-structured photonic crystal fiber with ultra-low loss and near-zero flat dispersion for terahertz waveguiding

Highly efficient hybrid-structured photonic crystal fiber with ultra-low loss and near-zero flat dispersion for terahertz waveguiding

Asynchronous optical sampling of on-chip terahertz devices for real-time sensing and imaging applications

We demonstrate that asynchronous optical sampling (ASOPS) can be used to measure the propagation of terahertz (THz) bandwidth pulses in a coplanar waveguide device with integrated photoconductive switches used for signal excitation and detection. We assess the performance of the ASOPS technique as a function of measurement duration, showing the ability to acquire full THz time-domain traces at rates up to 100 Hz. We observe a peak dynamic range of 40 dB for the shortest measurement duration of 10 ms, increasing to 88 dB with a measurement time of 500 s. Our work opens a route to real-time video-rate imaging via modalities using scanned THz waveguides, as well as real-time THz sensing of small volume analytes; we benchmark our on-chip ASOPS measurements against previously published simulations of scanning THz sensor devices, demonstrating sufficient dynamic range to underpin future video-rate THz spectroscopy measurements with these devices.

Enhancement of terahertz fields in LiTaO3 waveguides using a conical pulse front

The development of methods for the generation of strong ultrafast electromagnetic pulses in the terahertz (THz) spectral range has led to a surge of progress in nonlinear THz spectroscopy and THz control of molecular and collective responses. For spectroscopy in the 1-THz range, the submillimeter wavelengths and associated large spot sizes, large optical elements, and short distances between final focusing elements and samples can lead to cumbersome experimental setups that are incompatible with some sample environments. Here, we introduce a novel terahertz ring excitation (TREx) optical pumping geometry to generate superposing, focusing fields in planar THz waveguides made out of the electro-optic material lithium tantalate. High THz fields, >175 kV/cm, are generated and measured optically with no free-space THz propagation. The field level achieved by pumping with a sequence of concentric rings of excitation light exceeds by about 20× the result of a single cylindrically focused line of pump light that has been used routinely in previous work. The technique opens new prospects for compact waveguide-based linear and nonlinear THz spectroscopy and signal processing.

Anti-Resonant Hollow-Core Fibers with High Birefringence and Low Loss for Terahertz Propagation

A new type of anti-resonant hollow-core fiber for terahertz waveguides is proposed. By introducing central support pillars and an elliptical structure, the fiber achieves high birefringence while maintaining low confinement loss and low material absorption loss. The fiber structure is optimized through simulation using the finite element method. The optimized fiber exhibits a birefringence of up to 1.22 × 10−2 at a frequency of 1 THz, with a confinement loss of 8.34 × 10−6 dB/cm and a material absorption loss of 7.17 × 10−3 dB/cm. Furthermore, when the bending radius of the fiber is greater than 12 cm, the bending loss of the anti-resonant optical fiber at 1 THz is less than 1.36 × 10−4 dB/cm, demonstrating good bending resistance and high practical value. It is expected to play a significant role in optical communication systems.

Study on mode properties of GaAs-based hybrid plasmonic terahertz waveguides

Terahertz (THz) fields are increasingly being used to address the critical challenges associated with achieving high data rates and rapid communication. In this study, a hybrid plasmonic THz waveguide is designed and analysed operating in the 2.5–3.5 THz frequency range. The waveguide is constructed using gallium arsenide as the high-refractive-index core, surrounded by aluminium arsenide and silver placed on a high-density polyethylene (HDPE) substrate. Graphene is strategically positioned between the HDPE layers to enhance light confinement. The mode properties of the proposed waveguide are simulated with Comol Multiphysics using the finite-element method and show unique characteristics. Observation of the simulated results at 2.5–3.5 THz reveals a high effective refractive index of 3.79, a maximum effective mode area of 1.88 mm2, a high birefringence of 0.2, a low dispersion of 0.10 ps THz−1 cm−1, a high mode field diameter of 15.8 mm, a high beat length of 123 mm and a low confinement loss of 1.79 × 10−9 mm−1. These features make the proposed waveguide suitable for applications in photonic integrated circuits for THz communications.

Manipulating terahertz guided wave excitation with Fabry-Perot cavity–assisted metasurfaces

Metasurfaces are emerging as powerful tools for manipulating complex light fields, offering enhanced control in free space and on-chip waveguide applications. Their ability to customize refractive indices and dispersion properties opens up new possibilities in light guiding, yet their efficiency in exciting guided waves, particularly through metallic structures, is not fully explored. Here, we present a new method for exciting terahertz (THz) guided waves using Fabry-Perot (FP) cavity-assisted metasurfaces that enable spin-selective directional coupling and mode selection. Our design uses a substrate-free ridge silicon THz waveguide with air cladding and a supporting slab, incorporating placed metallic metasurfaces to exploit their unique interaction with the guided waves. With the silicon thin layer and air serving as an FP cavity, THz waves enter from the bottom of the device, thereby intensifying the impact of the metasurfaces. The inverse-structured complementary metasurface could enhance excitation performance. We demonstrate selective excitation of TE00 and TE10 modes with directional control, confirmed through simulations and experimental validations using a THz vector network analyzer (VNA) system. This work broadens the potential of metasurfaces for advanced THz waveguide technologies.

