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Vortex beams (VBs), characterized by helical phase front and orbital angular momentum (OAM), have shown perspective potential in improving communication capacity density for providing an additional multiplexing dimension. Here, we propose a diffractive deep neural network (D2NN) method for OAM mode multiplexing and demultiplexing. By designing the D2NN model and simulating light propagation through multiple diffractive screens, the phase and amplitude values can be automatically adjusted to manipulate the wavefront of light beams. Training the D2NN model with mode coupler and separator functions, we convert VBs into target light fields with the diffraction efficiency exceeds 97%, and the mode purities are over 97%. Constructing an OAM multiplexing link, we successfully multiplex and demultiplex two OAM channels that carry 16-QAM signals in simulation, and the demodulated bit-error-rates are below 1×10-4. It is anticipated that the D2NN can perform flexible modulation of multiple OAM modes, which may open a new avenue for high-capacity OAM communication and all-optical information processing, etc.

A wideband omnidirectional circularly polarized (CP) antenna using a conformal artificial anisotropic polarizer is proposed for millimeter-wave applications. The antenna consists of three parts: an omnidirectional linearly polarized (LP) radiator, an annular hyperbolic lens, and a conformal anisotropic polarizer. The annular hyperbolic lens regulates the spherical wavefront from the LP radiator into a cylindrical shape prior to propagating into the conformal artificial anisotropic polarizer. Each curved slab of the polarizer is conformally tilted 45 degrees to the incident electric field. Therefore, the conformal polarizer is the three-dimensionalization of the two-dimensional planar artificial anisotropic polarizer. The polarizer designing methodology is the first of its kind to generate wideband CP wave omnidirectionally. The hyperbolic lens and the conformal polarizer are fabricated together using stereolithography (SLA) 3D printing technology. Measurement results show that the antenna has a wide operating bandwidth of 45% (from 24 to 38 GHz), which completely covers potential 5G 28-GHz spectra. The proposed design has a low fabrication complexity and brings possibilities for high-speed wireless communications utilizing circular polarization.

In this paper, the study initiated in its first part on the traveling waves (TWs) launched by faults on threephase transmission lines is continued, giving major focus to TWs reflection and refraction matrices at line terminations and fault point. By doing so, mathematical expressions that represent the behavior of reflected and refracted voltage and current TWs are obtained in modal domain, for all fault types, allowing the proper estimation of wavefronts measured at the line terminals. Hence, once the amplitude and polarity of wavefronts measured at the line terminals can be predicted for specific fault features, the setup of wavefront detection thresholds and polarity evaluation schemes can be enhanced in practical applications. To demonstrate the validity of the obtained results, the Alternative Transients Program (ATP) is used to simulate fault-induced transients, from which several TWs are analyzed to compare the obtained analytical mathematical TW representation with those verified in the assessed fault records. From the obtained results, the mixing mode phenomena is proven, and the TW reflection and refraction matrices are validated, highlighting the usefulness of the presented mathematical study during the development of modern TW-based applications.

In the fields of optics and photonics, phase-only spatial light modulators (SLMs) play an increasingly important role in wave-front engineering. However, the SLMs are subject to wavefront distortion arising from the imperfection in the birefringence effect and physical structure of modulators. This paper presents a simple self-interference phase calibration method applicable to liquid-crystal SLM. We build a interferometric imaging system basing on the Pancharatnam-phase-shifting to measure the phase distribution of a light beam coming from SLMs. Two types of phase modulation errors of SLMs can be characterized in the measurement process: the erroneous gamma curve and shape aberration. The former belongs to dynamic phase distortion and is measured through a four-step Pancharatnam phase shifting interference, which allows a one-shot recording of interference pattern via a polarization camera; the latter represents static phase distortion and is extracted from the interference between light waves coming from different regions of the SLM panel by using Zernike polynomial fitting. Our method has the advantages of high-precision pixel-wise phase correction and robustness against environmental disturbance, and thus can facilitate the applications of SLM in the optical field manipulation.

The generation and measurement of shear waves are critical in the ultrasonic elasticity imaging.Generally, the resulting wave front direction is very important for accurately measuring the shear speed and estimating the medium elasticity. In this paper, the proposed method can generate a compound shear wave front with the same direction as speed reconstruction and zero angle between the wave front and the focus direction, which can improve the estimation accuracy of shear wave velocity. Also, this method, called time-division multi-point excitation image fusion (TDMPEIF), can reconstruct the shear wave propagation images acquired at different depths of a medium according to the frame sequence to produce the shear waves front with regulable angle. Moreover, the shear wave speed and the elasticity of a medium can be mapped quantitatively with this method. The results demonstrate that the TDMPEIF can improve the quality of the shear wave velocity images, which have wide application value and good promotion prospect for quantitative evaluation of tissue elasticity.

