Abstract: We present details of numerical simulations of the gravitational radiation produced by a first order thermal phase transition in the early universe. We confirm that the dominant source of gravitational waves is sound waves generated by the expanding bubbles of the low-temperature phase. We demonstrate that the sound waves have a power spectrum with a power-law form between the scales set by the average bubble separation (which sets the length scale of the fluid flow Lf) and the bubble wall width. The sound waves generate gravitational waves whose power spectrum also has a power-law form, at a rate proportional to Lf and the square of the fluid kinetic energy density. We

Abstract: The capability of locally engineering the nonlinear optical properties of media is crucial in nonlinear optics. Although poling is the most widely employed technique for achieving locally controlled nonlinearity, it leads only to a binary nonlinear state, which is equivalent to a discrete phase change of π in the nonlinear polarizability. Here, inspired by the concept of spin-rotation coupling, we experimentally demonstrate nonlinear metasurfaces with homogeneous linear optical properties but spatially varying effective nonlinear polarizability with continuously controllable phase. The continuous phase control over the local nonlinearity is demonstrated for second and third harmonic generation by using nonlinear metasurfaces consisting of nanoantennas of C3 and C4 rotational symmetries, respectively. The continuous phase engineering of the effective nonlinear polarizability enables complete control over the propagation of harmonic generation signals. Therefore, this method seamlessly combines the generation and manipulation of harmonic waves, paving the way for highly compact nonlinear nanophotonic devices.

Abstract: Throughout optics and photonics, phase is normally controlled via an optical path difference. Although much less common, an alternative means for phase control exists: a geometric phase (GP) shift occurring when a light wave is transformed through one parameter space, e.g., polarization, in such a way as to create a change in a second parameter, e.g., phase. In thin films and surfaces where only the GP varies spatially—which may be called GP holograms (GPHs)—the phase profile of nearly any (physical or virtual) object can in principle be embodied as an inhomogeneous anisotropy manifesting exceptional diffraction and polarization behavior. Pure GP elements have had poor efficiency and utility up to now, except in isolated cases, due to the lack of fabrication techniques producing elements with an arbitrary spatially varying GP shift at visible and near-infrared wavelengths. Here, we describe two methods to create high-fidelity GPHs, one interferometric and another direct-write, capable of recording the wavefront of nearly any physical or virtual object. We employ photoaligned liquid crystals to record the patterns as an inhomogeneous optical axis profile in thin films with a few μm thickness. We report on eight representative examples, including a GP lens with F/2.3 (at 633 nm) and 99% diffraction efficiency across visible wavelengths, and several GP vortex phase plates with excellent modal purity and remarkably small central defect size (e.g., 0.7 and 7 μm for topological charges of 1 and 8, respectively). We also report on a GP Fourier hologram, a fan-out grid with dozens of far-field spots, and an elaborate phase profile, which showed excellent fidelity and very low leakage wave transmittance and haze. Together, these techniques are the first practical bases for arbitrary GPHs with essentially no loss, high phase gradients (∼rad/μm), novel polarization functionality, and broadband behavior.

Abstract: Modulating the phase of electromagnetic waves has many applications in photonic research. A new mechanism allows a thin graphene metasurface to reliably achieve an extremely large phase modulation in THz radiation.

Abstract: We present a full-range complex spectral domain optical coherence tomography with an ultra-broadband light source based on sinusoidal modulation. For the sinusoidal modulation strategy, a lead zirconate titanate stack actuator is employed to achieve the sinusoidal vibration of a mirror and therefore to get a series of spectral interferogram with different phase delays. The purpose of this strategy is to get higher performance complex-conjugate artifact elimination. Bessel separation of the signal sequence at each wavelength of the spectrometer was used to reconstruct the real and imaginary components of interference fringes; however, the sinusoidal modulation method is independent of light source wavelength. The experimental results demonstrated that the method had an excellent performance in a complex-conjugate suppression of 50 dB for a full width at half maximum bandwidth of 236 nm, and it has better anti-artifact ability and more flexible range in phase shifting than the conventional wavelength-dependent phase-shifting method on a full-range complex spectral optical coherence tomography system. Furthermore, the effect of the hysteresis error of lead zirconate titanate actuators on the performance of complex-conjugate artifact elimination was investigated and the solution of lead zirconate titanate positioning performance for both conventional phase-shifting and sine-modulation methods was suggested.