High birefringence low loss nearly zero flat dispersion similar to slotted core photonic crystal fibers

Abstract Studying high-performance photonic crystal fibers (PCF) is of significant scientific importance for terahertz (THz) waveguide systems. This study introduces a novel PCF design with a core composed of the smallest sub-wavelength units resembling a slotted structure, aiming to achieve high birefringence and low loss. The optical properties of the proposed PCF are analyzed through simulations, yielding impressive results. The PCF exhibits an ultra-high birefringence of 0.07848, a minimum limiting loss of 10−17 dB/cm, and an effective material loss as low as 0.04251 cm−1. Moreover, it demonstrates near-zero flat dispersion of −0.012 ± 0.074 ps/THz/cm over a broad frequency range of 1.2–2.2 THz. This fiber stands out by not only providing high birefringence but also by striking an optimal balance among birefringence, transmission loss, and dispersion for THz waveguides. The implications of this work are profound for the development of THz communication systems, THz polarization-maintaining transmission, and sensing applications. Furthermore, it established an important benchmark for the design of THz-PCFs that prioritize high birefringence, low loss, and near-zero flat dispersion, offering an essential reference for future research and development in this field.

Engineering topological interface states in metal-wire waveguides for broadband terahertz signal processing.

Innovative terahertz waveguides are in high demand to serve as a versatile platform for transporting and manipulating terahertz signals for the full deployment of future six-generation (6G) communication systems. Metal-wire waveguides have emerged as promising candidates, offering the crucial advantage of sustaining low-loss and low-dispersion propagation of broadband terahertz pulses. Recent advances have opened up new avenues for implementing signal-processing functionalities within metal-wire waveguides by directly engraving grooves along the wire surfaces. However, the challenge remains to design novel groove structures to unlock unprecedented signal-processing functionalities. In this study, we report a plasmonic signal processor by engineering topological interface states within a terahertz two-wire waveguide. We construct the interface by connecting two multiscale groove structures with distinct topological invariants, i.e., featuring a π-shift difference in the Zak phases. The existence of this topological interface within the waveguide is experimentally validated by investigating the transmission spectrum, revealing a prominent transmission peak in the center of the topological bandgap. Remarkably, we show that this resonance is highly robust against structural disorders, and its quality factor can be flexibly controlled. This unique feature not only facilitates essential functions such as band filtering and isolating but also promises to serve as a linear differential equation solver. Our approach paves the way for the development of new-generation all-optical analog signal processors tailored for future terahertz networks, featuring remarkable structural simplicity, ultrafast processing speeds, as well as highly reliable performance.

Low Loss THz Waveguides and Its Potentials towards 6G Communication: A Brief Chronicle Review

Advancement in technology has opened the doors for the terahertz (THz) frequency range to be applied in different fields for various applications. The future communication technology, especially 6G, will also intend to utilize the THz frequency band due to its large bandwidth that has the capabilities to achieve a high data rate. Great losses are presented in the early research into terahertz transmission medium. It is critical to design an appropriate waveguide that can integrate the THz waves into the system efficiently with minimum loss and provides the ease of transmission of data and overcomes the free space loss issues. Communication, sensing, and other application parameters are highly affected by transmission losses; therefore, low transmission loss and dispersion loss waveguide designs are required for proper utilization. In this paper, the review on reduction in the transmission loss in different types of waveguides operating at the Terahertz frequency range is studied. The design and the experimental setup for several classes of THz waveguides for minimizing transmission loss are also discussed. The review study shows that these waveguides can be a promising transmission medium for future 6G communication.

Copper micromachined WR‐2.2 band waveguide and bandpass filter

AbstractThis paper presents a WR‐2.2 band (330–500 GHz) waveguide with E‐plane bends and a waveguide bandpass filter. A micro‐metal additive manufacturing technology employs copper to process these devices. This technology includes several micromachining processes, which can produce integrated, miniaturized, and complex three‐dimensional metal microstructures when meeting the process constraints. To successfully apply this technology to the fabrication of terahertz waveguide devices, many design details are considered. First, the E‐plane bent transition structures in the waveguide overcome size limitations imposed by the manufacturing process, allowing for accurate measurement using standard waveguide interfaces. Second, the rectangular resonators compose the fifth‐order waveguide bandpass filter spanning 20 GHz with a center frequency of 380 GHz. Given that the excess photoresist needs to be removed, some release holes are designed in the proper positions of the filter. Third, to increase the uniformity of the device layout and improve the machining quality in the electroforming process, a lot of rectangular holes are arranged around the device. By adopting a meticulous and novel design method in accordance with the process advantages and limitations, the fabrication accuracy of the device size is greatly increased. The integrated filter with exceptional performance is obtained. The measured average insertion loss within the passband is better than 1.2 dB, and the return loss exceeds 15 dB. Additionally, the filter demonstrates a center frequency offset of approximately 0.5%. Good consistency between simulation and measurement shows the validity of design and fabrication.

