Waveguide Reflection Research Articles

CHO and HepG2 Single-Cell Characterization With Planar Microchip Sensors up to 40 GHz

The article deals with broadband microwave measurements performed on single dead and living biological cells from CHO and HepG2 cell lines. It reports results obtained with coplanar waveguide reflection and transmission type sensors, respectively. A straight-forward single liquid calibration procedure allows to extract the complex cell permittivity and compare it to that of the surrounding medium. The contrast is analyzed through <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p$</tex-math></inline-formula> -value tests and in terms of the usual Cole-Cole parameters. The results demonstrate the distinguishability of the cell lines based on the permittivity.

200 Gb/s Optical-Amplifier-Free IM/DD Transmissions Using a Directly Modulated O-Band DFB+R Laser Targeting LR Applications

We experimentally demonstrate an O-band single-lane 200 Gb/s intensity modulation direct detection (IM/DD) transmission system using a low-chirp, broadband, and high-power directly modulated laser (DML). The employed laser is an isolator-free packaged module with over 65-GHz modulation bandwidth enabled by a distributed feedback plus passive waveguide reflection (DFB+R) design. We transmit high baud rate signals over 20-km standard single-mode fiber (SSMF) without using any optical amplifiers and demodulate them with reasonably low-complexity digital equalizers. We generate and detect up to 170 Gbaud non-return-to-zero on-off-keying (NRZ-OOK), 112 Gbaud 4-level pulse amplitude modulation (PAM4), and 100 Gbaud PAM6 in the optical back-to-back configuration. After transmission over the 20-km optical-amplifier-free SSMF link, up to 150 Gbaud NRZ-OOK, 106 Gbaud PAM4, and 80 Gbaud PAM6 signals are successfully received and demodulated, achieving bit error rate (BER) performance below the 6.25%-overhead hard-decision (HD) forward-error-correction code (FEC) limit. The demonstrated results show the possibility of meeting the strict requirements towards the development of 200Gb/s/lane IM/DD technologies, targeting 800Gb/s and 1.6Tb/s LR applications.

Revisiting Multiple-Scattering Principles in a Crustal Waveguide: Equipartition, Depolarization and Coda Normalization

Seismic waves radiated by small crustal earthquakes are prone to multiple mode conversions caused by reflection and transmission at interfaces, and scattering by small-scale heterogeneities in the bulk of the medium. The goal of this study is to clarify the complex interplay between volume scattering and interface reflections in crustal waveguides and how it will impact the crustal energy propagation. To carry out this task, we have incorporated a rigorous description of wave polarization in the context of Monte–Carlo simulations of the multiple-scattering process by introducing a five-dimensional Stokes vector. To shed light on the wave content of the regional short-period seismic wavefield, we investigate the asymptotic partitioning of seismic energy onto P, SV and SH polarizations in the coda, as well as the angular distribution of energy flux in the waveguide. In full elastic space, equipartition theory predicts that (1) the energy ratio between P- and S-wave energies tends to $$\beta ^3/(2\alpha ^3)$$ , (2) an equal distribution of energy among SV- and SH-waves and (3) that energy fluxes are isotropic. In the presence of interfaces, we find that the isotropy of the wavefield is systematically broken and that energy ratios are shifted to the detriment of P-waves and in favor of SV-waves in a non-absorbing medium. This implies that a residual polarization is preserved in the waveguide. Through an extensive parametric study, we illustrate in detail how the anisotropy of the wavefield, the partitioning ratios and the shear wave polarization depend on the crustal attenuation parameters. The role of the initial polarization at the source has also been examined. In the case of an explosion and a shear dislocation with equal magnitude, we find that the energy level in the coda can differ by more than one order of magnitude when the effect of crustal scattering becomes very weak compared to reflections or transmissions at interfaces. When comparing different shear dislocation mechanisms, we find that the energy level in the coda can differ by up to 60%. While equipartition, depolarization and coda normalization remain fundamental guides to our understanding of the coda, their application requires a good a priori knowledge of the attenuation properties of the crust.

Design and Performance of Diamond‐Based Mid‐Infrared Sensor

Herein, finite‐element analysis is used to optimize the performance of mid‐infrared (MIR) (7.7–13.7 μm) waveguides by selecting optimal waveguide and substrate materials, waveguide size, and boundary field. The results show that a diamond waveguide has a substantially higher sensitivity than Si‐ or Ge‐based waveguides owing to its higher boundary evanescent field at the same depth. Furthermore, it is found that AlN substrates have better optical stabilities than SiO2 and Si3N4 substrates, because AlN substrates do not have apparent absorption characteristics in the MIR range (7.7–13.7 μm). Geometry of diamond waveguide on AlN substrate is optimized, and a section length of 45 μm is chosen for optimal signal transmission quality. The calculations of the infrared attenuated total reflection (ATR) of the diamond waveguide applied to water, alcohol, and diisopropyl methyl phosphate are highly consistent with the actual infrared absorption spectrum. This proves the feasibility of applying AlN/diamond waveguides in MIR ATR detection, which is of great significance for the preparation of high‐sensitivity MIR detectors.

