Phase-shifting Technique Research Articles

Quadriwave gradient light inteference microscopy for lable-free thick sample imaging

Due to the multiple scattering effect, quantitative phase imaging of thick specimens is challenging in biomedicine research. Phase gradient methods with partially coherent illumination in the reflection geometry have significant potential. However, to reconstruct two-dimensional (2D) phase information robustly, these methods cannot avoid changing the shear direction orthogonally. Here we propose a rotation-free method named quadriwave gradient light interference microscopy (qGLIM). qGLIM excludes conventional shear components and uses an amplitude-type spatial light modulator (SLM) to perform lateral shearing and phase shifting. By displaying checkerboard gratings on the SLM, we can reconstruct phase gradient information in orthogonal shear directions simultaneously. We extract the phase quantitatively by applying the phase-shifting technique and deconvolution algorithm. We demonstrate this approach by standard samples, thin samples, and thick multiple scattering samples.

Real-Time Double-Layer Thin Film Thickness Measurements Using Modified Sagnac Interferometer with Polarization Phase Shifting Approach

This paper describes a modified Sagnac interferometer with a self-referenced polarization and phase-shifting technique for real-time thickness measurement of single- and double-layer transparent thin films. The proposed interferometric setup generated outstanding rotating linearly polarized light with a degree of polarization (DOP) of 99.40%. A beam splitter placed at the interferometer output separated the beam into two identical linearly polarized beams. One of the beams served as a reference, while the other served as a sensing arm. The output linear polarizer set at 45° relative to a reference plane was positioned anterior to the photodetectors to get rotating light intensities for phase shift measurement; hence, the intensities at various polarizations of 0°, 45°, and 90° were automatically acquired without any polarizing device adjustments. These intensities were then transformed into a phase retardation introduced by a sample, and the resulting phase shift was eventually converted into film thickness. The samples were properly prepared, with pure BK7 substrate being deposited by WO3-, Ta2O5-, and WO3/Ta2O5 films of known thicknesses. The thickness measurement obtained from the proposed system yielded reading errors of 1.3%, 0.2%, and 1.3/2.5% for WO3-, Ta2O5-, and WO3/Ta2O5 films, respectively. The mathematical theory was effectively demonstrated and empirically confirmed. The experimental results show that the proposed setup has a lot of potential for real-time, non-destructive thickness assessment of transparent thin films without the need to modify polarizing device orientations.

Dynamic Wind Turbine Blade Inspection Using Micro-Polarisation Spatial Phase Shift Digital Shearography

Shearography, as a novel non-destructive evaluation technique, has shown notable ability in the detection of composite materials. However, in current shearography practices, the phase shifting and loading methods applied are mainly static. For instance, vacuum hood or force loading facilities are often used in phase-shifting shearography, and these are hard to realise with robotic control, especially for on-board inspection. In this study, a dynamic process for detecting defects in the subsurface of a wind turbine blade (WTB) using spatial phase shift with dynamic thermal loading was proposed. The WTB sample underwent a dynamic thermal loading operation, and its status is captured by a Michelson interferometric-based spatial phase shift digital shearography system using a pixelated micro-polarisation array sensor. The captured images were analysed in a 2D frequency domain and low-pass filtered for phase map acquisition. The initial phase maps underwent a window Fourier filtering process and were integrated to produce a video sequence for realisation of visualising the first derivative of the displacement in the process of thermal loading. The approach was tested in experimental settings and the results obtained were presented and discussed. A comparative assessment of the approach with shearography fringe pattern analysis and temporal phase shift technique is also presented and discussed.

Quantitative phase imaging with single-path phase-shifting digital holography using a light-emitting diode

We propose a quantitative phase imaging technique with single-path phase-shifting digital holography using a light-emitting diode (LED). A reference wave is generated from an object wave in the Fourier plane using a single-path interferometer, based on self-reference digital holography. The object wave interferes with the reference wave, and the quantitative phase information of the object wave is recorded as a digital hologram. Quantitative phase images of objects are obtained by applying a phase-shifting interferometry technique. All the light diffracted from the objects can be utilized to generate a digital hologram. Its validity is experimentally demonstrated by constructing an optical system with a wide-field optical microscope.

