Waveguide Research Articles

Detailed investigations on double confocal waveguide for a gyro-TWT

Detailed investigations on double confocal waveguide for a gyro-TWT

Photonic circuits written by femtosecond laser in glass: improved fabrication and recent progress in photonic devices

Integrated photonics is attracting considerable attention and has found many applications in both classical and quantum optics, fulfilling the requirements for the ever-growing complexity in modern optical experiments and big data communication. Femtosecond (fs) laser direct writing (FLDW) is an acknowledged technique for producing waveguides (WGs) in transparent glass that have been used to construct complex integrated photonic devices. FLDW possesses unique features, such as three-dimensional fabrication geometry, rapid prototyping, and single step fabrication, which are important for integrated communication devices and quantum photonic and astrophotonic technologies. To fully take advantage of FLDW, considerable efforts have been made to produce WGs over a large depth with low propagation loss, coupling loss, bend loss, and highly symmetrical mode field. We summarize the improved techniques as well as the mechanisms for writing high-performance WGs with controllable morphology of cross-section, highly symmetrical mode field, low loss, and high processing uniformity and efficiency, and discuss the recent progress of WGs in photonic integrated devices for communication, topological physics, quantum information processing, and astrophotonics. Prospective challenges and future research directions in this field are also pointed out.

Trench Structure Improvement of Thermo-Optic Waveguides

ABSTRACT The heat generated by a thin film heater causes the temperature of a nearby waveguideto increase. The thermal coupling increases with the waveguide depth. Thermal coupling couldbe reduced by etching a trench between the waveguides. A rib structure under the trench betweenthe waveguides was proposed to further reduce the thermal coupling. The temperature profiles ofthermo-optic waveguides are analyzed by the finite element method and show significant improvementon reducing thermal coupling between the waveguides.

Design of high-power wide-band G-band third harmonic amplifier

To meet the demand of high-power and wide-band signal sources for G-band vacuum electronic devices, the research on G-band third harmonic amplifier is carried out. The amplifier utilizes the third harmonic current in the nonlinear beam-wave interaction of E-band TWT, and realizes G-band electromagnetic wave amplification by cascading harmonic interaction section. The design scheme of high performance and practical G-band wide-band high-power source adopts folded waveguide slow wave structure with modified circular bends, and the G-band third harmonic amplifier is simulated and optimized by using the microwave tube simulator package (MTSS) software. The result shows that the device can obtain harmonic output power greater than 3.6 W in the range of 15 GHz, with conversion gain＞33.3 dB and electronic efficiency＞0.36%. Compared with other miniaturized terahertz radiation sources in this band, it has superior performance in terms of output power and bandwidth, and thus provides a design basis for the subsequent research of G-band third harmonic amplifier.

The Plasmon Effects of AgNPs on Wave Guide Consisting of Polymers Mixed with Rhodamine Dyes

In this research, the optical properties refractive index, absorption spectrum, and fluorescence spectrum of solutions of different concentrations have been studied in order to prepare thin films to obtain an efficient waveguide. A wave guide consisting of three layers has been prepared in which the middle layer has a relatively higher refractive index than the upper and lower layers. This optical wave guide was prepared by using different solutions of two concentrations of poly vinyl pyrrolidone (PVP) & poly vinyl alcohol (PVA) polymers. Different concentrations of the rhodamine pigments RhB & Rh6G were prepared. It is added to the middle layer of the optical wave guide in order to raise its refractive index first and to obtain a laser profit. The practical results have proven that there are specific concentrations of polymers and dyes that can be used to obtain wave guides that have the ability to transmit and amplify the input signal and operate within certain wavelengths. The PVA + RhB(10-4M) model showed the best laser emission performance and the PVA + Rh6G (10-5M) model showed the best signal transmission performance. Finally, the plasmon effect is clearly appears when we added the AgNPs on our samples it’s effecting on threshold pumping and increase the efficiency of wave guide.

