Total Phase Shift Research Articles

Study on thermally induced depolarization of a probe beam by considering the thermal lens effect

In this paper, we present an accurate theoretical description of the birefringence characteristics in a Nd : YAG rod by taking the thermal lens effect into account. Considering that the birefringence is strongly dependent on the distance away from the centre of a birefringent rod, the convergent features of an incident probe beam were first evaluated for a side-pumped laser rod. A segmental accumulation method was then employed to calculate the total phase shift between the radial and the tangential components of polarization of a converged probe beam. The theoretical conclusions were compared with the measured results in both the degree of depolarization and the spatial birefringent distribution of a transmitted He–Ne laser beam. The experimental results are in good agreement with the theoretical ones so that we believe the algorithm given in this paper should be effective for the construction of a high-powered laser or amplifier system.

Binary-Coded 4.25-bit $W$-Band Monocrystalline–Silicon MEMS Multistage Dielectric-Block Phase Shifters

This paper presents a novel concept of a microwave microelectromechanical systems (MEMS) reconfigurable dielectric-block phase shifter with best loss/bit at the nominal frequency and best maximum return and insertion loss ever reported over the whole W-band. A seven-stage phase shifter is constructed by lambda/2-long high-resistivity silicon dielectric blocks, which can be moved vertically by MEMS electrostatic actuators based on highly reliable monocrystalline silicon flexures on-top of a 3-D micromachined coplanar transmission line. The dielectric constant of each block is artificially tailor made by etching a periodic pattern into the structure. Stages of 15deg, 30deg, and 45deg are optimized for 75 GHz and put into a binary-coded 15deg + 30deg + 5 times 45deg configuration with a total phase shift of 270deg in 19 times 15deg steps (4.25 bits). Return and insertion losses are better than -17 and -3.5 dB at 75 GHz, corresponding to a loss of -0.82 dB/bit, and a phase shift efficiency of 71.1deg/dB and 490.02deg/cm. Return and insertion losses are better than -12 and -4 dB for any phase combination up to 110 GHz (98.3deg/dB; 715.6deg/cm). The intercept point of third order, determined by nonlinearity measurements and intermodulation analysis, is 49.15 dBm for input power modulation from 10 to 40 dBm. The power handling is only limited by the transmission line itself since no current-limiting thin air-suspended metallic bridges as in conventional MEMS phase shifters are utilized. This is confirmed by temperature measurements at 40 dBm at 3 GHz with skin effect adjusted extrapolation to 75 GHz by electrothermal finite-element method simulations.

Unusually High Differential Attenuation at C Band: Results from a Two-Year Analysis of the French Trappes Polarimetric Radar Data

Abstract The differential phase (ΦDP) measured by polarimetric radars is recognized to be a very good indicator of the path integrated by rain. Moreover, if a linear relationship is assumed between the specific differential phase (KDP) and the specific attenuation (AH) and specific differential attenuation (ADP), then attenuation can easily be corrected. The coefficients of proportionality, γH and γDP, are, however, known to be dependent in rain upon drop temperature, drop shapes, drop size distribution, and the presence of large drops causing Mie scattering. In this paper, the authors extensively apply a physically based method, often referred to as the “Smyth and Illingworth constraint,” which uses the constraint that the value of the differential reflectivity ZDR on the far side of the storm should be low to retrieve the γDP coefficient. More than 30 convective episodes observed by the French operational C-band polarimetric Trappes radar during two summers (2005 and 2006) are used to document the variability of γDP with respect to the intrinsic three-dimensional characteristics of the attenuating cells. The Smyth and Illingworth constraint could be applied to only 20% of all attenuated rays of the 2-yr dataset so it cannot be considered the unique solution for attenuation correction in an operational setting but is useful for characterizing the properties of the strongly attenuating cells. The range of variation of γDP is shown to be extremely large, with minimal, maximal, and mean values being, respectively, equal to 0.01, 0.11, and 0.025 dB °−1. Coefficient γDP appears to be almost linearly correlated with the horizontal reflectivity (ZH), differential reflectivity (ZDR), and specific differential phase (KDP) and correlation coefficient (ρHV) of the attenuating cells. The temperature effect is negligible with respect to that of the microphysical properties of the attenuating cells. Unusually large values of γDP, above 0.06 dB °−1, often referred to as “hot spots,” are reported for 15%—a nonnegligible figure—of the rays presenting a significant total differential phase shift (ΔϕDP > 30°). The corresponding strongly attenuating cells are shown to have extremely high ZDR (above 4 dB) and ZH (above 55 dBZ), very low ρHV (below 0.94), and high KDP (above 4° km−1). Analysis of 4 yr of observed raindrop spectra does not reproduce such low values of ρHV, suggesting that (wet) ice is likely to be present in the precipitation medium and responsible for the attenuation and high phase shifts. Furthermore, if melting ice is responsible for the high phase shifts, this suggests that KDP may not be uniquely related to rainfall rate but can result from the presence of wet ice. This hypothesis is supported by the analysis of the vertical profiles of horizontal reflectivity and the values of conventional probability of hail indexes.

