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The phase-coding method is useful in 3D shape measurement due to its low sensitivity to surface contrast and camera noise. However, as the number of fringe periods increases, the wrapped phase recovered from the sinusoidal phase-shifting patterns is always misaligned with the fringe order calculated by the stair-coding patterns. To solve this, an improved dual-frequency phase-coding fringe projection method is designed to realize absolute phase retrieval. Specifically, the auxiliary fringe order determined by phase-shifting is used to get the absolute phase, which can eliminate fringe-order errors. Moreover, to increase speed and the number of codewords, this paper presents a scheme that only requires seven patterns, including a uniform gray image, two high-frequency sinusoidal fringe patterns, two low-frequency sinusoidal fringe patterns and two phase-coding fringe patterns. Therefore, this method requires fewer patterns to realize high-resolution measurement than existing methods. The success of the proposed method can be proved by experiments. [ABSTRACT FROM AUTHOR]

In this paper, we show how to enhance the transmission of the surface plasmon field using several interacting two-level quantum emitters placed in a plasmonic environment. Our model relies on quantum interference effect and, therefore, can be treated as a plasmonic analog of the electromagnetic induced transparency, usually referred to in the context of driven atomic systems. Moreover, our model with multiple interacting quantum emitters, similar to Ising spin chain, can be used for broadband transmission of the surface plasmon field. [ABSTRACT FROM AUTHOR]

Acoustic radiation force optical coherence elastography (ARF-OCE) has been widely employed for elasticity imaging of ocular tissues, however, it has not been applied to detecting the biomechanical properties of the human cornea. In this paper, we performed the experiments on ex vivo human eyes by using ARF-OCE, where the 2D OCT structural images and elastic wave propagations from human corneas were achieved, and the resulting Young's modulus agreed well with the results measured by other methods, indicating the feasibility and reliability of ARF-OCE. With the advantages of non-invasive measurement, high resolution, high sensitivity and real-time imaging, ARF-OCE could be an effective way to rebuild the cornea elasticity and may be applied in clinical ophthalmology in the future. [ABSTRACT FROM AUTHOR]

This paper proposes a dual-function speckle interferometry system based on the temporal phase-shifting technique for both the digital speckle pattern interferometry (DSPI) and digital shearography (DS) measurement. The principle of the dual-function system has been described comprehensively based on the scalar diffraction theory. The simulation results show that the dual-function system which is based on the object beam multiplexing can simultaneously measure the out-of-plane displacement and slope under the single loading. The sensitivity of the out-of-plane displacement solved by the DSPI and DS method is discussed. Due to the error of the integration, the accuracy of the out-of-plane displacement calculation in DSPI is better than in DS. Finally, the dual-function speckle interferometry system has been proven effective in the edge detection of internal defects. [ABSTRACT FROM AUTHOR]

Spectroscopic data often suffers from spectral distortions due to the influence of the bandwidth function of the spectrograph. In this paper, a spectroscopic bandwidth correction method based on multi-bandwidth functions is proposed. Different from the original bandwidth correction method which only employs one bandwidth function, the proposed method simultaneously uses multi-bandwidth functions collected at different wavelengths to estimate the real spectrum, which effectively eliminates the correction error caused by the differences in bandwidth functions of the whole band. The proposed method and the Richardson-Lucy (R-L) method were used to correct a simulated measured light-emitting diode (LED) spectrum and a simulated measured compact fluorescent lamp (CFL) spectrum. The correction errors, type A uncertainties, and root mean square errors (RMSEs) for the two methods were compared. The result of the comparison shows the superiority of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In this paper, a new image fusion algorithm based on non-subsampled contourlet transform (NSCT) is proposed for the fusion of multi-focus images. The selection of different subband coefficients obtained by the NSCT decomposition is critical to image fusion. So, in this paper, firstly, original images are decomposed into different frequency subband coefficients by NSCT. Secondly, the selection of the low-frequency subband coefficients and the bandpass directional subband coefficients is discussed in detail. For the selection of the low-frequency subband coefficients, the non-negative matrix factorization (NMF) method is adopted. For the selection of bandpass directional subband coefficients, a regional cross-gradient method that selects the coefficients according to the minimum of the regional cross-gradient is proposed. Finally, the fused image is obtained by performing the inverse NSCT on the combined coefficients. The experimental results show that the proposed fusion algorithm can achieve significant results in getting a new image where all parts are sharp. [ABSTRACT FROM PUBLISHER]

A hybrid particle swarm optimization algorithm for determining extrinsic parameters of the camera, with the intrinsic parameters known, is presented in this paper. An adaptive inertia weighting strategy is designed, and improved crossover and mutation operation are performed. Taking the result of the particle swarm optimization algorithm as the initial value, the extrinsic parameters of the camera are optimized by Gauss–Newton method. The simulation results demonstrate that, when the standard deviation of image noise is 0.1 pixels, the mean relative error of rotation angle is less than 0.04844% and the mean relative error of translation vector is less than 0.05583%. The experimental results show that the mean reprojection error of the proposed algorithm is no more than 0.06045 pixels. The algorithm can achieve high precision and robustness in practical applications. Besides, the algorithm is computational efficient. [ABSTRACT FROM AUTHOR]

