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Showing papers on "Phase (waves) published in 2001"


Journal Article
TL;DR: In this paper, a grating-based phase-control delay line was proposed for optical coherence domain reflectometry (OCD) and optical coherent tomography (OCT) applications.
Abstract: A rapid-scanning optical delay line that employs phase control has several advantages, including high speed, high duty cycle, phase- and group-delay independence, and group-velocity dispersion compensation, over existing optical delay methods for interferometric optical ranging applications. We discuss the grating-based phase-control delay line and its applications to interferometric optical ranging and measurement techniques such as optical coherence domain reflectometry and optical coherence tomography. The system performs optical ranging over an axial range of 3 mm with a scanning rate of 6 m/s and a repetition rate of 2 kHz. The device is especially well suited for applications such as optical coherence tomography that require high-speed, repetitive, linear delay line scanning with a high duty cycle.

479 citations


Journal ArticleDOI
TL;DR: Spectral interference between a white-light continuum generated in a hollow-fiber and its second harmonic is demonstrated and shot-by-shot changes of the carrier-envelope phase are estimated.
Abstract: We demonstrated single-shot measurements of spectral interference between a white-light continuum generated in a hollow-fiber and its second harmonic. The interference has information on the carrier-envelope phase of an input pulse to the fiber and the time delay of the blue wing of the continuum. By analyzing the observed spectral interference, we estimated shot-by-shot changes of the carrier-envelope phase. This method is useful for determining the carrier-envelope phase changes of a low-repetition-rate, high-intensity laser.

240 citations


Patent
21 Aug 2001
TL;DR: In this paper, a phase tracking loop for an OFDM receiver including a phase rotator receiving an incoming signal, a fast Fourier transform coupled to a phase rotation output, and a pilot phase error metric including a discrete Fourier transformation portion coupled to the phase rotation is presented.
Abstract: A pilot phase tracking loop for an OFDM receiver including a phase rotator receiving an incoming signal, a fast Fourier transform coupled to a phase rotator output, and a pilot phase error metric including a discrete Fourier transform portion coupled to the phase rotator output. The pilot phase error metric determines a phase error estimate associated with a received OFDM symbol, e.g., a data symbol, from the phase rotator output. A loop filter is coupled to the pilot phase error metric output and an oscillator is coupled to the loop filter output. The oscillator output is coupled to the phase rotator to adjust the phase of subsequent OFDM symbols of the incoming signal. Phase noise introduced by a radio portion of the OFDM receiver and OFDM transmitter is reduced by the baseband portion of the OFDM receiver improving OFDM signal tracking under poor SNR conditions.

225 citations


Journal ArticleDOI
TL;DR: It is shown that remarkable spectral changes take place in the neighborhood of phase singularities near the focus of a converging, spatially fully coherent polychromatic wave diffracted at an aperture.
Abstract: It is shown that remarkable spectral changes take place in the neighborhood of phase singularities near the focus of a converging, spatially fully coherent polychromatic wave diffracted at an aperture. In particular, when the spectrum of the wave in the aperture consists of a single line with a narrow Gaussian profile, the spectrum near a phase singularity (i.e., near points of zero intensity of some particular spectral component) changes drastically along a closed loop around the singularity. The spectrum is redshifted at some points, blueshifted at others, and is split into two lines elsewhere.

208 citations


Patent
06 Jun 2001
TL;DR: In this paper, a wavefront coding mask is used to encode phase variations induced by the wavefront and cause the optical transfer function to remain essentially constant within some range away from the in-focus position.
Abstract: The present invention provides extended depth of field or focus to conventional Phase Contrast imaging systems. This is accomplished by including a Wavefront Coding mask in the system to apply phase variations to the wavefront transmitted by the Phase Object being imaged. The phase variations induced by the Wavefront Coding mask code the wavefront and cause the optical transfer function to remain essentially constant within some range away from the in-focus position. This provides a coded image at the detector. Post processing decodes this coded image, resulting in an in-focus image over an increased depth of field.

