Phase-shifting Mechanism Research Articles

Controlling 1550-nm light through a multimode fiber using a Hadamard encoding algorithm.

To meet the demand for higher capacity fiber-optic communication, multimode fibers have gradually attracted attention, but they introduce spatial distortions. To overcome this limitation, wavefront shaping technology promises to control scattered light after it is transmitted through multimode fibers. In this work, we introduce a Hadamard encoding algorithm (HEA) to control 1550-nm light that has passed through a multimode fiber. A series of Hadamard bases is iteratively added to the current optimum phase map, and the coefficient of each order is determined through a simple four-step phase-shifting mechanism. Using a laser source at 1550-nm wavelength, we experimentally achieved an optical focus through a 2-meter-long multimode fiber. With 1024 orders, the experimental enhancement reached 690, which is 86% of the theoretical value. As far as we know, this is the best result ever reported in focusing 1550-nm light through a multimode fiber. Moreover, we note that the HEA can also be used to reduce the intensity of the targeted light, suggesting broad applications in glare suppression. These results demonstrate superior performance in controlling targeted light transport through a multimode fiber at a telecommunication wavelength. We anticipate that this work will open new possibilities in a variety of applications in fiber optics.

Terahertz homodyne spectroscopic imaging of concealed low-absorbing objects

Terahertz (THz) homodyne and direct spectroscopic images of low-absorbing materials packaged between up to six layers of a cotton fabric are recorded at 0.3 and 0.6 THz at room temperature. More than two orders of magnitude higher dynamic range is revealed due to the detection in a homodyne scheme, which is realized using paper sheets as a phase-shifting mechanism. It is demonstrated that the homodyne approach can serve as a convenient imaging tool to identify and resolve objects manifesting low absorbance of THz radiation, such as paper tissue, nitrile, and low-density polyethylene concealed in a textile environment.

An improved narrowband active noise control system without secondary path modelling based on the time domain

Several secondary path, acoustic noise cancellation modelling causes the problems to increase the complexity of ANC implementation, reduction of performance caused by modelling error and requirement of auxiliary noise for secondary path modelling. The acoustic noise generated is further compounded by using secondary path identification which makes the system complex. There are several available ANC algorithms that do not require secondary path estimation for modifying the FxLMS algorithms. Due to drawbacks such as slow convergence speed and, complexity of the phase shift mechanism, a novel approach with no secondary path modelling is adopted, in which the adaptation stability is guaranteed by switching the sign of the step size. It is combined with the online tuneable delay of the reference signal to significantly improve the adaptation convergence properties of the algorithm. A new mathematical modelling has been proposed to reduce the acoustic noise that increases the convergence criteria.

An improved narrowband active noise control system without secondary path modelling based on the time domain

Several secondary path, acoustic noise cancellation modelling causes the problems to increase the complexity of ANC implementation, reduction of performance caused by modelling error and requirement of auxiliary noise for secondary path modelling. The acoustic noise generated is further compounded by using secondary path identification which makes the system complex. There are several available ANC algorithms that do not require secondary path estimation for modifying the FxLMS algorithms. Due to drawbacks such as slow convergence speed and, complexity of the phase shift mechanism, a novel approach with no secondary path modelling is adopted, in which the adaptation stability is guaranteed by switching the sign of the step size. It is combined with the online tuneable delay of the reference signal to significantly improve the adaptation convergence properties of the algorithm. A new mathematical modelling has been proposed to reduce the acoustic noise that increases the convergence criteria.

Two-step carrier-wave stitching method for aspheric and freeform surface measurement with a standard spherical interferometer.

Measurement of aspheric and freeform surfaces remains challenging due to the various shapes of the surface under test (SUT), especially when the SUT has a large aperture and strong deviation from the spherical surface. This paper proposes a two-step carrier-wave stitching method to enlarge the measurement bandwidth of a digital Moiré interferometry. Then, measurements of aspheric and freeform surfaces with a standard spherical interferometer without a phase-shifting mechanism are demonstrated. Experimental results with a root-mean-square repeatability of better than 1/200λ present good consistency to UA3P contact measurement results. Further simulation results with different residual wavefronts confirm measurement accuracies of peak-to-valley value of 10-3λ. The method is effective for large residual wavefronts and thus has potential for flexible measurement of aspheric and freeform surfaces.