Advances in Dual-Three-Phase Permanent Magnet Synchronous Machines and Control Techniques

Multiphase electrical machines are advantageous for many industrial applications that require a high power rating, smooth torque, power/torque sharing capability, and fault-tolerant capability, compared with conventional single three-phase electrical machines. Consequently, a significant number of studies of multiphase machines has been published in recent years. This paper presents an overview of the recent advances in multiphase permanent magnet synchronous machines (PMSMs) and drive control techniques, with a focus on dual-three-phase PMSMs. It includes an extensive overview of the machine topologies, as well as their modelling methods, pulse-width-modulation techniques, field-oriented control, direct torque control, model predictive control, sensorless control, and fault-tolerant control, together with the newest control strategies for suppressing current harmonics and torque ripples, as well as carrier phase shift techniques, all with worked examples.

Single-exposure modulation-based structured illumination microscopy using spatial area phase-shift

In structured illumination microscopy (SIM) for three-dimensional (3D) measurement, the vertical scanning position with the maximum modulation is implemented to reshape the surface topography. Generally, to obtain the modulation distribution for each scanning position, the modulation decoding algorithms mainly include temporal phase-shifting (TP) method and frequency analysis technique. In TP method, at least three images with a fixed phase-shift are required, which results in low efficiency and complex phase-shifting mechanism. Frequency analysis technique can realize modulation distribution from single image, but the high frequency information of the sample will be inevitably lost. In this paper, we propose a spatial area phase-shifting reconstruction method which requires only one exposure to decode the modulation distribution. In this technique, n pixels from one period of illuminated pattern are used to replace the corresponding n images in the temporal phase shift. Through combining the phase information of each pixel with the least square algorithm, the modulation distribution is achieved. The proposed method can achieve an accurate 3D reconstruction. Also, the high frequency information of the sample can be effectively retained compared with frequency analysis method. The simulations and experiments are conducted to verify the feasibility of this method, demonstrating the potential to be applied in high precision, complex surface and real-time measurement.

Single-Stage Wireless Battery Charging Circuit with Coupling Coefficient Prediction

This paper proposes a single-stage wireless battery charging circuit with a coupling coefficient prediction method. The proposed circuit consists of only two stages: full bridge inverter with transmitter coil in the first stage and full bridge rectifier with receiver coil in the second stage. This circuit implements the constant current (CC) charging mode at the resonant frequency of two coils and the constant voltage (CV) charging mode at a specific frequency that is dependent on the coupling coefficient of two coils. The operation at a specific frequency guarantees the CV operation regardless of load condition and reduces the switching losses than the operation at the resonant frequency owing to a zero-voltage switching (ZVS) operation. In CC-CV modes, the phase-shift technique is additionally applied to improve the output voltage/current regulation. Unlike other approaches, the proposed single-stage wireless battery charging circuit does not require multiple stages of power conversion, or additional components, a pre-measured coupling coefficient or a complex control algorithm for CC-CV charging operation. The prototype proposed circuit was tested under various coil alignment conditions, and successfully implemented the CC-CV charging operation for a 36 V battery pack. The predicted coupling coefficient had an error of ≤0.62% in the coil alignment condition, and the circuit had errors of ≤0.32%, ≤0.1% in the output current and voltage regulation, respectively.