191 citations


Journal ArticleDOI
TL;DR: To investigate the influence of scattering, pure phase objects consisting of chromium layers containing steps of approximately 100-200-nm height were imaged and the limit of phase imaging through these layers was at approximately 8-9 mean free path lengths thick (single pass).
Abstract: Differential phase-contrast optical coherence tomography allows one to measure the path-length differences of two transversally separated beams in the nanometer range. We calculate these path-length differences from the phase functions of the interferometric signals. Pure phase objects consisting of chromium layers containing steps of approximately 100–200-nm height were imaged. Phase differences can be measured with a precision of ±2°, corresponding to a path-difference resolution of 2–3 nm. To investigate the influence of scattering, we imaged the phase objects through scattering layers with increasing scattering coefficients. The limit of phase imaging through these layers was at approximately 8–9 mean free path lengths thick (single pass).

184 citations


Patent
13 Jul 2001
TL;DR: In this paper, a beam splitting member is manufactured and a thin-film, beam-splitting, metal coating is applied to the member, and the member and coating are baked so as to modify the phase shift produced by the coating to enable the phase quadrature relationship.
Abstract: A retroreflector (32) has three mutually-orthogonal reflective surfaces arranged around an optical axis (12). The reflective surfaces stop short of the optical axis to provide a central region of the retroreflector which transmits incident light (M,N) and a peripheral region of the retroreflector which retroreflects incident light (C,D). When the reflector is used in a Jamin-type interferometer (10) with another reflector (34), this enables the interferometer to be used for measuring displacement between the reflectors. In the interferometer, a projected beam (M) is disposed between a pair of return beams (D,N) and/or one of the return beams (N) is disposed between a pair of the projected beams (C,M). This enables a first contiguous area of a face of a beam splitter (22) to be provided with a phase-shifting coating (28) to produce a phase quadrature relationship between a pair of interferogram beams (G,I). This simplifies the masking required when applying the coating (28). In manufacture of the beam splitting member (22), a thin-film, beam-splitting, metal coating is applied to the member, and the member and coating are baked so as to modify the phase shift produced by the coating to enable the phase quadrature relationship. During baking a beam of light is projected at the coating with an angle of incidence of substantially π/4 radians so that the beam is split into a transmitted component and a reflected component. The intensities or phases of the transmitted and reflected components are monitored during baking, and the baking is terminated when the monitored intensities or phases have a predetermined relationship. This improves the reliability and/or accuracy of the resulting phase shift.

182 citations


Journal ArticleDOI
TL;DR: In this paper, two mutually orthogonal coils fed with phase-quadrature currents comprise the excitation source, which is equal to a mechanically rotating magnetic dipole, and the resulting excitation field rotates elliptically at any position in the near field region.
Abstract: The method is based on two-axis generation of a quasi-static rotating magnetic field and three-axis sensing. Two mutually orthogonal coils fed with phase-quadrature currents comprise the excitation source, which is equal to a mechanically rotating magnetic dipole. The resulting excitation field rotates elliptically at any position in the near-field region. The AC part of the squared field magnitude is a sinusoidal wave at twice the excitation frequency. The following set of parameters uniquely characterize the excitation at the sensor's position: the phase of the squared field waveform, relative to the excitation currents, the minimum field value, the ratio of the field extremes, and the orientation of the excitation field plane. Simple and explicit analytical expressions are given which relate the first three parameters to the azimuth, elevation, and distance from the source to the sensor, respectively. The orientation of the sensor axes, relative to the plane of the excitation, can easily be determined by comparing the phase and amplitude of the measured signals against the phase and amplitude of the excitation field at the sensor's position. Apart from simplicity, the proposed method increases the speed of tracking; a single period of excitation is in principle sufficient to obtain all of the information needed to determine both the sensor's position and orientation. A continuous sinusoidal excitation mode allows an efficient phase-locking and accurate detection of the sensor output. It also improves the electromagnetic compatibility of the method.

