Terahertz Fiber Research Articles

Artificial Intelligence-Assisted Accurate Spectrum Prediction in Design of Terahertz Fiber Operating in 6G Communication Window

Artificial Intelligence-Assisted Accurate Spectrum Prediction in Design of Terahertz Fiber Operating in 6G Communication Window

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.

Ultra‐Wideband Terahertz Integrated Polarization Multiplexer

AbstractPolarization‐division multiplexing is crucial for increasing channel capacity and spectral efficiency in communications. A key component is the polarization multiplexer, which combines or separates signals with orthogonal polarizations. Existing planar multiplexers lack an ultrawide band for terahertz communications. While microwave‐inspired orthomode transducers (OMTs) provide broadband operation, they suffer from high ohmic loss and bulkiness at terahertz frequencies. Optical integrated polarization beam splitters (PBSs) offer low loss and good integrability but have narrow bandwidths. This work presents a substrateless all‐silicon polarization multiplexer based on tapered directional couplers and air‐silicon effective mediums, integrated monolithically on a compact footprint. The device demonstrates a 37.8% fractional bandwidth, an average insertion loss of 1 dB, and a polarization extinction ratio above 20 dB over 225–330 GHz. This superior performance is enabled by the anisotropy of the effective medium claddings, affecting the two orthogonal guided modes differently. The multiplexer enables simultaneous two‐channel terahertz fiber communications with polarization diversity. It supports aggregated data rates up to 155 and 190 Gbit with bit error rates below hard‐ and soft‐decision forward‐error‐correction limits, respectively. This advancement holds promise for 6G terahertz integrated systems with enhanced channel capacities.

Research on ultra-high birefringence terahertz fibers with simple structures

Research on ultra-high birefringence terahertz fibers with simple structures

Tunable band-stop fiber filter based on laser-induced graphene metamaterial in THz frequency.

As an important device in the application of terahertz (THz) technology, a THz filter has broad application prospects in the fields of THz communication, imaging, and sensing. In this paper, a THz filter based on grating structure laser-induced graphene (LIG)/ side polishing terahertz fiber composite structure is proposed. In the experiment, we achieved the maximum Q factor of 23.83 at the central resonant frequency of 0.715 THz. By modifying the grating structure, a tunable operational span of 269 GHz was achieved, along with a tunable range of 21 GHz through laser stimulation. In testing, we found that LIG materials prepared with circular filling are more sensitive to relatively high-power pump lasers, while LIG samples prepared with line filling exhibit better linear response to laser power. Furthermore, the compact and highly integrated nature of the device suggests its broad potential utility in the realm of THz frequency selection.

Influence of cladding tube structure on transmission characteristics of negative curvature terahertz fiber

A novel type of polarization negative curvature terahertz fiber has been designed, which has a cladding region composed of two long semi-circular cladding tubes in the horizontal direction and four long semi-elliptical cladding tubes in the oblique direction. The optimal fiber dimensions are determined to investigate the internal relationship between polarization characteristics and fiber cladding structure. The transmission performances of the negative curvature fiber are investigated by varying the thickness of fiber cladding tubes and adjusting the structural characteristics of cladding tubes in different directions. Relatively good transmission performances can be obtained with a cladding tube thickness of 80 μm. The birefringence can be stably maintained at the order of 10−4, and the confinement loss of the x-polarized mode at 2.55 THz is 0.036 dB cm−1. Moreover, the dispersion coefficient of the two polarized modes is stable between ±0.6 ps (THz·cm)−1 in the 2.3–2.6 THz band. The bent performance of the designed fiber at 2.52 THz is also discussed. The results show that the fiber has low bending sensitivity, and can still maintain excellent birefringence and low confinement loss in the bending state. For the y polarization, the birefringence can be basically stabilized at the order of 10−4 within a bending radius of 10–60 cm.

Research on hollow-core terahertz fiber based on Bragg anti-resonant elements arranged in a hexagonal structure

A hollow-core terahertz fiber composed of Bragg anti-resonant elements in a hexagonal structure is proposed. The function of Bragg elements on the transmission losses and bending losses of the hollow-core terahertz fiber is investigated using finite element method. Numerical simulations demonstrate that the introduction of Bragg elements for the anti-resonant cladding can significantly reduce the confinement losses of the fiber, the appropriate choice of the outer cladding diameter can also contribute to the reduction of the total loss. The bending loss shows low dependence on the bending angle for the proposed fiber with the Bragg elements. Compared with the anti-resonant hollow-core terahertz fiber composed of only a single dielectric layer, the bending losses of the hollow-core terahertz fiber with the Bragg elements can be reduced by more than an order of magnitude.

