In this study, we examine the statistical properties of speckle patterns produced by the scattering of Hermite-Gauss beams (HGB), Laguerre-Gauss beams (LGB), and Bessel-Gauss beams (BGB). We have considered entropy, speckle contrast, skewness, and kurtosis as the evaluation parameters for statistical analysis. It is observed that the entropy is increased by increasing the transverse modes of HGB, radial index p, and topological charge l in the case of LGB and BGB speckles, whereas the speckle contrast=decreases with the increase in transverse modes number of HGB and it increases with the increase in radial or azimuthal indices of LGB and BGB. The positive skewness has been observed for all the modes which is attributed to the existence of large dark points in the speckle patterns, which is being confirmed as well with the distribution plots. It is also observed that these speckle patterns have a very high value of kurtosis compared to the Gaussian profile, for which it is close to 3, which indicates the high randomness with the increase in radial and azimuthal indices. We have experimentally captured the speckles by scattering HG, LG, and BG coherent beams through two distinct ground glass plates (GGPs), i.e., GGP1 (Thor lab DG 10-120) and GGP2 (Thor lab DG 10-220). The statistical analysis presented in this work will make it easier to distinguish between the structured beam speckles in various fields, such as optical information security, optical imaging, free space communication, metrology, and other related fields.

In the present era, Artificial Intelligence (AI) plays a crucial role by offering effective solution across various domains. AI is a broad area that includes both Machine Learning (ML) and Deep Learning (DL) as its key branches. In this chapter, we discussed applications of DL in the field of optical cryptography. It provides a cost-effective and powerful solution to various cryptographic challenges based on supervised and unsupervised learning approach. The chapter begins by introducing optical cryptosystems and their connection to DL algorithms. Some of the characteristics of DL along with its different architectures are discussed for better understanding of readers. Further, the integration of various DL models with optical image encryption techniques is discussed, followed by an overview of practical applications. The chapter also discusses future directions, existing challenges, and potential solutions in this field. Finally, the chapter concludes with key insights and contributions to ongoing research in DL-based optical encryption.

Singular optics is a branch of modern electromagnetics and optics that investigates solutions to Maxwell’s equations that exhibit nontrivial topological features under various boundary conditions. These solutions give rise to light fields containing singularities, points or regions at which certain optical properties, such as phase or polarization, become undefined. Over time, singular optics has evolved into a unifying framework for understanding and engineering optical fields that possess phase, polarization, coherence, and spatiotemporal singularities, each characterized by quantized topological properties. Such structured light fields enable high-dimensional information encoding, robust light–matter interactions, and sensitive probing of complex media, thereby impacting optical communication, imaging, sensing, and materials processing. Parallel advances in theory, fabrication techniques, detection hardware, and computational methods have created a diverse and rapidly expanding landscape, underscoring the need for an integrated and forward-looking perspective. This roadmap synthesizes emerging applications of singular optics across multiple platforms, offering a concise overview of current developments and highlighting key physical concepts, new architectures, and transformative technologies that bridge subfields. In addition to reflecting the insights of leading contributors to these research directions, it also surveys selected recent advances, providing a concise overview of current trends and a foundation for shaping the future of singular optics and its applications.

Measuring the topological charge (TC) of optical vortices is crucial for advancing applications in areas such as optical communication and quantum information processing. Although various interferometric and non-interferometric techniques have been developed for coherent and partially coherent beams, most of these methods are ineffective for fractional-vortex beams, especially when the beam gets perturbed. In this work, we propose and experimentally demonstrate a simple, non-interferometric technique based on autocorrelation for assessing and quantitatively measuring the TC of fractional vortex beams. We generated fractional optical vortex beams using computer-generated fork-shaped holograms and then obtained the corresponding random optical patterns after scattering through a rough surface. The autocorrelation rings of random patterns provide the TC of fractional vortex beams, and the asymmetry gradually becomes symmetric as the TC approaches an integer value. Additionally, by examining the divergence of the first dark ring with respect to propagation distance, we can quantitatively estimate the fractional TC. The measured divergence closely matches theoretical results, achieving an accuracy of over 98 %. The proposed method eliminates the need for phase retrieval, coherence modulation, or interferometry, providing a practical and robust solution for measuring fractional TCs, even in the presence of perturbations such as scattering and mild atmospheric turbulence, which are common in free-space optical communication systems.

