Mode Attenuation Research Articles

Ultracompact TE0- and TE1-pass/TM0- and TM1-stop dual-mode polarizer for 1.55/2 µm dual-wavelength using silicon-based cross-like hybrid plasmonic waveguides

By leveraging cross-like hybrid plasmonic waveguides (HPWs) and subwavelength gratings, a silicon-based ultracompact T E 0 - and T E 1 - p a s s / T M 0 - and T M 1 -stop dual-mode polarizer for 1.55/2 µm dual-wavelength is proposed and analyzed in detail. The HPWs are located above the bottom Si waveguide to form a hybrid plasmonic silicon nitride waveguide (HPSNW), in which the T E 0 / T E 1 mode is well supported in the bottom Si layer while the T M 0 / T M 1 mode is confined in the S i O 2 / S i 3 N 4 layer of the HPSNW and thus sees high absorption loss at 1.55/2 µm. Accordingly, the T E 0 / T E 1 mode at 1.55/2 µm can directly pass through the device once it is transited from input waveguide to the HPSNW. In contrast, the T M 0 / T M 1 mode at 1.55/2 µm suffers from great mode radiation and mode attenuation, respectively, caused by the modal mismatch and metal absorption, leading to mode blocking. Therefore, a polarizer with dual-mode/dual-wavelength operation is realized for the first time, to the best of our knowledge. Numerical results show that the proposed polarizer has an insertion loss (IL) of 0.37 dB/0.29 dB for the T E 0 / T E 1 mode and an extinction ratio (ER) of 17.3 dB/29.7 dB for the T M 0 / T M 1 mode at 1.55 µm (an IL of 0.42 dB/0.76 dB for the T E 0 / T E 1 mode and an ER of 33.1 dB/23.3 dB for the T M 0 / T M 1 mode at 2 µm) in an ultracompact length of 6.5 µm. The operating bandwidth is up to 630 nm when the ER is over 18.5 dB/19.7 dB and the IL is below 0.52 dB/1 dB for fundamental/first-order mode, indicating an ultrabroadband operation. Additionally, fabrication tolerances of the proposed device are investigated, and electric field evolution is also illustrated.

Broadband Determination of the Propagation Constant of the Slot Mode of a Rectangular Waveguide

A broadband technique to extract the attenuation and phase constants of the slot mode in a rectangular waveguide from either simulation or measurement results is proposed in this letter. The method is based on processing the values of the reflection coefficient of several slotted waveguides with different lengths and the same termination and feeding. The accuracy of the method can be improved by increasing the number of simulated or measured waveguides. The proposed technique is specially conceived to separate the contribution of the slot mode from other modes. An implementable structure and a measurement method to apply the extraction technique are proposed and used. Measured and simulation results of the proposed technique obtained from waveguides filled with two different materials are shown up to 10 GHz and validated using an approximate model. The proposed method can be regarded as a powerful technique to compute the propagation constants of leaky modes in leaky-wave antennas.