Comparison of low-amplitude oscillatory shear in experimental and computational studies of model foams

A fundamental difference between fluids and solids is their response to applied shear. Solids possess static shear moduli, while fluids do not. Complex fluids such as foams display an intermediate response to shear with nontrivial frequency-dependent shear moduli. In this paper, we conduct coordinated experiments and numerical simulations of model foams subjected to boundary-driven oscillatory planar shear. Our studies are performed on bubble rafts (experiments) and the bubble model (simulations) in two dimensions. We focus on the low-amplitude flow regime in which T1 events, i.e., bubble rearrangement events where originally touching bubbles switch nearest neighbors, do not occur, yet the system transitions from solid- to liquidlike behavior as the driving frequency is increased. In both simulations and experiments, we observe two distinct flow regimes. At low frequencies omega, the velocity profile of the bubbles increases linearly with distance from the stationary wall, and there is a nonzero total phase shift between the moving boundary and interior bubbles. In this frequency regime, the total phase shift scales as a power law Delta approximately omegan with n approximately 3. In contrast, for frequencies above a crossover frequency omega>omegap, the total phase shift Delta scales linearly with the driving frequency. At even higher frequencies above a characteristic frequency omeganl>omegap, the velocity profile changes from linear to nonlinear. We fully characterize this transition from solid- to liquidlike flow behavior in both the simulations and experiments and find qualitative and quantitative agreements for the characteristic frequencies.

级联四倍频调制法产生光毫米波中载波抑制问题的研究

The optical carrier suppression in optical quadruple frequency modulation by cascaded external modulators is investigated theoretically and experimentally. Theoretical analysis demonstrates that the optical carrier suppression ratio is related with not only the initial phase difference of electrical signals applied on the two modulators, but also the optical phase shift between the two modulators. The maximum suppression ratio can be achieved when the total phase difference is equal to n\pi+\pi/2 (n=1,2,...), which is verified by experiments. By properly controlling the total phase shift, 40-GHz millimeter-wave is generated by using a 10-GHz radio frequency (RF) source and the modulators.

Dynamic Characteristics and Linewidth Enhancement Factor of Quantum-Dot Vertical-Cavity Surface-Emitting Lasers

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This study explores the relative intensity noise characteristics of quantum-dot vertical-cavity surface-emitting lasers (QD VCSELs). The resonance frequency and eye diagram are presented. The linewidth enhancement factor (<formula formulatype="inline"><tex Notation="TeX">$\alpha$</tex></formula> factor) of QD VCSEL is also investigated experimentally. The values of <formula formulatype="inline"><tex Notation="TeX">$\alpha$ </tex></formula> factor were measured to be between 0.48 and 0.60. Moreover, a photonic RF phase shifter is examined using the QD VCSEL. A phase shifter with a total phase shift of 2<formula formulatype="inline"><tex Notation="TeX">$\pi$</tex> </formula> was demonstrated. These investigations and demonstrations will be useful in the field of QD VCSEL. </para>

Left-Handed/Right-Handed Transmission Line Subwavelength Cavity Resonators

In this letter, a new kind of cavity resonator based on left-handed/right-handed transmission lines is presented. The left-handed transmission line (LHTL), which can realize a negative phase shift, is formed by resonant-slot coupled cavity chain unit cells, while the right-handed transmission line (RHTL), which can realize positive phase shift, is made of coaxial waveguides. Resonance condition can be satisfied by setting the total phase shift between two ends of the cavity resonators to be zero. The design approach of the subwavelength cavity resonator is presented. Simulation and experimental results prove that the lengths of these cavity resonators can be much shorter than the conventional half-wavelength while working at the same frequency.

Explicit expression for the reflection and transmission probabilities through an arbitrary potential barrier

Without solving the Schrödinger equation, exact and general expressions of the reflection and transmission probabilities for a quantum particle through an arbitrary potential barrier are presented by using the analytical transfer matrix method. It is seen that in addition to the parameters of the ambience and both the start and the final point of the barrier, the unique dependence on the formulae is the total phase shift accumulated by the mainwaves and the subwaves.

