Local Phase Shifts Research Articles

Single-unit metalens integrated micro light-emitting diodes

Metalenses, characterized by their discontinuous local phase shifts, are optically analogous to macroscopic curved lenses but are flat and scaled down to micrometer dimensions. Their compactness and compatibility with semiconductor manufacturing processes facilitate monolithic integration into existing optical devices. Here, we report on the integration of metalenses with micro light-emitting diodes (μ-LEDs), resulting in enhanced extraction efficiency and directionality. The metalenses were composed of identical nanohole units, each 150 nm in diameter, strategically arranged to induce desired local phase shifts at specific coordinates by varying the density of these units. Both simulated and experimental results demonstrated that these easy-configuration metalenses effectively focused a plane wave at a predetermined spot and collimated a diverging light source at the focal spot, exemplifying optical reciprocity. When integrated with ultraviolet (λ = 390 nm) 60 μm-sized μ-LEDs, the metalenses significantly improved device performance, exhibiting a 338% enhancement in peak intensity and a ±8° reduction in beam divergence compared to an unpatterned μ-LED. We believe that metalens-integrated μ-LEDs with high brightness, directionality, and resolution are optimally suited for near-eye applications, including virtual reality and augmented reality displays.

Windowed Radon Transform for Robust Speed-of-Sound Imaging With Pulse-Echo Ultrasound.

In recent years, methods estimating the spatial distribution of tissue speed of sound with pulse-echo ultrasound are gaining considerable traction. They can address limitations of B-mode imaging, for instance in diagnosing fatty liver diseases. Current state-of-the-art methods relate the tissue speed of sound to local echo shifts computed between images that are beamformed using restricted transmit and receive apertures. However, the aperture limitation affects the robustness of phase-shift estimations and, consequently, the accuracy of reconstructed speed-of-sound maps. Here, we propose a method based on the Radon transform of image patches able to estimate local phase shifts from full-aperture images. We validate our technique on simulated, phantom and in-vivo data acquired on a liver and compare it with a state-of-the-art method. We show that the proposed method enhances the stability to changes of beamforming speed of sound and to a reduction of the number of insonifications. In particular, the deployment of pulse-echo speed-of-sound estimation methods onto portable ultrasound devices can be eased by the reduction of the number of insonifications allowed by the proposed method.

Optimal function estimation with photonic quantum sensor networks

The problem of optimally measuring an analytic function of unknown local parameters each linearly coupled to a qubit sensor is well understood, with applications ranging from field interpolation to noise characterization. Here we resolve a number of open questions that arise when extending this framework to Mach-Zehnder interferometers and quadrature displacement sensing. In particular, we derive lower bounds on the achievable mean square error in estimating a linear function of either local phase shifts or quadrature displacements. In the case of local phase shifts, these results prove, and somewhat generalize, a conjecture by Proctor []. For quadrature displacements, we extend proofs of lower bounds to the case of arbitrary linear functions. We provide optimal protocols achieving these bounds up to small (multiplicative) constants and describe an algebraic approach to deriving new optimal protocols, possibly subject to additional constraints. Using this approach, we prove necessary conditions for the amount of entanglement needed for any optimal protocol for both local phase and displacement sensing. Published by the American Physical Society 2024

First-in-human diagnostic study of hepatic steatosis with computed ultrasound tomography in echo mode