Nonlinearities in the application of fringe projection metrology make it very difficult to acquire perfect 3D data. This paper describes a six-step phase-shifting technique for a structured light measurement system with an off-the-shelf projector. First, the phase error is analysed and a gamma model is established by deriving the relative expression between the wrapped phase and input images. This is then expressed in matrix form to derive a unique solution, which is used for the gamma solver. The complex gamma calibration and projector error compensation can be removed once the gamma value of the off-the-shelf projector has been determined. The ideal model reconstruction results are obtained through simulations and experiments, and the standard deviation of the phase error is found to be only 0.0039 radians. Hence, the proposed method eliminates the nonlinear errors associated with fringe projection technology using existing projectors and improves the overall image reconstruction quality. [ABSTRACT FROM AUTHOR]

In idealized secret image sharing (SIS), all of the shared images (shadows) play the same role, but in real life, the shared images are often hierarchical. This paper proposes a hierarchical secret image sharing (HSIS) method by means of optical imaging. To implement the scheme, a generalized single-phase modulation algorithm is proposed in Fresnel transform domain. Its features that multiple secret images can be recovered through combination of some shared images though each participant only holds one share of images. Theoretically, the secret images are divided into multiple phase encodings (shared images) by phase modulation, each secret image can be directly captured by the intensity detector when illuminating some of the shared images orderly displayed with parallel light. Experimental simulation shows that the shared images and the restored secret images do not have any size distortion, and further verifies the feasibility of the proposed scheme. [ABSTRACT FROM AUTHOR]

Edge detection is the basis of image segmentation and object recognition, as edge generally contains important information of an object. In this paper, we propose a novel speckle-shifting ghost imaging (SSGI) method to extract the edge of an unknown object. In this method, the gradient operation is directly carried out to the illumination patterns rather than the captured object image. The structured patterns for illumination are only divided into two groups, which can extract the edge in all directions. The imaging result is clearer than the conventional SSGI, but the noise is still serious. To solve the problem, we further investigate a denoising method with morphology algorithms, such as frame difference and connected region labelling. Numerical simulations and experiments are carried out to verify the feasibility and effectiveness. [ABSTRACT FROM AUTHOR]

In this paper, we propose a single-mode double-cavity photonic crystal (PhC) sensor for simultaneous detection of ambient refractive index (RI) and temperature. L3 cavity and L4 cavity are cascaded on both sides of the photonic crystal W1 waveguide. Two 0th-order modes generated by the two cavities with Q-factors over 16,330.80 and 8358.21 are used for sensing, which have a strong constraint on photons than the higher-order modes. By simulating the refractive index and temperature of the PhC structure, the sensing matrix can realize simultaneous sensing of two parameters. The maximum crosstalk of the two cavities is very low and can increase the accuracy of the detection. And the structure shows a good fabrication tolerance considering the deviation of the hole radius. The application of the PhC to dual-parameter sensing with high accuracy is proposed, which provides an idea for dual-parameter sensing. [ABSTRACT FROM AUTHOR]

Derivation of effective-medium permittivities (in the traditional sense) of one-dimensional gratings is revisited. In the present derivation, carried out in Fourier-space and for conical mounting, systematic treatment and mathematical rigour are emphasized. An error of a previous paper published in this journal concerning the 2nd-order effective permittivity in TM polarization is corrected. The derived formulas of the 4th-order effective permittivity and the 2nd-order effective permittivity, when restricted to TE and TM polarizations respectively, agree well with the previous results. The symmetry of the effective permittivities with respect to the sign of the Floquet exponential factor and the sign of grating period is noted and proven. [ABSTRACT FROM AUTHOR]

In this paper, we aim to design an all-optical device, which can perform XOR and XNOR functions in a single structure. The proposed structure will be realized by cascading two nonlinear resonant rings. The functionality of the proposed structure is based on controlling the optical behaviour of optical rings via optical intensity. The final structure has one bias and two input control ports, along with two output ports. One port acts as an XOR and the other acts as an XNOR gate. The maximum delay times for the XOR and XNOR gates are 1.5 and 2.5 ps, respectively. Therefore, the working bit rates for the XOR and XNOR gates are 666 and 400 Gbit/s, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we consider the situation that three identical two-level atoms are separately trapped in the three single-mode cavities. Each atom resonantly interacts with cavity via a one-photon hopping. The dynamics of nonlocality in the system is investigated via Mermin-Ardehali-Belinksii-Klyshko inequality. The results show that when three atoms are initially in W state and three-cavity fields are in vacuum states both the quantum state of three atoms and that of three cavities all display nonlocality On the other hand, when three atoms are initially in Greenberger-Horne-Zeilinger state and three-cavity fields are in vacuum states, the quantum state of three atoms and that of three cavities all do not display nonlocality. [ABSTRACT FROM AUTHOR]

