Cylinder Waveguide Research Articles

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.

Slow Light Rainbow Trapping in a Uniformly Magnetized Gyromagnetic Photonic Crystal Waveguide

We present a hybrid gyromagnetic photonic crystal (GPC) waveguide composed of different GPC waveguide segments possessing various cylinder radii and waveguide widths but biased by a uniform external magnetic field. We demonstrate in frequency and time domains that based on the strong coupling of two counter-propagating topologically protected one-way edge states, the intriguing slow light rainbow trapping (SLRT) of electromagnetic (EM) waves can be achieved, that is, EM waves of different frequencies can be slowed down and trapped at different positions without cross talk and overlap. More importantly, due to the existence of one-way edge states, external EM waves can be non-reciprocally coupled to the SLRT waveguide channel, although the incident position of the EM wave is far away from the waveguide channel. Besides, the frequency range of the slow light states can also be easily regulated by tuning the intensity of an external magnetic field, which is very beneficial to solve the contradiction between slow light and broad bandwidth. Our results can be applied to the design of high-performance photonic devices, such as an optical buffer, optical switch, and optical filter.

Symmetry and asymmetry nonlinear modes in dual cylinder waveguide shells coupled by a rotating double-well connection

We study the fundamental nonlinear modes in a dual-cylinder waveguide shell, which features a self-focusing Kerr effect, coupled by a double-well connection. This double-well connection is twisted by a pitch rate and creates a spatial dependent linear mixing, which plays the role of an effective rotating double-well potential. Symmetry transition between the waveform and the power distribution of the fundamental nonlinear modes in this system can be induced both by the total power and by the rotation speed of the connection. Four types of modes — wave symmetry and power symmetry (WSPS), wave symmetry and power asymmetry (WSPA), wave asymmetry and power symmetry (WAPS) and wave asymmetry and power asymmetry (WAPA) — are found from the system. The dependence of these modes on the total power of the light field, the rotation speed and the coupling strength of the connection are systematically studied through the paper. The finding of this paper may offer potential applications in fabrication of new types of nonlinear all-optical devices.

Spatiotemporal solitary modes in a twisted cylinder waveguide shell with the self-focusing Kerr nonlinearity

We study the spatiotemporal solitary modes that propagate in a hollow twisted cylinder waveguide pipe with a self-focusing Kerr nonlinearity. Three generic solitary modes, one belonging to the zero-harmonic (0H) and the other two belonging to the first-harmonic (1H), are found in the first rotational Brillouin zone. The 0H solitary modes can be termed as a quasi-1D (one-dimensional) temporal soliton. Their characteristics depend only on the energy flow. The 1H solitary mode can be termed a quasi-2D (two-dimensional) bullet, whose width is much narrower than the angular domain of the waveguide. In contrast to the 0H mode, the characteristics of the 1H solitary mode depend on both their energy flow and the rotating speed of the waveguide. We demonstrate numerically that the 1H solitary modes are stable when their energy flow is smaller than the threshold norm of the Townes soliton. The boundaries of the bistable area for these two types of solitary modes are predicted by the analyses via two-mode approximation. This prediction is in accordance with the numerical findings. We also demonstrate analytically that the 1H solitary mode of this system can be applied to emulate the nonlinear dynamics of solitary modes with 1D Rashba spin-orbit (SO) coupling by optics. Two degenerated states of the 1H solitary mode, semi-dipole and mixed mode, are found from this setting via the mechanism of SO coupling. Collisions between the pair of these two types of solitary modes are also discussed in the paper. The pair of the 0H solitary mode features only the elastic collision, whereas the pair of 1H solitary modes can feature both elastic and inelastic collision when the total energy flow of the two modes are smaller or close to the threshold norm of the Townes soliton.

Development and Demonstration of a Ka-Band Gyrotron Traveling-Wave Tube

The design and experiment of a pulsed Ka-band TE01-mode gyrotron traveling-wave tube are presented. This tube was designed to use the fundamental cyclotron resonance interaction with TE01 cylinder waveguide mode. Backward-wave oscillations of various origins were suppressed by ceramic loading technology. With the electron beam voltage of 66 kV and a beam current of 11 A, a saturated peak power of 110 kW was measured at 33.9 GHz, corresponding to a saturated gain of 34.4 dB, with a −3-dB bandwidth of 1.75 GHz.

Guided modes in the plane array of optical waveguides

It is known that for an isolated dielectric cylinder waveguide there exists the cutoff frequency $\omega_\ast$ below which there is no guided mode. It is shown in the paper that the infinite plane periodic array of such waveguides possesses the guided modes in the frequency domain which is below the frequency $\omega_\ast$. In the case of a finite array, the modes in this frequency domain are weakly radiating ones, but their quality factor $Q$ increases with the number of waveguides $N$ as $Q(N)\sim N^3$. This dependence is obtained both numerically, using the multiple scattering formalism, and is justified with a simple analytical model.

