Cylindrical Waveguide Research Articles

High-temperature-sensitive and spectrum-contrast-enhanced sensor using a bullet-shaped fiber cavity filled with PDMS.

Low temperature sensitivity and low spectral contrast are serious but common issues for most Fabry Perot (FP) sensors with an air cavity. In this paper, a high-temperature-sensitive and spectrum-contrast-enhanced Fabry Perot interferometer (FPI) is proposed and experimentally demonstrated. The device is composed of a hollow cylindrical waveguide (HCW) filled with polydimethylsiloxane (PDMS) and a semi-elliptic PDMS end face. The semi-elliptic PDMS end face increases the spectral contrast significantly due to the focusing effect. Experimentally, the spectral contrast is 11.97 dB, which is two times higher than the sensor without semi-elliptic PDMS end face. Ultra-high temperature sensitivity of 3.1501 nm/°C was demonstrated. The proposed sensor exhibits excellent structural stability, high spectral contrast and high temperature sensitivity, showing great potential in biomedicine, industrial manufacturing, agricultural production and other applications.

Thermalization of Light's Orbital Angular Momentum in Nonlinear Multimode Waveguide Systems.

We show that the orbital angular momentum (OAM) of a light field can be thermalized in a nonlinear cylindrical multimode optical waveguide. We find that upon thermal equilibrium, the maximization of the optical entropy leads to a generalized Rayleigh-Jeans distribution that governs the power modal occupancies with respect to the discrete OAM charge numbers. This distribution is characterized by a temperature that is by nature different from that associated with the longitudinal electromagnetic momentum flow of the optical field. Counterintuitively and in contrast to previous results, we demonstrate that even under positive temperatures, the ground state of the fiber is not always the most populated in terms of power. Instead, because of OAM, the thermalization processes may favor higher-order modes. A new equation of state is derived along with an extended Euler equation resulting from the extensivity of the entropy itself. By monitoring the nonlinear interaction between two multimode optical wave fronts with opposite spins, we show that the exchange of angular momentum is dictated by the difference in OAM temperatures, in full accord with the second law of thermodynamics. The theoretical analysis presented here is corroborated by numerical simulations that take into account the complex nonlinear dynamics of hundreds of modes. Our results may pave the way toward high-power optical sources with controllable orbital angular momenta, and at a more fundamental level, they may open up opportunities in drawing parallels with other complex multimode nonlinear systems like rotating atomic clouds.

Microfluidic volume optical monitoring system based on functional channels integrated by hollow cylindrical waveguide

Real-time monitoring and manipulating various liquids in the microflow channels have great potentials in micro total analysis system. A novel microfluidics volume optical monitoring system (MVOMS) is proposed. Functional channels embedded with hollow cylindrical waveguide (HCW) are integrated in MVOMS, which is convenient to realize the real-time monitoring and manipulating microfluidic. The microfluidic volume can be monitored in real time and the sensitivity can reach 20.0 dB/μL. In addition, the MVOMS can realize the monitoring of various liquid for the designed sensor structure is insensitive to the refractive index of liquid. The temperature cross and the pressure cross are tested that can be ignored. Microfluidic volume monitoring, delivering and mixing can be achieved in MVOMS. On this basis, we design an integrated light-driven microfluidic quantitative sampling system, which can sample a specific volume of microfluidic in microchips automatically and accurately.

Compact cyclotron resonance high-power accelerator for electrons

Exact numerical solutions for the single particle equations of motion have revealed conditions for highly nonlinear rapid acceleration near cyclotron resonance for electrons injected into a ${\mathrm{TE}}_{111}$-rotating-mode cylindrical microwave cavity immersed in a uniform axial magnetic field. We dub this the eCRA interaction. Magnitudes of acceleration energy in eCRA are shown to exceed to a large degree the limits for the related cyclotron autoresonance acceleration (CARA) interaction, wherein autoresonance acceleration is sustained for traveling rotating ${\mathrm{TE}}_{11}$-mode waves in a cylindrical waveguide. As with CARA, all injected electrons in an idealized eCRA enjoy equal energy gain without bunching. Injection of high currents that involve heavy beam loading allow acceleration in eCRA to multi-MeV levels for beams with average powers of hundreds of kW and rf-to-beam power efficiencies that exceed 80%. It is shown, to cite one example, that an effective acceleration gradient of over $90\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ can be sustained with a maximum cavity surface field of only $40\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, when producing a 4.5 MeV, 300 kW average power electron beam, with an rf-to-beam efficiency of about 86%. In that example, the cavity operates at 2.856 GHz, and the cavity's average surface heating rate is $100\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$. Other examples are given for beams with over one MW levels of average power and energies up to about 20 MeV. This paper's goal is only to elucidate and give examples of the basic mechanism for the strongly nonlinear acceleration that is predicted to occur in eCRA, rather than to present a particular engineered design. Still, the predicted parameters for an idealized eCRA suggest that practical realizations could emerge to satisfy a range of needs for efficient, compact accelerators for industrial, commercial, and national security applications.