In this paper, we introduce a new configuration based on the combination of photonic crystal directional coupler and nonlinear electromagnetically induced transparency (EIT) phenomenon in solid-state materials. The proposed structure has the abilities of switching, tunable multi/demultiplexing and tunable power beam splitting. These applications are attainable in the same structure by modulating the refractive index of special regions via EIT effect. This effect causes a high reduction in the required optical control power for the desired refractive index change, compared to the other nonlinear methods. Band structure calculations and simulations of optical field propagation through the device are done by plane wave expansion and finite difference time domain methods, respectively. In the switching mechanism, extinction ratios of 11.38 dB in the linear regime (with the control signal being off) and 26.63 dB in the nonlinear regime (with the presence of control signal) are achievable. Also, the proposed structure operates as a two-channel multi/demultiplexer for wavelengths of 1550 nm and 1480 nm in the linear regime, for wavelengths of 1550 nm and 1600 nm in both linear and nonlinear regimes, and for wavelengths of 1480 nm and 1600 nm in the nonlinear regime (the nonlinear regime is the same as the nonlinear regime for the switching). Since different refractive indices are obtained by changing the power of the control signal, the wavelengths for multi/demultiplexer operation can be tunable. Finally, simulation results show that the suggested structure can operate as a tunable power beam splitter at the wavelength of 1550 nm. [ABSTRACT FROM AUTHOR]

This paper introduces a novel lensless full colour diffractive computational imaging system with a planar Multilevel Phase Mask (MPM) as a diffractive optical element (DOE). The novelty concerns: a methodology of MPM design for improved depth of focus (DoF); design of PSFs for RGB imaging and an inverse imaging algorithm with sparse colour image modelling simultaneous for all RGB channels. MPMs are step-wise invariant. The cubic wavefront coding (WFC) is incorporated in MPMs with optimization of number of levels and width of invariant steps. This design of MPM makes the system robust with respect to defocus (improves DoF) and diminish chromatic aberrations typical for DOEs. Broadband multichannel test-images are exploited for design and testing of the lensless system. We consider two alternative optical setups: Wavelength Multiplexing (WM) and Wavelength Division (WD). In WM, the light beam is broadband multichannel with light sources radiating all wavelengths simultaneously and a CMOS sensor is equipped with a Bayer colour filter array (CFA) for registration of spectral measurements. In this setup, a single MPM is designed for the broadband multichannel light beams. In WD, separate exposures of RGB channels are registered by a broadband grey-scale CCD sensor. Different MPMs are designed for each of the RGB channels. Simulation experiments demonstrate the essentially extended DoF of the designed lensless systems and the advanced accuracy and quality of imaging with respect to the corresponding WM and WD systems with refractive lenses. Due to robustness of the designed lensless system to chromatic aberrations, this advantage has a place even with respect to the lens-system. [ABSTRACT FROM AUTHOR]

This paper describes a series of simulation experiments designed to demonstrate the feasibility of using solid-state lasers in white-light mixtures. The mixed-laser sources are evaluated in terms of the luminous efficacy of the radiation (LER) as well as different measures of colour performance. The latter include the CIE colour rendering index (Ra) and the IES colour fidelity index (Rf) as well as a selection of additional parameters in the two systems. Optimization of the mixtures is achieved by the use of purpose-designed differential evolution algorithms. The best results to date (with four real laser wavelengths) are Rf of 84 with LER 364 lm/W, which indicate the feasibility of the mixed-laser approach to provide highly efficient, energy-saving light sources. These prospects will be further enhanced by potential future developments in semiconductor lasers, with the possibility of producing Rf of 86 with LER of 380 lm/W. [ABSTRACT FROM AUTHOR]

High accuracy of locating the sphere center imaging points is crucial for the vision measurement system. This paper investigates the effect of projection projective model on extraction of the sphere center, upon which the sub-pixel edge-location algorithm based on the sphere projection model is proposed. The sphere center projection model is established by analysing the process of sphere imaging, and the sub-pixel edge-location algorithm consisted of the novel edge model and the improved Zernike moment computing is studied. The novel edge model based on the Erf (error function) is adopted for modelling the practical edge part, which obtains the edge distribution points with high precision. Then a closed-form solution of edge locating error compensation is calculated based on Zernike moments. Finally, the proposed method is verified via simulations and experiments. The relevant results show that the proposed method can accurately locate the sphere center imaging point, which further improves the precision and robustness of the vision measurement system. [ABSTRACT FROM AUTHOR]

Image fusion makes the fused image more reliable and intelligible, and more suitable for human vision and computer detection, classification, recognition and understanding. This paper proposes a pixel-level image fusion method for merging two source images of the same scene using wavelet transform and gray-level features (GLF). First, a three-level discrete two-dimensional wavelet transform is used to decompose the two source images into low-frequency image components and horizontal, vertical, and diagonal high-frequency components. Then, the spatial frequency correlation coefficient is used to determine the pixel fusion rule to apply to each of the low-frequency images, and the correlation coefficient of the GLF is used to determine the pixel fusion rule to apply to each of the high-frequency images. Finally, the fused image is reconstructed using inverse wavelet transform. The results of the experiments conducted indicate that the proposed method is more effective than relevant conventional methods. [ABSTRACT FROM AUTHOR]