Radial-Shaped Single Varactor-Tuned Phasing Line for Active Reflectarrays

A novel phasing line is proposed in this communication for a broadband dynamic tuning of an active aperture-coupled reflectarray cell. A couple of wideband radial stubs, loaded by a single varactor diode, is adopted to realize the dynamic phase shift mechanism, thus combining unit cell beam-scanning and/or reshaping pattern capabilities with frequency reconfigurability feature, as demanded by several radar or satellite communication applications. When compared with the existing solutions on the same task, the proposed configuration integrates a single tunable lumped element (i.e., varactor diode), requiring a very simple biasing network. The proposed approach is adopted to design an $X$ -band reflectarray cell giving 320° phase agility within a measured frequency range of about 8.5%, significantly greater than that achievable through the use of a standard linear phasing line. As a further feature, the designed cell shows a useful improvement of the instantaneous bandwidth at the middle of the tuning band.

Analytical and Numerical Investigation of the Phase Shift and Magnetization Rotation in the PPM Undulator

This paper describes two modifications in the pure permanent magnet (PPM) undulators: 1) phase shift and 2) magnetization rotation, and studies their effects on the radiation harmonics properties. An analytical description for these modifications has been presented and two numerical codes, RADIA and B2E, have been used to model the PPM undulator in the presence of the aforementioned modifications and to calculate their effects on the synchrotron radiation properties. A short description of these codes has been presented. The two most important properties of the harmonics are their energy and intensity. This paper uses a simple theoretical approach to show that the phase shift mechanism can affect the ${K}$ -value of the undulator and then change the harmonics energy and their intensity, while the rotation mechanism does not change harmonics properties notably. Recently, a new combined method called phase combined undulator (PCU) has been supposed. The PCU structure has been fabricated using the phase shift mechanism and applying a specific magnets arrangement to eliminate the magnetic force between upper and lower arrays. The radiation harmonic generation of this structure has been studied.

Investigation on thermal coupled three stage pulse tube cryocooler

Pulse Tube Cryocoolers (PTCs) have been investigated in recent times with the focus on achieving much lower temperature and reliable operation. Lower temperatures can be obtained by cascading the stages of the PTC. These stages can either be gas coupled or thermal coupled. This paper presents the design and development of two different configurations of three stage thermal coupled PTC, one with room temperature phase shifting mechanism (PSM) and the other with cold phase shifting mechanism. For room temperature PSM, the first and second stage are provided with inertance tube, while that for the third stage is provided with inertance tube and a double inlet valve. For the cold PSM, only an inertance tube is used as a phase shifter. In case of PTC with room temperature PSM, a minimum temperature of 19.61 K is achieved with a refrigerating effect of 220 mW at 30 K at the cold end of the third stage pulse tube, with an input power of 600 W. While for the PTC with cold PSM, a minimum temperature of 32.41 K is achieved. A reliability test is carried out; the PTC performed well during the entire operation and the repeatability is established.

Substrate‐integrated waveguide phase shifter with rod‐loaded artificial dielectric slab

A substrate-integrated waveguide (SIW) broadband phase shifter is presented and studied. The phase shift mechanism is based on the synthesis of an artificial dielectric slab using an array of metallic rods in the middle of a SIW. This technique enables a large phase shift within a compact size and enhances the density of integration. As an example, 45° and 90° phase shifters are designed and showcased on a single-layer substrate at a centre frequency of 26 GHz. The amplitude imbalance between the two paths is also avoided while the phase error is less than 5° over a frequency band of 20–32 GHz or around 46% relative bandwidth. The measured return loss is found to be better than 12 dB over the whole frequency band.

Solving stereo transparency with an extended coarse-to-fine disparity energy model.