Multi-Basin Real-Time Perforation Assessment Using Tube Wave Measurements

This article addresses a means to improve hydraulic fracturing operations by measuring the perforation effectiveness on a stage-by-stage basis before the hydraulic fracturing process begins. Observations lead to the conclusion that pre-frac measurements provide meaningful insight about well-to-reservoir opening, allowing operators to identify the difficult-to-treat stages before the treatment begins. Based on the results of a case study from a North American unconventional basin, the limitations and conditions for employing pre-frac measurements are discussed. Background Often, perforation operations fail to initiate a well-established hydraulic communication between the wellbore and the reservoir rock. When hydraulic fracturing operations begin, a lack of wellbore to reservoir connectivity may cause unexpected difficulties such as unusually high pumping pressures, difficulty injecting the design volumes of fluid and proppant, and/or the inability to achieve design pumping rate or screenouts. The hydraulic fracturing industry is increasingly looking for an efficient, nonintrusive method for identifying poor wellbore to reservoir connectivity. Currently, step-rate tests are commonly used (Massaras et al. 2007) to give the operator an estimate of open perforations taking fluid, as well as frictional losses within the wellbore and near-field region. However, these tests are costly, time-consuming, and rarely accurately confirm the number of poor perforations (Cramer et al. 2019). Fiber-optic technologies can improve these uncertainties but are costly and susceptible to damage during installation and/or operation. How the Method Works Low-frequency hydraulic tube waves, or Stoneley waves (Stoneley 1924), are induced at the surface by equipment connected to the wellhead. Tube waves travel rapidly through the fluid within the wellbore and reflect by any changes within the hydraulically connected parts of the wellbore. In this case, the reflection off the bottom of the well influences the tube-wave properties - dispersion and attenuation of the normal modes (Hsu, Kostek, and Johnson 1997), depending on the condition and number of the perforations, the quality of their connection with the near-field region, and the quality of the near-field region itself (e.g., a region already naturally fractured) [Dunham et al. 2017].

Thermoelastic guided wave in fractional order functionally graded plates: An analytical integration Legendre polynomial approach

In this paper, an analytical integration Legendre polynomial approach (AILPA) is proposed to investigate the guided thermoelastic wave in functionally graded material (FGM) plates in the context of the fractional order Lord-Shulman (LS) thermoelastic theory. Coupled wave equations and fractional order heat conduction equation are solved by the presented approach, which proposes the analytical integral instead of numerical integration in the available conventional Legendre polynomial approach (CLPA). Comparison of the CPU time between two approaches indicates the higher efficiency of the presented approach. Furthermore, a new treatment of the adiabatic boundary condition for the Legendre polynomial is developed, other than the CLPA can only deal with the isothermal boundary condition. Finally, the phase velocity dispersion curves, attenuation curves, the displacement and temperature distributions for functionally graded plates with different fractional orders are analysed. Both the fractional order and relaxation time have weak influence on the elastic mode velocity, but they have considerable influence on the elastic mode attenuation.

Predicting the noise in hybrid (phase and attenuation) x-ray images acquired with the edge illumination technique.

To analyze the noise performance of the edge illumination phase-based x-ray imaging technique when applying "single-shot" phase retrieval. The latter consists in applying a sample-specific low-pass filter to the raw data, leading to "hybrid" images in which phase and attenuation contrast are merged with each other. The second objective is to compare the hybrid images with attenuation-only images based on their respective signal-to-noise ratio (SNR). Noise is propagated from the raw images into the retrieved hybrid images, yielding analytic expressions for the variances and noise power spectra of the latter. An expression for the relative SNR between hybrid and attenuation images is derived. A comparison with simulated data is performed. Experimental data are also shown and discussed in the context of the theory. The noise transfer into the retrieved hybrid images is strongly related to the setup and acquisition parameters, as well as the imaged sample itself. Consequently, the relative merit between hybrid and attenuation images also depends on these criteria. Generally, the hybrid approach tends to perform worse for highly attenuating samples, as the availability of phase contrast is outweighed by the loss of photons that is necessarily encountered in hybrid acquisitions. On the contrary, the hybrid approach can lead to a much better SNR for weakly attenuating samples, as here phase effects lead to much stronger contrast, outweighing the reduction in photon numbers. The analytic expressions inform the design of edge illumination setups that lead to minimum noise transfer into the retrieved hybrid images. We also anticipate our theory to guide the decision as to which imaging mode (hybrid or attenuation) to use in order to maximize SNR for a specific sample.

Attenuation analysis of flexural modes with absorbent lined flanges and different edge conditions.