In this paper, we consider the situation that four identical two-level atoms are separately trapped in separated tetrahedral structure single-mode optical cavities, which are placed at the vertices of a tetrahedron and are coupled by four fibres. Each atom resonantly interacts with cavity via a one-photon hopping. The evolution of the state vector of the system is given by solving the Schrödinger equation when the total excitation number of the system equals one. Negativity is adopted to quantify the degree of entanglement between two subsystems. The entanglement dynamics between atoms and between cavities is studied. The influences of atom-cavity coupling coefficient on the entanglement between atoms and that between cavities are discussed. The results obtained using the numerical method show that the atom-atom entanglement and the cavity-cavity entanglement are all strengthened with increase of atom-cavity coupling coefficient. [ABSTRACT FROM AUTHOR]

In this paper, we have proposed AND and XOR logic gates simultaneously in one structure. The presented structure is based on two-dimensional (2D) nonlinear photonic crystal with T-shaped waveguide and micro-ring resonator. In the proposed structure, the power consumption is that is lower than similar logic gates and the extinction ratio is about 6.5 dB. Also, the switching time is attained to be 0.2 and 0.26 ps for AND and XOR logic gates, respectively. Simplicity and small size (18.4 µm×18.4 µm) of the structure make it suitable for photonic integrated circuits (PICs). All simulations are based on finite-difference time-domain (FDTD) and plane wave expansion (PWE) numerical methods. [ABSTRACT FROM AUTHOR]

Realization of wavelength conversion based on second-order femtosecond dark solitons with hyperbolic secant pulse is presented. This is achieved by introducing localized dispersion perturbation along the optical fiber. We demonstrate that an initial 30 fs second-order pulse decays to similar sub-pulses by applying perturbation using a step increment of β2 from 6.3 to 15.75 ps2 km-1. This shows that the realization of a 1 × 2 channel wavelength converter for femtosecond pulses is possible. Recent research shows the possibility of realizing wavelength conversion generated from picosecond solitons neglecting nonlinear effects. However, employing the same method for femtosecond pulses fails due to the manifestation of nonlinear effects. In this paper, pulse deformation under different levels of perturbation was tested, and appropriate perturbation leading to similar sub-pulses is achieved. [ABSTRACT FROM AUTHOR]

There are rather few articles which, so to speak, serve to change the landscape in a scientific field. One of those was the discovery of the 'directional sensitivity of the retina' by Walter Stanley Stiles and Brian Hewson Crawford (first reported in 1933). Subsequently, their findings were subdivided by Hansen into two logical components, 'the Stiles-Crawford Effects of the First and Second Kinds (SCE-1 and SCE-2)'. The former (SCE-1) dealt with aspects of their research which addressed alterations in perceived brightness of a visual stimulus; the second (SCE-2) was associated with the perceived hue and saturation of these visual stimuli. These discoveries arose out of a failed attempt by W.S. Stiles and B.H. Crawford to measure properly the areas of the entrance pupils of their experimental subjects as part of a research program which addressed problems of glare, e.g. disability glare in illuminating engineering. Their research was conducted at the National Physical Laboratory (NPL), which is located in Teddington, Middlesex, England. These two fine scientists properly deduced the reason for the failure of their experimental design, and they effectively described and defined a new feature of the visual system which was largely ascribed to the retina. In time, it was realized that this phenomenon was associated in large measure with the waveguide/fiber-optics properties of photoreceptors, and that this was a feature shared by virtually all vertebrate species. This paper is divided into two parts. In the first part, Enoch describes, as best he can, the culture and working conditions at NPL during 1959/60 when he served as a post-doctoral fellow with W.S. Stiles. And in the second part of this paper, the authors describe the findings of W.S. Stiles and B.H. Crawford at the time of their discovery. Today, we celebrate the 75th anniversary of that research. The organizing committee for this program (alphabetically) is David Atchison, Jay M. Enoch, Vasudevan Lakshminarayanan, and Pieter Walraven. Our group of speakers today will follow with discussions of aspects of subsequent work which has evolved from the initial discoveries made by the late W.S. Stiles and B.H. Crawford. [ABSTRACT FROM AUTHOR]

The present paper considers a new approach to the case of an atom in an overdamped cavity. The dissipation is modelled via a bath of harmonic oscillators coupled to the cavity mode, which is assumed to be in a coherent state when the atom enters the cavity. The path integral over both the cavity mode and the bath is taken to derive the optically active electron's influence functional, which can be used further in the study of the time asymptotic dynamics of the internal states of any atom coupled with the cavity mode by using Monte Carlo methods. More specifically the present paper considers the dynamics of the ground state of hydrogen. Oscillations are observed in the survival probability of its ground state, which for asymptotic results is always smaller than one. [ABSTRACT FROM AUTHOR]