Abstract: Purpose Frequency and phase drifts are a common problem in the acquisition of in vivo magnetic resonance spectroscopy (MRS) data If not accounted for, frequency and phase drifts will result in artifactual broadening of spectral peaks, distortion of spectral lineshapes, and a reduction in signal-to-noise ratio (SNR) We present herein a new method for estimating and correcting frequency and phase drifts in in vivo MRS data Methods We used a simple method of fitting each spectral average to a reference scan (often the first average in the series) in the time domain through adjustment of frequency and phase terms Due to the similarity with image registration, this method is referred to as “spectral registration” Using simulated data with known frequency and phase drifts, the performance of spectral registration was compared with two existing methods at various SNR levels Results Spectral registration performed well in comparison with the other methods tested in terms of both frequency and phase drift estimation Conclusions Spectral registration provides an effective method for frequency and phase drift correction It does not involve the collection of navigator echoes, and does not rely on any specific resonances, such as residual water or creatine, making it highly versatile Magn Reson Med 73:44–50, 2015 © 2014 Wiley Periodicals, Inc

Abstract: An ultralow reflectivity spiral phase plate (SPP) is proposed to generate an orbital angular momentum (OAM) beam at millimeter-wave frequency. The SPP is composed of unit cells whose equivalent permittivity and thickness are designed to satisfy the impedance matching condition based on transmission line theory. The designed SPP is fabricated by a 3D printing technique. The near-field and far-field phase distributions clearly exhibit the azimuth phase shifting, and the far field directivity pattern shows that the direction, gain, and 3-dB beam-width of the main lobe are about $10.5^\circ $ , 14.6 dB, and $14.5^\circ $ , respectively. Compared with no impedance-matched SPP, the reflectivity of the SPP is improved by more than 20 dB.

Abstract: This paper investigates experimental means of measuring the transmission matrix (TM) of a highly scattering medium, with the simplest optical setup. Spatial light modulation is performed by a digital micromirror device (DMD), allowing high rates and high pixel counts but only binary amplitude modulation. We used intensity measurement only, thus avoiding the need for a reference beam. Therefore, the phase of the TM has to be estimated through signal processing techniques of phase retrieval. Here, we compare four different phase retrieval principles on noisy experimental data. We validate our estimations of the TM on three criteria : quality of prediction, distribution of singular values, and quality of focusing. Results indicate that Bayesian phase retrieval algorithms with variational approaches provide a good tradeoff between the computational complexity and the precision of the estimates.

Abstract: Optical tweezing typically refers to the trapping and manipulation of particles using lasers. Here, Jang et al. demonstrate analogous manipulation of ultrashort cavity soliton-pulses in the time domain, trapped by the phase modulation of a continuous wave laser beam, and moved by modifying the phase profile.

Abstract: We propose a novel approach to generate distributed fiber sensing system based on phase-sensitive optical time domain reflectometer (Φ-OTDR) and phase-generated carrier demodulation algorithm. An unbalanced Michelson interferometer is introduced at the receiving end of the system. The back Rayleigh scattering light from a certain position along the sensing fiber would interfere to generate interference light signal versus time, whose phase carries the sensing information. Phase-generated carrier demodulation algorithm is proposed and carried out to recover the phase information. A single frequency vibration event is applied to a certain position along the sensing fiber and we realize to demodulate it correctly. The noise level of the phase sensitive OTDR system is about $3 \times 10^{-3}$ rad/SHz and a signal to noise ratio about 30.45 dB is achieved. The maximum sensing length and the spatial resolution of the Φ-OTDR system are 10 km and 6 m with pulse repetition rate at 10 kHz and 6 m fiber delay in MI with interrogating pulse width of 30 ns.

Abstract: Optically controlled phase shifters are desirable for optical communication, sensors, and signal processing due to their simple implementation and low cost. We propose an all-fiber phase shifter assisted by graphene’s photothermal effect. In a graphene-coated microfiber, graphene’s ohmic heating promises efficient fiber index change and phase shift via the thermo-optic effect. On a fabricated device with a length of 5 mm, we obtain a phase shift exceeding 21π with a nearly linear slope of 0.091 π/mW (0.192 π/mW) when pumped by 980 nm (1540 nm) light, which enables all-optical switching with an extinction ratio of 20 dB and a rise (fall) time of 9.1 ms (3.2 ms) following the 10%–90% rule. This graphene-assisted index change and phase shifter featured with all-in-fiber, low power requirement, and ease of fabrication may open the door for graphene’s realistic applications in all-optical signal processing.