A metasurface structure-assisted terahertz negative curvature fiber

Negative curvature fibers have the benefits of high bandwidth, low loss, and provide higher transmission performances. Birefringence of the fiber is particularly important, with potential application value in communication, imaging and other fields. In this paper, a metasurface structure-assisted terahertz negative curvature fiber is designed to improve the birefringence characteristic. This work breaks through the conditional design ideas, and theoretically analyzes the effect of adding gold microstructures in the cladding structures on the transmission characteristics of negative curvature fibers. The investigation results show that the birefringence of the designed fiber exhibits a significant increase in most frequency range between 1.75–2.4 THz compared to the results before adding gold microstructures. The maximum birefringence reaches as high as 0.00216 when the frequency is 2.175 THz and θ is 90°. Compared to the original frequency, the birefringence has increased by nearly an order of magnitude. The highest birefringence has been increased to 3.5 times. In addition, the influences of the gold microstructures on the confinement loss, waveguide dispersion, and effective mode field area are also investigated. This fiber provides a reference for the design of high birefringence terahertz fibers in the future.

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.

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.

Investigation on low-loss hollow-core anti-resonant terahertz fiber.

In this work, a hollow-core anti-resonant terahertz (THz) fiber with elliptical cladding and nested tubes is proposed and fabricated. It is an effective way to reduce the loss of THz waves by transmitting them in an air core and breaking the material absorption. After parameter optimization of the initial structure, multiple transmission windows exist in the 0.2-0.8THz band, where confinement loss is as low as 3.47×10-3cm-1 at 0.8THz. At 0.2-0.7THz, confinement losses lie between 10-3 and 10-2cm-1. The 3D printed samples are characterized by a THz time-domain spectroscopy system. Experimental results showed that the designed fiber structure transmits loss coefficients up to 10-2cm-1 in the 0.2-0.8THz band (the minimum value is located at 0.46THz, corresponding to a loss coefficient of 0.0284cm-1). The experiments show that the designed THz fiber achieves a good transmission effect.

Graphene-coated D-shaped terahertz fiber modulator

A terahertz (THz) fiber is of interest due to low loss and easy beam shaping. Graphene plays an important role in modulating the optical signal. In this paper, a graphene-coated D-shaped THz fiber modulator is proposed. The performance of the proposed modulator is investigated by the finite element method. The inference of geometric parameters of the structure on the proposed modulator is also analyzed, and an optimal structure is obtained. Simulation results show that the confinement loss and the full width at half-maximum (FWHM) can be tuned by adjusting the Fermi level of graphene. The proposed THz fiber modulator shows potential in future THz fiber communications.

A low-loss polarization-maintaining terahertz fiber

A novel low-loss THz polarization-maintaining fiber is analyzed numerically. The proposed fiber consists of two small thin dielectric tubes nested in a large dielectric tube. Numerical simulations performed using the full-vector finite element method show that the difference between the effective refractive index of LPx01 and the adjacent modes is up to 10−2 orders of magnitude in the frequency range from 0.32 to 0.7 THz. At the same time, the proposed fiber has low loss characteristics, and the total loss of LPx01 is only 0.17 dB/cm at 0.35 THz. In addition, near-zero flat dispersion of 0.3 ± 0.36 ps/THz/cm can be achieved by adjusting the structural parameters of the fiber.

Fiber-terahertz-fiber bridge system in the 355-GHz band using a simple optical frequency comb and a photonics-enabled receiver.

This Letter demonstrates a high-speed fiber-terahertz-fiber system in the 355-GHz band using stable optical frequency comb generation and a photonics-enabled receiver. At the transmitter, a single dual-drive Mach-Zehnder modulator is employed to generate a frequency comb by driving the modulator under an optimal condition. At the antenna site, a photonics-enabled receiver consisting of an optical local oscillator signal generator, a frequency doubler, and an electronic mixer is used to downconvert the terahertz-wave signal to the microwave band. Simple intensity modulation and a direct detection method are used for transmitting the downconverted signal to the receiver over the second fiber link. To demonstrate the proof of concept, we transmitted a 16-quadrature amplitude modulation (QAM) orthogonal frequency-division multiplexing signal over a system consisting of two radio-over-fiber links and a 4 m wireless link in the 355-GHz band and achieved a line rate of 60 Gb/s. We also successfully transmitted a 16-QAM subcarrier multiplexing single-carrier signal over the system and achieved a capacity of 50 Gb/s. The proposed system can facilitate the deployment of ultra-dense small cells in high-frequency bands in beyond-5G networks.