168 citations


Patent
11 Dec 2001
TL;DR: In this article, the authors proposed a CMOS-implementable system to measure distance and brightness by illuminating a target with emitted optical energy having a modulated periodic waveform whose high frequency component may be idealized as S 1 = cos(ω·t).
Abstract: A preferably CMOS-implementable system measures distance and/or brightness by illuminating a target with emitted optical energy having a modulated periodic waveform whose high frequency component may be idealized as S 1 =cos(ω·t). A fraction of the emitted optical energy is reflected by a target and detected with at least one in a plurality of semiconductor photodetectors. Photodetector quantum efficiency is modulated to process detected signals to yield data proportional to the distance z separating the target and photodetector. Detection includes measuring phase change between the emitted optical energy and the reflected fraction thereof. Quantum efficiency can be modulated with fixed or variable phase methods and may be enhanced using enhanced photocharge collection, differential modulation, and spatial and temporal multiplexing. System power requirements may be reduced with inductors that resonate with photodetector capacitance at the operating frequency. The system includes on-chip photodetectors, associated electronics, and processing.

168 citations


Journal ArticleDOI
TL;DR: In tapping-mode atomic force microscopy, the phase shift between excitation and response of the cantilever is used as a material-dependent signal complementary to topography, and the phase signal is found to correlate with modulations of the tip oscillation amplitude, induced by topography.

163 citations


Journal ArticleDOI
TL;DR: A prolonged phase shift suggestive of overcompensation was observed in some conditions, which poses a challenge to pure phase correction models.
Abstract: Recent studies of synchronized finger tapping have shown that perceptually subliminal phase shifts in an auditory sequence are rapidly compensated for in the motor activity (B. H. Repp, 2000a). Experiment 1 used a continuation-tapping task to confirm that this compensation is indeed a phase correction, not an adjustment of the central timekeeper period. Experiments 2-5 revealed that this phase correction occurs even when there is no ordinary sensorimotor asynchrony--when the finger taps are in antiphase or arbitrary phase relative to the auditory sequence (Experiments 2 and 3) or when the tap coinciding with the sequence phase shift is withheld (Experiments 4 and 5). The phase correction observed in the latter conditions was instantaneous, which suggests that phase resetting occurs when the motor activity is discontinuous. A prolonged phase shift suggestive of overcompensation was observed in some conditions, which poses a challenge to pure phase correction models.

Journal ArticleDOI
02 Nov 2001-Science
TL;DR: It is shown that the propagation of a femtosecond laser pulse inside a photonic structure can be directly visualized and tracked as it propagates using a time-resolved photon scanning tunneling microscope.
Abstract: We show that the propagation of a femtosecond laser pulse inside a photonic structure can be directly visualized and tracked as it propagates using a time-resolved photon scanning tunneling microscope. From the time-dependent and phase- sensitive measurements, both the group velocity and the phase velocity are unambiguously and simultaneously determined. It is expected that this technique wilt find applications in the investigation of the local dynamic behavior of photonic crystals and integrated optical circuits.

Journal ArticleDOI
TL;DR: Detection of phase synchronization of coupled chaotic oscillators is examined experimentally for the case of a linear laser array by applying a Gaussian filter to the signal obtained from the intensity time series of the individual lasers.
Abstract: Detection of phase synchronization of coupled chaotic oscillators is examined experimentally for the case of a linear laser array. Phase variables are computed by applying a Gaussian filter, peaked at a positive frequency, to the signal obtained from the intensity time series of the individual lasers. Relationships between different frequency components of the oscillator dynamics that are not otherwise apparent are unambiguously detected.

Journal ArticleDOI
TL;DR: In this article, an algorithm for phase demodulation of a single interferogram that may contain closed fringes is presented, which uses the regularized phase-tracker system as a robust phase estimator, together with a new scanning technique that estimates the phase that initially follows the bright zones of the interferograms.
Abstract: An algorithm for phase demodulation of a single interferogram that may contain closed fringes is presented. This algorithm uses the regularized phase-tracker system as a robust phase estimator, together with a new scanning technique that estimates the phase that initially follows the bright zones of the interferogram. The combination of these two elements constitutes a powerful new method, the fringe-follower regularized phase tracker, that makes it possible to correctly demodulate complex, single-image interferograms for which traditional methods fail.