Abstract: Spatial structure of a light beam is an important degree of freedom to be extensively explored. By designing simple configurations with phase-only spatial light modulators (SLMs), we show the ability to arbitrarily manipulate the spatial full field information (i.e. amplitude and phase) of a light beam. Using this approach to facilitating arbitrary and independent control of spatial amplitude and phase, one can flexibly generate different special kinds of light beams for different specific applications. Multiple collinear orbital angular momentum (OAM) beams, Laguerre-Gaussian (LG) beams, and Bessel beams, having both spatial amplitude and phase distributions, are successfully generated in the experiments. Some arbitrary beams with odd-shaped intensity are also generated in the experiments.

Abstract: Transmission and reflection are two fundamental properties of the electromagnetic wave propagation through obstacles. Full control of both the magnitude and phase of the transmission and reflection independently are important issue for free manipulation of electromagnetic wave propagation. Here we employed the equivalent principle, one fundamental theorem of electromagnetics, to analyze the required surface electric and magnetic impedances of a passive metasurface to produce either arbitrary transmission magnitude and phase or arbitrary reflection magnitude and phase. Based on the analysis, a tunable metasurface is proposed. It is shown that the transmission phase can be tuned by 360° with the unity transmissivity or the transmissivity can be tuned from 0 to 1 while the transmission phase is kept around 0°. The reflection magnitude and phase can also been tuned similarly with the proposed metasurface. The proposed design may have many potential applications, such as the dynamic EM beam forming and scanning.

Abstract: A radio-frequency power transmitter. The radio-frequency power transmitter includes an array of patch antennas, an array of phase modulators, each phase modulator having an input port and associated with one or more of the patch antennas, a local oscillator that provides an oscillatory signal to the input port of each of the phase modulators, an array of amplifiers, each amplifier receiving an input from one of the phase modulators, and a microprocessor configured to interface with the array of phase modulators and control a holistic radiative power transmission vector pattern generated by the radio-frequency power transmitter.

Abstract: Phase estimation, at the heart of many quantum metrology and communication schemes, can be strongly affected by noise, whose amplitude may not be known, or might be subject to drift. Here we investigate the joint estimation of a phase shift and the amplitude of phase diffusion at the quantum limit. For several relevant instances, this multiparameter estimation problem can be effectively reshaped as a two-dimensional Hilbert space model, encompassing the description of an interferometer phase probed with relevant quantum states--split single-photons, coherent states or N00N states. For these cases, we obtain a trade-off bound on the statistical variances for the joint estimation of phase and phase diffusion, as well as optimum measurement schemes. We use this bound to quantify the effectiveness of an actual experimental set-up for joint parameter estimation for polarimetry. We conclude by discussing the form of the trade-off relations for more general states and measurements.

Abstract: A novel distributed fiber vibration sensing technique based on phase extraction from time-gated digital optical frequency domain reflectometry (TGD-OFDR) which can achieve quantitative vibration measurement with high spatial resolution and long measurement range is proposed. A 90 degree optical hybrid is used to extract phase information. By increasing frequency sweeping speed, the influence of environmental phase disturbance on TGD-OFDR is mitigated significantly, which makes phase extraction in our new scheme more reliable than that in conventional OFDR-based method, leading to the realization of long distance quantitative vibration measurement. By using the proposed technique, a distributed vibration sensor that has a measurement range of 40 km, a spatial resolution of 3.5 m, a measurable vibration frequency up to 600 Hz, and a minimal measurable vibration acceleration of 0.08g is demonstrated.

Abstract: The Hilbert transform has been used to characterize wave propagation and detect phase singularities during cardiac fibrillation. Two mapping modalities have been used: optical mapping (used to map atria and ventricles) and contact electrode mapping (used only to map ventricles). Due to specific morphology of atrial electrograms, phase reconstruction of contact electrograms in the atria is challenging and has not been investigated in detail. Here, we explore the properties of Hilbert transform applied to unipolar epicardial electrograms and devise a method for robust phase reconstruction using the Hilbert transform. We applied the Hilbert transform to idealized unipolar signals obtained from analytical approach and to electrograms recorded in humans. We investigated effects of deflection morphology on instantaneous phase. Application of the Hilbert transform to unipolar electrograms demonstrated sensitivity of reconstructed phase to the type of deflection morphology (uni- or biphasic), the ratio of R and S waves and presence of the noise. In order to perform a robust phase reconstruction, we propose a signal transformation based on the recomposition of the electrogram from sinusoidal wavelets with amplitudes proportional to the negative slope of the electrogram. Application of the sinusoidal recomposition transformation prior to application of the Hilbert transform alleviates the effect of confounding features on reconstructed phase.