There are several research projects going on around the world, which are attempting to develop a prosthetic device to restore sight to the blind. This paper describes the efforts of Second Sight of New York, Inc. The device being developed is called an Artificial epi-Retinal Prosthesis (AeRP), which is basically a small optical computer that fits into the intraocular space of the eye. The AeRP is designed to draw light into the device by specially designed fibre optics. The light is ‘digitized’ by the fibre optic system and then directed to individual photodiode cells making up concentric cylinders thus providing several hundred photodiode cells in the device. The produced electrical stimulation from each cell is then delivered to the retinal ganglion cells by a specially designed delivery system utilizing electrically conducting polymer strands (ECP), which sit on an ‘umbrella’ at the back of the device. The retinal ganglion cells receive the electrical stimulation, which would then be transmitted through the visual system of the brain. There are several innovations in this approach as compared to the other projects. They include, first the design, which will allow for a high number of PC to produce electrical stimulation that will stimulate multiple RGC per PC; the use of the ECP strands has not been used in such an approach before this. Tests have revealed that nerve cells have a good affinity for the material of the ECP. The use of the ECP as well as the fact that the AeRP is completely photovoltaic, with no external power sources, implies that there will not be high heat build-up in the back of the eye, which might damage RGC. A smaller version of the AeRP called the Mini epi-Retinal Prosthesis (MeRP) is the subject of a complimentary paper. It is being built now and will be tested in cell culture studies to determine the efficacy of the design and materials. No actual implants have been performed yet. [ABSTRACT FROM AUTHOR]

In this paper, a robust compressed sensing image encryption algorithm based on generative adversarial network, convolutional neural network (CNN) denoising network and chaotic system is developed. Firstly, we use a sampling network to get the measurement of plain image. Second, the cipher image is obtained by scrambling the measurement through the Logistic-Tent chaotic system. After getting cipher image, the decryption party obtains decrypted measurement by inverse scrambling the cipher image, and then sends it to the reconstruction network to obtain decrypted reconstructed image. Finally, by using the CNN denoiser, the image quality and the visual expression of final decrypted image can be improved. In this scheme, the dual denoiser structure based on reconstruction network and CNN denoiser can effectively resist noise attacks. Besides, the proposed training strategy with noise injection can further improve the robustness of network. Experiments show our method has high reconstruction quality, efficiency, robustness and security. [ABSTRACT FROM AUTHOR]

In this paper, for the first time, a highly ultra-broadband QD-SOA based on superimposed Quantum Dots has been proposed to accomplish a broader optical gain spectra range of almost 3.5 µm from blue to Mid-infrared, considering solution-processed nanotechnology as a simple and cost-effective fabrication method. The realization of the ultra-broadband optical gain can be accomplished by the superimposition of the various size-distributed QD groups made of different materials in a way that the broader energy span is covered as a consequence of the variation of the bandgap energy for each QD groups. To this end, different QD groups made of Bismuth Tellurium Sulphide (Bi2Te3-xSx) and Cadmium Tellurium Sulphide (CdTe1-xSx) in the ZnS shell implemented in the active region of QD-SOA have been superimposed, in which the radii of each QD groups can be easily distributed due to incorporating solution-processed method. The performance of the proposed QD-SOA has been modelled based on the developed rate equation framework by assuming inhomogeneous broadening of energy levels as a result of the size distribution of QDs and the superimposition of various QD groups. Furthermore, the bandwidth and, the spectral range, and the flatness of the optical gain in the QD-SOA can be managed by the number of QD groups, the percentage of Tellurium and Sulphur in the Bi2Te3-xSx and CdTe1-xSx alloys, and the size distribution of each QD groups. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the propagation of short pulses in an inhomogeneous long optical fibre within the framework of a generalized nonlinear Schrö dinger equation with an additional distributed nonlinear correction term involving the time derivative of the pulse envelope and linear gain or loss. A class of nonlinear wave solutions is derived for the first time via a transformation connected with the constant-coefficient Chen–Lee–Liu-type nonlinear Schrödinger equation. These structures possess a number of attractive features such as a self-similarity in pulse shape, a nonlinear behaviour in pulse chirp, localization in structure and a non-zero background. We demonstrate that the presence of self-steepening nonlinearity in the inhomogeneous optical material makes self-similar solitons present an extra frequency chirping property that is directly proportional to the intensity of the wave. The conditions on the optical fibre parameters for the existence of these nonlinearly chirped self-similar localized pulses are presented. As a practical example, we investigate their propagation dynamics in a specified soliton control system. The results are useful in the design of transmission lines with spatial parameter variations and give an effective support for the realization of nonlinearly chirped self-similar solitons on a continuous-wave (cw) background in experiment. [ABSTRACT FROM AUTHOR]

Existing laser scanning approaches for highly reflective surfaces generally require multiple scans to cope with specular reflection. This paper proposes a dual-camera, line-laser scanning strategy to reconstruct them efficiently, which only needs a single scanning path. To bypass complicated point cloud processing algorithms for outlier elimination, a feasible image processing scheme was designed to delete the disturbed stripe regions. By merging two sets of point clouds computed from residual stripes on a common world frame, these removed noise patches can be compensated by the opposite camera. Therefore, the data fusion result can reconstruct the 3D geometry of targets completely. Experimental results demonstrate good performance with the ability to handle highly reflective surfaces. The scanning period is significantly shortened and scanning accuracy can meet the industrial requirement. [ABSTRACT FROM AUTHOR]