The analysis of fluid-structure coupled waveforms and the attenuation of these waveforms in a flexible waveguide is carried out. The physical configuration contains an expansion chamber connected by an extended inlet/outlet by means of vertical lined flanges. The governing boundary value problem is solved by using Mode-Matching (MM) technique. The associated eigen expansions of field potentials include non-orthogonal eigenfunctions and the related eigen-sub-systems are classified in the non-Sturm Liouville category, whereby the use of generalized orthogonal characteristics has ensured the point-wise convergence of solution. The low frequency approximation (LFA) which relies on the limited propagating modes is developed and is compared with MM solution. In the low frequency regime, a good agreement between MM and LFA results is found. Furthermore, the numerical experiments are performed to analyze the effects of absorbent linings and edge conditions on the attenuation of flexural modes. The guiding structure is exited with the structure-borne mode incident as well as the fluid-borne mode incident. It is found that the use of edge conditions and the absorbent linings significantly affect the attenuation of structure-borne mode and fluid-borne mode, respectively.

Higher Order Mode Attenuation in Microstrip Patch Antenna with DGS H Filter Specification from 5 to 10 GHz Range

Abstract This work proposes the application of a slot in the ground plane, Defected Ground Structure (DGS), of a microstrip patch antenna. The application of this technique aims to attenuate higher-order excited modes without deteriorating the antenna parameters in the fundamental mode. The methodology for the design of the slot in H-format is presented, based on the physical dimensions of the microstrip patch antenna. The positioning of the DGS concerning the feed line was determined from a detailed parametric analysis. The antenna was designed for the fundamental mode at 2.45 GHz frequency. Two antenna prototypes were built, with and without DGS, and measurements of reflection coefficient, gain, and radiation pattern were performed. The measured results show that the application of DGS considerably attenuated higher-order excited modes. A good agreement between simulated and measured results is achieved.

Modal response and vibration attenuation of carbon fiber composite sandwich cylindrical panels made of bi-directional corrugated strip cores

To explore desirable structures with both higher fundamental frequency and better vibration suppression, we designed and fabricated carbon fiber composite bi-directional corrugated sandwich cylindrical panels (BCSCPs) by a hot press molding and post-assembly approach. Modal response and vibration attenuation performance of such structures were investigated experimentally and numerically. Furthermore, the free and forced vibration responses of simple laminated cylindrical panels (SLCPs), axial corrugated sandwich cylindrical panels (ACSCPs) and circular corrugated sandwich cylindrical panels (CCSCPs) with almost the same relative density were investigated and compared with that of BCSCPs. The results indicated that the numerical models were reasonable to estimate the vibration properties of BCSCPs, and the vibration attenuation performance can be improved by suitably increasing the thickness of face sheet and bi-direction corrugated core. Besides, it was revealed that the BCSCPs, ACSCPs and CCSCPs all had comparatively better vibration attenuation performance than that of the SLCPs, and the present BCSCPs generally had higher natural frequencies than those of the ACSCPs and CCSCPs with almost the same weight, which may provide some references for further engineering application of such kinds of composite sandwich structures.

Spatial Density and Splicing Characteristic Optimized Few-Mode Multi-Core Fiber

Few-mode fiber design suitable for long-haul dense space division multiplexing (SDM) transmission is proposed, where the spatial density and the splicing characteristics of the fiber is optimized. We numerically investigate the impact of the number of modes per core in a multi-core structure on the total number of spatial channels possible and the splice loss property. It is shown that increased number of mode per core enables us to improve the spatial density while maintaining feasible splice-induced differential modal attenuation. We then successfully fabricate a 10-mode 12-core fiber with a cladding diameter of 217 μm, that achieves a relative core multiplicity factor (RCMF) of 101.7 and maximum number of spatial channels among the possible few-mode multi-core fiber designs with a cladding diameter of less than 250 μm. Experiments confirm that its splice-induced differential modal attenuation characteristics were better than those of previously reported 114-spatial-channel fiber.