For the traditional subwavelength gratings, we can code different units to construct the coded metagratings. In this paper, we propose an innovative principle of adding coded gratings, which can be used to add or subtract two or more traditional coded metagratings sequences and obtain a new coded metagratings sequence. Based on the proposed addition principle, the coded metagratings can adjust the scattering angle flexibly. This method overcomes the limitation that traditional grating can only obtain discrete diffraction angle. Importantly, compared with traditional gratings, the coded metagrating sequences with addition operation have enhanced diffraction efficiency at the same diffraction angle. This phenomenon may be attributed to the enhanced interaction between the coding particles of the new disordered coding sequence metagratings constructed. Our proposed coded grating addition principle provides a new degree of freedom for the flexible modulation of the terahertz wavefront. At the same time, this method can be extended to optical band or microwave band, which opens a new path for electromagnetic wave modulation and beam scanning.

The required surface shape of the intra-cavity deformable mirror (DM) is not conjugate with the aberration in an unstable standing-wave resonator, which makes the adaptive correction inside the resonator complicated. In this letter, an unstable travelling-wave resonator structure with an intra-cavity adaptive optics (AO) system is proposed to solve this problem. More specifically, the Shark-Hartmann wavefront sensor (SHWFS) and a 980 nm probe beam are employed to measure the aberration of the Nd:YAG slab during lasing operation. A tip/tilt mirror (TTM) is used to correct the intra-cavity tilt, and a DM is employed to compensate for all the remaining intra-cavity aberration. By placing both the wavefront correctors (DM and TTM) and the Nd:YAG slab in the collimated part of the travelling-wave resonator, the required surface shape of the DM is well conjugate with the measured aberration. Experimental results show the proposed method can effectively improve the performance of solid-state slab lasers. After correction, the output power increased from 1312 W to 1587 W, and the corresponding optical-to-optical efficiency increased from 19.5% to 23.6%. Meanwhile, the beam quality $\beta $ was improved from 9.7 to 1.8.

Large scale atom interferometers promise unrivaled strain sensitivity to midband (0.1 - 10 Hz) gravitational waves, and will probe a new parameter space in the search for ultra-light scalar dark matter. These atom interferometers require a momentum separation above 10^4 \hbar k between interferometer arms in order to reach the target sensitivity. Prohibitively high optical intensity and wavefront flatness requirements have thus far limited the maximum achievable momentum splitting. We propose a scheme for optical cavity enhanced atom interferometry, using circulating, spatially resolved pulses, and intracavity frequency modulation to overcome these limitations and reach 10^4 \hbar k momentum separation. We present parameters suitable for the experimental realization of 10^4 \hbar k splitting in a 1 km interferometer using the 698 nm clock transition in 87Sr, and describe performance enhancements in 10 m scale devices operating on the 689 nm intercombination line in 87Sr. Although technically challenging to implement, the laser and cloud requirements are within the reach of upcoming cold-atom based interferometers. Our scheme satisfies the most challenging requirements of these sensors and paves the way for the next generation of high sensitivity, large momentum transfer atom interferometers., Comment: 24 pages, 6 figures

The time of flight of a plane wavefront generated from an acoustic pulse is expected to decrease when the medium length between the wave emitter and receiver is shortened. This simple idea is extrapolated to the case of reservoir compaction in order to obtain a geophysical parameter R (dilation factor) that relates the rock deformation to the variation of time of flight (also called time-lapse time shift in 4D seismics) or acoustic velocity of a plane wave propagating in the same direction of deformation. Interpretation of a few laboratory compressive tests with simultaneous ultrasonic acquisition, performed on oil-saturated calcarenite samples, are presented and discussed. The samples were subjected to several stress regimes and simultaneous ultrasonic acquisitions. Despite the formerly ultrasonic acquisition rate limitations, it was possible to obtain R values for various lateral-vertical stress ratios for each sample's linear and nonlinear stress-strain trends.

We investigate the interaction between a singular surface and a strong shock in the self-gravitating interstellar gas clouds with the assumption of spherical symmetry. Using the method of the Lie group of transformations, a particular solution of the flow variables and the cooling–heating function for an infinitely strong shock is obtained. This paper explores an application of the singular surface theory in the evolution of an acceleration wave front propagating through an unperturbed medium. We discuss the formation of an acceleration, considering the cases of compression and expansion waves. The influence of the cooling–heating function on a shock formation is explained. The results of a collision between a strong shock and an acceleration wave are discussed using the Lax evolutionary conditions.

In linear optical processes, compact and effective wavefront shaping techniques have been developed with the artificially engineered materials and devices in the past decades. Recently, wavefront shaping of light at newly generated frequencies was also demonstrated using nonlinear photonic crystals and metasurfaces. However, the nonlinear wave-shaping devices with both high nonlinear optical efficiency and high wave shaping efficiency are difficult to realize. To circumvent this constraint, we propose the idea of metasurface decorated optical crystal to take the best aspects of both traditional nonlinear crystals and photonic metasurfaces. In the proof-of-concept experiment, we show that a silicon nitride metasurface decorated quartz crystal can be used for the wavefront shaping of the second harmonic waves generated in quartz. With this crystal-metasurface hybrid platform, the nonlinear vortex beam generation and nonlinear holography were successfully demonstrated. The proposed methodology may have important applications in nonlinear structured light generation, super-resolution imaging, and optical information processing, etc.

