Showing papers on "Phase (waves) published in 1997"
TL;DR: The grating-based phase-control delay line is discussed, which 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.
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 6m/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.
585 citations
TL;DR: In this article, the authors extend the notion of phase locking to the case of chaotic oscillators and investigate the phase dynamics of a single self-sustanined chaotic oscillator subjected to external force.
518 citations
TL;DR: In this article, the phase evolution within a resonance of a quantum dot can be explained by a model that ignores the interactions between the electrons within the dot, and the phase behaviour is identical for all resonances, and there is a sharp jump of the phase between successive resonance peaks.
Abstract: The transport properties of electronic devices are usually characterized on the basis of conductance measurements. Such measurements are adequate for devices in which transport occurs incoherently, but for very small devices—such as quantum dots1,2—the wave nature of the electrons plays an important role3. Because the phase of an electron's wavefunction changes as it passes through such a device, phase measurements are required to characterize the transport properties fully. Here we report the results of a double-slit interference experiment which permits the measurement of the phase-shift of an electron traversing a quantum dot. This is accomplished by inserting the quantum dot into one arm of an interferometer, thereby introducing a measurable phase shift between the arms. We find that the phase evolution within a resonance of the quantum dot can be accounted for qualitatively by a model that ignores the interactions between the electrons within the dot. Although these electrons must interact strongly, such interactions apparently have no observable effect on the phase. On the other hand, we also find that the phase behaviour is identical for all resonances, and that there is a sharp jump of the phase between successive resonance peaks. Adequate explanation of these features may require a model that includes interactions between electrons.
424 citations
TL;DR: Preliminary results of non-invasive FDPM measurements obtained from normal and tumour-containing human breast tissue show that physiological changes caused by the presence of small (about 1 cm diameter) palpable lesions can be detected using a handheld FDPM probe.
Abstract: A multiwavelength, high bandwidth (1 GHz) frequency-domain photon migration (FDPM) instrument has been developed for quantitative, non-invasive measurements of tissue optical and physiological properties. The instrument produces 300 kHz to 1 GHz photon density waves (PDWs) in optically turbid media using a network analyser, an avalanche photodiode detector and four amplitude-modulated diode lasers (674 nm, 811 nm, 849 nm, and 956 nm). The frequency of PDW phase and amplitude is measured and compared to analytically derived model functions in order to calculate absorption, mu a, and reduced scattering, mu s, parameters. The wavelength-dependence of absorption is used to determine tissue haemoglobin concentration (total, oxy- and deoxy- forms), oxygen saturation and water concentration. We present preliminary results of non-invasive FDPM measurements obtained from normal and tumour-containing human breast tissue. Our data clearly demonstrate that physiological changes caused by the presence of small (about 1 cm diameter) palpable lesions can be detected using a handheld FDPM probe.
315 citations
TL;DR: The recently proposed technique of temporal phase unwrapping has been used to analyze the phase maps from a projected-fringe phase-shifting surface profilometer, showing the error in height is shown to decrease inversely with the number of phase maps used.
Abstract: The recently proposed technique of temporal phase unwrapping has been used to analyze the phase maps from a projected-fringe phase-shifting surface profilometer. A sequence of maps is acquired while the fringe pitch is changed; the phase at each pixel is then unwrapped over time independently of the other pixels in the image to provide an absolute measure of surface height. The main advantage is that objects containing height discontinuities are profiled as easily as smooth ones. This contrasts with the conventional spatial phase-unwrapping approach for which the phase jump across a height discontinuity is indeterminate to an integral multiple of 2π. The error in height is shown to decrease inversely with the number of phase maps used.
311 citations
01 Jan 1997
TL;DR: It is shown that points of symmetry and asymmetry give rise to easily recognized patterns of local phase, which can be used to construct a contrast invariant measure of symmetry that does not require any prior recognition or segmentation of objects.