BackgroundNon-alcoholic fatty liver disease is rapidly emerging as the leading global cause of chronic liver disease. Efficient disease management requires low-cost, non-invasive techniques for diagnosing hepatic steatosis accurately. Here, we propose quantifying liver speed of sound (SoS) with computed ultrasound tomography in echo mode (CUTE), a recently developed ultrasound imaging modality adapted to clinical pulse-echo systems. CUTE reconstructs the spatial distribution of SoS by measuring local echo phase shifts when probing tissue at varying steering angles in transmission and reception.MethodsIn this first-in-human phase II diagnostic study, we evaluated the liver of 22 healthy volunteers and 22 steatotic patients. We used conventional B-mode ultrasound images and controlled attenuation parameter (CAP) to diagnose the presence (CAP≥ 280 dB/m) or absence (CAP < 248 dB/m) of steatosis in the liver. A fully integrated convex-probe CUTE implementation was developed on the ultrasound system to estimate liver SoS. We investigated its diagnostic value via the receiver operating characteristic (ROC) analysis and correlation to CAP measurements.ResultsWe show that liver CUTE-SoS estimates correlate strongly (r = −0.84, p = 8.27 × 10−13) with CAP values and have 90.9% (95% confidence interval: 84–100%) sensitivity and 95.5% (81–100%) specificity for differentiating between normal and steatotic livers (area under the ROC curve: 0.93–1.0).ConclusionsOur results demonstrate that liver CUTE-SoS is a promising quantitative biomarker for diagnosing liver steatosis. This is a necessary first step towards establishing CUTE as a new quantitative add-on to diagnostic ultrasound that can potentially be as versatile as conventional ultrasound imaging.

Realizing spin squeezing with Rydberg interactions in an optical clock.

Neutral-atom arrays trapped in optical potentials are a powerful platform for studying quantum physics, combining precise single-particle control and detection with a range of tunable entangling interactions1-3. For example, these capabilities have been leveraged for state-of-the-art frequency metrology4,5 as well as microscopic studies of entangled many-particle states6-11. Here we combine these applications to realize spin squeezing-a widely studied operation for producing metrologically useful entanglement-in an optical atomic clock based on a programmable array of interacting optical qubits. In this demonstration of Rydberg-mediated squeezing with a neutral-atom optical clock, we generate states that have almost four decibels of metrological gain. In addition, we perform a synchronous frequency comparison between independent squeezed states and observe a fractional-frequency stability of 1.087(1) × 10-15 at one-second averaging time, which is 1.94(1) decibels below the standard quantum limit and reaches a fractional precision at the 10-17 level during a half-hour measurement. We further leverage the programmable control afforded by optical tweezer arrays to apply local phase shifts to explore spin squeezing in measurements that operate beyond the relative coherence time with the optical local oscillator. The realization of this spin-squeezing protocol in a programmable atom-array clock will enable a wide range of quantum-information-inspired techniques for optimal phase estimation and Heisenberg-limited optical atomic clocks12-16.

Transmission line fault classification based on spatiotemporal characteristic analysis with global and local discriminant analysis

To ensure the reliability of power supply, ultra-fast and reliable fault classification of the transmission line is the critical stage of the wide-area transmission network protection. As the distributed generation (DG) current injection to the transmission line, the amplitude characteristic of the break current protection reduces and the system reliability decreases. With the wide-area measurement generated to the power system, an online fault classification method with the global and local discriminant analysis (GLDA) is proposed to enhance the phase characteristic and decrease calculation load. In the single line to ground (SLG) fault process, the local current phase shift is analyzed to enhance the spatiotemporal characteristic. To fully measure the ordering degree of the spatiotemporal characteristic, the axiomatic definition for the characteristic entropy (CE) of the grid impedance in the individual bus in the wide-area transmission network is proposed according to the characteristic distribution. Based on the current spatiotemporal characteristic analysis, a multi-priority GLDA classifies the fault phase in a coordinating way using with the phasor measurement unit (PMU). The multi-priority GLDA-CE fault classification method reduces the computational load, ensures resilience against measurement noise and the transition resistance effect. Compared with the statistical entropy and neural network method, the classification accuracy and response speed of the GLDA-CE fault classification method are validated in the IEEE 39-bus system with 10 PMUs. Compared with the conventional statistical entropy and neural network methods, the GLDA-CE method is able to classify 226 entire power outages and 600 single phase outages within 1.621 s.

Linear stability of elastic 2-line solitons for the KP-II equation

The KP-II equation was derived by Kadomtsev and Petviashvili to explain stability of line solitary waves of shallow water. Using the Darboux transformations, we study linear stability of 2 2 -line solitons whose line solitons interact elastically each other. Time evolution of resonant continuous eigenfunctions is described by a damped wave equation in the transverse variable which is supposed to be a linear approximation of the local phase shifts of modulating line solitons.