Patent
31 Aug 2001
TL;DR: ImprovedWavefront Coding Optics as mentioned in this paper apply a phase profile to the wavefront of an object to be imaged, retain their insensitivity to focus related aberration, while increasing the heights of the resulting MTFs and reducing the noise in the final images.
Abstract: Improved Wavefront Coding Optics, which apply a phase profile to the wavefront of light from an object to be imaged, retain their insensitivity to focus related aberration, while increasing the heights of the resulting MTFs and reducing the noise in the final images. Such improved Wavefront Coding Optics have the characteristic that the central portion of the applied phase profile is essentially flat (or constant), while a peripheral region of the phase profile around the central region alternately has positive and negative phase regions relative to the central region.

Journal ArticleDOI
TL;DR: An error analysis to investigate how well PSs can be localized found that for both simulation as well as experimental data, there existed a wide range for the choice of origin for which PSs could be identified and a precise determination of origin was not necessary.
Abstract: A phase variable that uniquely represents the time course of the action potential has been used to study the mechanisms of cardiac fibrillation. A spatial phase singularity (PS) occurs during reentrant wave propagation and represents the organizing center of the rotating wave. Here, we present an error analysis to investigate how well PSs can be localized. Computer simulations of rotating spiral waves scaled appropriately for cardiac tissue were studied with various levels of noise added. The accuracy in identifying and localizing singularities depended on three factors: (i) the point chosen as the origin in state space used to calculate the phase variable; (ii) signal to noise ratio; and (iii) discretization (number of levels used to represent data). We found that for both simulation as well as experimental data, there existed a wide range for the choice of origin for which PSs could be identified. Discretization coupled with noise affected this range adversely. However, there always existed a range for choice of the origin that was 20% or more of the action potential amplitude within which the accuracy of localizing PSs was better than 2 mm. Thus, a precise determination of origin was not necessary for accurately identifying PSs. © 2001 Biomedical Engineering Society. PAC01: 8719Nn, 8710+e, 8719Hh

Journal ArticleDOI
TL;DR: A modified form of a Maxwell equation model-based image reconstruction algorithm which directly incorporates log-magnitude and phase of the measured electric field data is introduced which recovers high-quality images without resorting to the use of a priori information on object contrast and/or size as previously required.
Abstract: Reconstructing images of large high-contrast objects with microwave methods has proved difficult. Successful images have generally been obtained by using a priori information to constrain the image reconstruction to recover the correct electromagnetic property distribution. In these situations, the measured electric field phases as a function of receiver position around the periphery of the imaging field-of-view vary rapidly often undergoing changes of greater than /spl pi/ radians especially when the object contrast and illumination frequency increase. Here, the authors introduce a modified form of a Maxwell equation model-based image reconstruction algorithm which directly incorporates log-magnitude and phase of the measured electric field data. By doing so, measured phase variation can be unwrapped and distributed over more than one Rieman sheet in the complex plane. Simulation studies and microwave imaging experiments demonstrate that significant image quality enhancements occur with this approach for large high-contrast objects. Simple strategies for visualizing and unwrapping phase values as a function of the transmitter and receiver positions within our microwave imaging array are described. Metrics of the degree of phase variation expressed in terms of the amount and extent of phase wrapping are defined and found to be figures-of-merit which estimate when it is critical to deploy the new image reconstruction approach. In these cases, the new algorithm recovers high-quality images without resorting to the use of a priori information on object contrast and/or size as previously required.

Patent
25 Jul 2001
TL;DR: By passing the vertical acceleration through a phase adjusting filter and a gain adjusting filter, the phase of vertical acceleration is advanced by 49 degrees so that the phase difference with respect to the actual relative velocity becomes 180 degrees in the neighborhood of the vehicle body resonance point as mentioned in this paper.
Abstract: By passing the vertical acceleration through a phase adjusting filter and a gain adjusting filter, the phase of the vertical acceleration is advanced by 49 degrees so that the phase difference with respect to the actual relative velocity becomes 180 degrees in the neighborhood of the vehicle body resonance point, thereby making the phase of the vertical acceleration, in effect, coincident with the phase of the relative velocity In the neighborhood of the vehicle body resonance point (1 Hz), the gain of the estimated relative velocity takes a small value In frequency regions other than the neighborhood of the vehicle body resonance point, the gain of the estimated relative velocity is increased Consequently, the controlled variable in the neighborhood of the vehicle body resonance point increases, and the controlled variable in higher frequency regions decreases Damping force is adjusted in correspondence to the controlled variable Thus, it is possible to improve ride quality in the neighborhood of the vehicle body resonance point (1 Hz)