Nondestructive Evaluation of Coatings Delamination Using Microwave Time Domain Reflectometry Technique

Ceramic based coatings such as Thermal Barrier Coatings (TBCs) are widely deposited onto gas turbine engine components to protect their metal substrate against high temperature. However, improper adhesive application, thermal stress and moisture penetration through the insulation materials can cause defects such as delamination to grow between the insulation and the metal surface. Such defects could lead to catastrophic failure if not immediately detected and repaired. Hence, it is imperative to non-destructively inspect these interfaces for delamination to avoid such an event. In this paper, a novel microwave non-destructive testing technique for ceramic-based coatings is proposed. This technique is based on scanning the surface of the coating with an open-ended rectangular waveguide and analyzing the reflections in the time domain. The proposed time-domain technique appears to reveal more about the depth of any existing delamination than any other microwave non-destructive testing (NDT) technique. Here, a ceramic sample with machined delamination is scanned using rectangular waveguides operating from 26.5 to 40 GHz. After applying Fourier analysis to the frequency domain waveguide reflections, time-domain results showed the delamination with significantly better depth resolution compared to frequency domain analysis. The results reported in this paper prove the advantages of the time-domain technique to forecast the relative delamination depth, which is important for many industrial applications. The depth information of delamination can be used in a condition-based predictive maintenance schedule to plan the inspection intervals efficiently, minimize the unnecessary replacements and provide practical guidance for future design.

Moment method approach to analyze waveguide array radiator with crossed dipole as a near field sensor

Moment method approach is used to estimate the error encountered by the sensor in the near field and probe measures co-pole and cross-pole voltages at the same time. Conversely, due to several reflections between the waveguide and dipole sensor, near field values are changed. Calculations are done to analyze the absolute sampled co-pole voltage pattern and relative sampled electric field (without probe) pattern in the scan plane, and inaccuracy induced by the sensor is determined. The waveguide reflection coefficient, radiation admittance and susceptance with measuring sensor are reformed with respect to the equivalent values in the absence of the sensor in the near field.

Solitonic waveguide reflection at an electric interface.

A refractive index interface is dynamically induced in a bulk photorefractive material by biasing two adjacent regions with different electric fields, thus building up an electric wall. Effects of this interface on reflection, refraction and breathing of bright photorefractive solitons and their associated waveguides are numerically and experimentally studied as a function of the induced purely electric field gradient. Reflection and refraction efficiency depends on the amplitude and sign of the applied voltages that affect both the self-confining beam and the signals propagating inside the waveguide. Experimental tests are performed in nominally undoped lithium niobate samples.

Ultralow-bending-loss surface-plasmon-polariton waveguides

We report the transmission, reflection and loss properties of 90-degree and 135-degree bent silicon waveguide and 90-degree and 135-degree bent surface-plasmon polariton (SPP) waveguides composed of metal thin film and silicon. Finite difference time domain simulation analysis shows that the maximum bending transmittances of 90-degree bent and 135-degree bent silicon waveguides are 51% and smaller than 10%, respectively, and the maximum bending transmittances of 90-degree bent and 135-degree bent SPP waveguides are 80% or so, and they are higher 30% and 70% than that of identically-bent silicon waveguides, respectively. Moreover, the SPP waveguide bend with metal thin film as inner layer of the bend and silicon as outer layer of the bend has much higher transmission than ones with silicon as the inner layer and metal thin film as the outer layer. The waveguide bend with metal as the inner layer and dielectric as the outer layer will be potential for integrated photonic devices and subsystem.

Excitation of higher order modes in total transmission by zero index metamaterials with embedded defects

A zero index metamaterial can be applied to perfect transmission or perfect reflection. In this paper we theoretically present a strategy of microwave transmission through a zero-index metamaterial waveguide loaded with defects. By simply adjusting the geometric and electromagnetic properties of the defects, higher modes can be excited in the total transmission or total reflection. To do so, a waveguide with two and three defects is considered and studied and the properties of defects are calculated from an analytical procedure. The results show excitation of higher modes in total transmission and reflection of waveguide.

New Permittivity Measurement Methods Using Resonant Phenomena For High-Permittivity Materials

This paper describes the characterization of high-permittivity materials with a dielectric constant ( $\epsilon _{r}$ ) up to 3000 using resonant phenomena. We propose and demonstrate two types of measurement techniques: the rectangular resonator method by controlling the sample insertion length and the waveguide reflection method with a sample terminated by a short circuit. We investigate the validity and the range of application of both methods by performing numerical calculations. We also experimentally demonstrate these two methods by measuring dielectric materials with $\epsilon _{r}$ ~100 and 200 for the former method and those with $\epsilon _{r}$ ~200, 1400, 1700, and 2900 for the latter method. By estimating the measurement uncertainty using Monte Carlo calculations, we clarify that the results obtained by both methods for a dielectric material with $\epsilon _{r}$ ~ 200 are almost consistent within the ranges of the uncertainties.