Effect of sheath thickness on the propagation constant of electromagnetic waves propagating along thin plasma layer coated metallic surface

Solving or mitigating the blackout problem suffered by hypersonic vehicles as they re-enter the atmosphere is essential for the smooth communication of hypersonic vehicles. An antenna–sheath–plasma layer configuration is proposed, whose analytical results indicate that the attenuation of the wave mode can be reduced significantly through optimizing the sheath thickness between the hypersonic vehicle antenna and the surrounding plasma layer. Detailed investigations show that because the wave frequency is greater than the plasma frequency, i.e., ωpe < ω, there exists great influence of the sheath thickness parameter δ on the propagation constant for the m = 1, 2, 3 modes as δ ∈ (0.01, 1) and for the m = 0 mode as δ > 1; for the ωpe > ω case, δ imposes a significant effect on the propagation constant for the m = 0, 2, 3 modes as δ ∈ (0.1, 2) and for the m = 1 mode as δ < 1; in addition, it shows that the attenuation constant for the m = 1 mode is always non-zero, which implies that the blackout problem is mainly caused by the m = 1 mode when ωpe > ω.

A high order continuation method to locate exceptional points and to compute Puiseux series with applications to acoustic waveguides

A numerical algorithm is proposed to explore in a systematic way the trajectories of the eigenvalues of non-Hermitian matrices in the parametric space and exploit this in order to find the locations of defective eigenvalues in the complex plane. These non-Hermitian degeneracies also called exceptional points (EP) have raised considerable attention in the scientific community as these can have a great impact in a variety of physical problems.The method requires the computation of successive derivatives of two selected eigenvalues with respect to the parameter so that, after recombination, regular functions can be constructed. This algebraic manipulation permits the localization of exceptional points (EP), using standard root-finding algorithms and the computation of the associated Puiseux series up to an arbitrary order. This representation, which is associated with the topological structure of Riemann surfaces allows to efficiently approximate the selected pair in a certain neighborhood of the EP.Practical applications dealing with guided acoustic waves propagating in straight ducts with absorbing walls and in periodic guiding structures are given to illustrate the versatility of the proposed method and its ability to handle large size matrices arising from finite element discretization techniques. The fact that EPs are associated with optimal dissipative treatments in the sense that they should provide best modal attenuation is also discussed.

Dielectric Loss Tangent Extraction Using Modal Measurements and 2-D Cross-Sectional Analysis for Multilayer PCBs

Frequency-dependent electrical properties of dielectric materials are one of the most important factors for high-speed signal integrity design. To accurately characterize material's dielectric loss tangent (tanδ) after multilayer printed circuit board fabrication a novel method was proposed recently to extract tanδ using coupled striplines' measured S-parameters and cross-section geometry. By relating modal attenuation factors to the ratio between the differential and common mode per-unit-length resistances, the surface roughness contribution is eliminated and the contributions of dielectric and conductor loss are separated. Here, we specifically decided to avoid using any physical dielectric model in the extraction algorithm in order to eliminate a need for any a priori information about dielectric behavior. Further analysis and improvement of the tanδ extraction approach is presented in this article. To evaluate the accuracy of the extraction, the impact of errors due to de-embedding, vector network analyzer measurement, and two-dimensional solver's calculation are taken into account by a statistical error model. A confidence interval of extracted tanδ is provided. To describe the frequency dependence of tanδ, a two-term Djordjevic model is proposed to fit the extracted tanδ curve, which guarantees causality and gives better agreement with measured insertion loss compared to the traditional Djordjevic model.

Supercontinuum generation in photonic crystal fibers infiltrated with nitrobenzene

A photonic crystal fiber made of fused silica glass and infiltrated with nitrobenzene (C6H5NO2) was proposed as a new nonlinear medium for supercontinuum generation (SG). The guiding properties of the fiber structure were studied numerically, including estimation of the effective refractive index, attenuation, and dispersion of the fundamental mode. Based on the obtained results, three optimized structures were selected and tested numerically for SG. With numerical simulations of nonlinear propagation, we demonstrated the feasibility of spectrally broad and coherent SG in the proposed structures. For the first we obtained a supercontinuum (SC) in the range of 0.8–1.8 µm, for the second in the range of 0.8–2.1 µm, and for the third 1.3–2.3 µm. The pulse energy was in the range of 0.06–0.5 nJ while the pulse duration was 90 fs or 120 fs. For all structures an SC was formed in the first centimeter of the light propagation and conveniently allowed to assume short segments of the fibers. The proposed fibers are good candidates for all-fiber SC sources constituting an attractive alternative to glass-core fibers, since the nonlinearity of nitrobenzene is significantly higher than that of silica. The proposed solution may lead to new low-cost all-fiber optical systems for SG.