Journal ArticleDOI
TL;DR: A new phase-shifting interferometry analysis technique has been developed to overcome the errors introduced by nonlinear, irregular, or unknown phase-step increments and the number of recorded interferograms required for analysis can be reduced.
Abstract: A new phase-shifting interferometry analysis technique has been developed to overcome the errors introduced by nonlinear, irregular, or unknown phase-step increments. In the presence of a spatial carrier frequency, by observation of the phase of the first-order maximum in the Fourier domain, the global phase-step positions can be measured, phase-shifting elements can be calibrated, and the accuracy of phase-shifting analysis can be improved. Furthermore, reliance on the calibration accuracy of transducers used in phase-shifting interferometry can be reduced; and phase-retrieval errors (e.g., fringe print-through) introduced by uncalibrated fluctuations in the phase-shifting phase increments can be alleviated. The method operates deterministically and does not rely on iterative global error minimization. Relative to other techniques, the number of recorded interferograms required for analysis can be reduced.

Journal ArticleDOI
TL;DR: It is shown that this highly sensitive (~5 degrees ) phase technique can complement optical coherence tomography, which measures electric field amplitude, by revealing otherwise undetectable dispersive variations in the sample.
Abstract: We report on phase-dispersion optical tomography, a new imaging technique based on phase measurements using low-coherence interferometry. The technique simultaneously probes the target with fundamental and second-harmonic light and interferometrically measures the relative phase shift of the backscattered light fields. This phase change can arise either from reflection at an interface within a sample or from bulk refraction. We show that this highly sensitive 5 phase technique can complement optical coherence tomography, which measures electric field amplitude, by revealing otherwise undetectable dispersive variations in the sample.

Journal ArticleDOI
TL;DR: In this paper, a surface contouring by phase-shifting digital holography is proposed that provides surface height from a change of reconstructed object phases due to the tilt of object illumination.

Journal ArticleDOI
TL;DR: Phase-shifting interferometry based on the integrating-bucket technique with sinusoidal phase modulation is studied theoretically and demonstrated experimentally to obtain phase maps from double-beam interferometers.
Abstract: Phase-shifting interferometry based on the integrating-bucket technique with sinusoidal phase modulation is studied theoretically and demonstrated experimentally to obtain phase maps from double-beam interferometers. The method uses four frames obtained by integration of the time-varying intensity in an interference pattern during the four quarters of the modulation period. An optimum sinusoidal phase modulation is found to minimize the effect of the additive noise. The absolute accuracy of the phase measurements is discussed. Possible applications of the method are demonstrated with two interference microscopes with which the phase modulation is achieved by sinusoidal oscillation of a mirror attached to a piezoelectric transducer and by sinusoidal birefringence modulation with a photoelastic modulator. In both experimental arrangements, phase images can be produced in real time at a rate of several hertz. Noise measurements are reported and compared with theory.

Journal ArticleDOI
TL;DR: The algorithm of a phase difference between two deformed fringes, the 3-D phase unwrapping method based on the phase difference algorithm, and the computer simulation and experiment results show that this method can efficiently deal with the dynamic3-D shape measurement.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate an all-fibre curvature sensor that uses two-core photonic crystal fiber (PCF) as the sensing element, in which phase difference is a function of curvature in the plane containing the cores.

Proceedings ArticleDOI
28 Sep 2001
TL;DR: In this article, a new method to increase the peak current of high brightness electron beams as those required to drive X-ray SASE FELs, that is based on a rectilinear compressor scheme utilizing the bunching properties of slow waves, is described.
Abstract: We describe here a new method to increase the peak current of high brightness electron beams as those required to drive X-ray SASE FEL’s, that is based on a rectilinear compressor scheme utilizing the bunching properties of slow waves. It is shown that whenever a beam, slower than the synchronous velocity, is injected into a RF wave at the zero acceleration phase and slips back in phase up to the peak acceleration phase, it can be compressed as far as the extraction happens at the synchronous velocity. In fact, the bunch undergoes a quarter of synchrotron oscillation that induces a net compression (i.e. a bunch length reduction) up to a factor of 20 when proper care is taken to preserve the longitudinal emittance. A few examples are presented to demonstrate the potentialities of this method, by which multi-kA beams at very low emittance can be generated at moderate energies (about 100 MeV).