A Study on the Analysis of Electromagnetic Characteristics and Design of a Cylindrical Photonic Crystal Waveguide with a Low-Index Core

A Study on the Analysis of Electromagnetic Characteristics and Design of a Cylindrical Photonic Crystal Waveguide with a Low-Index Core

A tabletop waveguide delivers focused x rays

A tabletop waveguide delivers focused x rays

Slight Looseness Detection of Reinforcing Bar’s Threaded Sleeve Connections Using Convolutional Neural Network Trained by Magnetostrictive Guided Wave Signals

The threaded sleeve connection (TSC) is widely used in the connection of reinforcing bars and the looseness is difficult to observe directly. The guided wave (GW) can be used to detect TSC’s looseness due to its ability to propagate to invisible regions, which is difficult to identify with traditional signal processing methods if the looseness is slight. In this study, we employ the convolutional neural network (CNN) to process the magnetostrictive GW signals for the detection of TSC’s slight looseness. Experiments are carried out on the thread-sleeve-connected reinforcing bars to obtain the passing GW signals as the dataset to train the CNNs and the states of the TSC contain tighten and slight looseness in which loosening angle is less than 5°. In order to improve the time–frequency resolution of CNN, a CNN with multi-scale kernel size is built. For comparison, another three CNNs with one kernel size are built. Using the GW signals, we train these four CNNs and then these four trained CNNs are employed to analyze the testing data. Only the CNN with multi-scale kernel size can achieve 100% slight looseness detection accuracy. The results show that the CNN can be used to detect the slight looseness of reinforcing bar’s TSC and the CNN trained with multi-scale kernel size performs better.

Spatiotemporal Terahertz Metasurfaces for Ultrafast All‐Optical Switching with Electric‐Triggered Bistability

AbstractOptoelectronic terahertz switching achieved by dynamically tuning metamaterials is viewed as a major breakthrough in promoting the advancement of terahertz technology. However, the main thrust toward the development of ultrafast switchable components and optical logic operations is still in a catch‐up stage for progressively increasing information and communication demands. Here, a novel spatiotemporal metadevice is proposed for terahertz wave steering in multidimensional domains with ultrahigh spatial and ultrafast temporal manipulations. By spatially changing the interconnect architecture via the embedded vanadium dioxide bridges, the state of electromagnetically induced transparency resonance is switched between “1” and “0” states under electrical stimuli, exhibiting a typical 1 bit coding bistability with a long retention time. Furthermore, with the characteristic of writable/erasable logic operation, ultrafast photoswitching of each memorized state is manifested by delivering optical excitations. The high‐speed temporal response of terahertz radiation exhibits an on–off–on switching cycle within 16 ps, owing to the defect‐rich germanium photoactive layer. By leveraging both degrees of freedom in space and time domains, this multifunctional spatiotemporal metaphotonic device can upgrade and improve the current capabilities of optical computing, data storage, and ultrahigh‐speed information processing, paving the way for a highly unexplored territory toward manipulations of light.

Multi-Dimensional Uniform Initialization Gaussian Mixture Model for Spar Crack Quantification under Uncertainty

Guided Wave (GW)-based crack monitoring method as a promising method has been widely studied, as this method is sensitive to small cracks and can cover a wide monitoring range. Online crack quantification is difficult as the initiation and growth of crack are affected by various uncertainties. In addition, crack-sensitive GW features are influenced by time-varying conditions which further increase the difficulty in crack quantification. Considering these uncertainties, the Gaussian mixture model (GMM) is studied to model the probability distribution of GW features. To further improve the accuracy and stability of crack quantification under uncertainties, this paper proposes a multi-dimensional uniform initialization GMM. First, the multi-channel GW features are integrated to increase the accuracy of crack quantification, as GW features from different channels have different sensitivity to cracks. Then, the uniform initialization method is adopted to provide more stable initial parameters in the expectation-maximization algorithm. In addition, the relationship between the probability migration index of GMMs and crack length is calibrated with fatigue tests on prior specimens. Finally, the proposed method is applied for online crack quantification on the notched specimen of an aircraft spar with complex fan-shaped cracks under uncertainty.

Multiple zero-group velocity resonances in elastic layered structures

To date, the phenomenon of zero group velocity (ZGV) Lamb wave in a stress-free elastic plate has been well studied and used in non-destructive material characterization, electroacoustic devices and some other applications. This phenomenon is associated with the backward mode appearing in the range limited by the ZGV and cutoff frequencies. The modal frequency response of the structure, primarily the spectrum of the corresponding guided wave (GW) excited in the plate by a force source, is featured by a sharp peak at the ZGV frequency, allowing its experimental detection. Other peaks appearing at the cutoff frequencies indicate thickness resonances. In a layered half-space of infinite thickness, the backward-mode bend of the dispersion curve turns into a double bend that gives rise to three GWs associated with the same branch (one backward and two forward modes). Moreover, several adjacent branches with double bends, and, thus, several peaks, can appear in a narrow range as the number of layers increases, indicating multiple ZGV resonances. Such dispersion curves with double ZGV points were also found in waveguides of finite thickness with anisotropic or contrast material properties; however, their resonance manifestation is poorly studied. In this article, we consider and discuss several kinds of multi-peak ZGV responses using examples of layered samples of various materials. Along with the expected increase in the number of peaks in multilayer structures with contrast layers, it was noted that some ZGV points may or may not appear in peaks, depending on the type of load.