The two-photon fluorescence imaging depth has been significantly improved in recent years by compensating for tissue scattering with wavefront correction. However, in most approaches the wavefront corrections are valid only over a small sample region on the order of 1 to 10 µm. In samples where most scattering structures are confined to a single plane, sample conjugate correction geometries can increase the observable field to a few tens of µm. Here, we apply a recently introduced fast converging scheme for sensor-less scattering correction termed “Dynamic Adaptive Scattering compensation Holography” (DASH) in a sample conjugate configuration with a high pixel count nematic liquid crystal spatial light modulator (LC-SLM). Using a large SLM allows us to simultaneously correct for scattering at multiple field points, which can be distributed over the entire field of view provided by the objective lens. Despite the comparably slow refresh time of LC-SLMs, we achieve correction times on the order of 10 s per field point, which we show is sufficiently fast to counteract scattering at multiple sites in living mouse hippocampal tissue slices.

Surface waves (SWs) can be coupled by phase gradient metasurfaces (PGMs) with high efficiency, but this methodology still suffers from inherent defects of narrow bandwidth, changeless coupled mode, difficult separation of hybrid modes SWs, and uncontrollable propagation direction. In this article, a series of innovative designs is proposed by combining different Pancharatnam–Berry (PB) PGMs with appointed phase distribution principles to resolve PGMs SWs couplers’ above problems. Both the simulated and measured results verify that the broadband conventional SWs coupler can couple transverse magnetic (TM) mode SWs under $x$ -polarized incidence and the broadband extraordinary SWs coupler can couple TM mode SWs under $y$ -polarized incidence in 8.5–11.5 GHz. By integrating these two SWs couplers, a bifunctional SWs coupler is obtained to couple TM mode SWs to the left and transverse electric (TE) mode SWs to the right simultaneously under $x$ -polarized incidence. Furthermore, another two SWs couplers are designed to excite TM mode SWs with 30° and 45° slant directions under $x$ -polarized incidence in 8.5–11.5 GHz, which indicates that coupled SWs’ wavefront direction can be controlled flexibly in a wide bandwidth. The above SWs couplers are proved to work with relatively high coupling efficiencies and have great potential in engineering applications.

Spin-selective reflection metadevices are usually realized by using chiral metamirrors that can reflect one state of circularly polarized (CP) waves and restrain the other one. However, most of the chiral metamirrors only exhibit chirality in a narrow band, which may impede their potential applications. Here, we propose a Pancharatnam–Berry (PB) coding metasurface composed of the spin-decoupled elements to realize broadband spin-selective reflections with arbitrary wavefront manipulations. The spin-selective anomalous reflection is designed and measured to validate the performance of the proposed PB coding metasurface. Both simulation and experiment results show that the designated CP wave can be efficiently reflected without reversing the spin state, while at the same time, its orthogonally polarized wave is suppressed by random diffusion, in a broad band from 16 to 24 GHz. The results also reveal that the proposed PB coding metasurface has the chiral-like characteristics, even though it is composed of nonchiral meta-elements.

We demonstrate a technique to realize fine target tracking and pointing using target-in-the-loop (TIL) concept via a coherent beam combining (CBC) system. A tracking and pointing system is composed of a densely packed array of 7 phase-control elements with simultaneous piston and tilt controls of the outgoing beams wavefront phases. A photo-detector (PD) with a pinhole is used as target detection and installed on a translation stage. Energy detected by the mobile PD is used for evaluating the beam combining and scanning performance, and to provide the feedback signal for controls of piston and tilt phases of the transmitted beams by using the stochastic parallel gradient descent (SPGD) algorithm for merit function maximization.

Vortex electromagnetic (EM) wave carrying orbital angular momentum (OAM), whose unique wavefront distribution exhibits angular diversity characteristics, which provides a richer degree of freedom f...

The Shack-Hartmann wavefront sensor restricts the dynamic range and detection accuracy of wavefront detection due to the limitation of the lens array aperture. This study proposes a system using signal light nutation to detect wavefront distortion, providing high spatial resolution and detection dynamic range. Simulations show that the root mean square (RMS) and mixing efficiency of the compensated wavefront are optimized. In the case of strong turbulence, the mixing efficiency is increased by nearly 105 times, and the RMS is reduced to the original value of 0.048.