Abstract: Symmetry is an important mechanism by which we identify the structure of objects. Man-made objects, plants and animals are usually highly recognizable from the symmetry, or partial symmetries that they often exhibit. Two difficulties found in most symmetry detection algorithms are firstly, that they usually require objects to be segmented prior to any symmetry analysis, and secondly, that they do not provide any absolute measure of the degree of symmetry at any point in an image. This paper presents a new measure of symmetry that is based on the analysis of local frequency information. It is shown that points of symmetry and asymmetry give rise to easily recognized patterns of local phase. This phase information can be used to construct a contrast invariant measure of symmetry that does not require any prior recognition or segmentation of objects.
290 citations
TL;DR: Reflections that are due to random surface roughness in periodic structures such as dielectric rings and disks inherently phase match forward- and backward-propagating modes and may impair the performance of traveling-wave resonators.
Abstract: Reflections that are due to random surface roughness in periodic structures such as dielectric rings and disks inherently phase match forward- and backward-propagating modes. Small reflections are thus considerably enhanced and may impair the performance of traveling-wave resonators. In addition, such contradirectional coupling leads to a splitting of the resonant peak. These effects are studied analytically.
264 citations
TL;DR: In this article, a method for digital phase imaging is proposed, which requires the measurement of intensity in two adjacent planes orthogonal to the optical axis and the phase is subsequently recovered by a Fast Fourier Transform of the Transport of Intensity Equation.
237 citations
TL;DR: In this paper, a 6-DOF magnetically levitated joystick was used to emulate stiff walls and stick-slip friction with a 6DOF PD controller, and it was shown that the PD controller severely limits achievable wall damping and stiffness.
Abstract: This technical brief addresses issues of mechanical emulation of stiff walls and stick-slip friction with a 6-DOF magnetically levitated joystick. In the case of stiff wall emulation, it is shown that the PD control implementation commonly used severely limits achievable wall damping and stiffness. It is also shown that the perceived surface stiffness can be increased without loss ofstability by applying a braking force pulse when crossing into the wall. For stick-slip friction, Karnopp's model was implemented using a PD controller within the stick friction threshold. Even though the PD controller allows some motion during the stick phase, the haptic feedback provided is remarkably similar to stick-slip friction.
215 citations
TL;DR: A two-dimensional regularized phase-tracking technique that is capable of demodulating a single fringe pattern with either open or closed fringes and gives the detected phase continuously so that no further unwrapping is needed over the detectedphase.
Abstract: We present a two-dimensional regularized phase-tracking technique that is capable of demodulating a single fringe pattern with either open or closed fringes. The proposed regularized phase-tracking system gives the detected phase continuously so that no further unwrapping is needed over the detected phase.
207 citations
Patent•
01 Oct 1997TL;DR: In this paper, a method for amplitude modulating signals, and a circuit that operates in accordance with the method is presented, which includes a first step of applying a modulating low frequency signal having a time-varying voltage to a tunable resonator.
Abstract: A method for amplitude modulating signals, and a circuit that operates in accordance with the method. The method includes a first step of applying a modulating low frequency signal having a time-varying voltage to a tunable resonator. The tunable resonator exhibits parallel and series resonances at frequencies which shift as a function of the time-varying voltage. A second step includes applying an RF carrier signal having a frequency that is between the parallel resonant frequency and the series resonant frequency to the tunable resonator. In response thereto, the tunable resonator causes the RF carrier signal to be attenuated as a function of the time-varying voltage of the modulating low frequency signal. Also provided is a method for phase modulating signals, and a circuit that operates in accordance therewith. A first step includes applying a modulating low frequency signal having a time-varying voltage to a tunable resonator. The tunable resonator yields a maximum phase shift at one of a parallel resonant frequency and a series resonant frequency in response to the modulating low frequency signal. The amount of phase shift yielded is a function of a variation of the modulating low frequency signal voltage. A further step includes applying an RF carrier signal having a frequency that is substantially equal to the one of a parallel resonant frequency and a series resonant frequency. In response thereto, the tunable resonator phase shifts the RF carrier signal by the amount of phase shift yielded by the tunable resonator.
