Showing papers on "Phase (waves) published in 1987"

The Adiabatic Phase and Pancharatnam's Phase for Polarized Light

Abstract: In 1955 Pancharatnam showed that a cyclic change in the state of polarization of light is accompanied by a phase shift determined by the geometry of the cycle as represented on the Poincare sphere. The phase owes its existence to the non-transitivity of Pancharatnam's connection between different states of polarization. Using the algebra of spinors and 2 × 2 Hermitian matrices, the precise relation is established between Pancharatnam's phase and the recently discovered phase change for slowly cycled quantum systems. The polarization phase is an optical analogue of the Aharonov-Bohm effect. For slow changes of polarization, the connection leading to the phase is derived from Maxwell's equations for a twisted dielectric. Pancharatnam's phase is contrasted with the phase change of circularly polarized light whose direction is cycled (e.g. when guided in a coiled optical fibre).

Light Propagation in Singly and Doubly Periodic Planar Waveguides

Abstract: Light propagation in singly and doubly periodic planar waveguides is investigated with respect to future applications in integrated optics. The waveguides used in our experiments reveal, in the vicinity of Bragg reflection, a strong difference between the directions of phase and group velocities, the beam steering. A clear graphical representation of the observable propagation effects is given in wave-vector diagrams, showing the directional dispersion of the elementary waves in periodic structures, the Floquet-Bloch waves. The dispersion phenomena were measured with high accuracy, using selective wave excitation. In conjunction with straight tapered transitions to smooth planar waveguides, the periodic structures show a great variety of strong frequency and direction-dependent effects such as lateral beam shifting and focusing with a frequency-variant focal length. Ray optics of Floquet-Bloch waves is used to describe these phenomena. Complex interference patterns observable in the vicinity of B...

Position detecting apparatus

Abstract: A method of detecting positions with a position detecting apparatus comprising: a position detecting section having a plurality of loop coils arrayed in a side-by-side-fashion in the direction of position detection for transmitting and receiving an electromagnetic wave with a predetermined frequency; and a position pointer (60) having a tuning circuit (61) including a coil (612) and a capacitor (613,615) and adapted to resonate with said electromagnetic wave; wherein the position of the position pointer (60) is determined from signals received by said loop coils from the tuning circuit (61) of the position pointer (60), when the latter is held in the vicinity of the position detecting section (10); and wherein, when said position pointer (60) is pressed onto the input surface of the position detecting section, a switch (611) associated with said tuning circuit (61) is turned on to change the phase of the oscillating current excited in the tuning circuit, and the phase of the electromagnetic wave received by said loop coils is detected, thereby to determine the status of said switch (611).

A pulse ribbon model of monaural phase perception.

Abstract: This article presents two sets of experiments concerning the ability to discriminate changes in the phase spectra of wideband periodic sounds. In the first set, a series of local phase changes is used to modify the envelopes of the waves appearing at the outputs of a range of auditory filters. The size of the local phase change required for discrimination is shown to be strongly dependent on the repetition rate, intensity, and spectral location of the signal. In the second set of experiments, a global phase change is used to produce a progressive phase shift between the outputs of successive auditory filters, without changing the envelopes of the filtered waves. Contrary to what is often assumed, listeners can discriminate between‐channel phase shifts once the total time delay across the channels containing the signal reaches 4–5 ms. In this case, however, the discrimination is largely independent of signal parameters other than bandwidth. A highly simplified model of the cochlea, consisting of an auditory filter bank and units that record the times of the larger peaks in the filter outputs, is developed to explain the two contrasting sets of results.

Phase retrieval and twin-image elimination for in-line Fresnel holograms

Abstract: Fourier phase-retrieval algorithms are modified and applied to in-line holography, where phase is lost during the hologram recording process. Retrieval of phase permits separation of real-object distributions from the twin-image interference that accompanies conventional optical reconstruction. The rate of convergence is enhanced by the availability of a good initial guess based on the digital equivalent of conventional optical reconstruction.