Fractional Gouy phase

In general, the total Gouy phase shift has the form n pi, where n need not be an integer. As a result of the Fourier transforming property of a lens, the Gouy phase is found to be related to the types of discontinuities at the upper or lower range of the pupil function Q(c) resulting from the asymptotic order of the Fourier transform. The sign of the Gouy phase is also related to the slope of the pupil function. The oscillations of the Gouy phase shift arise from the strength of the nondominant discontinuity.

Electron collision effects on the eikonal cross-section in a warm plasma

The electron–electron collision effects on the eikonal cross-section for the elastic electron–ion collisions are investigated in a warm plasma. The second-order eikonal method and effective interaction potential including the far-field terms caused by the electron collisions are employed to obtain the eikonal phase shift and eikonal cross-section as functions of the collision frequency, impact parameter, collision energy thermal energy and Debye length. It is shown that the major contribution of the electron collision effects is given by the second-order eikonal phase shift. It is also shown that the electron collision effects strongly suppress the total eikonal phase shift and eikonal cross-section. In addition, the electron collision effects are found to decrease with an increase in the impact parameter. It is also found that thermal effects enhance the eikonal cross-section and decrease with an increase in the impact parameter.

Calibration methods for a multi-channel multi-frequency EIT system

Multi-channel multi-frequency electrical impedance tomography (EIT) systems require a careful calibration to minimize systematic errors. We describe novel calibration methods for the recently developed KHU Mark1 EIT system. Current source calibration includes maximization of output resistance and minimization of output capacitance using multiple generalized impedance converters. Phase and gain calibrations are used for voltmeters. Phase calibration nulls out the total system phase shift in measured voltage data. Gain calibrations are performed in two steps of intra- and inter-channel calibrations. Intra-channel calibration for each voltmeter compensates frequency dependence of its voltage gain and also discrepancy between design and actual gains. Inter-channel calibration compensates channel-dependent voltage gains of all voltmeters. Using the calibration methods described in this paper, we obtained 1 MΩ minimal output impedance of the current source in the frequency range 10 Hz–500 kHz. The reciprocity error was as small as 0.05% after intra- and inter-channel voltmeter calibrations. To demonstrate effects of calibration in reconstructed images, we used a homogenous phantom from which uniform images should be produced. Reconstructed time- and frequency-difference images using uncalibrated data showed spurious anomalies. By using calibrated data, standard deviations of time- and frequency-difference images of the homogenous phantom were reduced by about 40% and 90%, respectively.

Inspection of refractive x-ray lenses using high-resolution differential phase contrast imaging with a microfocus x-ray source

A refractive x-ray lens was characterized using a magnifying cone beam setup for differential phase contrast imaging in combination with a microfocus x-ray tube. Thereby, the differential and the total phase shift of x rays transmitted through the lens were determined. Lens aberrations have been characterized based on these refractive properties.

Optimum-Iris-Set Concept for Waveguide Polarizers

Novel profiled irises for the design of waveguide polarizers are presented. The two degrees of freedom of their piecewise-circular profile allow one to better control the frequency behavior of the differential phase shift. Thanks to this feature, an optimum iris set can be found by selecting the discontinuities for which the differential-phase-shift deviation from the average value is minimum in the operative bandwidth. This optimum iris set can be identified for several values of the ratio r/lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where r is the waveguide radius and lambda <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength at the central frequency. Hence, even if both the waveguide size and central frequency are assigned in the specifications, polarizers with a very low deviation from 90deg of the total differential phase shift can be designed. In this way, the number of waveguide transitions in the antenna feed system can be reduced and the effect of spurious higher-order-mode coupling can be minimized. A Ka-band polarizer in circular waveguide with piecewise-circular-profile irises is described, showing a return loss better than 55 dB and a phase error of about 0.9deg in a 10% bandwidth

Urban seagrass: Status of Posidonia oceanica facing the Genoa city waterfront (Italy) and implications for management

A system of five adjacent Posidonia oceanica meadows facing the waterfront of Genoa city (Ligurian Sea, NW Mediterranean) was investigated over different spatial scales (meters–kilometers) using three environmental indices: conservation index (CI), substitution index (SI) and phase-shift index (PSI). CI revealed differences mostly at large spatial scale, distinguishing the poor condition of the meadows closest to Genoa centre and harbour from the comparatively healthy condition of the farthest meadows. SI showed differences mostly at small spatial scale (i.e., within meadows), suggesting the influence of local factors in the re-colonisation of regressed meadows by the seagrass Cymodocea nodosa and/or the invasive alga Caulerpa racemosa. Mapping of PSI showed that the meadows closest to Genoa centre and harbour have undergone a nearly total phase shift and have no real potential for recovery: attempts to re-establish P. oceanica there might be a waste of time and money. On the contrary, the meadows farthest from Genoa centre and harbour showed a comparatively low level of phase shift and could still fully recover given specific management actions.