For dipole-carrying excitations observed in a high-quality resonator, strong-coupling modes can appear as composite bosons with the spontaneous formation of quantized vortices in the condensed phase of a polariton fluid. In this paper, we show that magnon-polaritons can be realized due to magnon condensation caused by magnetic dipole-dipole interaction. In a quasi-2D ferrite disk placed in a microwave cavity, one observes quantum confinement effects of magnetic-dipolar-mode (MDM) oscillations. These modes, characterized by energy eigenstates with rotational superflows and quantized vortices, are exhibited as spinor condensates. Along with the condensation of MDM magnons, electric dipole condensation is also observed. At the MDM resonances, transfer between angular momenta in the magnetic insulator and in the vacuum cavity, demonstrates generation of vortex flows with fixed handedness. The unique topological properties of the polariton are manifested by curved wavefronts and supperradiance effects in microwave structures. In an environment of scattering states of microwave waveguide, electromagnetic (EM) waves can carry topological phases of MDM resonances. [ABSTRACT FROM AUTHOR]

Phase retrieval occurs in many research areas. There are some classical phase retrieval methods such as hybrid input-output (HIO) and difference map (DM). However, phase retrieval results are sensitive to noise, and the reconstructed images always include artefacts. In this paper, we use the DM algorithm together with DNN to get better phase retrieval results. We train one deep neural network using amplitude images and phase images, respectively. First, using DM, we get initial reconstructed amplitude and phase results. Then, using DNN improves both amplitude and phase results. Finally, using the DM algorithm again improves the DNN results further. The numerical experimental results show that using DM gives better results than HIO, and using DNN improves phase information better than just using DNN to train for amplitude information alone. Compared with only using DNN improves amplitude methods, our method using DM plus DNN plus DM yields a better reconstruction performance for both amplitude and phase. [ABSTRACT FROM AUTHOR]

In this paper, an asymmetric cryptosystem with unequal modulus decomposition in the Fourier domain is presented. The input-colour image is decomposed into its red, green, and blue components. Each component is bounded with random phase mask and undergoes Fourier Transform followed by unequal modulus decomposition. One of resulting masks acts as first private key and other one is again Fourier Transformed and undergoes unequal modulus decomposition. Further two masks are obtained, where one acts as second private key and other is phase truncated to obtain encrypted image. Encrypted image is attenuated by a factor and appended with host image to obtain watermarked image. Numerical simulations on MATLAB are performed for authenticating and validating proposed scheme. Statistical, correlation distribution, information entropy and histogram analyses are performed to demonstrate scheme efficacy. The results illustrate that the scheme resists classical cryptographic, special and occlusion attacks. The proposed scheme is also highly sensitive to its private keys and attenuation factor. [ABSTRACT FROM AUTHOR]

In the paper, we present the analytical expression of propagation characteristics of the autofocusing Airy beam (AAB) with power-exponent-phase beam carrying orbital angular momentum (OAM) mode (named AAB-PEPV), in weak anisotropic oceanic turbulence. We discuss the influence of the weak oceanic turbulence on the detection probability of the AAB-PEPV beams with different power phases and wavelengths. The results show that the AAB-PEPV beam has a higher detection probability when the anisotropic ocean turbulence has a larger unit mass fluid dynamic energy dissipation rate, a larger internal ratio factor and a higher anisotropy factor. At the same time, the detection probability decreases with the temperature change dissipation rate, the temperature and salinity contribution to the refractive index spectrum. Additionally, for a larger power exponential phase and a longer wavelength, the AAB-PEPV beam has a better anti-interference performance in the underwater channel. [ABSTRACT FROM AUTHOR]

Laser-based optical links offer the possibility of secure, high data rate underwater communication. Challenges include quickly modulating the light, and rapidly and reliably decoding the received symbols, despite degradation due to optical turbulence and scattering. This paper builds upon a framework introduced in 2016 to address these challenges. We constructed two novel 5-beam Laguerre-Gaussian basis sets, creating 25 symbol alphabets via superposition. We collected 139,000 images of the symbols, transmitted 4.3 meters through water with very strong optical turbulence. We use a novel convolutional neural network to decode them. We believe this work is the first to achieve high accuracy (93.7–99.9%) in an environment with extremely high levels (2∼107-108 m-2/3) of carefully documented experimentallyinduced optical turbulence. We improve upon previous work in several ways: using a larger alphabet (47 vs. 32), faster classification rates (10,000 Hz vs. 1,000 Hz), and a larger set of test images (96,000 vs 9,600). [ABSTRACT FROM AUTHOR]

This paper presents two novel contrast enhancement approaches using texture regions-based histogram equalization (HE). In HE-based contrast enhancement methods, the enhanced image often contains undesirable artefacts because an excessive number of pixels in the non-textured areas heavily bias the histogram. The novel idea presented in this paper is to suppress the impact of pixels in non-textured areas and to exploit texture features for the computation of histogram in the process of HE. The first algorithm named as Dominant Orientation-based Texture Histogram Equalization (DOTHE), constructs the histogram of the image using only those image patches having dominant orientation. DOTHE categories image patches into smooth, dominant or non-dominant orientation patches by using the image variance and singular value decomposition algorithm and utilizes only dominant orientation patches in the process of HE. The second method termed as Edge-based Texture Histogram Equalization, calculates significant edges in the image and constructs the histogram using the grey levels present in the neighbourhood of edges. The cumulative density function of the histogram formed from texture features is mapped on the entire dynamic range of the input image to produce the contrast-enhanced image. Subjective as well as objective performance assessment of proposed methods is conducted and compared with other existing HE methods. The performance assessment in terms of visual quality, contrast improvement index, entropy and measure of enhancement reveals that the proposed methods outperform the existing HE methods. [ABSTRACT FROM AUTHOR]