The Use of Microwave Superradiance Pulses for High-Gradient Acceleration of Electrons in a Cylindrical Waveguide with a Dielectric Insert

The Use of Microwave Superradiance Pulses for High-Gradient Acceleration of Electrons in a Cylindrical Waveguide with a Dielectric Insert

Tunable SPPs in graphene-based cylindrical structures with gyroelectric layers

In this paper, we analytically study Surface Plasmon Polaritons (SPPs) in graphene-based cylindrical structures with gyroelectric layers. In the general waveguide, each graphene layer is surrounded by two various gyro-electric materials. New closed-form relations are derived for the field contributions of SPP waves. As a special case, a gyro-electric cylindrical waveguide with double-layer graphene is considered in this article. For the designed structure, the figure of merit (FOM) of 51 is reported for B= 2 T and μc= 0.7 eV, at the frequency of 33 THz. It is demonstrated that the FOM of the studied waveguide is varied by tuning the chemical potential and the magnetic bias. Harnessing the gyro-electric media together with graphene layers will open a new promising platform for the design and fabrication of novel plasmonic devices in the mid-infrared region.

Exciting Circular TM11 Mode Using Symmetric Probes Based on Ridge Gap Waveguide

This article proposes a method to excite the TM $_{11}$ mode in circular waveguides. The principle of synthesizing a circular TM mode is deduced based on the electric dipole moment theory first, and the output mode and its purity are analyzed theoretically. Then, a mode conversion scheme to convert the rectangular TE $_{10}$ into circular TM $_{11}$ mode via a pair of out-of-phase quasi-TEM mode is proposed. In order to achieve the broadband excitation in a compact size, the ridge gap waveguide is used as a medium between the rectangular and cylindrical waveguide. Simulation results present that the proposed exciter has a propagation bandwidth up to 10 GHz in Ka-band with a mode purity over 98%. A prototype is manufactured and measured, and the presence of TM $_{11}$ mode and the mode purity are confirmed by a port radiation pattern measurement. The mode exciter features high mode purity, broad bandwidth, and a compact size, which provides a low-power generator for the research of novel gyrobackward-wave devices and devices in the high-power transmission line.

Computing Eigenvalues of Dielectric Waveguides by a Method of Auxiliary Sources With Two Excitation Sources

The Method of Auxiliary Sources with an Excitation Source (MAS-ES) has been successfully employed to compute the eigenvalues of arbitrarily-shaped, simply and multiply-connected hollow waveguides with perfectly electric conducting (PEC) walls. The main advantages of this method are its simplicity, and that it is free of spurious eigenvalues, in contrast to the standard MAS approach. In this paper, we demonstrate that the MAS-ES is also effective in computing the propagation constants (eigenvalues) <inline-formula><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> of a cylindrical dielectric waveguide with core of arbitrary cross section. It is emphasized that two excitation sources (an electric and a magnetic current filament lying within the core) are required to excite hybrid modes of the dielectric waveguide; a hollow PEC waveguide requires only one source. The modified method, thus obtained, is named MAS with Two Excitation Sources (MAS-TES). The fact that the propagating modes are localized in the vicinity of the core allows us to determine the eigenvalues by measuring the response of the core to the excitation sources. This is performed by employing a response function <inline-formula><tex-math notation="LaTeX">$F(\beta)$</tex-math></inline-formula> which is maximized when a standing wave is formed in the core. Plotting <inline-formula><tex-math notation="LaTeX">$F(\beta)$</tex-math></inline-formula> for a dense set of <inline-formula><tex-math notation="LaTeX">$\beta$</tex-math></inline-formula> results in a response curve the peaks of which correspond to the waveguide&#x2019;s eigenvalues. The method is tested for several dielectric waveguides&#x2019; geometries, including two multimode cases, and it is shown to be free from discrete and continuous spurious solutions. All the MAS-TES results are compared with those obtained by an FEM-based commercial software and an excellent agreement is exhibited.