Optical random patterns, commonly known as speckles, have gained significant interest due to their wide range of applications in imaging, metrology, and cryptography. In this work, we utilise controlled spatial modes of light to generate speckle patterns whose size can be precisely tuned to obtain the desired functional variations. Unlike conventional approaches, where the speckle size varies inversely with the topological charge, we demonstrate that speckle patterns exhibit inverse, constant, or modulated (sinusoidal and Gaussian) functional dependencies on TC. To realize this control, we scatter four tunable Laguerre–Gaussian beams through a rough surface and show that the resulting speckle sizes can be tailored and even rendered invariant through an appropriate scaling factor. These speckle size invariant characteristics open new avenues for robust orbital angular momentum encoding, with potential benefits for free-space optical communications, imaging through scattering media, and speckle-based information processing.

Perfect Optical Vortex (POV) beams have gained significant attention due to their ability to maintain a constant ring size with increasing topological charge (TC). This property of the POV beam helps to attain a vortex beam with large TC and controllable ring size simultaneously. In this paper, we propose a new simple way to generate twin ring POV (TR-POV) beam by introducing a conical phase into the Bessel phase function. In TR-POV, we can precisely control the transverse cross-section profile, where the ring radius, ring width, and TC of both rings can be assigned arbitrarily, depending on the application. We have experimentally generated these beams and studied their detailed propagation characteristics in free space. Through the interferometric analysis, we have also determined the TCs correspond to both the rings. We believe that the proposed beams can have profound application in various optical domains, such as microscopy, imaging through turbid media, communication, security etc.

This study presents a new robust asymmetric optical watermarking scheme using Schur decomposition and the Laguerre-Gaussian (LG) beam speckles as security keys. A LG beam with a nonzero azimuthal index possesses orbital angular momentum (OAM) and has a donut-shaped intensity profile having helical phase structure, characterized by radial (p) and azimuthal (l) indices. Owing to their orthogonality and OAM characteristic, LG beam possesses potential applications in optical information security. We have scattered LG beams of different indices through a diffuser to synthesize the distinctive encryption keys. The obtained speckle patterns are unique and nearly impossible to duplicate, as they are generated through physical process. Here, we propose a watermarking technique in which the input plaintext image is first phase encoded followed by modulation with the encryption key synthesized from LG beam speckles. Afterwards, the obtained complex wavefront is Fresnel propagated over a distance d 1 and the output is modulated with another encryption key, followed by Schur decomposition to make the system asymmetric and to generate the private key. Furthermore, the processed part is again modulated with third encryption key, and an Improved ZigZag sequence is utilized to enhance the randomness in the system, which helps in boost the security. Then the resulting wavefront is propagated to distance d 2 and embedded into a host image to get the final watermarked image. The efficacy of the proposed technique is examined against multiple established attacks, including contamination attacks, chosen plaintext attacks, and known plaintext attacks.

Single and multi-armed self-rotating beams (SRBs) exhibit distinctive propagation characteristics in which the transverse intensity distribution rotates about the optical axis while remaining invariant in shape. In this study, binarized SRBs (BSRB) are generated by binarizing the conventional SRB-generating phase mask. Multi-armed SRBs are realized through phase multiplexing of multiple binary SRB phase masks. Unlike earlier demonstrations of multi-armed SRBs, where the angular separation between arms remains constant during propagation, the proposed approach produces beams with angular separation that vary with propagation distance. The generation and evolution of BSRBs are investigated through theoretical analysis, numerical simulations, and experimental measurements, showing good agreement among all three. Proof-of-concept imaging studies are performed within a coded-aperture imaging framework using different deconvolution methods, and the results demonstrate promising performance. These findings provide enhanced insight into SRB generation and dynamics, as well as their applicability to imaging. Beyond optical imaging, the proposed multi-armed SRBs are expected to have strong potential for applications in optical trapping, structured illumination microscopy, and advanced optical communication systems.