In this paper, we describe a two-dimensional photonic crystal-based biosensor that consists of a waveguide and a nanocavity with high sensitivity. A new method is employed for increasing sensitivity of the biosensor. The simulation results show that biosensor is highly sensitive to the refractive index (RI) variations due to injected biomaterials, like glycated haemoglobin, into the sensing surface. The proposed biosensor is designed for the wavelength range of 1514.4–1896.3 nm. The sensitivity and the quality factor are calculated to be 3000 and 272.43 nm/RIU, respectively. The designed structure can detect a 0.002 change in the RI via resonant wavelength shift of 0.9 nm. The band diagram and transmission spectra are computed using plane wave expansion and finite difference time domain methods. [ABSTRACT FROM AUTHOR]

The theoretical and experimental results of the Moiré effect observed by superposing two grids containing fractal Cantor structures are presented in this paper. It is also analysed the equivalence between the information obtained by the Fraunhofer diffraction through those fractal grids and that obtained through Moiré . In a recently published paper [1] it was verified that the diffraction pattern is highly sensitive to variations in dimension, order of growth and lacunarity of the Cantor fractal, becoming a powerful tool to analyse and determine these parameters. So, in this paper it is intended to determine the effect that the order of growth, the dimension, and the lacunarity of one-dimensional fractal Cantor structures have over the Moiré patterns that result from superposing these structures over replicas of themselves which have been rotated through a small angle α. The main goal is to verify if there exists an intimate relation between the resulting Moiré pattern and the parameters that describe this fractal structure, as occurs in the case of the diffraction pattern. [ABSTRACT FROM AUTHOR]

Acoustic emission location is important for finding the structural crack and ensuring the structural safety. In this paper, an acoustic emission location method by using fiber Bragg grating (FBG) sensors and particle swarm optimization (PSO) algorithm were investigated. Four FBG sensors were used to form a sensing network to detect the acoustic emission signals. According to the signals, the quadrilateral array location equations were established. By analyzing the acoustic emission signal propagation characteristics, the solution of location equations was converted to an optimization problem. Thus, acoustic emission location can be achieved by using an improved PSO algorithm, which was realized by using the information fusion of multiple standards PSO, to solve the optimization problem. Finally, acoustic emission location system was established and verified on an aluminum alloy plate. The experimental results showed that the average location error was 0.010 m. This paper provided a reliable method for aluminum alloy structural acoustic emission location. [ABSTRACT FROM PUBLISHER]

The article discusses several reports published within the issue including one on video-based eye tracking, another on a computational concept to characterize the pattern of eye movements and one on the effect of changes in convergence stimuli.

Optical Coherence Tomography (OCT) is often employed to observe the retinal layers in the human eyes. The retinal scans are susceptible to artefacts such as head movements or eye blinks. Along with this, the quality of the images is degraded by speckle noise caused due to the constructive and destructive interference of the waves used for capturing data. Recently, image restoration techniques have geared up in terms of quality with the exertion of deep learning. Despeckling using deep learning, in general, necessitates a large set of training images. On the contrary, deep image prior is a novel model that performs denoising operations using a single training image, based on a prior assumption about the noise distribution. This paper extends the concept of the deep image prior towards non-local restoration for speckle noise assuming that the speckle follows Gamma distribution. Such a framework can be incorporated to enhance the OCT images. The proposed framework is assessed qualitatively with visual comparisons and quantitatively using statistical measures like PSNR, CNR and ENL. Comparative studies confirm that the proposed method outperforms the existing methods in restoring speckled input images. [ABSTRACT FROM AUTHOR]

Fourier transform profilometry (FTP) is widely used for real-time three-dimensional (3-D) surface shape measurement with a single frame of projection fringe pattern. The band-pass filter is very important to the shape retrieval accuracy of this technique. On the basis of the Hanning band-pass filter, a cross-shaped Hanning filter is developed in the paper to extract the first-order spectrum of deformed fringe pattern, and the effect of fringe angle on the proposed filter is analysed. The phase retrieval results using the proposed filter and Hanning filter are compared in the simulation and measurement experiment. The results show that the cross-shaped Hanning filter coordinating with the fringe pattern of about 45 degrees holds the higher accuracy of 3-D shape retrieval. [ABSTRACT FROM AUTHOR]

It is challenging to removing atmospheric turbulence-induced geometric distortion and blurry degradation simultaneously. The improved principal component analysis (i-PCA) method is proposed in this paper. The image set selection strategy is implemented by the Euclidean distance between each sub-module image and its corresponding reference image to remove large geometric deformations and blurs directly. The eigenvector representing the original image data is uniquely determined by combining the maximum correlation with the original image and the maximum variance of the corresponding principal component for resolving the direction issue of the eigenvector. The algorithm is tested using synthetic and real turbulence-distorted images. The experimental results show that the i-PCA method proposed can effectively alleviate the atmospheric turbulence effects and significantly enhance visual quality, promising for its application to turbulence-distorted image. [ABSTRACT FROM AUTHOR]