Direct measurement of density-matrix elements using a phase-shifting technique

A direct measurement protocol allows reconstructing specific elements of the density matrix of a quantum state without using quantum state tomography. However, the direct measurement protocols to date are primarily based on weak or strong measurements with an ancillary pointer, which interacts with the investigated system to extract information about the specified elements. Here, we present a direct measurement scheme based on phase-shifting operations which do not need ancillary pointers. In this method, estimates of at most six expectation values of projective observables suffice to determine any specific element of an unknown quantum density matrix. A concrete quantum circuit to implement this direct measurement protocol for multiqubit states is provided, which is composed of just single-qubit gates and two multiqubit controlled-phase gates. This scheme is also extended for the direct measurement of the density matrix of continuous-variable quantum states. Our method can be used in quantum information applications where only partial information about the quantum state needs to be extracted, for example, problems such as entanglement witnessing, fidelity estimation of quantum systems, and quantum coherence estimation.

Adaptive investigation of the optical properties of polymer fibers from mixing noisy phase shifting microinterferograms using deep learning algorithms.

In this article, an adaptive denoising method is suggested to accurate investigate the optical and structural features of polymeric fibers from noisy phase shifting microinterferograms. The mixed class of noise that may produce in the phase-shifting interferometric techniques is established. To our knowledge, this is an early study considered the mixing noises that may occur in microinterferograms. The suggested method utilized the convolution neural networks to detect the noise class and then denoising, it according to its class. Four convolution neural networks (Googlenet, VGG-19, Alexnet, and Alexnet-SVM) are refined to perform the automatic classification process for the noise class in the established data set. The network with the highest validation and testing accuracy of these networks is considered to apply the suggested method on realistic noisy microinterferograms for polymeric fibers, polypropylene and antimicrobial polyethylene terephthalate)/titanium dioxide, recoded using interference microscope. Also, the suggested method is applied on noisy microinterferograms include crazing and nanocomposite material. The demodulated phase maps and the three-dimensional birefringence profiles are calculated for tested fibers according to the suggested method. The obtained results are compared with the published data for these fibers and found to be in good agreements.

High-Accuracy Surface Profile Measurement Based on the Vortex Phase-Shifting Interferometry

According to the principle of phase-shifting interferometry and spiral phase characteristics of the vortex beam, this article proposes a method for detecting the surface profile of a transparent object, in which the +1 order vortex beam is generated by a spatial light modulator and is taken as the reference light. The influence of the nonlinear phase modulation characteristics of the spatial light modulator on the measurement precision is studied. The results show that nonlinear phase modulation has a great impact on the measurement. Then, the vortex lights with initial phases of 0, π/2, π, and 3π/2 are used to measure the H-type thin film sample based on the Twyman-Green interference system after correcting the nonlinear phase modulation characteristics. The experimental results show that the measurement error of the surface profile to an object with the theoretical value of 20 nm is 1.146 nm, and the feasibility of the optical vortex phase-shifting technique used to measure the surface profile of an object is verified.

POWER BALANCING TOPOLOGY FIVE-LEVEL CASCADED H-BRIDGE INVERTER WITH PHASE SHIFT TECHNIQUE FOR PHOTOVOLTAIC SOURCES

This research paper proposes a power balance optimization topology for a five-level cascaded H-bridge inverter with a phase shift technique. This topology uses two phase-shifted sine waveforms 180 degrees apart to modulate the two triangular waveforms. These two triangular waveforms are assigned a 90-degree phase shift. When the outputs of the two H-bridge inverters are connected in series, the total output waveform is 5 levels. The principles and methods of this research will focus on a cascaded H-bridge inverter with photovoltaic sources. Two independent units are connected in series to allow linear and non-linear loads at a maximum one-kilowatt rating. However, the researcher will create a prototype mechanism to test the power balance and power distribution efficiency of the two inverters compared with the simulation results using MATLAB/Simulink. Nevertheless, the results showed that the power balance efficiency could be improved, resulting in the mean efficiency of both inverters of 96%. When the harmonics were measured, the load was not Linear produced third- and fifth-order harmonics greater than linear load. This research confirms that the simulation with MATLAB/Simulink program and the prototype is correct and acceptable.