Steady-State Magnetizations in Rapid NMR Imaging Using Small Flip Angles and Short Repetition Intervals

Abstract: The steady-state magnetizations in three versions of rapid NMR imaging using small flip angles and short repetition intervals are studied. It is shown that in the original version, the estimation using (1 - E1) sin ?/(1 - E1 cos ?) contains errors that depend on the increment of the phase rotation angle arising from the phase encoding process. The modified version of rapid imaging, where the phase rotation due to the phase encoding process is compensated for in each time interval, can have sensitivity superior to the original version where the phase rotation is not compensated for. Here, flip angles larger than the Ernst angle must be used. In the third version, the steady-state magnetization is obtained by a rapid imaging sequence in which the phase rotations arising not only from the application of the phase encoding gradient but also from the applications of other gradients are compensated for. Analysis of this version showed a remarkable increase in sensitivity although it required the use of an extremely uniform field. It is estimated that this increase reaches 80 percent with a repetition interval of 10 ms, although a field uniformity less than 1 ?T is necessary.

Digital phase-measuring interferometry with a tunable laser diode.

Abstract: A digital phase-measuring interferometer with a laser-diode source has been developed that is based on a fringe-scanning technique with a stepwise wavelength change by variation of the laser injection current. The phase is changed to produce a relative phase difference between the beams in the two arms of the interferometer. Calibrated phase shifts used for a phase-extraction algorithm are derived from one-dimensional least-squares fits to cosine fringe functions to achieve accurate results. Experimental results are presented.

Submicrosecond electro‐optic switching in the liquid‐crystal smectic A phase: The soft‐mode ferroelectric effect

Abstract: A new liquid‐crystal electro‐optic modulating device similar to the surface‐stabilized ferroelectric liquid‐crystal device is described. It uses the same kind of ferroelectric chiral smectics and the same geometry as that device (thin sample in the ‘‘bookshelf ’’ layer arrangement) but instead of using a tilted smectic phase like the C* phase, it utilizes the above‐lying, nonferroelectric A phase, taking advantage of the electroclinic effect. The achievable optical intensity modulation that can be detected through the full range of the A phase is considerably lower than for the surface‐stabilized device, but the response is much faster. Furthermore, the response is strictly linear with respect to the applied electric field. The device concept is thus appropriate for modulator rather than for display applications. We describe the underlying physics and present measurements of induced tilt angle, of light modulation depth, and of rise time.

A method of range and depth estimation by modal decomposition

Abstract: Normal mode amplitudes are definite functions of depth and have a characteristic phase as a function of source range rs [i.e., exp(−ikirs), where ki is the ith mode wavenumber]. The range and depth of an acoustic source in the ocean can then be determined by decomposing array data and beamforming on the mode amplitudes. In particular, the product of the normal mode amplitudes with the steering vector Ui [where Ui=exp(ikir) ] is maximum for the true source range (r=rs). Similarly, the correlation of the measured (decomposed) mode amplitudes with the theoretically calculated mode amplitudes is maximum at the source depth. Accurate range and depth estimation with this approach, however, requires reliable estimates of the mode amplitudes. In this article, an eigenvector decomposition technique is used to extract the mode amplitudes for data received on a long (1‐km) vertical array. Range and depth are successfully estimated both for simulated data and for data from the 1982 FRAM IV experiment in the Arctic Oc...

Effect of piezoelectric transducer nonlinearity on phase shift interferometry.

Abstract: If the nonlinearity of the motion of a piezoelectric transducer (PZT) can be described as a quadratic function, the integrated intensity of one frame in phase shift interferometry can be calculated using the Fresnel integral. For a PZT with smaller nonlinearity, the rms phase error is almost linearly proportional to the quadratic coefficient. The effects of PZT nonlinearity on the three- and the four-bucket algorithms are compared.

Optical modulation apparatus and measurement method

Abstract: In an optical micromechanical method for changing the phase of guided waves and a measurement method for measuring very small mechanical displacements and/or mechanical forces or pressures, including the pressure of sound waves and ultrasonic waves, and/or accelerations, the distance d between a section (1') of an optical waveguide (1) in an integrated optic or fibre optic circuit and a phase-shifting element (5) separated from said section (1') by a gap (4) is varied by forces (6) or by thermal expansion due to changes in temperature. The phase of the guided wave (3) is thereby modulated, and reciprocally the changes in distance d and hence small mechanical displacements and the forces (6) which produce them are determined from the measured phase changes.