Purpose. Determination of the influence of the intraocular lens (IOL) inclination and decentration on the magnitude of induced astigmatism in a theoretical study using software on an eye model. Material and methods. An eye model with the specified parameters was performed to carry out the calculation. Modulation of the change in the wavefront was carried out using the Zemax program (LLC, USA). In the model eye, the probability of induction of astigmatism was analyzed depending on the change in the position of the aspherical IOL Acrysof IQ 16.0, 22.0 and 24.0 diopters and the toric model Acrysof IQ Toric SN6AT3, SN6AT4 and SN6AT5. The angle of inclination of the IOL relative to the horizontal plane was examined from 0° to 10° with a step of 1°, decentration from 0.1 to 1.5 mm with a step of 0.1 mm. At each IOL position, aberration data of the 2nd order Z (2, 2) were recorded. The obtained results were used to calculate the critical tilt angle and decentration. Results. The magnitude of induced astigmatism increased with the rise of the degree of inclination and decentration, corresponding to an increase in the optical power of the IOL. Accordingly, critically significant were the values of 3.0° inclination for the aspherical IOL with an optical power of 22.0 and 22.0 diopters and 3.5° for 16.0 diopters, decentration – 0.7 mm and 1.0 mm. The inclination of the TIOL relative to the horizontal plane revealed the induction of the magnitude of inverse astigmatism, according to an increase in the inclination angle of 0.3 diopters at a slope of 3–4°. Conclusions. The tilt and decentration of the aspherical and TIOL patterns induce astigmatism depending on the increase in IOL power. The inclination of the TIOL in relation to the horizontal plane set at 90 ° promotes the induction of astigmatism. Key words: astigmatism, toric intraocular lenses, tilt and decentration of the intraocular lens, ray tracing

In a classical metasurface-based holographic display system, a clear holographic reconstruction image can be obtained only in the back-focal-plane of the lens. However, when the receiving plane deviates from the focal plane, the reconstructed holographic image suffers from degradations that limit the quality of the images. Hence, we propose a novel metasurface-based holographic display to realize clearly continuous imaging within the specified position range by superimposing the meta-axilens phase. It can effectively relieve the alignment requirements of the imaging system. Firstly, the parameters and properties of all-dielectric meta-atom is analyzed. Then we compare and demonstrate two sets of metasurface-based optical elements (meta-axicon, meta-lens, and meta-axilens), made by silicon meta-atoms working at 610 nm. Furthermore, we show that the metasurface hologram with the axilens phase can form a series of the relatively clear holographic images away from the focal plane. Our proposal suggests a method to reconstruct holographic wavefront in different planes simultaneously, and one can find their application domain, such as 3D biological imaging, spectroscopy, optical information storage, and encryption.

All-dielectric nanophotonics has become one of the most active fields of research in modern optics, largely due to the opportunities offered by the simultaneous resonant control of electric and magnetic components of light at the nanoscale. In this rapidly evolving scenario, the possibility to design artificial Huygens sources by overlapping electric and magnetic resonances has established a new paradigm in flat optics, bringing devices closer to efficient wavefront shaping with a direct phase engineering at the level of the individual meta-atoms. However, their efficiency is fundamentally limited by the near field coupling between the constituents of the metalattice. In this work, we challenge this well-conceived notion and propose an alternative concept to achieve phase control and full transmission in metasurfaces, based on the unusual properties of the nonradiating sources known as Hybrid Anapoles (HAs). We analyze theoretically an array of such sources and demonstrate that HAs are characterized by a negligible coupling with their neighbors. Therefore, in contrast to Huygens particles, the proposed sources can operate as individual meta-atoms even in highly compact designs, becoming robust against strong disorder and preserving its characteristics when deposited on dielectric substrates. Remarkably, the phase of the transmitted wave can be modulated with negligible reflection. To illustrate the capabilities of our platform, we also utilize a disordered HA array to implement a controlled phase modulation to an ultrafast gaussian pulse. The results of our study represent a departure from the currently established designs and open an avenue towards the realization of new devices for flat optics with unprecedented efficiency., 10 pages, 6 figures

—Atmospheric turbulence has been simulated under laboratory conditions, where a household heat fan has been used as a source of air flows of different temperatures. The wavefront distortions of laser radiation passing through a heated air flow have been studied by means of a Shack-Hartmann wavefront sensor, which is part of a fast adaptive optical system that has a correction rate of up to 2000 Hz (frames per second). The energy spectra of laser radiation wavefront disturbances are presented, which help determine the frequency bandwidth of the disturbing effect. Based on the calculated Fried parameter, a graph is plotted for the turbulent flow, which compares the results of the laboratory simulation with the real conditions of the Earth’s atmosphere.

The conditions securing stability in configurations that employ gain media, carry vital information for the operation and functionality of the respective systems. These constraints are determined for a generic photonic setup comprising two concentric, passive or active, cylindrical impedance metasurfaces, by assuming their size small compared to the oscillation wavelength. Such an approximation, permits the analytical determination of the unstable poles across the complex frequency plane, which is otherwise a computationally cumbersome task. The absorbing and scattering response of the structure, when excited by various primary sources, unveils the dynamics behind the supported resonances and reveals the limits in its performance while respecting stability restrictions. The reported results may assist substantially the modeling and stable design of devices involving this ubiquitous cylindrical component in numerous applications spanning from radiation pattern control and angular momentum transformation to active cloaking and reconfigurable wavefront manipulation.