Phase-Shifting Projected Fringe Profilometry Using Binary-Encoded Patterns

A phase unwrapping method for phase-shifting projected fringe profilometry is presented. It did not require additional projections to identify the fringe orders. The pattern used for the phase extraction could be used for phase unwrapping directly. By spatially encoding the fringe patterns that were used to perform the phase-shifting technique with binary contrasts, fringe orders could be discerned. For spatially isolated objects or surfaces with large depth discontinuities, unwrapping could be identified without ambiguity. Even though the surface color or reflectivity varied periodically with position, it distinguished the fringe order very well.

Design and Implementation of Improved High Step-Down DC-DC Converter for Electric Vehicles

An improved high step-down DC-DC converter for charging the batteries in an electric vehicle application is proposed in this paper. It adopts the topology of the conventional full-bridge converter, which has a coupled inductor current-doubler rectifier as the secondary side of the transformer. In addition, four power switches are driven using a phase-shifting technique. The proposed converter can achieve a high step-down voltage with low-voltage stress on the rectifier diodes. In addition, the coupled inductor current-doubler rectifier of the secondary side can reduce the ripple current and losses of the secondary side to achieve high efficiency. Furthermore, the proposed converter can overcome the drawbacks of the conventional full-bridge converter, such as switching loss caused by high switching frequency, duty-cycle loss, voltage stress, and numerous components, and can increase the efficiency with the soft-switching technique. A 600 W laboratory prototype of the proposed converter was manufactured. The results of the experiments performed with the prototype proved the effectiveness and validated the use of the proposed converter for better charging of electric vehicles.

Measurement in-plane deformations in electronic speckle pattern interferometry using phase-shifting modulated by polarization

We propose to combine electronic speckle pattern interferometry with polarizing phase-shifting techniques to measure in-plane displacement fields. We present the technical and theoretical procedures for its implementation, added with the necessary calibration procedures employing a commercial polarimeter. Finally, we tested our proposal experimentally using a two-phase step algorithm to measure in-plane displacements on a latex sample.

Optoelectronic chromatic dispersion and wavelength monitoring in a photodiode.

The optoelectronic process of light absorption and current formation in photodiodes is shown to be a significant source of optoelectronic chromatic dispersion (OED). Simple design rules are developed for fabricating a photodiode-based dispersion device that possesses large, small, zero, and either positive or negative OED. The OED parameter is proportional to a spectrally-dependent absorption term α-1dα/dλ . Silicon-based devices are predicted to display significant OED throughout the near IR, while Ge and InGaAs have high OED in the C- and L-bands and 1650 nm region, respectively. The OED of a commercial Ge PN photodiode is measured to be 3460 ps/nm at 1560 nm wavelength with 500 kHz modulation, demonstrating 8pm spectral resolution with the phase-shift technique. Temperature-tuning of the OED in the Ge photodiode is also demonstrated. The ubiquitous photodiode is a tunable OED device, with applications in high-resolution optical spectroscopy and optical sensing.

Fringe analysis: single-shot or two-frames? Quantitative phase imaging answers.

Conditions of the digital recording of the fringe pattern determine the phase reconstruction procedure, which in turn directly shapes the final accuracy and throughput of the full-field (non-scanning) optical measurement technique and defines the system capabilities. In this way, the fringe pattern analysis plays a crucial role in the ubiquitous optical measurements and thus is under constant development focused on high temporal/spatial resolution. It is especially valuable in the quantitative phase imaging technology, which emerged in the high-contrast label-free biomedical microscopy. In this paper, I apply recently blossomed two-frame phase-shifting techniques to the QPI and merge them with advanced adaptive interferogram pre-filtering algorithms. Next, I comprehensively test such frameworks against classical and adaptive single-shot methods applied for phase reconstruction in dynamic QPI enabling highest phase time-space-bandwidth product. The presented study systematically tackles important question: what is the gain, if any, in QPI realized by recording two phase-shifted interferograms? Counterintuitively, the results show that single-shot demodulation exhibited higher phase reconstruction accuracy than two-frame phase-shifting methods in low and medium interferogram signal-to-noise ratio regimes. Thus, the single-shot approach is promoted due to not only high temporal resolution but also larger phase-information throughput. Additionally, in the majority of scenarios, the best option is to shift the paradigm and employ two-frame pre-filtering rather than two-frame phase retrieval. Experimental fringe analysis in QPI of LSEC/RWPE cell lines successfully corroborated all novel numerical findings. Hence, the presented numerical-experimental research advances the important field of fringe analysis solutions for optical full-field measurement methods with widespread bio-engineering applications.