Ray-matrix analysis for integrative ommatidium of bionic optical compound eyes

A new model of integrative ommatidium for bionic optical compound eye is proposed in this paper. The structure of the integrative ommatidium for bionic optical compound eye is constructed. The ray matrix of the integrative bionic optical compound eyes is deduced detailedly with ray-matrix method, and the principle points and focal points of the integrative bionic compound eye are calculated. The ray matrix of the integrative bionic compound eye is related tightly with the length of the cylinder waveguide part, so as the image principle point and the image focal point. The length of the cylinder waveguide has no influence on the position of the object principle point and the object focal point of the integrative bionic compound eye. However, difference length of the cylinder waveguide will lead to different positions of the image principle point and image focal points. Self-focus effect can be employed to fabricate the integrative bionic optical compound eyes with some nonlinear optical polymer.

Hybrid Plasmonics Waveguide Properties of Dielectric Nanowires Coupling with Metal Substrate

A hybrid plasmonic waveguide system consisting of a high-permittivity cylinder waveguide embedded in a low-permittivity dielectric deposited on a metal substrate is comprehensive investigated. With the strong coupling between dielectric cylindrical waveguide mode and the long-range surface plasmon polaritons (LRSPP) mode of a thin metal film, the basic waveguiding properties, including the effective mode area, the propagation length, the mode character, and the figure of merit (FoM) can be achieved. Our results may provide valuable references for waveguiding metal -supported dielectric nanowires for practical applications. An investigation of the effect of structural perturbations indicates that the disturbance of the dielectric nanowires of our proposed waveguide with different surrounding dielectric layer would have a great influence on the experiment results.

Theoretical study on sensing performance of hydrogen annealed silicon waveguides

Due to the surface diffusion movement of Si atom in hydrogen annealing process, the sharply formed corners of waveguides will be rounded and its sidewall profile could be reformed. In this paper, the performances of microring sensors based on three different gradual annealed structures, strip with large/small round corners and cylinder waveguide, are investigated theoretically. Characteristic parameters of sensors based on cylinder waveguide, sensitivity, Q factor, and measuring range are analyzed and compared with that of sensors based on the widely-used strip and slot waveguides. Simulation results demonstrate that the sensitivity of microring is significantly increased after annealing with comparable Q factor and measuring range. The hydrogen annealing process promises a feasible and effective method to improve the performance of biosensors in the future.

Numerical simulation of multipactor phenomenon on the surface of cylinder window disk

A particle model that is based on Monte Carlo particle simulation arithmetic is built up to investigate the multipactor behavior on the surface of cylinder window disk in pill-box window. The regime of multipactor in the inhomogeneous electric field is obtained. The simulation results prove that the interaction between secondary electrons and window disk is sustained by magnetic field force on the upstream side. The multipactor phenomenon acts intensively in the area with a great electric field. The ponderomotive force does not devote any effort to multipactor on the upstream side. On the downstream side, the multipactor cannot be excited without strong enough surface electrostatic field because of the positive magnetic field force. With the increase of transmitting power, secondary electrons can obtain more energies. Due to the effect of ponderomotive force, the multipactor region transfers from the area with powerful electric field to the weak one on the downstream side. Besides, the resistance effect of electrostatic isolation on multipactor is also confirmed in the input port of cylinder waveguide.

Propagation of Electroelastic Waves in Multilayer Piezoelectric Cylinders with a Sector Notch

A method for the theoretical analysis of the spectra and properties of electroelastic waves in multilayer piezoelectric cylinders with a longitudinal sector notch with arbitrary angle is developed. The real and imaginary branches of the dispersion curves and ratios of period-averaged power flows in the inside and outside layers of the cylinder (waveguide) are studied. It is shown that the dispersion characteristics of cylinders vary widely with the material characteristics of the layers and the geometry of the cross-section

Design of an Exposure Chamber for Biological Experiments

The main aim of this work is to design and to simulate an exposure chamber which can simulate mobile phone emission patterns in order to analyze the influence of electromagnetic field on small animals. During our previous research we found the most suitable type of an exposure chamber for this purpose. The basic properties such as electromagnetic field distribution and impedance matching of our designed chamber were optimized and verified by the aid of a 3D electromagnetic field simulator. As a result of our effort a cylinder waveguide chamber with a working frequency 900MHz has been designed. In the cylindrical structure a circular polarization is excited in order to even the exposure. The chamber is terminated by matched loads on both lateral sides which serve for preventing a possible resonance between sides and the animal.