Modeling stereo transparency with physiologically plausible mechanisms is challenging because in such frameworks, large receptive fields mix up overlapping disparities, whereas small receptive fields can reliably compute only small disparities. It seems necessary to combine information across scales. A coarse-to-fine disparity energy model, with both position- and phase-shift receptive fields, has already been proposed. However, because each scale decodes only one disparity for each location and uses the decoded disparity to select cells at the next scale, this model cannot represent overlapping surfaces at different depths. We have extended the model to solve stereo transparency. First, we introduce multiplicative connections from cells at one scale to the next to implement coarse-to-fine computation. The connection is the strongest when the presynaptic cell's preferred disparity matches the postsynaptic cell's position-shift parameter, encouraging the next scale to encode residual disparities with the more reliable phase-shift mechanism. This modification not only eliminates the artificial decoding and selection steps of the original model but also enables maintenance of complete population responses throughout the coarse-to-fine process. Second, because of this modification, explicit decoding is no longer necessary but rather is for visualization only. We use a simple threshold criterion to decode multiple disparities from population energy responses instead of a single disparity in the original model. We demonstrate our model using simulations on a variety of transparent and nontransparent stereograms. The model also reproduces psychophysically observed disparity interactions (averaging, thickening, attraction, and repulsion) as the depth separation between two overlapping planes varies.

Three-dimensional model of thermal-induced optical phase shifts in rotation sensing

By studying the thermal-induced phase shift mechanism of an interferometric fiber-optic gyroscope (IFOG) sensing coil, a novel generalized expression based on a three-dimensional (3D) model is proposed. Compared with the traditional pure Shupe effect model, the simulation results show that the new 3D model, including elastic strain and the elasto-optical effect, can describe the thermal effect of the coils more accurately. Experiments with temperature change rates between −40°C and 70°C are performed to verify the effectiveness of the proposed generalized expression. The results of our work can guide researchers in identifying countermeasures to reduce the thermal-induced bias error in IFOG.

Solving stereo transparency with an extended coarse-to-fine disparity energy model

Modeling stereo transparency with physiologically plausible mechanisms is challenging because in such frameworks, large receptive fields mix up overlapping disparities, whereas small receptive fields can reliably compute only small disparities. It seems necessary to combine information across scales. A coarse-to-fine disparity energy model, with both position-and phase-shift receptive fields, has already been proposed. However, because each scale decodes only one disparity for each location and uses the decoded disparity to select cells at the next scale, this model cannot represent overlapping surfaces at different depths. We have extended the model to solve stereo transparency. First, we introduce multiplicative connections from cells at one scale to the next to implement coarse-to-fine computation. The connection is the strongest when the presynaptic cell's preferred disparity matches the postsynaptic cell's position-shift parameter, encouraging the next scale to encode residual disparities with the more reliable phase-shift mechanism. This modification not only eliminates the artificial decoding and selection steps of the original model but also enables maintenance of complete population responses throughout the coarse-to-fine process. Second, because of this modification, explicit decoding is no longer necessary but rather is for visualization only. We use a simple threshold criterion to decode multiple disparities from population energy responses instead of a single disparity in the original model. We demonstrate our model using simulations on a variety of transparent and nontransparent stereograms. The model also reproduces psychophysically observed disparity interactions averaging, thickening, attraction, and repulsion as the depth separation between two overlapping planes varies.

Theoretical and experimental investigations on Stirling-type pulse tube cryocoolers with U-type configuration to achieve temperature below 20 K

To achieve lower temperatures is a subject of recent research and development activities in the field of pulse tube cryocoolers. To reach a temperature of 20 K, multi-staging is necessary in Stirling-type pulse tube cryocoolers. In the present work, Sage software is used to design a three-stage gas-coupled as well as thermal-coupled pulse tube cryocooler. A single-stage and a two-stage pulse tube cryocoolers are developed, tested and are coupled by a thermal link to build up a three-stage thermal-coupled pulse tube cryocooler. The lowest temperature of 19.61 K is obtained with a cooling capacity of 220 mW at 30 K at the third stage operating at 17 bar charge pressure and 68 Hz frequency. The phase-shifting mechanism used is a double inlet valve at the third stage while the inertance tube is used for the other stages.

Secondary-Side Phase-Shift-Controlled ZVS DC/DC Converter With Wide Voltage Gain for High Input Voltage Applications

In this paper, a soft-switching dc/dc converter with secondary-side phase-shift control strategy is proposed to improve the conversion efficiency and minimize the primary switch voltage stress in the high input voltage applications. Zero-voltage-switching performance is achieved for both the primary- and secondary-side power devices in a wide load range to reduce the switching losses due to the secondary-side phase-shift control scheme. Furthermore, compared with the conventional phase-shift control mechanism, the circulating current at the freewheeling stage is effectively suppressed as well to minimize the conduction losses. Moreover, the voltage stress of the primary switches is only half of the input voltage by employing the improved three-level structure, which makes the low-voltage rated power devices available to improve the circuit performance. In addition, the converter can work in the buck, balance, and boost modes to achieve a relatively wide input voltage range, which is an expected advantage for the communication power system to minimize the electrolytic capacitors with an acceptable hold-up time. The operation principle is analyzed and experimental results of a 1-kW 100-kHz prototype are provided to verify the effectiveness and the advantages of the proposed converter.