Anti-resonant fiber with high-resistivity silicon for THz wave transmission

A novel anti-resonant fiber for low-loss terahertz waveguides is proposed and analyzed. The terahertz fiber uses high-resistivity silicon as the bulk material and nine nested double-layer concentric circular tubes in the cladding to reduce propagation losses. The effects of the geometric parameters on the propagation characteristics are analyzed by the finite element method. The result indicates that an ultra-low total loss of 4.9×10−4dB/m is achieved at f=1THz. The low-loss propagation window is 0.48 THz ranging from 0.6 to 1.4 THz. In addition, the influence of mechanical bending on the propagation loss is investigated and the bending loss can be maintained at less than 7.3×10−3dB/m at f=1THz even if the bending radius is larger than 60 cm. The properties of this anti-resonant fiber are significantly superior to those of previously reported structures and the fiber thus has large commercial potential.

Graphene based waveguide fed hybrid plasmonic terahertz patch antenna

Abstract The terahertz (THz) technology has fascinated lot of attention due to its enormous potential for a wide range of applications in the public, private and enterprise domains. This research work demonstrates the design structure and analysis of graphene based waveguide fed hybrid plasmonic THz patch antenna (HPTPA) constructed at around 3 THz. Hybrid plasmonic THz waveguide (HPTW) as a feeding line for the proposed THz patch antenna can increases antenna efficiency. The graphene is sandwiched between gallium arsenide (GaAs) and silver (Ag) to confine THz waves efficiently. Using mode analysis in finite element method for the proposed HPTW the propagation length, effective refractive index has been thoroughly examined. Based on the finite element method (FEM) approach, the results of the designed graphene-based waveguide fed HPTPA shows a high effective refractive index of 2.9, large propagation length of 230 µm, gain of 2.29 dBi, bandwidth of 200 GHz and efficiency of 85 % has obtained. The proposed graphene-based waveguide fed HPTPA could be beneficial to enable several photonic integrated circuit applications in next-generation wireless communication.

Subcycle surface electron emission driven by strong-field terahertz waveforms

The advent of intense terahertz (THz) sources opened a new era when the demonstration of the acceleration and manipulation of free electrons by THz pulses became within reach. THz-field-driven electron emission was predicted to be confined to a single burst due to the single-cycle waveform. Here we demonstrate the confinement of single-cycle THz-waveform-driven electron emission to one of the two half cycles from a solid surface emitter. Either the leading or the trailing half cycle was active, controlled by reversing the field polarity. THz-driven single-burst surface electron emission sources, which do not rely on field-enhancement structures, will impact the development of THz-powered electron acceleration and manipulation devices, all-THz compact electron sources, THz waveguides and telecommunication, THz-field-based measurement techniques and solid-state devices.

Anti-resonant fiber with nested U-shape tubes for low-loss terahertz waveguides

Anti-resonant fiber with nested U-shape tubes for low-loss terahertz waveguides

Research on anti-resonant terahertz hollow waveguides with cascaded bridges

A low loss terahertz waveguide based on anti-resonant parameters is proposed to construct a periodic support structure of an arch bridge in Bragg air layer. Simulation results show that terahertz waves can be transmitted with low loss in the anti-resonant band. After numerical simulation to determine the parameters of the waveguide, the waveguide samples are manufactured by 3D printing technology and experimental tests are carried out. Experimental results demonstrate that the terahertz wave within the 0.84–0.887 THz band can be transmitted with a low loss of only 0.245dB/m, which is nearly ten times lower than that of the conventional multi-support structure terahertz Bragg waveguide, and comparable to that ofthe ideal air-core Bragg waveguide.

Terahertz link with orthogonal polarization over silicon dielectric waveguide

AbstractThe authors studied the transmission performance for orthogonal polarization fundamental modes in a dielectric silicon terahertz waveguide for doubling the data rate. The maximum data rate of practical error‐free condition (bit‐error rate < 10−11) for both polarizations is comparable over 20 Gbit/s under on‐off keying modulation at 0.3‐THz band.

The perspectives and trends of THz technology in material research for future communication - a comprehensive review

In recent years, the realm of terahertz (THz) has seen a new paradigm of unprecedented development and offered new possibilities to strengthen the communication sector by studying the dielectric properties of different materials. The aim of this article is to present a comprehensive review of various THz technologies that have been employed to investigate the intrinsic characteristics of different materials. In addition, the study highlights the significance use of THz wave guides with some discussion on sources, and detectors and components. Towards the end, it highlights the future trends of THz technology and the challenges. The paper concludes that THz technology has a promising potential and offer new opportunities for applications in characterization of composite materials.