Temperature and pressure effect on GaN waveguide at 428.71 terahertz frequency for sensing application

Effect of temperature and pressure on gallium nitride semiconductor (GaN) waveguide at terahertz frequency is thoroughly discussed in this paper. This effect acts as both temperature and pressure sensor using same waveguide. Temperature as well as pressure of GaN is investigated at wavelength 700nm. Both reflection and absorption losses of GaN waveguide are considered to compute transmitted energy. Reflectance from such structure is simulated using plane wave simulation method. Simulation results revealed that reflectance varies linearly with respect to both temperature and pressure. It is also found that absorption of GaN is zero at wavelength 700nm. Experimentally, set up is designed to obtain transmitted energy emerging from GaN waveguide with respect to different temperature and pressure. Finally, simulation result showed that transmitted energy through such structure varies an excellently linearship with both temperature and pressure which acts as accurate temperature and pressure sensor.

Modified TM and TE waveguide modes and reflectivity by graphene layer in coupled-graphene-metal multilayer structure in sub-terahertz frequency

In this paper we focus on the dispersion characteristics of TM and TE waveguide modes and the reflectivity of plane waves, incident on the four-layer structure consisting of air/graphene monolayer/dielectric buffer layer/metal substrate. The TM waveguide modes split up into two branches for small frequencies, one of the branches (cutoff waveguide branch) undergoes cutoff at a certain cutoff buffer thicknesses. There is no splitting of TE waveguide modes. However, these modes can be converted into short-range waves for smaller buffer thickness with subsequent modes cutoff depending on frequency and graphene electron concentration. Reflection coefficients of the TM polarized incident electromagnetic waves from air on the multi-layer structure vanish in the vicinity of cutoff buffer thicknesses. It is demonstrated that waveguide mode propagation constants and reflectivity in the multilayer structure can be considerably influenced by the presence of a graphene layer in the vicinity of the cutoff thicknesses of the waveguide modes.

Sensing the Earth’s low ionosphere during solar flares using VLF signals and goes solar X-ray data

An analysis of D-region electron density height profile variations, induced by four isolated solar X-ray flares during period from September 2005 to December 2006, based on the amplitude and the phase delay perturbation of 22.1kHz signal trace from Skelton (54.72N, 2.88W) to Belgrade (44.85N, 20.38E), coded GQD, was carried out. Solar flare data were taken from NOAA GOES12 satellite one-minute listings. For VLF data acquisition and recordings at the Institute of Physics, Belgrade, Serbia, the AbsPAL system was used. Starting from LWPCv21 code (Ferguson, 1998), the variations of the Earth-ionosphere waveguide characteristic parameters, sharpness and reflection height, were estimated during the flare conditions. It was found that solar flare events affected the VLF wave propagation in the Earth-ionosphere waveguide by changing the lower ionosphere electron density height profile, in a different way, for different solar flare events.

A dispersion compensation procedure to extend pulse-echo defects location to irregular waveguides

Abstract A time–frequency signal processing procedure aimed at extending pulse-echo defect detection methods based on guided waves to irregular waveguides is proposed. In particular, the procedure returns the distance traveled by a guided wave that has propagated along a waveguide composed by segments with different dispersive properties by processing the detected echo signal. To such aim, the acquired signal is processed by means of a two-step procedure. First, a warped frequency transform (WFT) is used to compensate the dispersion of the guided wave due to the traveled distance in a portion of the waveguide that is assumed as reference. Next, a further compensation is applied to remove from the warped signal the group delay introduced by the remaining irregular portion of the waveguide. Thanks to this processing strategy, the actual distance traveled by the wave in the regular portion of the irregular waveguide is revealed. Thus, the proposed procedure is suitable for automatically locate defect-induced reflections in irregular waveguides and can be easily implemented in real applications for structural health monitoring purposes. The potential of the procedure is demonstrated and validated numerically by simulating and processing Lamb waves propagating in waveguides made up of different uniform, tapered and curved segments.

Lateral beam shift at transmission through layered structures with negative index material

We studied electromagnetic wave transmission through layered structures that include negative index materials. The excitation of leaky guided modes leads to the formation of anomalous lateral shifts in the reflected beam with a double-peak structure and in the transmitted beam with a single-peak structure. In the absence of losses, we demonstrate that the total transparency (i.e. zero reflection) of the slab waveguide with the negative index material can be achieved under conditions in which high reflectivity is normally expected. We demonstrate the trade-off effect between the high transmission and the high lateral shift. This peculiar effect exists not only for the pure TE or the pure TM polarization of the obliquely incident radiation, but also under certain circumstances for both of them simultaneously i.e. for the nonpolarized radiation.