Polaritons in anisotropic materials result in exotic optical features, which can provide opportunities to control light at the nanoscale1-10. So far these polaritons have been limited to two classes: bulk polaritons, which propagate inside a material, and surface polaritons, which decay exponentially away from an interface. Here we report a near-field observation of ghost phonon polaritons, which propagate with in-plane hyperbolic dispersion on the surface of a polar uniaxial crystal and, at the same time, exhibit oblique wavefronts in the bulk. Ghost polaritons are an atypical non-uniform surface wave solution of Maxwell's equations, arising at the surface of uniaxial materials in which the optic axis is slanted with respect to the interface. They exhibit an unusual bi-state nature, being both propagating (phase-progressing) and evanescent (decaying) within the crystal bulk, in contrast to conventional surface waves that are purely evanescent away from the interface. Our real-space near-field imaging experiments reveal long-distance (over 20 micrometres), ray-like propagation of deeply subwavelength ghost polaritons across the surface, verifying long-range, directional and diffraction-less polariton propagation. At the same time, we show that control of the out-of-plane angle of the optic axis enables hyperbolic-to-elliptic topological transitions at fixed frequency, providing a route to tailor the band diagram topology of surface polariton waves. Our results demonstrate a polaritonic wave phenomenon with unique opportunities to tailor nanoscale light in natural anisotropic crystals.

We propose a broadband silicon four-mode multi/demultiplexer which consists of three asymmetric directional couplers, and the asymmetric directional couplers were designed by a wavefront matching method to operate as mode multi/demultiplexers for TE1, TE2, and TE3 modes, respectively. Simulated results show that the -0.5-dB bandwidths of normalized transmission of the couplers designed by a wavefront matching method are 112, 114, and 134 nm, respectively. Those for the conventional couplers are 80, 72, 65 nm, respectively. The superiority of asymmetric directional couplers designed by a wavefront matching method are experimentally demonstrated. In the additional investigation, ultrabroadband tapered asymmetric directional couplers are theoretically demonstrated. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Attosecond delay lines are key to enable time-resolved measurements on atoms, molecules, plasma and solid-state materials. This tutorial review presents the current status of a wide variety of attosecond delay lines operating from the infrared to the X-ray spectral region. Depending on the wavelength regime of the pump and probe pulses, we have divided attosecond delay lines into four broad categories: IR–IR, XUV–IR, XUV–XUV and X-ray–X-ray delay lines. Further, the designs differ as to whether they are based on amplitude division or wavefront division of the laser beam. We discuss the design ideas, compactness, calibration and stability of various attosecond delay lines and compare their performance in corresponding experiments. Applications of the delay lines to resolve selected attosecond phenomena are shown along with future perspectives towards achieving zeptosecond resolution.

This paper is devoted to the study of vortex beam transmission from an adjustable magnetized plasma-ferrite structure with negative refraction index. We use the angular spectral expansion technique together with the $$4\times 4$$ 4 × 4 matrix method to find out the transmitted intensity and phase profiles of incoming Laguerre-Gaussian beam. Based on numerical analysis we demonstrate that high transparency and large amount of Faraday rotation in the proximity of resonance frequency region, reverse rotation of spiral wave front, and side-band modes generation during propagation are the remarkable features of our proposed structure. These controllable properties of plasma-ferrite metamaterials via external static magnetic field and other structure parameters provide novel facilities for manipulating intensity and phase profiles of vortex radiation in transmission through the material. It is expected that the results of this work will be beneficial to develop active magneto-optical devices, orbital angular momentum based applications, and wavefront engineering.

Stemming from the law of energy conservation applied to scattering, generalized exact partial-wave series expressions are derived for the extrinsic and intrinsic acoustic scattering, extinction and absorption cross-sections for a pair of fluid/liquid-like (viscous) cylinders of arbitrary radii. The incident insonifying field is of arbitrary shape such that any structured wavefront in two-dimensions is accomodated by this formalism, in contrast with the case of plane waves. The modal expansion method in combination with the translational addition theorem for cylindrical wave functions are used to derive the exact analytical expressions for the quadratic (nonlinear) cross-sections, and numerical computations for a non-paraxial focused Gaussian acoustical sheet chosen as an example illustrate the analysis. The results clearly show the difference between the behavior of the extrinsic and intrinsic cross-sections. The formalism presented here is generalized for any acoustical sheet such that Airy, Hermite-Gaussian and other wavefronts (in 2D) can be considered provided the appropriate beam-shape coefficients are used. The analogy with the optical counterpart is also noted.