Augmented Reality Near-Eye Display System Based on Cylindrical Holographic Waveguide

Augmented Reality Near-Eye Display System Based on Cylindrical Holographic Waveguide

Analysis by Asymptotic Boundary Conditions of Strip-Grated Dielectric Pipe Over Dielectric Rod With Wide Total Band-Gap as Multifrequency Cylindrical Leaky-Wave Antennas

In this paper, the method of classical vector potential analysis along with the asymptotic strips boundary conditions (ASBC) is used to treat conducting strip grated dielectric pipes wrapped over core dielectric cylindrical rods. By virtue of the periodically-textured surface, this structure is able to exhibit plasmonic behaviors that facilitate strong surface field localization and wave propagation, thereby offering itself as cylindrical surface-wave waveguides or antennas. It can also be configured to exhibit electromagnetic band-gap (EBG) properties, yielding what is known as cylindrical EBG structures. As opposed to a typical counterpart whose core rod is instead conducting, the core dielectric is herein demonstrated to be vital in realizing wide total band-gaps in which neither slow surface nor fast space waves exist, something that the conducting core rod version is incapable of, being only able to offer surface-wave band-gaps, as do many others in the literature that have neglected the suppression of fast space waves as well. By coaxially connecting various such rod structures, each with its own distinct total band-gap, multi-frequency, multi-functional cylindrical antennas with mitigated inter-band interference even under simultaneous operations can be achieved when the pass-band of any one rod (in which its operating frequency lies) falls within the total band-gaps of all others, as herein investigated. Manufactured prototypes are also measured, yielding experimental results that agree well with theoretical predictions.

Metamaterial Liner for MRI Excitation—Part 2: Design and Performance at 4.7T

The theoretical foundations of a metamaterial (MM) liner for the MRI bore that facilitates the propagation of reduced-cutoff cylindrical waveguide modes are presented in the Part 1 companion paper to this work. Here, in Part 2, the practical design and modelling of the novel MM liner is applied to a body MRI radio-frequency (RF) transmitter for 4.7T. An equivalent network mesh model is developed to reduce the distributed structure of the MM to one that uses lumped discrete tuning elements. The close match between full-wave simulation and the network model is demonstrated by comparison of the longitudinal propagation dispersion curves and input impedance. The application of the methods developed for analysis of the MM liner behavior are demonstrated in the design of a practical MM liner as an effective MRI RF transmitter. The liner’s simulated performance was evaluated using three key metrics of MR radio-frequency (RF) coil performance: transmit efficiency, the variation of the transmit field (a measure of homogeneity), and the 10g averaged local specific absorption rate (SAR). These metrics are compared to those of the commonly used birdcage (BC) coil. The main advantage of the MM liner is the 29.6% reduction in maximum SAR normalized to transmit field relative to the BC coil, with comparable transmit efficiency and homogeneity. Thus, the liner can potentially replace the BC coil as an RF transmitter and provide an enhanced safety margin, or allow the use of faster, more SAR-aggressive imaging sequences.

Transition Effects of THz Helical Undulator Radiation in a Waveguide

The radiation of a particle instantly injected into an infinite ideal cylindrical waveguide and implementing a helical motion is considered. Additionally, the problem of the radiation of a time-varying point charge moving stationary along a helical orbit in the same waveguide is also solved. Additionally, an explicit expression is obtained for the longitudinal component of the electric field of radiation with a wavefront moving together with the particle. The basic properties of radiation are determined: the conditions for its forward propagation are obtained, and its angular directivity is determined. A formula is given that describes radiation upon gradual introduction of a bunch into a waveguide (modeling the injection process) and during its subsequent propagation.

RETRACTED ARTICLE: Investigation on elastic guided wave propagation in a parallel axisymmetric stressed viscoelastic cylindrical waveguide

We, the Editor & Publisher of Mechanics of Advanced Materials and Structures, have retracted the following article: T. Jothi Saravana (2021) Investigation on elastic guided wave propagation in a parallel axisymmetric stressed viscoelastic cylindrical waveguide. DOI: 10.1080/15376494.2021.2017524 After publication, the author, T.J. Saravana, requested the retraction of this article due to his use of third-party data without the required permissions. Further investigations revealed that the article contained data from an unpublished thesis titled “Analyses on Acoustic Emission Wave Propagation in a Stay Cable using Semi-Analytical FEM” authored by Yang Yaohua in 2018, that was used without permission. As the reuse of data from a third party without acquiring the required permissions is a serious breach of publishing ethics, we are retracting the article from the journal. The author agrees to this retraction. We have received guidance from our policy on publishing ethics and integrity and the COPE guidelines on retractions, which have informed our decision-making process. To maintain the scholarly record, the retracted article will remain available online. We will ensure that it is identified as “Retracted” by adding a digital watermark on each page.