Soliton versus the gas: Fredholm determinants, analysis, and the rapid oscillations behind the kinetic equation

AbstractWe analyse the case of a dense modified Korteweg–de Vries (mKdV) soliton gas and its large time behaviour in the presence of a single trial soliton. We show that the solution can be expressed in terms of Fredholm determinants as well as in terms of a Riemann–Hilbert problem. We then show that the solution can be decomposed as the sum of the background gas solution (a modulated elliptic wave), plus a soliton solution: the individual expressions are however quite convoluted due to the interaction dynamics. Additionally, we are able to derive the local phase shift of the gas after the passage of the soliton, and we can trace the location of the soliton peak as the dynamics evolves. Finally, we show that the soliton peak, while interacting with the soliton gas, has an oscillatory velocity whose leading order average value satisfies the kinetic velocity equation analogous to the one posited by V. Zakharov and G. El.

Metamaterial lenses for monostatic and bistatic 77 GHz radar systems

AbstractMetamaterial lenses are appealing thin alternatives to conventional dielectric lenses. In this contribution we describe their design and application in two exemplary 77 GHz automotive radar sensors operating in monostatic and bistatic modes. The frontends are built around commercially available MMICs and small feed antennas are used in coordination with the six-layer printed circuit board-based realizations of metamaterial lenses. The design follows the principles of dielectric lenses, while the required local phase shift is obtained from a set of metasurface bandpasses. Their design uses a novel interpolation procedure to extract layout parameters for a given phase shift. Despite the small structural sizes due to the high frequency, the fabricated frequency-selective surfaces show very good performance in the required frequency range. Verification measurements were conducted on single bandpasses as well as on metamaterial lenses mounted on the radar frontend. The results agree very well with the simulation and confirm the applicability of thin lenses operating at mm-wave frequencies for automotive radar applications.

Two-beam interferometry with a definitive phase-shift sign

Subject of study. The shift direction of interference fringes depending on the sign of the local phase shift introduced to one of the interfering waves was investigated in terms of two-beam interferometry. Aim of study. This study aimed to validate the fact that two-beam interferometry based on a single interferogram enables definitive determination of the phase-shift sign using the shift direction of the interference fringe. Method. Positions of the interference fringes and their shifts were calculated considering the phase distribution of interfering waves in the observation plane. The Mach–Zehnder interferometer was used to experimentally confirm the obtained theoretical results. Two closely adjacent substrates were used as objects. A subwavelength layer of a standard material was deposited on a part of the surface of one substrate, and a layer of metamaterial was deposited on the part of the second substrate. Main results. Expressions determining the direction and amplitude of the shift of interference fringes depending on the sign and amplitude of the local phase shift in one of the two interfering waves with a plane or spherical front were obtained. Strict rules of interference fringe shift depending on the sign of the phase shift were formulated based on the calculations. Results of the experiment using the Mach–Zehnder interferometer with different combinations of beams with spherical and plane wavefronts confirmed the theoretical calculations. Practical significance. Classic interferometric methods require significant time and the application of complex experimental procedures to determine the sign of the phase shift. The application of the results obtained in this study enables the determination of the sign of the introduced local phase shift based on a single interferogram without additional time expenditures. Thus, the method investigating the metamaterial layers of a subwavelength thickness is significantly simplified.

Localization effects from local phase shifts in the modulation of waveguide arrays