Weighted subspace detection method based on modal attenuation law in shallow water

In this paper, the modal space detector (MSD) is investigated in shallow water environment when utilizing a vertical linear array. The processing gain of the MSD is derived, and the result demonstrates that the processing gain of the MSD degrades when the number of the propagated normal modes excited by the underwater acoustic source increases, and therefore the detection performance of the MSD decreases. By exploiting the orthogonality among the modal depth functions, the MSD can be decomposed into a group of modal subspace detectors (MSSDs). The processing gains of these MSSDs are derived as well and it is found out that the processing gain of a MSSD is in direct proportion to its corresponding modal attenuation coefficients. By designing a group of weighting coefficients based on the mode attenuation law, a weighted modal subspace detector (WMSSD) is proposed to alleviate the degradation of the processing gain processing of the MSD. We analyze the influences of acoustic source locations and sound velocity profiles (SVPs) on the detection performance of the WMSSD theoretically, and verify the theoretical analyses by comparing its processing gain with the MSD in simulation experiments. The results show that the WMSSD presents various processing gains versus different acoustic source locations. In the waveguide having a negatively-gradient SVP, there exists a ‘weak detection area’ for the WMSSD, that is, the processing gain of the WMSSD is smaller than that of the MSD when the acoustic source locations are close to sea surface. The reason is because there are inversion points on the lower-order modal depth functions and the depths of the inversion points are close to sea surface. In other most areas, the processing gain of the WMSSD is larger (even remarkably larger) than that of the MSD. In the waveguide having a positively-gradient SVP, due to the phenomenon that the modal inversion points of the lower-order modal depth functions are near sea floor, there is a contrary consequence, that is, the ‘weak detection area’ is close to sea floor. And meanwhile the WMSSD outperforms the MSD in other most areas as well. There are no modal inversion points in the waveguide having a constant SVP, and therefore the WMSSD always outperforms the MSD.

Elastic anomalies at the first order transition in Lu5Ir4Si10

Ultrasonic measurements on a single crystal of the intermetallic compound Lu5Ir4Si10 are presented. Large anomalies in the velocity and ultrasonic attenuation of the elastic modes are observed at the structural phase transition TS∼80 K. The velocity of the longitudinal C11 and C33 mode exhibits a second order transition behavior. In contrast the velocities of the shear C44 and C66 modes exhibit a first order transition behavior. The longitudinal C11 mode is strongly coupled to the ordering system below TS. Similarities in the longitudinal elastic anomalies with known reduced dimensional charge density wave systems suggest that the nature of the structural phase transition TS in Lu5Ir4Si10 could be associated with a charge density wave phase transition.

Longitudinal sound and diffusion in holographic massive gravity

We consider a simple class of holographic massive gravity models for which the dual field theories break translational invariance spontaneously. We study, in detail, the longitudinal sector of the quasi-normal modes at zero charge density. We identify three hydrodynamic modes in this sector: a pair of sound modes and one diffusion mode. We numerically compute the dispersion relations of the hydrodynamic modes. The obtained speed and the attenuation of the sound modes are in agreement with the hydrodynamic predictions. On the contrary, we surprisingly find disagreement in the case of the diffusive mode; its diffusion constant extracted from the quasi-normal mode data does not agree with the expectations from hydrodynamics. We confirm our numerical results using ana- lytic tools in the decoupling limit and we comment on some possible reasons behind the disagreement. Finally, we extend the analysis of the collective longitudinal modes beyond the hydrodynamic limit by displaying the dynamics of the higher quasi-normal modes at large frequencies and momenta.