SU‐GG‐I‐166: Design and Evaluation of an Optical Tactile Imaging Device for Tumor Detection

Purpose: To present a novel tactile imaging device for cancer detection. Method and Materials: Unlike traditional tactile devices, which are formed of pressure sensor array, this new device uses an optical waveguide and total internal reflection principle to maximize the tactile resolution. In order to emulate the detection range of the human tactile sensation, a multi‐layer polydimethylsiloxane waveguide has been fabricated as a sensing probe. The elastic modulus of each layer has been matched to the dermis, epidermis, and subcutaneous of the human finger. The light is illuminated under the critical angle for full reflection within the waveguide. When a waveguide is compressed by an object, the contact area of the waveguide deforms, which causes the light to scatter. The scattered light is then captured by a high resolution camera. The applied forces can be detected by measuring changes in the amount of diffused light. To test the performance of the proposed device, a realistic tissue phantom with hard inclusions is developed. Total of nine inclusions with different diameters and depth were placed in the phantom. We estimated the diameter and the depth of the inclusions with the tactile imaging device. We also performed experiments using the mice with globus tumors. We grew three different sizes of tumors and imaged them using the proposed device. Results: The result showed that the proposed sensor can estimate the inclusion diameter within 4.09% and the inclusion depth within 7.55%. The mice test results show that the proposed device successfully detects the tumors. In the animal study, the sensor detected a subsurface tumor as small as 2.74 mm. Conclusion: A novel tactile imaging device for tumor identification has been designed and experimentally evaluated to be effective.

Measurement of Complex Permittivity for Liquid Materials Using the Open-Ended Cut-Off Waveguide Reflection Method

Various studies of specific absorption rates (SARs) using liquid phantoms imitating human body tissues have been widely carried out in electromagnetic compatibility (EMC) research fields. In order to establish accurate SARs for measurement, a faithful mockup of human body tissue is needed. Therefore, knowledge of the accurate measurement of sample materials with high permittivity and high loss is very important. In this study, the complex permittivity of tap water, ethanol, methanol and isopropanol is measured by the open-ended cut-off circular waveguide reflection method. The effectiveness of the method presented here of measuring a liquid phantom with high-permittivity and high-loss is also confirmed by comparing the measured results with the results obtained by the TM010 circular cavity resonator method. At this time, the effects on the input impedance under variations of the insertion length and termination conditions were studied. Then the complex permittivity of tap water, ethanol, methanol and isopropanol was measured at frequencies ranging from 0.5 to 3.0GHz using the measurement procedure above. As a result, we confirmed the frequency characteristics of the complex permittivity for a wide variety of high-loss liquid materials.

All-optical set–reset flip-flop based on frequency bistability in semiconductor microring lasers

The electric field of the modes of semiconductor microring lasers (SMRLs) in the presence of bus waveguide reflections are linear combinations of the clock wise (CW) and the counter clock wise (CCW) electric fields. The mode structures can be controlled by the waveguide reflection coefficients. The power ratio and phase difference of the CW and CCW fields of one mode is proportional to the ratio of the reflection coefficients of the left and right waveguides. It is shown that the degenerate CW and CCW modes in the presence of bus waveguide reflections are split into two modes with different frequencies. Employing these new modes, SMRL can be used as an element to design flip-flops used in photonic integrated circuits. For a symmetric structure, the inter-frequencies of CW and CCW waves relating to each mode can be considered as the output of the optical flip-flop. Output of asymmetric mode is zero while the symmetric mode has a nonzero output.

Shaping waveguide transmission and reflection characteristics using conducting fabrics

AbstractConductive fabrics are finding many applications and improved techniques for assessment required. This article presents a measurement technique using waveguide high‐Q cavities and a finite element model. Reflection and absorption properties of fabrics have been characterized to 10 GHz, and good agreement obtained between experimental and modeled results. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1416–1419, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24341

Modal properties of all-active InGaAsP/InP microring lasers

An experimental investigation of the multimode dynamics of 1.55 μm-InGaAsP/InP microring lasers is demonstrated. Different operation regimes are observed, bidirectional multimode, unidirectional single mode, bidirectional single mode and mode-hopping. The extent of each of the above operation regimes is examined with respect to the ring current level, bus waveguide reflectivity and ring radius. The back-reflections generated from the bus waveguide facets are indirectly controlled via the bus waveguide current. In order to clarify the physical mechanisms beyond experimental results, a multimode model based on the rate equation approximation is utilized. The experimental results are in good agreement to those predicted by the multimode model.