High-Speed Beam Steering With Phased Vertical Cavity Laser Arrays

We demonstrate electronic beam steering using phased vertical cavity laser arrays at record high speed (1.4·10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> deg/s) and sensitivity to current (1.2 deg/100 μA). The relative phase and coherence between the array elements are extracted with a Fraunhoffer propagation method. The spatially resolved spectrum and beam steering dynamics are also analyzed. The thermo-optic effect is found to dominate the phase-shifting mechanism at lower speed steering, while the electronic variation in index dominates at higher speeds (≥10 MHz).

Giant phase shift effect in Tb0.3Dy0.7Fe2/Pb(Zr,Ti)O3 laminated composite

In this letter we present a magnetic field-induced giant phase shift effect under resonant frequency in the bilayered magnetoelectric composite of Tb0.3Dy0.7Fe2(Terfenol-D) and Pb(Zr,Ti)O3. When the bias magnetic field is varied from 0.1 T to 0.3 T, the phase shift of the magnetoelectric effect under 83.2 kHz was as large as 180°, which implies a complete transformation from capacitor behavior to inductor behavior. The phase shift was analyzed in the polar coordinates, and the mechanism of this giant phase shift was considered as the ΔE effect of Terfenol-D. This giant phase shift effect may benefit existing phase modulation techniques.

Low-cost, phase-shifting mechanisms for Newton-type interferometers

Using standard optical shop equipment, it is possible to implement simple, low-cost, phase-shifting Newton interferometers sufficiently accurate for surface evaluation. The simplification of the phase-shifting mechanism is compensated with image-processing algorithms that can deal with vibrations and uneven, nonsequential steps. The results are cross-compared with a Fizeau phase-shifting interferometer to verify the effectiveness of the method.

A method for phase reconstruction in optical three-dimensional shape measurement

In optical three-dimensional shape measurement, a method of improving the measurement precision for phase reconstruction without phase unwrapping is analyzed in detail. Intensities of any five consecutive pixels that lie in the x-axis direction of the phase domain are given. Partial derivatives of the phase function in the x- and y-axis directions are obtained with a phase-shifting mechanism, the origin of which is analysed. Furthermore, to avoid phase unwrapping in the phase reconstruction, we derive the gradient of the phase function and perform a two-dimensional integral along the x- and y-axis directions. The reconstructed phase can be obtained directly by performing numerical integration, and thus it is of great convenience for phase reconstruction. Finally, the results of numerical simulations and practical experiments verify the correctness of the proposed method.

Phase and coherence extraction from a phased vertical cavity laser array

The relative coherence and phase are extracted from two-element, coherently coupled, vertical cavity surface emitting laser arrays. The array elements are defined optically by a photonic crystal pattern and electrically by ion implantation. We obtain the near and far fields experimentally under varying current injection. The Fraunhofer approximation is used to simulate propagation from the near to far field. The phase and coherence are extracted as fitting parameters to match the experimental and propagated far field patterns. The phase and coherence will aid in future array designs and in elucidating the phase-shifting mechanism.

Phase-shifting Zernike phase contrast microscopy for quantitative phase measurement

Zernike phase contrast microscopy is extended and combined with a phase-shifting mechanism to perform quantitative phase measurements of microscopic objects. Dozens of discrete point light sources on a ring are constructed for illumination. For each point light source, three different levels of point-like phase steps are designed, which are alternatively located along a ring on a silica plate to perform phase retardation on the undiffracted (dc) component of the object waves. These three levels of the phase steps are respectively selected by rotating the silica plate. Thus, quantitative evaluation of phase specimens can be performed via phase-shifting mechanism. The proposed method has low "halo" and "shade-off" effects, low coherent noise level, and high lateral resolution due to the improved illumination scheme.