Longitudinal wave steering using beam-type elastic metagratings

Metagratings have recently received much attention for effective realization of anomalous wave steering. Governed by the diffraction grating theory and the concept of metamaterials, metagratings allow to suppress superfluous propagations of high-order scattering modes in a selective manner such that wavefronts are accurately steered as designated. While numerous metagratings have been reported in electromagnetic wave research field, little has been explored in the elastic wave regime because of difficulties caused by complicatedly coupled motions among various types of elastic waves. In this circumstance, we newly propose a novel elastic metagrating model to realize anomalous steering of longitudinal waves in elastic continuum medium. Modeled by a periodic arrangement of a single or array of so-called beam-type elastic members, the present elastic metagratings resolve the difficulties in steering a specific scattered mode of elastic longitudinal waves by suppressing undesired modes in the scattered wave field. As the metagratings are attached to a boundary of elastic continuum, both longitudinal and flexural motions in the beam-type members are so coupled with elasticity wave solutions in the elastic medium as to thoroughly manipulate the reflected longitudinal waves from the interface. A set of appropriate geometric parameters of the beam-type members are searched for a direct control of the scattered modes quantitatively. As practical applications, the proposed elastic metagratings are applied to realize anomalous reflections and asymmetric splitting of longitudinal elastic waves. As well as experimental verifications, performance of the designed elastic metagratings are physically interpreted in the perspective of phase modulation.

Electromagnetic Energy Surface Modes in Metamaterial-Filled Bi-layer Graphene Structures

This paper presents a theoretical study on the propagation of electromagnetic surface waves supported by the metamaterial-filled bi-layered graphene structure. The effective surface conductivity approach based upon the Kubo’s formalism is used to model the atomically thick graphene layer, while the analytical modeling of the metamaterials used the framework of causality principle-based Kramers-Kroing relations. With respect to the index of refraction, the two configurations of metamaterials have been considered—i.e., double positive (DPS) and double negative (DNG). The impedance boundary conditions (IBCs) have been employed at the interface for the computation of characteristics equations of odd and even surface modes under DPS and DNG configurations. The numerical results regarding the dispersion relations, effective mode index, and phase speed for the odd and even modes of electromagnetic surface waves supported by each configuration of structure have been presented. Further, the influence of chemical potential and thickness of metamaterial filling in parallel graphene layers on the wave propagation characteristics has been analyzed. To check the accuracy of the numerical results, special conditions were employed, which converge to the published results. The proposed work may have potential applications in plasmonic based logic designs, renewable energy devices, THz surface wave guides, and near-field communication devices.

Silicon-Based Multilayer Waveguides for Integrated Photonic Devices from the Near to Mid Infrared

Advancements in spectroscopy, quantum optics, communication, and sensing require new classes of integrated photonic devices to host a wide range of non-linear optical processes involving wavelengths from the visible to the infrared. In this framework, waveguide (WG) structures designed with innovative geometry and materials can play a key role. We report both finite element modeling and experimental characterization of silicon nitride multilayer WGs from the visible to the mid-infrared spectral regions. The simulations evaluated optical behavior and mechanical stress as a function of number of WG layers and photonic structure dimensions. WGs were optimized for waveguiding at 1550 nm and 2640 nm. Experimental characterization focused on optical behavior and coupling losses from 532 nm to 2640 nm. Measured losses in WGs indicate a quasi-perfect waveguiding behavior in the IR range (with losses below 6 dB), with a relevant increase (up to 20 dB) in the visible range.

Fluid-dynamic and thermo-mechanical analyses of the Monoblock Mitre Bend for the ITER electron cyclotron Upper launcher

The ITER Electron Cyclotron Heating (ECH) system will be used to counteract magneto-hydrodynamic plasma instabilities by aiming up to 20 MW of mm-wave power at 170 GHz. The primary vacuum boundary at the Electron Cyclotron Upper Launcher (EC UL) extends into the port cell region through eight beamlines, defining the so-called First Confinement System (FCS). Each beamline, designed for the transmission of 1.31 MW, is delimited by the closure plate at the port plug back-end and by a diamond window in the port cell. The FCS essentially consists of a Z-shaped set of straight corrugated waveguides (WG) connected by Mitre Bends (MB) with a nominal inner diameter of 50 mm. Due to the space restrictions, the eight MBs at the last FCS section are grouped into two monoblocks. Each Monoblock Mitre Bend (MBMB) consists of a body with corrugated feedthroughs defining a specific angle for each beamline and four mirrors attached by bolted connection to reflect the mm-wave power. The thermal expansion arising from the ohmic losses, the cooling pressure, the bolt pre-tension and the imposed displacements coming from the connection with the transmission lines are the primary design loads for the MBMBs. The fluid-dynamic analyses performed for both upper and lower MBMBs show that highest temperature takes place in the MB mirrors, reaching a maximum value of 203 °C at the beam center. The thermo-mechanical analyses demonstrate that the peak stress also occurs at this location with a maximum value of 324 MPa. These stresses are categorized and compared with the allowable limits defined in the ASME code, what probes that the current design of both upper and lower MBMBs are able to withstand the loads taking place during the mm-wave normal operation.