Efficient modeling method for emitting focusing grating coupler based on complex mode matching and effective index method.

In this paper, an efficient modeling method for a photonics-focusing grating coupler is proposed and studied. The focusing grating coupler can be divided into two parts: the cylindrical coordinate slab waveguide and the Cartesian coordinate slab waveguide. Using the cylindrical slab modes and the two-dimensional complex mode-matching method, we can obtain the efficient compact model for the focusing grating coupler. This model reduces the three-dimensional structure into a two-dimensional structure by using the effective index method to reduce the computation time as well as the computational resources. The simulation result, which is dependent on the finite-difference time-domain method, demonstrates the accuracy of the advanced compact model. This model can also be integrated into the circuit simulation.

Toward improved accuracy in shear wave elastography of arteries through controlling the arterial response to ultrasound perturbation in-silico and in phantoms

Dispersion-based inversion has been proposed as a viable direction for materials characterization of arteries, allowing clinicians to better study cardiovascular conditions using shear wave elastography. However, these methods rely on a priori knowledge of the vibrational modes dominating the propagating waves induced by acoustic radiation force excitation: differences between anticipated and real modal content are known to yield errors in the inversion. We seek to improve the accuracy of this process by modeling the artery as a fluid-immersed cylindrical waveguide and building an analytical framework to prescribe radiation force excitations that will selectively excite certain waveguide modes using ultrasound acoustic radiation force. We show that all even-numbered waveguide modes can be eliminated from the arterial response to perturbation, and confirm the efficacy of this approach with in silico tests that show that odd modes are preferentially excited. Finally, by analyzing data from phantom tests, we find a set of ultrasound focal parameters that demonstrate the viability of inducing the desired odd-mode response in experiments.

Terahertz hybrid plasmonic waveguides with ultra-long propagation lengths based on multilayer graphene-dielectric stacks.

To develop on-chip photonic devices capable of transmitting terahertz signals beyond the propagation distance of millimeter while keeping deep subwavelength field confinement has been a challenging task. Herein, we propose a novel multilayer graphene-based hybrid plasmonic waveguide (MLGHPW) consisting of a cylindrical dielectric waveguide and hyperbolic metamaterials. The device is based on alternating graphene and dielectric layers on a rib substrate, operating in the terahertz range (f = 3 THz). We couple the fundamental dielectric waveguide mode with the fundamental volume plasmon polarition modes originated from the coupling of plasmon polaritons at individual graphene sheets. The resulting hybrid mode shows ultra-low loss compared with the conventional GHPW modes at the comparable mode sizes. The present MLGHPW demonstrated a few millimeters of propagation length while keeping the mode area of 10-3A0, where A0 is the diffraction-limited area, thus possessing a thirty times larger figure of merit (FoM) compared to other GHPWs. The additional degree of freedom (the number of graphene layers) makes the proposed MLGHPW more flexible to control the mode properties. We investigated the geometry and physical parameters of the device and identified optimal FoM. Moreover, we analyzed the crosstalk between waveguides and confirmed the potential to construct compact on-chip terahertz devices. The present design might have the possible extensibility to other graphene-like materials, like silicene, germanen, stanene etc.

Generation of Subpicosecond Pulse Trains in Fiber Cascades Comprising a Cylindrical Waveguide with Propagating Refractive Index Wave

A cylindrical waveguide structure with the running refractive index wave has been recently demonstrated as a means for the generation of high-repetition-rate pulse trains. The operation mechanism involves a proper combination of the frequency modulation and modulation instability simultaneously experienced by the input continuous wave (CW) signal as it propagates through the cylinder waveguide. Here, we explore the same idea but employ the cylindrical waveguide only as a part of the cascaded optical fiber configuration now comprising both passive and active optical fiber segments. The new system design enables the improved control of the pulse train formation process in the cascaded system elements, relaxes strong requirements for the CW signal power, and provides an additional optical gain for the advanced pulse peak power scaling. In particular, using a low-amplitude, weakly modulated, continuous wave as an input signal we explore and optimize the nonlinear mechanisms underlying its cascaded transformation into the train of kilowatt peak power picosecond pulses.