Artificial gauge fields enable the intriguing possibility to manipulate the propagation of light as if it were under the influence of a magnetic field even though photons possess no intrinsic electric charge. Typically, such fields are engineered via periodic modulations of photonic lattices such that the effective coupling coefficients after one period become complex-valued. In this work, we investigate the possibility of introducing randomness into artificial gauge fields by applying local random phase shifts in the modulation of lattices of optical waveguides. We first study the elemental unit consisting of two coupled single-mode waveguides and determine the effective complex-valued coupling coefficient after one period of modulation as a function of the phase shift, modulation amplitude, and modulation frequency. Thereby we identify the regime where varying the modulation phase yields sufficiently large changes of the effective coupling coefficient to induce Anderson localization. Using these results, we demonstrate numerically the onset of Anderson localization in 1D and 2D lattices of x- and helically modulated waveguides via randomly choosing the modulation phases of individual waveguides. Besides further fundamental investigations of wave propagation in the presence of random gauge fields, our findings enable the engineering of coupling coefficients without changing the footprint of the overall lattice. As a proof of concept, we demonstrate how to engineer out-of-phase modulated lattices that exhibit dynamic localization and defect-free surface states. Therefore, we anticipate that the modulation phase will play an important role in the judicious design of functional waveguide lattices.

High-speed videography of transparent media using illumination-based multiplexed schlieren

Schlieren photography is widely used for visualizing phenomena within transparent media. The technique, which comes in a variety of configurations, is based on detecting or extracting the degree to which light is deflected whilst propagating through a sample. To date, high-speed schlieren videography can only be achieved using high-speed cameras, thus limiting the frame rate of such configurations to the capabilities of the camera. Here we demonstrate, for the first time, optically multiplexed schlieren videography, a concept that allows such hardware limitations to be bypassed, opening up for, in principle, an unlimited frame rate. By illuminating the sample with a rapid burst of uniquely spatially modulated light pulses, a temporally resolved sequence can be captured in a single photograph. The refractive index variations are thereafter measured by quantifying the local phase shift of the superimposed intensity modulations. The presented results demonstrate the ability to acquire a series of images of flame structures at frame rates up to 1 Mfps using a standard 50 fps sCMOS camera.

Gauge invariance of the local phase in the Aharonov-Bohm interference: Quantum electrodynamic approach

In the Aharonov-Bohm (AB) effect, interference fringes are observed for a charged particle in the absence of the local overlap with the external electromagnetic field. This notion of the apparent “nonlocality” of the interaction or the significant role of the potential have recently been challenged and are under debate. The quantum electrodynamic approach provides a microscopic picture of the characteristics of the interaction between a charge and an external field. We explicitly show the gauge invariance of the local phase shift in the magnetic AB effect, which is in contrast to the results obtained using the usual semiclassical vector potential. Our study can resolve the issue of the locality in the magnetic AB effect. However, the problem is not solved in the same way in the electric counterpart wherein virtual scalar photons play an essential role.

Local phase shift due to interactions in an atom interferometer

The authors study the local phase shift induced by interactions in a light pulse atom interferometer with a Bose-Einstein condensate using a method based on the Feynman path integral. These effects are crucial for the sensitivity and accuracy of the atom interferometers. The theoretical results are verified by experimental measurements without adjustable parameters.

Compact and efficient elastic metasurface based on mass-stiffness relation for manipulation of flexural waves

Metasurfaces are a group of lower dimensional metamaterials. They have shown excellent capacities in precise and efficient manipulation of wavefront at-will. However, most of them suffer from low transmission performances since they only consider the control of phase but ignore the impedance that determines transmission behaviours. To optimize the behaviours of metasurface, we employ the mass-stiffness relation to realize efficient manipulation of flexural waves. We use external mass blocks (pillars) to tune the effective mass and cut grooves in connecting beams to release effective stiffness. The two degrees of freedom are used to control the two design targets: local phase shift and impedance. Based on the theoretical analysis and finite element simulations, a three-unit metasurface with high transmission performances and compact geometry is designed. From the comparisons with currently existed designs, we show that our proposed metasurface is much more efficient and compact. This research may play an important role in guidance of the design of highly efficient and compact metasurfaces for precise engineering of elastic wavefront.