Ultrasonic transient bounded-beam propagation in a solid cylinder waveguide embedded in a solid medium

A semianalytical solution alternative and complementary to modal technique is presented to predict and interpret the ultrasonic pulsed-bounded-beam propagation in a solid cylinder embedded in a solid matrix. The spectral response to an inside axisymmetric velocity source of longitudinal and transversal cylindrical waves is derived from Debye series expansion of the embedded cylinder generalized cylindrical reflection/transmission coefficients. So, the transient guided wave response, synthesized by inverse double Fourier-Bessel transform, is expressed as a combination of the infinite medium contribution, longitudinal, transversal, and coupled longitudinal and transversal waveguide sidewall interactions. Simulated (f, 1/lambdaz) diagrams show the influence of the number of waveguide sidewall interactions to progressively recover dispersion curves. Besides, they show the embedding material filters specific signal portions by concentrating the propagating signal in regions where phase velocity is closer to phase velocity in steel. Then, simulated time waveforms using broadband high-frequency excitation show that signal leading portions exhibit a similar periodical pattern, for both free and embedded waveguides. Debye series-based interpretation shows that double longitudinal/transversal and transversal/longitudinal conversions govern the time waveform leading portion as well as the radiation attenuation in the surrounding cement grout. Finally, a methodology is deduced to minimize the radiation attenuation for the long-range inspection of embedded cylinders.

Waveguide scattering from flanges, ribs, and defects in fluid-loaded, laminated cylinders

The vibration of laminated, fluid-loaded cylinders is efficiently predicted with a wave transmission line analysis. The transmission line approach expresses the motion of homogeneous cylinder sections in terms of propagating and evanescent waves. The full set of wave dispersion relationships is computed with a semi-analytic technique, which uses a finite element radial discretization of the laminated shell and interior fluid. External fluid is represented using a state-space representation of the rational function approximation (RFA). Scattering of waves from discontinuities, including flanges, delamination, and pitting, is predicted through coupling a two-port admittance of the structure or defect to the semi-infinite admittance of the cylinder waveguide. Issues regarding the measurement of scattered and reflected waves, and identification of structural wave numbers, are discussed. The use of causality and reciprocity constraints substantially reduces measurement requirements and noise. By exciting and measuring a mixture of structural waves, defects may be classified and located. An example of predicting and measuring scattering of a defect beyond a flange is presented. [Work sponsored by the Office of Naval Research, Code 33.]

Traverse electric mode characteristics in a cylinder waveguide with a periodic dielectric cladding

The transverse electric mode characteristics in a cylinder waveguide with a periodic dielectric cladding have been analytically studied. The periodic dielectric cladding induces band structures in the characteristics and enhances the confinement of the electromagnetic energy in the core compared to a cylinder waveguide with a uniform cladding. Potential applications based on the characteristics are discussed in optical communications and photonics.

Computation and Optimization of Beam Efficiency for Reflector Antennas*

ABSTRACT This paper presents several topics on the beam efficiency of a reflector antenna. (i) A simple definition for the “main beam” is suggested for calculating beam efficiency. This definition is related to the reflector aperture diameter, but is independent of the feed edge taper. Use of this definition allows a fair comparison of beam efficiencies due to different feeds to be made. (ii) Physical optics theory does not conserve power. Therefore conventional reflector pattern computation methods based on PO can calculate beam efficiency only within 2% to 3% accuracy. A method for calibrating out this PO error is described. (iii) Beam efficiency curves are presented for typical parabolic reflectors fed by open-ended circular cylinder waveguide feeds. While directivity is optimized by a 10 dB edge taper, beam efficiency is optimized for a higher edge taper of over 20 dB. (iv) Beam efficiency curves for cases in which the beam is scanned off-axis are presented. (v) A cluster feed is utilized to improve b...

Circular to rectangular waveguide mode conversion through a parabolic cylinder waveguide–TEON incident

AbstractThe output mode of the gyrotron used as a high‐power millimeter wave source for nuclear fusion plasma heating is the TEOn of a circular waveguide. It is desirable that this mode be converted to a linearly polarized mode such as the TEmO in a rectangular waveguide. This paper discusses mode conversion from a circular TEOn mode to rectangular waveguide modes in an oversized waveguide system in which a parabolic cylinder waveguide with its axis as a focal axis is inserted between the circular and rectangular waveguides. First, an approximate analysis is introduced based on the geometrical optics approximation by taking advantage of an oversized waveguide system. Subsequently, the mode matching method is used by expanding the fields into eigen‐modes. The results for the optimum length of the parabolic cylinder waveguide obtained by the mode matching period agreed with those from the geometrical optics approximation. Hence, to a certain extent, an estimate based on the geometrical optics is effective in the oversized waveguide system. Since no accurate eigenvalues have been reported for the parabolic cylinder waveguide, the computed results are presented.