Anti-resonant based nested terahertz fiber design for illicit drugs detection

Anti-resonant hollow-core fibers (AR-HCFs) have gotten a lot of interest lately because of their potential uses in different medical sensing applications. In this work, an anti-resonant THz fiber (ATF) biosensor is implemented to check for illicit drugs and identify them at airport borders. Three different unlawful medicines have been chosen for the proposed design, Cocaine, Amphetamine, and Ketamine. A novel hollow-core anti-resonant fibers (HC-ARF) Matryoshka shape sensor has been designed for detecting the illegal drugs. The proposed design shows a robust sensitivity ranging from 99.8-99.9% and shallow confinement losses compared to other articles in the same field, as the higher losses are 9.3×10-4 dB/m with cocaine. Bending loss lessens as the bending radius rises while it is still below 1 dB/cm for radius more than 10 cm. The numerical simulation outcomes displayed that the designed HC-ARF has 0.0643±0.0238 ps/THz/cm flat dispersion at 0.6-2 THz. As the first application in this field, this work will be the first published in the literature.

Terahertz fiber with multi-concentric ring cores for OAM modes propagation

A novel fiber incorporating central hollow, porous isolated layers, and concentric ring cores is proposed for the simultaneous propagation of multi-terahertz (THz) orbital angular momentum (OAM) modes with low-level inter-core and inter-mode crosstalk. The designed fiber can efficiently support 132 OAM modes in 0.6 ∼ 1.5 THz, 178 OAM modes in 0.7 ∼ 1.5 THz, etc, the high-order radial modes are suppressed within the whole frequency range meanwhile, and the number of OAM modes can be further boosted by further increasing the number of ring cores. In addition, the fiber has low confinement loss, flat dispersion, and high purity over a wide operating range. Hence it can be applied in mode-division multiplexing (MDM) based on OAM combined with core-division multiplexing (CDM) in THz range, and is also compatible with wavelength-division multiplexing (WDM) and multi-level modulation formats. The realized fiber is expected to dramatically extend the transmission capacity and spectral efficiency.

Terahertz fiber link using dielectric silicon waveguide interface.

Nascent data-intensive emerging technologies are mandating low-loss, short-range interconnects, whereas existing interconnects suffer from high losses and low aggregate data throughput owing to a lack of efficient interfaces. Here, we report an efficient 22-Gbit/s terahertz fiber link using a tapered silicon interface that serves as a coupler between the dielectric waveguide and hollow core fiber. We investigated the fundamental optical properties of hollow-core fibers by considering fibers with 0.7-mm and 1-mm core diameters. We achieved a coupling efficiency of ∼ 60% with a 3-dB bandwidth of 150 GHz in the 0.3-THz band over a 10 cm fiber.

Design and analysis of low loss solid-core hexagonal photonic crystal fiber for applications in terahertz regime

An index-guiding novel solid-core photonic crystal fiber (SC-PCF) formed by a hexagonal lattice of circular-shaped air holes arranged in silicon background is realized. By varying the radius ‘r’ of the air holes from 0.1a to 0.5a (where ‘a’ is defined as the lattice constant), the characteristic electromagnetic modes of the low loss Terahertz (THz) fiber were solved through eigenmode analysis using finite element method (FEM). The effective mode area and the nonlinearity of the proposed PCF are calculated for different radii of the air holes and it is found that the effective mode area decreases when the radius of the air holes is increased. On the other hand, the nonlinearity increases for an increase in the air holes radii. At 1 THz, the confinement loss of the proposed fiber is in the order of 10−23 dB/m and transmittance efficiency above 96% has been attained. As 5-G technology emanates, THz wave propagation becomes essential and the designed hexagonal lattice SC-PCF will be useful for the advancement of communication systems, sensing devices and several medical applications.

Novel Optically Controlled GaAs/Side-Polished Terahertz Fiber Modulator

Novel Optically Controlled GaAs/Side-Polished Terahertz Fiber Modulator

Design for Terahertz Circular-Core Photonic Crystal Fiber Supporting Orbital Angular Momentum Modes

We propose a new terahertz fiber based on a circular-core photonic crystal fiber (PCF) structure to support high-performance orbital angular momentum (OAM) modes transmission. The modal characteristics of the proposed terahertz fiber were thoroughly analyzed to vary the parameters of air holes radius and the annular thickness by the full-vector finite element method (FEM). The optimal parameters are selected to realize the stable transmission of five-order OAM mode with high mode quality, low confinement loss and wide bandwidth. The mode purity is in excess of 91%, and the confinement loss is less than 10−7 dB/m over the 0.2 THz to 0.55 THz band. Furthermore, the design of this PCF is relatively simple and flexible, since it consists only of circular air holes. Due to its excellent transmission characteristics, the proposed OAM fiber has a potential application in terahertz mode division multiplexing (MDM) communication system.