Over-the-air (OTA) measurement is mandatory for 5G mm-wave wireless devices. The compact antenna test range (CATR) is the baseline method in the current version of TR 38.810 in 3rd generation partnership project (3GPP) and cellular telecommunications industry association (CTIA) millimeter-wave (mm-Wave) test plan. For CATR, both amplitude and phase variations inside the quiet zone (QZ) could affect the final OTA results significantly and hence need to be characterized carefully. Especially in the phase validation of QZ, even slight misalignments between sampling plane and incident plane wavefront due to the limited precision of the positioner or tolerance in antenna fixture could result in large phase variations, which is not the true phase property of QZ. This letter presents a method to remove the effect of the angular error due to misalignment when measuring the phase variation inside QZ. By adopting the proposed method to the measured phase data, any angular error due to misalignment with respect to the incident plane wavefront will be eliminated mathematically, leaving the true phase variations of QZ only. In the meanwhile, the proposed method can alleviate the requirements of fixture manufacture and alignment precision and reduce the test cost.

In this article, a holograph-inspired flat lens antenna capable of simultaneously transmitting two independent coaxially propagating orbital angular momentum (OAM) beams operating at 60 GHz is proposed. In the flat lens design, holographic theory including the processes of recording and reconstruction are developed to obtain the desired compensation phase distribution of the flat lens. Novel wideband $C$ -shaped polarization-conversation transmit array element and broadband magneto-electric (ME) dipole antenna are designed as the building block and feed source of the flat lens, respectively, resulting in the wideband performance of the whole antenna. The ME dipole sources do not carry OAM modes while the flat lens can transform the spherical wavefront from the two ME dipole sources into transmitted vortex waves with different OAM numbers $\ell =-1$ and +1 simultaneously. For validation, an antenna prototype was fabricated and the radiation performances including return loss, isolation between the two OAM channels, near-field, and far-field performance are experimentally characterized. Both numerical and experimental results validate that the designed flat lens antenna can successfully demonstrate OAM mode multiplexing. The proposed OAM-multiplexing antenna shows promising potential in millimeter-wave high-speed wireless communications.

Numerical simulations were carried out to evaluate the effects of different aberrations modes on the performance of optical system, when observing and imaging the solar surface. Karhunen-Loeve aberrations modes were simulated as a wave front error in the aperture function of the optical system. To identify and apply the appropriate rectification that removes or reduces various types of aberration, their attribute must be firstly determined and quantitatively described. Wave aberration function is well suitable for this purpose because it fully characterizes the progressive effect of the optical system on the wave front passing through the aperture. The Karhunen-Loeve polynomials for circular aperture were used to describe wave front deviations and to predict the initial state of adaptive optics corrections. The results showed that increasing the aberration modes causes an increase in the blurring of the observed image. Also, we conclude that the optical phase error is increased significantly when aperture’s radii are increased.

Airy patterns, formed by the Fraunhofer diffraction of plane waves via circular apertures, have been widely utilized as criterions in areas such as imaging optics and energy transmission. With deeper insights into the spatial structure of light, the use of Airy patterns as criterions today becomes inadequate in many scenarios. Here, a new concept of higher-order Airy patterns is proposed by introducing the orbital angular momentum (OAM) of light, namely the Fraunhofer diffraction pattern of a plane wave via the defined annular aperture with helical wavefront tailoring. For the m -order Airy pattern, the tailored helicity is m , and the scaling factor of the annular aperture and is determined by the m -related equation set, which is derived based on the paraxial diffraction theory. As a potential application of the proposed concept, a coherent fiber laser array system capable of customizing OAM beams is presented and analyzed. Using the higher-order Airy pattern to define the performance metric of combined beam, the fiber laser array system is optimally designed and the properties in energy concentration and high mode purity of the generated OAM beams could be realized. This work could be beneficial to the theoretical study and applications of OAM beams, especially the generation and manipulation of high-power, fast switchable OAM beams with fiber laser arrays.

Direct exoplanet imaging with a stellar coronagraph increases the contrast of the image in the diffraction vicinity of the star. Insufficient reduction of the stellar background is due to the required quality of the wavefront, which exceeds the capabilities of modern optical and astronomical systems. This study evaluates the achievable coronagraphic contrasts for ground-based and extra-atmospheric telescopes without the use of adaptive optics (AO); further, it is planned to use AO devices: tip-tilt mirror and pixel-based AO for the correction of the zonal error. For practical testing of a prospective multicircuit telescope system with active wavefront-correcting optics, we constructed a coronagraph with a small telescope aperture, which makes it possible to observe the effect of coronagraphic attenuation of a star. The latter is important for the testing of precision guidance of the star by the automated parallax drive of the telescope to construct a practical sequence of the operation of adaptive optics devices. The errors of the wavefront inside the interference coronagraph were estimated, experiments were commenced, and line of sight retention was obtained.

Results of the numerical study of a possibility of compensating for aero-optical aberration distortions of the beam wavefront using the aperture sensing technique based on atmospheric backscatter signals are described. It is shown that the technique makes it possible to partially compensate for aero-optical aberrations. The cross section beam size becomes several times smaller than that of a beam without the wavefront adaptive control, and the intensity distribution becomes more symmetric about the optical axis.