Over 720 Ghz (5. 8nm) frequency tuning by a 1.5 μm DBR laser with phase and Bragg wavelength control regions

Abstract: A 15 μm distributed Bragg reflector (DBR) laser with phase and Bragg wavelength control regions was newly developed Over 720 GHz (58 nm) continuous frequency tuning with 2mW light output were achieved for the first time

A New Phase Correction Method in NMR Imaging Based on Autocorrelation and Histogram Analysis

Abstract: A new statistical approach to phase correction in NMR imaging is proposed. The proposed scheme consists of first-and zero-order phase corrections each by the inverse multiplication of estimated phase error. The first-order error is estimated by the phase of autocorrelation calculated from the complex valued phase distorted image while the zero-order correction factor is extracted from the histogram of phase distribution of the first-order corrected image. Since all the correction procedures are performed on the spatial domain after completion of data acquisition, no prior adjustments or additional measurements are required. The algorithm can be applicable to most of the phase-involved NMR imaging techniques including inversion recovery imaging, quadrature modulated imaging, spectroscopic imaging, and flow imaging, etc. Some experimental results with inversion recovery imaging as well as quadrature spectroscopic imaging are shown to demonstrate the usefulness of the algorithm.

Arrangement for generating natural resonant oscillations of a mechanical oscillating system

Abstract: An arrangement for generating natural resonant oscillations of a mechanical oscillating system includes an electromechanical oscillation exciter which on excitation by an electrical excitation signal generates a drive force setting the oscillating system in mechanical oscillations, an oscillation sensor which is formed as displacement sensor and senses the mechanical oscillations of the oscillating system and converts them to an electrical sensor signal, and an excitation circuit which receives the sensor signal and supplies to the oscillation exciter the electrical excitation signal with the frequency of the sensor signal. The excitation circuit includes a phase control circuit which controls the phase position of the excitation signal in dependence upon the phase position of the sensor signal. A phase shift circuit produces a phase displacement of 90° between the sensor signal and the excitation signal so that the phase condition for the excitation of the mechanical oscillations at the natural resonant frequency of the mechanical oscillating system is fulfilled. This makes it possible to maintain the natural resonant frequency of the mechanical oscillating system with very great accuracy and high stability with time even with oscillating systems of high quality.

Instantaneous and time-averaged energy transfer in acoustic fields

Abstract: The fundamentals of energy transfer in an acoustic field are addressed and it is shown that describing the flux of energy in an acoustic field with the active intensity alone is inaccurate. A single active intensity vector describes only the time‐average energy flux at a point in space, but not where the energy came from nor where it is going. Consequently, the instantaneous intensity must be used to properly describe energy flux as a time‐dependent process. The phenomenon of the acoustic vortex is examined and, from the perspective of active intensity, it is seen to represent a resultant wave rotating around a zero pressure line or point at which the pressure phase is discontinuous. It is shown that this resultant wave travels with a phase speed cp, which is generally different than the plane‐wave phase speed c. The instantaneous intensity, however, shows that energy is flowing through the vortex and not with the resultant waves. Although the complex intensity vector is normally separated into the active...

Optical tracking novelty filter.

Abstract: We demonstrate an optical filter that displays the time-dependent features of a scene. The heart of the device is an interferometer that is sensitive not to the difference between two optical paths lengths but to changes in the path-length difference. The interferometer arms share a phase-conjugating mirror. The phase conjugator ensures that, at steady state, the output of the interferometer is dark. The response of the interferometer to a step differential change in the optical lengths is a decaying exponential having a time constant governed by the time response of the phase conjugator. The interferometer may be used to monitor time- and space-dependent optical phase changes that are due, for example, to transparent fluid motion. With a modified liquid-crystal television used as a spatial light phase modulator in the interferometer, we detect time-dependent features of an image viewed by a video camera.