TL;DR: In this article, an errorexpansion method was proposed to construct phase-shifting algorithms that can compensate for nonlinear and spatially nonuniform phase shifts, and three new algorithms (six-sample, eight-sample and nine-sample) were presented.
Abstract: In phase-shifting interferometry spatial nonuniformity of the phase shift gives a significant error in the evaluated phase when the phase shift is nonlinear. However, current error-compensating algorithms can counteract the spatial nonuniformity only in linear miscalibrations of the phase shift. We describe an error-expansion method to construct phase-shifting algorithms that can compensate for nonlinear and spatially nonuniform phase shifts. The condition for eliminating the effect of nonlinear and spatially nonuniform phase shifts is given as a set of linear equations of the sampling amplitudes. As examples, three new algorithms (six-sample, eight-sample, and nine-sample algorithms) are given to show the method of compensation for a quadratic and spatially nonuniform phase shift.
TL;DR: Aperiodic quasi-phase-matching gratings impart a frequency-dependent phase shift on the second-harmonic pulse relative to the fundamental pulse and can be engineered to correct for arbitrary phase distortions.
Abstract: We propose a simple means for compressing optical pulses with second-harmonic generation. Aperiodic quasi-phase-matching gratings impart a frequency-dependent phase shift on the second-harmonic pulse relative to the fundamental pulse and can be engineered to correct for arbitrary phase distortions. The mechanism is discussed, and a detailed analysis of the compression of quadratic phase (linear frequency) chirped pulses is presented.
TL;DR: Temporal phase unwrapping is a method of analyzing fringe patterns in which the fringe phase at each pixel is measured and unwrapped as a function of time t as mentioned in this paper, and two methods for improving temporal phase unwrap are proposed.
Abstract: Temporal phase unwrapping is a method of analyzing fringe patterns in which the fringe phase at each pixel is measured and unwrapped as a function of time t. We propose two methods for improving th ...
Patent•
16 Dec 1997
TL;DR: The P-APSK constellation (70, 70') has an even number of phase point rings (74, 76) and equal numbers of phase points (72) in pairs of the rings as discussed by the authors.
Abstract: A digital communication system (20) communicates using a polar amplitude phase shift keyed (P-APSK) phase point constellation (70, 70'). Pragmatic encoding and puncturing is accommodated. The pragmatic encoding uses the P-APSK constellation (70, 70') to simultaneously communicate both encoded and uncoded information bits. The P-APSK constellation (70, 70') has an even number of phase point rings (74, 76) and equal numbers of phase points (72) in pairs of the rings (74, 76). Encoded bits specify secondary modulation and uncoded bits specify primary modulation. The constellation (70, 70') is configured so that secondary modulation sub-constellations (78) include four phase points (72) arranged so that two of the four phase points (72) exhibit two phase angles at one magnitude and the other two of the four phase points exhibit phase angles that are at another magnitude. The difference between the phase angles at different magnitudes within a secondary sub-constellation (78) is constant.
TL;DR: Modifications of the RARE sequence are discussed, and an approach that eliminates the artifact producing signals from the very first echo is presented that is applied to diffusion imaging of the human brain in normal volunteers and one patient.
Abstract: Although RARE and GRASE can produce single-shot images of excellent quality, their utility has been restricted because preparation of the magnetization with interesting contrast before imaging can cause severe artifacts. These artifacts relate to the strong sensitivity of multiple spin echo sequences to the phase of the prepared magnetization. Modifications of the RARE sequence to eliminate these artifacts are discussed, and an approach that eliminates the artifact producing signals from the very first echo is presented. The approach is applied to diffusion imaging of the human brain in normal volunteers and one patient.
TL;DR: This work presents what is believed to be the first experimental demonstration of guided-wave phase-matched frequency mixing and harmonic conversion in gases using an ultrafast Ti:sapphire amplifier system using 2?