Abstract: We investigate electron momentum distributions from single ionization of Ar by two orthogonally polarized laser pulses of different color. The two-color scheme is used to experimentally control the interference between electron wave packets released at different times within one laser cycle. This intracycle interference pattern is typically hard to resolve in an experiment. With the two-color control scheme, these features become the dominant contribution to the electron momentum distribution. Furthermore, the second color can be used for streaking of the otherwise interfering wave packets establishing a which-way marker. Our investigation shows that the visibility of the interference fringes depends on the degree of the which-way information determined by the controllable phase between the two pulses.

Abstract: This report introduces the first results obtained using phase-contrast scanning transmission electron microscopy (P-STEM). A carbon-film phase plate (PP) with a small center hole is placed in the condenser aperture plane so that a phase shift is introduced in the incident electron waves except those passing through the center hole. A cosine-type phase-contrast transfer function emerges when the phase-shifted scattered waves interfere with the non-phase-shifted unscattered waves, which passed through the center hole before incidence onto the specimen. The phase contrast resulting in P-STEM is optically identical to that in phase-contrast transmission electron microscopy that is used to provide high contrast for weak phase objects. Therefore, the use of PPs can enhance the phase contrast of the STEM images of specimens in principle. The phase shift resulting from the PP, whose thickness corresponds to a phase shift of π, has been confirmed using interference fringes displayed in the Ronchigram of a silicon single crystal specimen. The interference fringes were found to abruptly shift at the edge of the PP hole by π.

Abstract: We explore the phase diagram of interacting spin-$1/2$ systems in the presence of anisotropic interactions, spontaneous decay, and driving. We find a rich phase diagram featuring a limit-cycle phase in which the magnetization oscillates in time. We analyze the spatiotemporal fluctuations of this limit-cycle phase based on a Gaussian-Floquet analysis. Spatial fluctuations destroy long-range limit-cycle ordering for dimension $d\ensuremath{\le}2$, as a time-dependent generalization of the Mermin-Wagner theorem. This result can be interpreted in terms of a spatiotemporal Goldstone mode corresponding to phase fluctuations of the limit cycle. We also demonstrate that the limit-cycle phase exhibits an asymmetric power spectrum measurable in fluorescence experiments.

Abstract: For a one-dimensional (1D) periodic system with inherent mirror symmetry, the value of the geometric "Zak" phase in a bulk band is related to the sign of reflection phase for wavelengths inside the bandgaps sandwiching the bulk band. Here, we designed an interference setup which allows us to measure the reflection phase of 1D phonic crystal fabricated for the optical range; this, in turn, enabled us to determine the Zak phases of the bands. We then found interface states whose existence can be traced to the topological properties of the bandgaps and the geometric phases of the bulk bands.

Abstract: A novel method is proposed to generate vector beams with arbitrary spatial variation of phase and linear polarization at the nanoscale using compact plasmonic metasurfaces with rectangular nanoapertures. The physical mechanism underlying the simultaneous control of light polarization and phase is explained. Vector beams with different spiral phasefronts are obtained by manipulating the local orientation and geometric parameters of the metasurfaces. In addition, radially and azimuthally polarized vector beams and double-mode vector beams are achieved through completely compensating for the Berry phase, which provides additional degrees of freedom for beam manipulation.

Abstract: Switched reluctance motors (SRMs) have been considered as low-cost machines for electric vehicle (EV) and hybrid EV applications However, the current sensors used in the system will not only increase the cost and volume but also degrade the running reliability of the motor drives Conventionally, the current sensors are used in each phase winding individually to obtain these phase currents To reduce the number of current sensors, a four-phase 8/6-pole SRM is applied to analyze the working states, and a novel phase current reconstruction method from the dc-link current employing double high-frequency pulses injection is then proposed Two kinds of high-frequency pulses with large duty cycles and phase shift are injected to the down switches in each phase, respectively, when the phase currents are overlapped in the turn-on region, and the dc-link current is decomposed to reconstruct phase currents in both current chopping control system and single pulse control system The transient performance in a closed-loop system based on the phase current reconstruction scheme is investigated The proposed method uses only one current sensor in the dc link and requires no additional circuits The simulation and experimental results are presented to confirm the implementation of the proposed method