Comparison Of Phase-Measurement Algorithms

Abstract: Phase-measurement algorithms for calculating the phase of a wavefront from interference fringe data are compared. Experimental data show that different algorithms yield different phase values when using the same intensity data. A computer simulation of errors due to phase-shifter miscalibration and nonlinearity, as well as detector nonlinearity is performed to show that certain algorithms are more sensitive to some errors than others. Dependences of each of these errors is found versus percent of error over a 2ic range of phase values. These results enable the determination of what system errors are present in a phase-measurement interferometer.

Method of moving and orienting a tool along a curved path

Abstract: A method of positioning a tool along a circular arc. The tool is carried by an automaton which is moved through a teaching phase during which it is taught coordinates and wrist orientation angles for three reference points. The method then proceeds into a work phase in which calculations are performed to determine coordinates and wrist angles for a series of work points spaced along the circular arc defined by the three reference points. Thereafter the automaton is direction to position the tool at the calculated coordinates and orientations.

An electrostatic probe technique for RF plasma

Abstract: The use of electrostatic probes in radio frequency (RF) generated plasmas is discussed. A technique is demonstrated in which the RF potential difference between probe and plasma is removed by driving the probe with synchronous RF of suitable phase and amplitude. An application of this technique is the measurement of electrical structure within a 13.56 MHz argon discharge.

Sinusoidal phase modulating interferometer using the integrating-bucket method

Abstract: We describe a sinusoidal phase modulating interferometer in which a CCD image sensor detects four values by integrating the time-varying intensity in an interference pattern for intervals of one-quarter period of the phase modulation. The optimum amplitude and phase of the sinusoidal phase modulation are determined. The measurement error caused by the additive noise and the deviation from the optimum phase modulation is analyzed. The experimental results for surface profiles of magnetic sliders show that the sinusoidal phase modulating interferometer proposed here yields a measurement accuracy of the order of 1 nm.

Lithography mask with a π-phase shifting attenuator

Abstract: The mask includes an attenuator which passes a fraction of the incident electromagnetic radiation and phase shifts the radiation relative to the radiation passing through open features of the mask by approximately an odd multiple of π radians. This phase shifting of light passing through the attenuator by π radians reduces the edge blurring that results from diffraction effects. The present invention steepens the slope of the intensity profile at the edges of features in x-ray lithographic replication relative to the slope obtained with a conventional x-ray mask. The steeper slope is a highly significant advantage because it permits improved linewidth control.

Neuronal coding of linear motion in the vestibular nuclei of the alert cat. I. Response characteristics to vertical otolith stimulation.

Abstract: The aim of the present study was to investigate some aspects of the central processing of otolith information during linear motion. For this purpose, the response characteristics of 69 vestibular nuclei units to sinusoidal otolith stimulation in the vertical Z axis were analysed in the alert cat. Among this population of neurons which responded to a 0.05 Hz, 290 mm translation, 47 units (70%) displayed a firing rate modulation which followed the input frequency (H1 units). The majority of these neurons exhibited an increase in discharge rate during upward displacement, with a response phase close to the motion velocity or slightly leading downward acceleration. The acceleration related units were divided into two groups according to whether they showed clear increases or only a slight change in discharge rate when the stimulus frequency was increased. The former group was characterized by an average -16.3 dB drop in gain (from 43.9 +/- 1.8 dB, S.D. to 27.6 +/- 7 dB, S.D.) within the 0.05 Hz-0.5 Hz frequency range, while the latter group displayed an average -31.2 dB gain attenuation (from 45.1 +/- 1.1 dB, S.D. to 13.9 +/- 0 dB) within the same decade. In contrast to differences in response gain, all the units tested exhibited a relatively stable phase lead of about 20 degrees with respect to downward peak acceleration. Conversely, units whose response was close to motion velocity in the lower frequency range (0.05 Hz-0.10 Hz) displayed a strong phase lead of about 100 degrees when the stimulus frequency was increased (up to 0.50 Hz). These neurons were thus characterized by an acceleration related response in the higher frequency range. At the same time, an average -24.8 dB gain attenuation (from 47.7 +/- 3.4 dB to 22.9 +/- 3.7 dB) was found in the 0.05 Hz-0.5 Hz decade. The remaining 22 neurons (30%) were called H2 units since they displayed a response waveform double that of the input frequency, a response already described during sinusoidal rotation. Unit discharge reached a peak approximately in phase with maximum upward and downward velocity. Asymmetrical change in unit firing rate about the resting discharge level and different dynamic behavior of the upward and downward response components were usually found. These response characteristics suggest that the H2 patterns are centrally constructed and could result from convergence of otolith afferents having opposite polarization vectors.(ABSTRACT TRUNCATED AT 400 WORDS)