Abstract: We present what is believed to be the first experimental demonstration of guided-wave phase-matched frequency mixing and harmonic conversion in gases. Broad-bandwidth ultrafast pulses, tunable around 270 nm, were generated from an ultrafast Ti:sapphire amplifier system using 2ω+2ω-ω parametric wave mixing in a capillary waveguide. We achieved nonresonant phase matching by coupling both the fundamental and the second-harmonic light into the lowest-order mode. The output 3ω pulses have an energy of >4 µJ at a 1–kHz repetition rate. Simple extensions of this method can generate higher-energy 10–20-fs pulses tunable throughout the vacuum ultraviolet.
TL;DR: In this paper, the authors analyzed theoretically an experiment in which a trapped Bose-Einstein condensate is cut in half, and the parts are subsequently allowed to interfere if the delay between cutting and atom detection is small.
Abstract: We analyze theoretically an experiment in which a trapped Bose-Einstein condensate is cut in half, and the parts are subsequently allowed to interfere If the delay between cutting and atom detection is small, the interference pattern of the two halves of the condensate is the same in every experiment However, for longer delays the spatial phase of the interference shows random fluctuations from one experiment to the other This phase diffusion is characterized quantitatively
TL;DR: The characteristic polynomials associated with the algorithms used in digital phase detection are used to investigate the effects of additive noise on phase measurements and it is shown that a loss factor eta can be associated with any algorithm.
Abstract: The characteristic polynomials associated with the algorithms used in digital phase
detection are used to investigate the effects of additive noise on phase
measurements. First, it is shown that a loss factor η can be associated with
any algorithm. This parameter describes the influence of the algorithm on the global
signal-to-noise ratio (SNR). Second, the variance of the phase error is shown to
depend mainly on the global SNR. The amplitude of a modulation of this variance at
twice the signal frequency depends on a single parameter β. The material
presented here extends previously published results, and as many as 19 algorithms are
analyzed.
TL;DR: This work investigates by numerical, analytical and experimental means the reliability of two recently proposed algorithms for unwrapping the resulting phase histories and proposes a new method in which the spatial frequency is changed exponentially with time.
Abstract: Projected fringes can be used to measure surface profiles unambiguously, even in the presence of surface discontinuities, if the fringe pitch is changed over time. We investigate by numerical, analytical and experimental means the reliability of two recently proposed algorithms for unwrapping the resulting phase histories. The first, which unwraps through a sequence of phase maps produced with a linear change in spatial frequency with time, is found to be superior to the second, which uses only the first and last maps in the sequence. A new method is proposed in which the spatial frequency is changed exponentially with time. It is shown to be significantly more robust than either of the other algorithms under most conditions. The computation time required to unwrap through a given phase range is proportional to and therefore also results in a reduction in computational effort by a factor compared with the linear algorithm.
TL;DR: In this paper, a three-dimensional spiraling collision of interacting two-dimensional spatial solitons is observed, where the collision provides the soliton with angular momentum which is manifested in a centrifugal repulsion force.
Abstract: We report the observation of three-dimensional spiraling collision of interacting two-dimensional spatial solitons. The solitons are photorefractive screening solitons and are phase incoherent to each other at all times. The collision provides the solitons with angular momentum which is manifested in a centrifugal repulsion force. When it is balanced by attraction, the solitons spiral about each other in a DNA-like structure.
TL;DR: In this paper, two types of interference were observed using two-photon spontaneous parametric radiation from two nonlinear interaction regions: Young and Mach-Zehnder interferometers.
Abstract: Two types of interference were observed using two-photon spontaneous parametric radiation from two nonlinear interaction regions. Two experimental setups analogous to the Young and Mach-Zehnder interferometers were used. An interesting feature of the two-photon Young interference is the opposite conditions for its observation by two different methods: by measuring intensity of light at a single frequency and by measuring correlation of intensities at two conjugated frequencies (method of coincidences). Two-photon Mach-Zehnder interference resembles the Ramsey method of separated fields, which is used in beam spectroscopy. A simple macroscopic quantum model agrees well with the experimental results and enables their interpretation in terms of ``biphotons'' carrying information about the pump phase.
Patent•
31 Jul 1997
TL;DR: An optical device includes a plurality of picture elements the phase and/or amplitude transmission of which vary in the lateral direction of the optical device reducing the level of diffraction caused by the device.