Mechanistic understanding of excitation of surface plasmons in a fiber-optic SPR sensor utilizing Al/Cu bimetallic configuration: mode field approach

This work reports on a novel approach of incorporating effective refractive indices of the guided modes obtained through wave optics to optimize the thickness of plasmonic metal in a fiber–optic surface plasmon resonance (SPR) sensor based on Kretschmann–Raether configuration. Using optical fibers with significantly smaller dimensions than used in conventional fiber–optic SPR sensors, a rigorous mathematical analysis has been carried out to conclude the existence of a single guided mode propagating in multi–layered fiber–optic sensing structure responsible for the excitation of SP mode. The effective refractive indices of the guided modes and modal attenuation for different thickness combinations of Al and Cu used in bimetallic layer configuration have been determined using wave optics. The optimized thickness of Al/Cu bimetallic layer, thus obtained, is subsequently used to simulate a fiber–optic SPR refractive index sensor. Operating in a refractive index range of 1.330–1.380 with sensitivity 3.16 μm/RIU, key attributes of the designed sensor include larger shift in resonance wavelength supplemented with simultaneous narrowing of SPR spectrum culminating in enhancing figure of merit. First and unique of its kind, this work is an attempt at the visualization of SP excitation in fiber–optic SPR sensor using wave optics, and thus, brings innovative insights towards exploration of fiber–optic SPR sensors using modal field approach.

Utilizing polarization-selective mode shaping by chalcogenide thin film to enhance the performance of graphene-based integrated optical devices

High refractive index (RI) thin films are capable of pulling waveguide mode profiles towards themselves. In this study, it is shown that by applying high RI coatings with specific thicknesses on the side of optical waveguides, significantly different mode profiles for orthogonal polarizations can be achieved. This phenomenon, that we call it polarization-selective mode shaping, can be extensively used in the enhancement of polarization-dependent integrated optical devices. As an illustrating application, a tri-layer structure consisting of poly(methyl methacrylate)/graphene/chalcogenide on a side-polished fiber is designed to realize an extremely high extinction ratio polarizer. This structure changes the mode profiles in a way that the attenuation of TE mode is maximized, while the power carried by the TM mode remains relatively constant. Simulations and experimental characterizations confirm that polarization-selective mode shaping coordinates four loss mechanisms to maximize the extinction ratio and minimize the insertion loss of the polarizer. The fabricated polarizer is examined in the O, C, and L telecommunication frequency bands. This configuration achieves the high extinction ratio of 51.3 dB and its maximum insertion loss in the tested wavelengths is 1.79 dB. The proposed polarizer has been compared with other state-of-the-art polarizers in the conclusion section which shows its superiority.

Controlling the attenuation of leaky modes in multimode W-type photonic crystal fibers in the infrared wavelength domain

Leaky mode losses for a range of parameters such as the spacing and size of air holes, as well as the wavelength in W-type multimode glass photonic crystal fiber, are reported. Using an effective index approach by numerical solution of the time-independent power flow equation, we obtained that the leaky mode losses increase as the wavelength increases, and this rise of losses is greater in the case of narrower inner cladding. This user-friendly, simple approach of computing leaky losses could be used by experimentalists and system users.

Análisis del consumo energético de la herramienta de un torno CNC a diferentes velocidades de corte usando la densidad del espectro de potencia

In a company, income must exceed expenses for the business to be profitable. The choices a company makes about its energy sourcing and consumption can profoundly influence its cost of production. The purpose of this paper is to examine the energy consumption of the cutting tool of a lathe using a numerical tool CNC. This study was designed to examine the relationship between speed of cutting and the spectral modes of the power spectral density. This work shows the impact of the current for different cutting speeds, the results of this study indicate that the power spectral density of the current of cutting, may be more than enough to determinate the energy consumption of the manufacturing process. The main contribution of this paper is the experimental validation of the attenuation of higher order modes of the electrical current at metal cutting process. These results can be used in the design and tuning of the speed control of the cutting tool.