Surface Functionalization Utilizing Mesoporous Silica Nanoparticles for Enhanced Evanescent-Field Mid-Infrared Waveguide Gas Sensing

This work focuses on the development of nanoparticle-based layer-by-layer (LbL) coatings for enhancing the detection sensitivity and selectivity of volatile organic compounds (VOCs) using on-chip mid-infrared (MIR) waveguides (WGs). First, we demonstrate construction of conformal coatings of polymer/mesoporous silica nanoparticles (MSNs) on the surface of Si-based WGs using the LbL technique and evaluate the coating deposition conditions, such as pH and substrate withdrawal speed, on the thickness and homogeneity of the assemblies. We then use the modified WGs to achieve enhanced sensitivity and selectivity of polar organic compounds, such as ethanol, versus non-polar ones, such as methane, in the MIR region. In addition, using density functional theory calculations, we show that such an improvement in sensing performance is achieved due to preferential adsorption of ethanol molecules within MSNs in the vicinity of the WG evanescent field.

Transverse Stability of Line Soliton and Characterization of Ground State for Wave Guide Schrödinger Equations

In this paper, we study the transverse stability of the line Schrödinger soliton under a full wave guide Schrödinger flow on a cylindrical domain \({\mathbb {R}}\times {\mathbb {T}}\). When the nonlinearity is of power type \(|\psi |^{p-1}\psi \) with \(p>1\), we show that there exists a critical frequency \(\omega _{p} >0\) such that the line standing wave is stable for \(0<\omega < \omega _{p}\) and unstable for \(\omega > \omega _{p}\). Furthermore, we characterize the ground state of the wave guide Schrödinger equation. More precisely, we prove that there exists \(\omega _{*} \in (0, \omega _{p}]\) such that the ground states coincide with the line standing waves for \(\omega \in (0, \omega _{*}]\) and are different from the line standing waves for \(\omega \in (\omega _{*}, \infty )\).

Compact Low-Loss Chip-to-Waveguide and Chip-to-Chip Packaging Concept Using EBG Structures

This letter presents a novel approach for packaging millimeter-wave (mmW) and terahertz (THz) circuits. The proposed technique relies on using an on-chip coupling structure that couples the signal to a quarter-wavelength cavity, which in turn couples to either a waveguide (WG) or another chip. The solution also uses a periodic electromagnetic bandgap (EBG) structure that controls the electromagnetic wave and prevents field leakage in undesired directions. The proposed solution is fabricated and demonstrated at the $D$ -band (110–170 GHz), and the measurement results show that it achieves a minimum insertion loss of 0.8 and a 3-dB bandwidth extending from 124 to 161 GHz. The proposed approach does not require any galvanic contacts and can be used for packaging integrated circuits in WG modules as well as for chip-to-chip communication.

Unidirectional Wave Guide Based on Valley Hall Effect in Optical Communication Band

Unidirectional Wave Guide Based on Valley Hall Effect in Optical Communication Band

The (2+1)-dimensional hyperbolic nonlinear Schrödinger equation and its optical solitons

&lt;abstract&gt; &lt;p&gt;A comprehensive study on the (2+1)-dimensional hyperbolic nonlinear Schrödinger (2D-HNLS) equation describing the propagation of electromagnetic fields in self-focusing and normally dispersive planar wave guides in optics is conducted in the current paper. To this end, after reducing the 2D-HNLS equation to a one-dimensional nonlinear ordinary differential (1D-NLOD) equation in the real regime using a traveling wave transformation, its optical solitons are formally obtained through a group of well-established methods such as the exponential and Kudryashov methods. Some graphical representations regarding optical solitons that are categorized as bright and dark solitons are considered to clarify the dynamics of the obtained solutions. It is noted that some of optical solitons retrieved in the current study are new and have been not retrieved previously.&lt;/p&gt; &lt;/abstract&gt;