Seismic Dispersion and Attenuation in Fractured Fluid‐Saturated Porous Rocks: An Experimental Study with an Analytic and Computational Comparison

Although different fluid pressure diffusion mechanisms caused by fractures have been extensively studied using analytical and numerical methods, there is little to no experimental work completed on them in laboratory conditions. In this paper, hydrostatic-stress oscillations (frequency − 0.04 to 1 Hz) are used on an intact and saw cut sample, in dry and water saturated conditions, in a triaxial cell at different effective pressures in undrained conditions. The objective is to study the fracture’s effect on the elastic properties of the sample and validate some computational fracture models, that have been explored in the literature. Experimental results highlight dispersion and attenuation in saturated conditions due to the fracture, which diminishes in amplitude as the effective pressure is increased, i.e. as the fracture is closed. From local strain gauge measurements, it is found that there is a local negative phase shift between stress and strain in water saturated conditions for the fractured sample, due to the location of the strain measurements. No attenuation observed in dry conditions. A simple 1D model using mass balance and mechanical equilibrium equations for a linear isotropic poroelastic homogeneous medium give prediction in very good agreement with the experimental results. A 3D model was also developed to allow a comparison between analytic, numerical and experimental results.

Metrological complementarity reveals the Einstein-Podolsky-Rosen paradox

The Einstein-Podolsky-Rosen (EPR) paradox plays a fundamental role in our understanding of quantum mechanics, and is associated with the possibility of predicting the results of non-commuting measurements with a precision that seems to violate the uncertainty principle. This apparent contradiction to complementarity is made possible by nonclassical correlations stronger than entanglement, called steering. Quantum information recognises steering as an essential resource for a number of tasks but, contrary to entanglement, its role for metrology has so far remained unclear. Here, we formulate the EPR paradox in the framework of quantum metrology, showing that it enables the precise estimation of a local phase shift and of its generating observable. Employing a stricter formulation of quantum complementarity, we derive a criterion based on the quantum Fisher information that detects steering in a larger class of states than well-known uncertainty-based criteria. Our result identifies useful steering for quantum-enhanced precision measurements and allows one to uncover steering of non-Gaussian states in state-of-the-art experiments.

Effect of localized doping in microknot fiber resonators for resonance-shift based sensing

On-fiber microstructures are favorable platforms for sensing applications. We have studied analytically the mechanical bending strength in undoped and doped micro-tapers, and numerically the photonic transmission in 3D resonating microknots defined on optical tapered fibers as functions of radius and doping. In favor of sensing applications, we deduced the microstructure sensitivities to localized refractive index variation in terms of local resonance phase shifts, slopes, dynamical range and refractive-index range of sensitivities. The spectral response in both microknots (MKRs) and microloops (MLRs) have been studied in terms of refractive index variation profile. Based on the analysis of the transmission characteristics in MKRs with varying ambient index variations, we observed a linear response to small refractive index gradients in the NIR wavelength range. We propose that microstructures of 50-micron radii and below, with moderate doping, can exhibit improved resonant-shift based sensing capabilities.

Phase-suppressed hydrodynamics of solitons on constant-background plane wave

The significance of local phase shifts in the experimental realization of soliton and breather waves in finite water depth as well as in deep water is explored. When suppressing the corresponding phase shift, the coherence of the wave envelope disintegrates by forming distinct soliton patterns. All experimental results are in excellent agreement with the predictions based on the nonlinear Schr\odinger equation framework, suggesting the universality of observed dip and extreme wave pattern dynamics.

An MDPSK homodyne receiver with adaptive phase-diversity

ABSTRACT We propose an adaptive phase-diversity method for optical M-ary differential phase-shift keying (MDPSK) homodyne receivers, to achieve coherent optical communication. This method involves eliminating the random fluctuations in the phase differences between the signal light and local oscillator and the in-plane and quadrature signal (IQ) imbalance compensation. For the former, a phase-diversity method, which can theoretically eliminate all phase-related noise, is proposed. The gain and phase imbalances between the I and Q channels can be compensated completely by using automatic phase- and gain-control systems. The core idea is the adaptability of the receiver to the local phase shift of the local oscillator. The performance of the receiver is not sensitive to environmental factors such as temperature and vibrations. Our simulation results show that the imbalances between the IQ channels can be completely compensated over a wide imbalance range, and the baseband signals can be accurately recovered using the proposed scheme.