In this study, we demonstrate the generation of multi-helix conical beams (MHCB) using the computer-generated holography by modifying the helico-conical phase function implemented through a spatial light modulator. These beams are governed by multiple parameters such as the topological charge (TC), helicity, and the number of spirals present in the beam. We propose a single-shot intensity measurement technique by making these beams interact with astigmatic phase modulation to detect the TC and the number of spirals. The experimental results are well supported by the numerically simulated results, and we also explore the effects of astigmatic phase parameter (β). The number of dark fringes present in the modulated intensity distribution indicates the magnitude of TC and its sign (helicity) has been revealed using the orientation of these fringes. The number of spirals is equal to the number of sectors present in the outer region of the modulated intensity distribution. We also demonstrate a potential application of these beams for optical encryption; the information is encoded in TC of the beam and further decoded experimentally.

Interferenceless Coded Aperture Correlation Holography (I-COACH) has emerged as a powerful computational imaging technique for retrieving three-dimensional information from an object without requiring two-beam interference. In this study, we propose and experimentally demonstrate an I-COACH system employing a Helico-Conical Vortex (HCV) mask. The HCV mask carries orbital angular momentum and features a phase profile with non-separable dependence on both azimuthal and radial coordinates. It is generated by combining helical and conical phase functions, resulting in a spiral-shaped intensity distribution at the focal plane. We compare the performance of I-COACH with the HCV mask against other coded masks (CMs), including random lens, ring lens, spiral axicon, axicon, and spiral lens. Additionally, we evaluate image reconstruction using four widely adopted algorithms: non-linear reconstruction (NLR), Lucy-Richardson algorithm (LRA), Lucy-Richardson-Rosen algorithm (LRRA), and non-linear LRA (NL-LRA). Quantitative analysis is conducted using figures of merit such as entropy, root mean squared error (RMSE), structural similarity index measure (SSIM), and peak signal-to-noise ratio (PSNR). The proposed approach holds promise for advancing incoherent holography and computational imaging applications.

Energy harvesting transduces untapped ambient energy into electrical power, supporting autonomous, sustainable devices. Magneto-mechano-piezoelectric nanogenerators (MMPNGs) leverage magnetic torque-induced mechanical strain to activate the piezoelectric mechanism, efficiently converting mechanical energy into electrical energy and driving innovation in energy-harvesting systems for next-generation applications. This work aims to designate flexible and biocompatible PNGs and MMPNG from the site-engineered BCZT-based ceramics synthesized through the solid-state reaction method with the thermal quenching process. The PNG was initially designated and tested for its energy harvesting properties under biomechanical tapping, yielding the power characteristics of 7.8 V/164.4 nA (corresponding peak power density of 711.1 µW cm−3). The designated MMPNG, under an alternating current magnetic field of 6 Oe, generated an open-circuit peak-to-peak voltage (Vp-p) and a short-circuit current of 4.4 V and 202 nA, respectively. The harvesting device also exhibits a maximum root mean square power output of 4.4 nW, equivalent to a power density of 395 nW cm−3. These energy harvesters demonstrated the ability to maintain consistent performance over 50 000 operational cycles without significant degradation in output. These findings reveal strong potential for powering autonomous miniature electronics, paving the way for sustainable and efficient compact energy solutions.

It is well known that the coherence vortices are robust against atmospheric turbulence and can be effectively utilized for communication and imaging applications. In this paper, we study, both theoretically and experimentally, the generation of coherence vortices by the cross-correlation between two scattered optical vortices with different topological orders and how the orders of the input fields affect the size of the generated coherence vortices. We have analyzed the size by considering the coherence vortex at a given plane as a ring with inner and outer radii. The inner and outer radii vary linearly with order and the propagation distance. The slope of radius vs. propagation distance is considered as the divergence by which one will be able to find the order. All the theoretical predictions have been validated with the experimental results. It is also observed that the propagation characteristics are similar to the coherent optical vortices.