In this paper, we calculated the radiation from the state where an electron in cyclotron motion under the uniform magnetic field Bex was accelerated by the externally applied circularly polarized wave with strong Ein and Bin. The electron was accelerated in the parallel direction by the term β⊥ × Bin (β⊥: perpendicular velocity of the electron) as well as in the perpendicular direction by the electric field of the wave Ein. Then, the electron can be resonantly accelerated when the Bex is set to the magnetic field strength which is equivalent to frequency of the externally applied circularly polarized wave. The radiation from such an accelerated electron was confirmed to have helical wavefront at harmonics cyclotron frequency.

Two physical phenomena, (i) diameter of the collecting area of a telescope and (ii) turbulence in the atmosphere which introduces fluctuations in the index of refraction along the light beam, limit the minimum resolvable angle at optical and infrared wavelengths. Sharpness of astronomical images thus obtained can be significantly enhanced by using a back end adaptive optics system which reduces the incoming wavefront distortion by suitably deforming a mirror in real-time, and speckle interferometry which is a post-processing technique. The Nobel prize-2020 in physics award to astronomers has recognised the efforts of using these techniques. After a short description of the black hole, this article elucidates the methodology employed to identify such an object having a mass of about 4 million solar masses.

The term space wave refers to a wave that is propagating through an open medium with a diverging wavefront as it moves away from the source. The term guided wave denotes a variety of wave configurations that are being carried by a closed/open/partially open structure [1]. A guided wave may also be known as a bounded wave, which is a term inspired by its propagation mechanism, where a traveling wave is bounded by two dissimilar mediums with different electromagnetic (EM) characteristics; the wave propagates along the interface and decays exponentially to the surrounding mediums.

Three physical elements are missing from the conventional formalism of quantum photonics: (1) the quantum Rayleigh spontaneous and stimulated emissions; (2) the unavoidable parametric amplification; and (3) the mixed time-frequency spectral structure of a photonic field which specifies its duration or spatial extent. As a single photon enters a dielectric medium, the quantum Rayleigh scattering prevents it from propagating in a straight-line, thereby destroying any possible entanglement. A pure dynamic and coherent state composed of two consecutive number states, delivers the correct expectation values for the number of photons carried by a photonic wave front, its complex optical field, and phase quadratures. The intrinsic longitudinal and lateral field profiles associated with a group of photons for any instantaneous number of photons are independent of the source. These photonic properties enable a step-by-step analysis of the correlation functions characterizing counting of coincident numbers of photons or intensities with unity visibility interference, spanning the classical and quantum optic regimes.

An expression is obtained for the point spread function of a four-wave radiation converter in a multimode waveguide with Kerr nonlinearity, taking into account the transfer of energy from the object wave to the signal wave and vice versa. For single-mode pump waves, the presence of generation points is shown and conditions are found on the waveguide parameters, characteristics of the interacting waves, under which the generation condition is realized. In the vicinity of the generation points, the shape of the point spread function is determined by one of the waveguide modes, the number of which coincides with the number of the pump wave mode. For a four-wave radiation converter in a waveguide with infinitely conducting surfaces, the quality of the wavefront conjugation near the second generation point coincides with the quality of the wavefront conjugation at a low reflection coefficient. For a four-wave radiation converter in a parabolic waveguide near the second and next generation points, the shape of the point spread function is determined by one of the waveguide modes.

We investigate the focal plane wavefront sensing technique, known as Phase Diversity, at the scientific focal plane of a segmented mirror telescope with an adaptive optics (AO) system. We specifically consider an optical system imaging a point source in the context of (i) an artificial source within the telescope structure and (ii) from AO-corrected images of a bright star. From our simulations, we reliably disentangle segmented telescope phasing errors from non-common path aberrations (NCPA) for both a theoretical source and on-sky, AO-corrected images where we have simulated the Keck/NIRC2 system. This quantification from on-sky images is appealing, as it's sensitive to the cumulative wavefront perturbations of the entire optical train; disentanglement of phasing errors and NCPA is therefore critical, where any potential correction to the primary mirror from an estimate must contain minimal NCPA contributions. Our estimates require a one-minute sequence of short-exposure, AO-corrected images; by exploiting a slight modification to the AO-loop, we find that 75 defocused images produces reliable estimates. We demonstrate a correction from our estimates to the primary and deformable mirror results in a wavefront error reduction of up to 67% and 65% for phasing errors and NCPA, respectively. If the segment phasing errors on the Keck primary are on the order of ~130 nm RMS, we show we can improve the H-band Strehl ratio by up to 10% by using our algorithm. We conclude our technique works well to estimate NCPA alone from on-sky images, suggesting it is a promising method for any AO-system., 14 pages, 17 figures, Accepted to MNRAS