Abstract: A systematic study of the Raman spectra of Pb(Zr1-xTix)O-3 (PZT) ceramics has been performed in a broad temperature interval (10-600 K) and a broad Ti/Zr concentration range around the morphotropic phase boundary (x = 0.25-0.70). The number of the spectral components was estimated by a standard fitting procedure with damped harmonic oscillators as well as by counting the number of peaks and shoulders with the help of a purposely designed mathematical analysis based on frequency derivatives of the Raman spectra. This last method proves to be very useful to study Raman spectra of disordered materials. For the case of PZT, the comparison with the Raman modes of PbTiO3 allows us to assign the phonon bands on both sides of the morphotropic phase boundary, and the crossover from the tetragonal to rhombohedral phase spectra is clearly visible. However, there are no indications of a systematic splitting of the E-symmetry modes into monoclinic A'-A '' doublets in the morphotropic samples. Detailed adjusting of the response function to the spectrum requires to assume additional Raman-active modes, but this holds for a much broader concentration range than that of the anticipated monoclinic phase. In particular, the lowest frequency transverse optic mode of E-symmetry (soft mode of the ferroelectric phase transition) is split into two components, a THz frequency anharmonic (central modelike) component and a resonant component (at omega similar to 80 cm(-1)), both related to the same normal coordinate. The additional Raman band appearing in this frequency range (omega similar to 65 cm(-1)) at low temperatures is rather associated with the antiphase tilt vibrations of the oxygen octahedra.

Abstract: A stable phase demodulation system for diaphragm-based acoustic sensors is reported. The system is based on a modified fiber-optic Sagnac interferometer with a stable quadrature phase bias, which is independent of the parameters of the sensor head. The phase bias is achieved passively by introducing a nonreciprocal frequency shift between the counter-propagating waves, avoiding the use of complicated active servo-control. A 100 nm-thick graphite diaphragm-based acoustic sensor interrogated by the proposed demodulation system demonstrated a minimum detectable pressure level of ~450 µPa/Hz(1/2) and an output signal stability of less than 0.35 dB over an 8-hour period. The system may be useful as a universal phase demodulation unit for diaphragm-based acoustic sensors as well as other sensors operating in a reflection mode.

Abstract: We study the effects of a phase difference on Yu-Shiba-Rusinov (YSR) states in a spinful Coulomb-blockaded quantum dot contacted by a superconducting loop. In the limit where charging energy is larger than the superconducting gap, we determine the subgap excitation spectrum, the corresponding supercurrent, and the differential conductance as measured by a normal-metal tunnel probe. In absence of a phase difference only one linear combination of the superconductor lead electrons couples to the spin, which gives a single YSR state. With finite phase difference, however, it is effectively a two-channel scattering problem and therefore an additional state emerges from the gap edge. The energy of the phase-dependent YSR states depend on the gate voltage and one state can cross zero energy twice inside the valley with odd occupancy. These crossings are shifted by the phase difference towards the charge degeneracy points, corresponding to larger exchange couplings. Moreover, the zero-energy crossings give rise to resonant peaks in the differential conductance with magnitude 4e(2)/h. Finally, we demonstrate that the quantum fluctuations of the dot spin do not alter qualitatively any of the results. (Less)

Abstract: We propose a systematic method for soliton formation in whispering-gallery-mode (WGM) resonators through input phase modulation. Our numerical simulations of a variant of the Lugiato–Lefever equation (LLE) suggest that modulating the input phase at a frequency equal to the resonator free spectral range and at modest modulation depths provides a deterministic route toward soliton formation in WGM resonators without undergoing a chaotic phase. We show that the generated solitonic state is sustained when the modulation is turned off adiabatically. Our results support parametric seeding as a powerful means of control, in addition to input pump power and pump-resonance detuning, over frequency comb generation in WGM resonators. Our findings also help pave the way toward ultrashort pulse formation on a chip.

Abstract: Recent work has shown that the many-body expansion of the interaction energy can effectively be used to develop analytical representations of global potential energy surfaces (PESs) for water. In this study, the role of short- and long-range contri- butions at different orders is investigated by analyzing water potentials that treat the leading terms of the many-body expansion through implicit (i.e., TTM3-F and TTM4-F PESs) and explicit (i.e., WHBB and MB-pol PESs) representations. It is found that explicit short-range representations of 2-body and 3-body interactions along with a physically correct integration of short- and long-range contributions are necessary for an accurate representation of the water interactions from the gas to the condensed phase. Similarly, a complete many-body representation of the dipole moment surface is found to be crucial to reproducing the correct intensities of the infrared spectrum of liquid water.