Criteria for the absence and existence of bounded solutions at the threshold frequency in a junction of quantum waveguides

In the junctionΩ\Omegaof several semi-infinite cylindrical waveguides, the Dirichlet Laplacian is treated whose continuous spectrum is the ray[λ†,+∞)[\lambda _\dagger , +\infty )with a positive cutoff valueλ†\lambda _\dagger. Two different criteria are presented for the threshold resonance generated by nontrivial bounded solutions to the Dirichlet problem for the Helmholtz equation−Δu=λ†u-\Delta u=\lambda _\dagger uinΩ\Omega. The first criterion is quite simple and is convenient to disprove the existence of bounded solutions. The second criterion is rather involved but can help to detect concrete shapes supporting the resonance. Moreover, the latter distinguishes in a natural way between stabilizing, i.e., bounded but nondecaying solutions, and trapped modes with exponential decay at infinity.

Precision Electrochemical Fabrication of Corrugated Waveguides

Advancements in high energy physics require continuous innovations in hardware to support the generation, amplification, transmission, modulation, and detection of radio frequency (RF) electromagnetic waves. One particular hardware component, waveguides, have garnered increasing interest due to their integral function in the transmission, amplification, and/or manipulation of electromagnetic waves. Waveguides are typically high-purity hollow metal structures that require precision fabrication. Waveguides operating in higher than conventional frequency ranges, e.g., 30 to 300 GHz, are of particular interest to the high energy physics community given the scaling of gradient and shunt impedance with frequency. These higher frequencies necessitate waveguides exhibiting features, such as corrugations, with significantly smaller dimensions. However, traditional manufacturing approaches are inadequate, in terms of manufacturing precision and cost, to meet these requirements. Thus, to satisfy the purity and dimensional tolerance requirements of waveguides operating at high frequencies, novel fabrication techniques are required.Faraday Technology, in consultation with Argonne Wakefield Accelerator (AWA) group, addressed this need by developing an economic fabrication process and apparatus for electroforming high-purity cylindrical copper waveguides with internal corrugations. Aluminum alloy mandrels with corresponding corrugations served as the substrate for copper electroforming. The electroforming approach was achieved within a custom electrolyte solution that was formulated by eliminating or minimizing conventional chemical additives – which is typically required to achieve uniform, conformal, and/or void-free deposits with direct current (DC) electroforming strategies. The custom, low-additive electrolyte was employed to mitigate any possibility of impurity (i.e. additive) inclusion within the copper electroform and thus, ensure high-purity copper waveguides. The low-additive electrolyte consisted of a high-purity copper sulfate solution consisting of 95–100 g/L CuSO4•5H2O, 210–215 g/L H2SO4, 60–70 ppm Cl− and 350 ppm polyethylene glycol. To compensate for the absence of traditional additives, pulse-modulated waveforms were employed during copper electrodeposition to selectively control ionic transport as well as the subsequent deposit morphology and thus facilitate complete copper filling of the corrugation valleys, as seen in the accompanying figure. Preliminary scale-up efforts from ~2-inch to ~6-inch copper electroformed waveguides were demonstrated and confirm the versatility of the pulse-modulated electroforming strategy. Upon mandrel removal, a cold test of the ~2-inch copper waveguide using a vector network analyzer (VNA) was conducted. The results of the S-parameter measurements and the bead-pull test indicate reasonable agreement with the design by CST simulation, which validates the novel pulse-modulated electroforming approach.Acknowledgements: The U.S. Department of Energy (DOE) provided financial support for this work under the contract award number: DE-SC0020782. Figure 1

Waves of a Magnetoplasma Solid-State Cylinder Under Quasi-Stationary Conditions

The theory of electromagnetic eigenwaves of a cylindrical plasma waveguide located in a constant coaxial magnetic field is developed. The dispersion equation for a waveguide with high electronic conductivity is obtained. It is shown that the waveguide supports the propagation of bulk and bulk-surface hybrid waves of helicon origin. The nonreciprocity effect of waveguide eigenwaves with the identical field distributions, but differing in the direction of propagation along the azimuthal coordinate and also when the direction of the external magnetic field is reversed, is discovered.