Photoelectron ejection is important in technological applications. Recently, the photoelectric effect was explained based on the electromagnetic (EM) wave concept. According to the EM wave concept, an electron within the conduction band of a photocell moves circularly. In this paper, we explain few facts regarding the photoelectric emission process, such as the radius of circular motion, maximum ejection angle, and depth of the photoelectron, based on the EM wave concept. Further, the effects of the intensity and frequency on these parameters are discussed. The ejection angle depends on the frequency and intensity of the light and the depth of the photoelectrons. The explanations herein may increase the applications of light energy. [ABSTRACT FROM AUTHOR]

Sensors play a significant role in detecting the gases for industrial and commercial applications. In this paper, we have simulated gold and silver thin films for the detection of oxygen in the software environment. The fabrication was done using a simple deposition method technique i.e. APTMS method and analysed the responses using UV-Spectroscopy for both thin films of gold and silver on porous glass substrates. The resistive responses of the sensor are analysed in a gas chamber. The comparison studies of simulation and fabrication revealed that the gold thin film nanoislands have better responses compared with silver thin film nanoislands for the detection of oxygen. [ABSTRACT FROM AUTHOR]

This paper proposes an optical amplification method of measuring the minute displacement of a laser beam. The relationship between the displacement of the incident laser beam and the reflective beam is calculated by geometric optical analysis. The equation of displacement is derived to calculate its magnification. We demonstrate that by employing the reflection characteristics of a cylindrical mirror, the minute-displacement of a laser beam can be enlarged to the millimetre level. Experimental results confirm that the magnification can be hundreds of times. Such an enlarged displacement measuring system of laser beam could be suitable for the study of Goos–Hänchen shift. [ABSTRACT FROM AUTHOR]

S-shaped polymer waveguides are heavily exploited to connect optical components. Reducing the bending loss of S-shaped polymer waveguides is critical for low-loss and small-size optical circuits. In this paper, the S-shaped waveguide with offsets and trenches (SW-OT) is designed. The dependence of the bending loss on crucial parameters like offsets, trench locations and trench widths is analyzed by the beam propagation method. A comparison of the bending loss among standard S-bend, shifted S-bend, S-bend employing trenches and SW-OT structure is conducted. Results show that the bending loss of the SW-OT with a bending radius of 1000μm is only 0.11dB, reducing by 89.70% compared with the S-shaped waveguide with only shifts. Moreover, a dramatic reduction in the bending loss is obtained by placing trenches properly in the curved region. Therefore, the combination of offsets and trenches can effectively decrease the bending loss of low index contrast polymer S-shaped waveguides. [ABSTRACT FROM AUTHOR]

Multimodal image registration is an important technique for many clinical applications. However, it is particularly challenging to obtain good spatial alignment. This paper introduces a novel architecture named the constrained affine network, which combines deformable image registration with affine transformation for multimodal MR image registration. A weakly supervised manner is adapted to train the network and anatomical labels are used in training. The network directly learns to predict a displacement vector field (DVF) between pairs of input images. Different from the existing deformable image registration methods based on the convolutional neural network (CNN), the method proposes a global constrained affine module, which can predict an affine transformation by pre-computing the range of affine parameters, and the model can be combined with a deformable registration network. We evaluated the proposed method on 3D multimodal medical images. Experimental results indicate that the proposed method has better performance. [ABSTRACT FROM AUTHOR]

In this paper, a high spatial resolution, high gating speed framing camera capable of four separate two-dimensional images is designed and tested. A mirror-based image splitter has been designed and developed to provide a separate image for each arm with equal path length and equal intensity splitting while having a spectral flat response. Fast gating of a single frame is accomplished by using a proximity-focused microchannle-plate image-intensifier (MCPII) gated by a MOSFET-based pulse module with adjustable gate width from 3 ns to D.C. operation. Multiple frames are obtained by using multiple gated tubes with time intervals between consecutive frames can be adjusted flexibly. Its spatial resolution reaches 36.5 lp/mm with each frame having a 4.6-ns gate width. Furthermore, a three-dimensional MCPII model is developed to investigate the transit time and spatial resolution of the proximity-focused MCPII based on the Finite Integral Technique (FIT) and Monte Carlo method (M–C method). [ABSTRACT FROM AUTHOR]

This paper presents a novel algorithm for improved shape recovery using polarisation-based photometric stereo. The majority of previous research using photometric stereo involves 3D reconstruction using both the diffuse and specular components of light; however, this paper suggests the use of the specular component only as it is the only form of light that comes directly off the surface without subsurface scattering or interreflections. Experiments were carried out on both real and synthetic surfaces. Real images were obtained using a polarisation-based photometric stereo device while synthetic images were generated using PovRay® software. The results clearly demonstrate that the proposed method can extract three-dimensional (3D) surface information effectively even for concave surfaces with complex texture and surface reflectance. [ABSTRACT FROM AUTHOR]