Abstract: An optical device includes a plurality of picture elements the phase and/or amplitude transmission of which vary in the lateral direction of the optical device reducing the level of diffraction caused by the device.
TL;DR: A method that uses two groups of fringe patterns on one grating for phase-measuring profilometry with a proper phase shift is presented, which is more tolerable to height discontinuity.
Abstract: We present a method that uses two groups of fringe patterns on one grating for phase-measuring profilometry. A two-frequency grating is projected onto the object. The high frequency is N (N = 3, 4, 5, :...) times greater than the low frequency. Using a proper phase shift, we calculated the wrapped phases of the two frequencies. When the linearity of the two phases are considered, an accurate phase of the high frequency can be unwrapped. Because the low frequency is N times more insensitive to height discontinuity, the system is more tolerable to height discontinuity.
TL;DR: In this article, it was shown that the evolution of the average intensity of cw beams in a quasi-phase-matched quadratic medium is strongly influenced by induced Kerr effects, such as self-and cross-phase modulation.
Abstract: We show that the evolution of the average intensity of cw beams in a quasi-phase-matched quadratic (or ${\ensuremath{\chi}}^{(2)}$) medium is strongly influenced by induced Kerr effects, such as self- and cross-phase modulation. We prove the existence of rapidly oscillating solitary waves (a spatial analog of the guided-center soliton) supported by the quadratic and induced cubic nonlinearities.
TL;DR: In this article, the tuning fork shear-force feedback system was used in a near-field scanning optical microscope to measure amplitude and phase of tuning fork oscillation as a function of driving frequency and tip-sample distance.
Abstract: The dynamics of a tuning fork shear-force feedback system, used in a near-field scanning optical microscope, have been investigated, Experiments, measuring amplitude and phase of the tuning fork oscillation as a function of driving frequency and tip-sample distance, reveal that the resonance frequency of the tuning fork changes upon approaching the sample. Either amplitude or phase of the tuning fork can be used as distance control parameter in the feedback system. Using amplitude a second-order behavior is observed while with phase only a first-order behavior is observed, and confirmed by numerical calculations. This first-order behavior results in an improved stability of our feedback system, A sample consisting of DNA strands on mica was imaged which showed a height of the DNA of 1.4 nm
TL;DR: In this article, a new formula for calculating the phase in interferometric measurements by the phase-stepping method was proposed, which utilizes equal phase steps with an arbitrary value.
TL;DR: A modified model in which mu(max) was replaced with a temperature function, and w0 replaced G0, was used to predict the effect of temperature on the growth of L. monocytogenes, and raises questions concerning the current definition of the lag phase.
TL;DR: In this article, real-time linear spectral interference measurements of ultrashort pulses are shown experimentally, which involves measurements of the two-dimensional interference pattern of the spectral interference between a reference and a signal pulse propagating at an angle with respect to each other.
Abstract: Real-time linear spectral interference measurements of ultrashort pulses are shown experimentally The technique involves measurements of the two-dimensional interference pattern of the spectral interference between a reference and a signal pulse propagating at an angle with respect to each other No postprocessing is needed to extract the spectral phase difference between the two pulses Quadratic spectral phase distortions as well as spectral phase discontinuities are measured The method is applicable to single-shot measurements of ultraweak pulses and is useful for identification of the critical adjustments of ultrashort pulse shapers and compressors
TL;DR: In this article, the authors demonstrate that two harmonic sources generated independently in a xenon gas jet using the same Nd:YAG laser are locked in phase, by separating a laser beam into two parallel beams focused at different locations under the nozzle of a gas jet.
Abstract: We demonstrate that two harmonic sources generated independently in a xenon gas jet using the same picosecond Nd:YAG laser are locked in phase. The experiment is performed by separating a laser beam into two parallel beams focused at different locations under the nozzle of a gas jet, and therefore producing two independent sources of harmonic radiation, and studying the pattern obtained in the far field when the radiations from these sources interfere. A high and robust fringe visibility is obtained.