Transmission Phase Control of Annular Array Transducers for Efficient Second Harmonic Generation in the Presence of a Stress-Free Boundary

The through-transmission (TT) method is mainly used to measure the amplitude of the second harmonic from which the acoustic nonlinear parameter is determined for early damage detection of materials. The pulse echo (PE) method, however, has been excluded from nonlinear studies of solid materials because the stress-free boundary suppresses the generation of second harmonics. It is more demanding to develop the PE method for practical applications and this paper considers a novel phase shift technique of annular array transducers to improve second harmonic generation (SHG) at the stress-free boundary. The fundamental and second harmonic fields after phase-shifted radiation are calculated, and their received amplitudes are investigated. The phase difference between the two second harmonic components after reflection from the stress-free boundary is analyzed to explain the enhanced SHG. The PE method with optimal phase shift can generate an improved second harmonic amplitude as high as about 45% of the TT method. Four element array transducers are also found to be more efficient in improved SHG than two element transducers.

Fast fiber mode decomposition with a lensless fiber-point-diffraction interferometer.

Recently, the growing interest in few-mode fibers in telecommunications and high-power lasers has stimulated the demand for fiber mode decomposition (MD). Here we present a fast fiber MD method with a lensless fiber-point-diffraction interferometer. The complex amplitude at the fiber end is achieved by the polarization phase-shifting technique and the lensless imaging technique. Then, the eigenmode coefficients are determined by the mode orthogonal operations of the complex amplitude. In the experiment, the SMF-28e fiber containing 10 linear polarized modes at the wavelength of 632.8 nm is studied for MD. The decomposition of the 50 * 50 pixels interferograms takes only 0.0168 s. The similarity of the intensity patterns of the testing light is larger than 97% before and after the MD. This new, to the best of our knowledge, method can achieve fast and accurate 10-mode MD without using any imaging systems.

High-resolution single-shot phase-shifting interference microscopy using deep neural network for quantitative phase imaging of biological samples.

White light phase-shifting interference microscopy (WL-PSIM) is a prominent technique for high-resolution quantitative phase imaging (QPI) of industrial and biological specimens. However, multiple interferograms with accurate phase-shifts are essentially required in WL-PSIM for measuring the accurate phase of the object. Here, we present single-shot phase-shifting interferometric techniques for accurate phase measurement using filtered white light (520±36 nm) phase-shifting interference microscopy (F-WL-PSIM) and deep neural network (DNN). The methods are incorporated by training the DNN to generate (a) four phase-shifted frames and (b) direct phase from a single interferogram. The training of network is performed on two different samples i.e., optical waveguide and MG63 osteosarcoma cells. Further, performance of F-WL-PSIM+DNN framework is validated by comparing the phase map extracted from network generated and experimentally recorded interferograms. The current approach can further strengthen QPI techniques for high-resolution phase recovery using a single frame for different biomedical applications.

Directional phase-unwrapping algorithm and phase shift technique on hydrogel.

Refractive index microstructures, which can be written by multiphoton absorption with femtosecond lasers, have many applications. Here we present a directional phase-unwrapping algorithm with phase-shifting technique and apply it to the metrology of hydrogel microstructures. A staircase phase-unwrapping algorithm is demonstrated. This fast quality-guided path phase-unwrapping applies well to situations that are geometrically well defined and is quite tolerant of phase noise. To achieve precise very small phase shifts, we also present a slant angle technique on a DC servo stage along with phase shift measurement, allowing us to achieve 6.5 nm step sizes.