Journal ArticleDOI
TL;DR: Surface contouring by phase-shifting digital holography is proposed that provides surface height from a change of reconstructed phase due to tilting of the object illumination and directly delivers surface shape after phase-unwrapping.
Abstract: Surface contouring by phase-shifting digital holography is proposed that provides surface height from a change of reconstructed phase due to tilting of the object illumination. After phase-unwrapping it directly delivers surface shape. Its sensitivity depends on the tilting angle as well as on the initial incident angle. Although the sensitivity is the same as in the conventional fringe projection, a simpler setup is used without imaging lens and measurement depth is increased due to numerical focusing. We also performed noise suppression by employing nonlinear image-data compression technique that considers amplitude values and attained standard height deviation less than 30 #x03BC;m from a flat surface.

Journal ArticleDOI
TL;DR: Using bosonization techniques, it is shown that strong forward scattering interactions between one-dimensional spinless Luttinger liquids can stabilize a phase where charge-density wave, superconducting, and transverse single particle hopping perturbations are irrelevant.
Abstract: Using bosonization techniques, we show that strong forward scattering interactions between one-dimensional spinless Luttinger liquids (LL) can stabilize a phase where charge-density wave, superconducting, and transverse single particle hopping perturbations are irrelevant. This new phase retains its LL-like properties in the directions of the chains, but with relations between exponents modified by the transverse interactions, whereas it is a perfect insulator in the transverse direction. The mechanism that stabilizes this phase is strong transverse charge-density wave fluctuations at incommensurate wave vector, which frustrates crystal formation by preventing lock-in of the in-chain density waves.

Patent
19 Jun 2001
TL;DR: In this article, a method for estimating the phase and amplitude distortions introduced by radio frequency or microwave power amplifiers even where polar modulation is used is presented. But this method is not suitable for the case of large amplitude amplifiers.
Abstract: The present invention, generally speaking, provides a method of obtaining very accurate estimates of the phase and amplitude distortions introduced by radio frequency or microwave power amplifiers even where polar modulation is used.

Journal ArticleDOI
TL;DR: An equivalent path-independent algorithm for three dimensions is developed that places branch-cut surfaces so as to prevent unwrapping through the phase singularity loops.
Abstract: The classical problem of phase unwrapping in two dimensions, that of how to create a path-independent unwrapped map, is extended to the case of a three-dimensional phase distribution. Whereas in two dimensions the path dependence problem arises from isolated phase singularity points, in three dimensions the phase singularities are shown to form closed loops in space. A closed path that links one such loop will cross a nonzero number of phase discontinuities. In two dimensions, path independence is achieved when branch-cut lines are placed between singular points of opposite sign; an equivalent path-independent algorithm for three dimensions is developed that places branch-cut surfaces so as to prevent unwrapping through the phase singularity loops. The placing of the cuts is determined uniquely by the phase data, which contrasts with the two-dimensional case for which there are many possible ways in which to pair up the singular points. The performance of the new algorithm is demonstrated on three-dimensional phase data from a high-speed phase-shifting speckle pattern interferometer.

Journal ArticleDOI
TL;DR: The three-dimensional shifting selectivity of volume holograms based on random phase encoding with ground glass is analyzed and it is found that the shift selectivity is different for different shifting directions, which include laterally horizontal, laterally vertical, and longitudinal directions.
Abstract: We analyze and demonstrate the three-dimensional shifting selectivity of volume holograms based on random phase encoding with ground glass. Under weak coupling, the diffraction characteristic is caused by the phase difference between the reference and the reading light. We find that the shifting selectivity is different for different shifting directions, which include laterally horizontal, laterally vertical, and longitudinal directions. The shifting selectivity depends on the diameter of the region of illumination on the random phase plate, the thickness of the hologram, and the distance between them.