Semiclassical treatment of nonadiabatic transitions: Multilevel curve crossing and nonadiabatic tunneling problems

Abstract: Nonadiabatic transition in a multilevel curve crossing system and the one accompanying quantum mechanical tunneling are investigated theoretically and numerically for the one‐dimensional case. The first problem is analyzed using the semiclassical formulation based on the sophisticated two‐state theory for nonadiabatic transition. This formulation is applied to three‐ and four‐level model systems and is found to work surprisingly well even when the avoided crossings (or the transition zones) cannot be regarded to be well separated. The significance of the Stokes phase is noticed. As for the second problem, analysis is made not only for the simple tunneling but also for the elastic scattering accompanied by the nonadiabatic tunneling. A combination of the following two formulas is recommended for practical use: (1) the formula essentially based on the one proposed by Coveney et al., and (2) the formula of Ovchinnikova with additional Stokes phase and tunneling corrections.

High resolution imaging doppler interferometer

Abstract: A system for simultaneously locating a plurality of targets and distinguishing the targets from noise which utilizes phase detector techniques to generate complex voltage signals and obtain phase information. Spectral analysis is performed on the complex voltage temporal functions to generate doppler frequency functions. Both spectral phase functions and spectral amplitude functions are generated from the doppler frequency functions. Spectral phase functions are analyzed using interferometry techniques to determine if a potential target has a common locational source from returns of a plurality of sensors. A zenith angle is also generated using interferometry techniques to provide locational information of the multiple targets. Range gating and two frequency range detection methods provide high resolution range information as to the location of the targets. High resolution range information and two dimensional zenith angle information are used to provide an image of the targets. The present invention uses a two-frequency pulse which can be generated simultaneously or sequenced within a pulse in a manner which is phase coherent. The two-frequency pulse eliminates problems associated with range aliasing, zenith angle aliasing, scattering point analysis and allows for range location with high resolution. An error correction factor is also generated which eliminates spectral smearing.

A new method for synthesis of low-peak-factor signals

Abstract: For a specified power spectrum, the minimum-to-maximum amplitude range of a periodic signal depends on the phase angles of the harmonics. A low value of this range, which as a fraction of the root-mean-square value is usually called the peak factor, is often desirable. A new phase angle adjusting method is proposed producing lower peak factors than the conventional method.

VO2 kinetics in subjects differing in aerobic capacity: investigation by spectral analysis.

Abstract: The power-V O 2 transfer functions of 38 subjects differing in aerobic capacity have been determined on the basis of breath-by-breath total oxygen uptake (V O 2.1) measurements during light cycle ergometer exercise (lactic acid concentrations below 2 mmol · l−1). At constant pedalling frequency (1 Hz) pseudorandom binary sequences (PRBS) of workload were used as the testing signal. TheV O 2.1 response was analysed by autocorrelating the ergometer power input and crosscorrelating the power input andV O 2.1 output. From the spectra of these functions the amplitude ratios and phase relationships were computed for the first six harmonics of the PRBS fundamental (14 mrad · s−1). We found that differences in aerobic capacity are associated with significant differences in the amplitude plots of theV O 2 transfer function.

Measurement of optical phase with subpicosecond resolution by time-domain interferometry.

Abstract: A new and extremely general interferometric technique has been experimentally demonstrated that permits the direct measurement of optical phase on a subpicosecond time scale. The intensity is characterized by cross correlation, and thus the optical field is completely determined.