In this communication, we propose a robust broadband anomalous refractor (BAR), which minimizes chromatic aberration. The design is based on engineering the dispersion curve of spoof surface plasmon polaritons (SSPPs) and manipulating the wavefront of the transmitted waves. We begin by deriving deflection conditions such that the discrete scatterers of the refractor need to have linear dispersion curves in the operating frequency band. The rich dispersion properties of the SSPP make it a good candidate for meeting the broadband deflection condition. Next, we design symmetric metallic blade structures (MBSs) to efficiently transform free-space waves into SSPPs and to realize the broadband linear dispersion relationship. The BAR is comprised of these MBSs with different strip heights. A prototype is designed, fabricated, and measured. Both the simulated and experimental results demonstrate excellent fixed-direction deflection in the 6.9–9.1 GHz band for the normal incidence case. Furthermore, the BAR still performs well when its outer profile is deformed to some extent, which is desirable in practical applications. This alternative approach to designing achromatic devices at microwave frequencies can be readily extended to higher frequencies.

The possibility of reconstructing the spatial distribution of average air density in a supersonic jet from results of laser transillumination is considered. It is shown that the reconstruction procedure for axisymmetric flows can be performed based on Abel transforms by results of measurements of local wavefront tilts. An algorithm for reconstructing the average density of air in a medium from the deviations of the front of the transillumination wave relative to the jet axis is developed. The algorithm is tested in experiments on the vertical jet facility of the Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences. The results agree well both with contact measurement data known from the literature and with the numerical solution of the hydrodynamic problem.

When sound interacts with geometrically asymmetric structures, it experiences coupling between pressure and particle velocity, known as Willis coupling. While in most instances this phenomenon is perturbative in nature, tailored asymmetries combined with resonances can largely enhance it, enabling exotic acoustic phenomena. In these systems, Willis coupling obeys reciprocity, imposing an even symmetry of the Willis coefficients with respect to time reversal and the impinging wave vector, which translates into stringent constraints on the overall scattering response. In this work, we introduce and experimentally observe a dual form of acoustic Willis coupling, arising in geometrically symmetric structures when time-reversal symmetry is broken, for which the pressure-velocity coupling is purely odd-symmetric. We derive the conditions to maximize this effect, we experimentally verify it in a symmetric subwavelength scatterer biased by angular momentum, and we demonstrate the opportunities for sound scattering enabled by odd Willis coupling. Our study opens directions for acoustic metamaterials, with direct implications for sound control, non-reciprocal scattering, wavefront shaping and signal routing, of broad interest also for nano-optics, photonics, elasto-dynamics, and mechanics. Exploiting Willis coupling in acoustic metamaterials with designed geometrical asymmetries opens up new opportunities related to sound control and manipulation. Here, the authors report a dual form of Willis coupling in geometrically symmetric acoustic scatterers.

Flexible and fast control of the phase and amplitude of coherent light, enabled by digital micromirror devices (DMDs) and spatial light modulators, has been a driving force for recent advances in optical tweezers, nonlinear microscopy, and wavefront shaping. In contrast, engineering spatially partially coherent light remains widely elusive due to the lack of tools enabling a joint analysis and control sequence. Here, we report an approach to coherence engineering that combines a quasi-monochromatic, thermal source and a DMD together with a ptychographic scanning microscope. The reported method opens up new routes to low-cost coherence control, with applications in micromanipulation, nanophotonics, and quantitative phase contrast imaging.

Electromagnetic metasurface cloaks provide an alternative paradigm toward rendering arbitrarily shaped scatterers invisible. Most transformation-optics (TO) cloaks intrinsically need wavelength-scale volume/thickness, such that the incoming waves could have enough long paths to interact with structured meta-atoms in the cloak region and consequently restore the wavefront. Other challenges of TO cloaks include the polarization-dependent operation to avoid singular parameters of composite cloaking materials and limitations of canonical geometries, e.g., circular, elliptical, trapezoidal, and triangular shapes. Here, we report for the first time a conformal-skin metasurface carpet cloak, enabling to work under arbitrary states of polarization (SOP) at Poincaré sphere for the incident light and arbitrary conformal platform of the object to be cloaked. By exploiting the foundry three-dimensional (3D) printing techniques to fabricate judiciously designed meta-atoms on the external surface of a conformal object, the spatial distributions of intensity and polarization of its scattered lights can be reconstructed exactly the same as if the scattering wavefront were deflected from a flat ground at any SOP, concealing targets under polarization-scanning detections. Two conformal-skin carpet cloaks working for partial- and full-azimuth plane operation are respectively fabricated on trapezoid and pyramid platforms via 3D printing. Experimental results are in good agreement with numerical simulations and both demonstrate the polarization-insensitive cloaking within a desirable bandwidth. Our approach paves a deterministic and robust step forward to the realization of interfacial, free-form, and full-polarization cloaking for a realistic arbitrary-shape target in real-world applications.