X-ray K-absorption studies of cobalt(II) semicarbazones

X-ray K-absorption edges along with their extended X-ray absorption fine structure (EXAFS) have been recorded using a laboratory XAFS spectrometer for the cobalt(II) semicarbazones viz., Co(emsc) 2Br 2, Co(emsc) 2SO 4, Co(mchsc) 2Br 2, Co(mchsc) 2SO 4 and Co(mchsc) 2(NCS) 2. The chemical shifts for these samples have been reported. The total phase shifts δ 1 and phase parameters β 1 for these samples have been estimated using the modified graphical method for the determination of bond distances. The variations in the values of chemical shift, phase parameter β 1 and average metal–ligand bond distances have been explained. The total phase shift values for the complexes indicate a linear variation with wave vector k.

Rotational resonance of magnetoinductive waves: Basic concept and application to nuclear magnetic resonance

Magnetoinductive waves propagating along a set of resonant metamaterial elements are studied under the condition when the wave travels round a closed circular path and the total phase shift is an integral multiple of 2π. The resonant frequency of the circulating wave is shown to be related to the resonant frequency of the element via the known dispersion relationship. The currents in the elements are determined with the aid of the impedance matrix when the excitation is by a rotating magnetic dipole located at the center of the structure. It is shown that the power taken out from one element in the loop may approach N times that from a single element, where N is the number of elements, provided the quality factor of the individual elements is sufficiently high and suitable modifications are made to nearby elements. Potential applications to magnetic resonance spectroscopy are discussed.

Design of tunable phase shifters by the image-parameters method

Based on the image-parameters (IP) method, a design technique is presented for electronically tunable phase shifters consisting of transmission lines periodically loaded with switched inductors and capacitors. The use of both inductors and capacitors allows large phase shifts with low return loss to be achieved, thus leading to very compact devices. Based on the analysis of the IP properties of the elementary cell, the design procedure presented allows an effective control of both the total phase shift and the return loss of the phase shifter, as well as its frequency band of operation. As a proof of concept, experimental test circuits have been fabricated and measured exhibiting a 105deg phase shift with 0.25-dB insertion loss at 4.5 GHz and a return loss of 20 dB over a two-octave frequency band

Quantum-well states in Ag/W(1 0 0) and their symmetric evolution in the atomic limit of thickness

The behavior of quantum-well states (QWS) in ultrathin Ag-films grown on W(1 0 0) with thickness from 1 to 12 monolayers (ML) is probed by angle-resolved photoemission for the first time. Unlike the related and established systems Ag/Fe(1 0 0) and Ag/V(1 0 0), the QWS energies are with increasing thickness seen to evolve symmetrically about the QWS of 1 ML Ag (−2.5 eV). The QWSs are well described by the phase accumulation model down to lowest thicknesses only if the nearly-free-electron description of the parent Ag band established for Ag/Fe(1 0 0) is replaced by the simplest tight-binding approximation (linear chain approximation) with the band centered around the energy of the QWS of 1 ML Ag. The total phase shift across the bulk band gap is found to be of the order of 2 π, i.e., larger than reported for Ag/Fe(1 0 0).

45.2: Electro-Optics of Liquid Crystals Doped with Ferroelectric Nano-Powder

Suspensions of ferroelectric nanoparticles in a nematic liquid crystal host possess enhanced dielectric anisotropy, and are sensitive to the sign of an applied electric field. Here we also show that the particles contribute to the total achievable phase shift of the composite material. This approach may be used to design new materials for displays.

Destructive interference effect on surface plasmon resonance in terahertz attenuated total reflection

We investigate the surface plasmon resonance at the interface between air and n-type (100) oriented-InAs as an active material with a time-domain attenuated total reflection technique with coherent terahertz pulses. The characteristic spectra of the attenuated total reflectivity and phase shift caused by surface plasmon are observed in the Otto configuration. The surface plasmon resonance frequency and the phase jump strongly depend on the wave vector of the evanescent wave, the refractive index of the prism, and the incident angle of the terahertz pulses and the distance between the prism and active material. These features can no longer be explained with conventional Otto's approximation. We show that the interference effect between the electromagnetic wave reflected at the prism-air interface and that reemitted from excited surface plasmon plays a key role in the surface plasmon resonance.