In this work, the properties of lead-free piezoelectric K0.5Na0.5NbO3 (KNN) were enhanced by antimony (Sb) doping on the B-site using a solid-state reaction method. XRD and Raman analysis confirmed phase purity, showing an orthorhombic structure. X-ray diffraction patterns were fitted using FullProf to determine lattice parameters, revealing reduced bond angles and lengths in Sb-doped KNN (KNNS). The dielectric properties showed a phase transition in pure KNN at 185 °C (orthorhombic to tetragonal) and 380 °C (tetragonal to cubic), while KNNS exhibited relaxer ferroelectric behaviour. KNNS displayed enhanced ferroelectricity (2Ps = 26.2 μC/cm2) and low leakage current (4.17 nA-cm−2). KNNS also demonstrated superior energy harvesting, producing 25.2 V and a power density of 7.71 mW-cm−2 under finger tapping, a 280% improvement over pure KNN. The study highlights the benefits of Sb doping in improving the electrical properties and Curie temperature of KNN, as well as its successful application in energy harvesting and ultrasonic testing of aluminium alloy specimens.

Ferroelectric thin-film capacitors are of interest for energy storage due to their high charge/discharge rates, essential for compact electronics. As alternatives to Pb-based materials, environmentally friendly barium titanate–based systems show great energy-storage potential. Herein, Ba0.7Sr0.3TiO3 (BST7)/Ba0.6Sr0.4TiO3 (BST6) thin films altering the layer structure are designed and constructed on boron-doped Si <100> substrates by solution-based spin-coating method. The structural and electric properties of trilayer thin films are investigated, and the results are compared with those of monolayer thin films such as BST7 and BST6. An enhanced polarization and improved breakdown strength are simultaneously achieved in the BST767 (Ba0.7Sr0.3TiO3/Ba0.6Sr0.4TiO3/Ba0.7Sr0.3TiO3) trilayer thin film caused by the interfacial effect, which leads to an ultrahigh energy-storage density (Wrec) of ≈56.9 J cm−3 accompanying an efficiency (η) of ≈72%. The BST767 trilayer capacitor processes a fast charging/discharging speed and a giant power density of 0.72 MW cm−3. These thin-film capacitors exhibit a relatively high resistive switching behavior with an improved on–off ratio compared to ceramic capacitors. The mechanisms underlying current conduction are thoroughly analyzed. Such performance makes them suitable for future portable electronics, hybrid vehicles, and aerospace applications.

The topological charge (TC) independent annular intensity distributions of perfect optical vortex (POV) beams made them exciting for various applications. In this work, we have experimentally generated POV beams of different TC orders and proposed a modified Mach-Zehnder interferometric arrangement for identifying the TC of the generated beam. We also investigated the free space evolution of the POV beam demonstrated that it naturally evolves into a Bessel-Gaussian (BG) beam with propagation. We confirmed this evolution by analysing the propagation of interference patterns as well as comparing the self-healing property of BG beams with the evolved POV beams. The findings are supported by theoretical and experimental results. The presented analysis will facilitate the application of POV beams in areas such as optical imaging, free space communication, optical trapping, etc.

Applications like disaster management, urban planning, and environmental monitoring rely on satellite image categorization. This project develops a machine learning pipeline using MobileNetV2, a CNN architecture, to classify high-resolution satellite images. It employs two convolutional layers (3x3 kernels) with ReLU activation, 2x2 max-pooling, a fully connected layer, and a SoftMax output for multi-class classification. Images are resized to 200x200 pixels (RGB) to balance detail and efficiency. MobileNetV2 was chosen for its low latency and high performance, using depth-wise separable convolutions and inverted residuals. The model, optimized with Adam and categorical crossentropy, achieved 98% validation accuracy and F1-scores above 0.96 across all classes, converging in 8 epochs. The architecture balances simplicity and performance for robust feature learning and generalization. This approach highlights CNNs' ability to classify satellite images effectively. Future work could explore transformer-based models or integrate temporal satellite data to enhance analysis. This work offers a scalable, automated solution for satellite image classification.

The topological charge (TC) of optical vortex beams can be measured using various interferometric and non-interferometric techniques in both coherent and partially coherent domains. However, these methods are not suitable for obstructed vortex beams, also known as open optical vortex (OOV) beams. Recently, several methods for studying open optical vortex (OOV) beams, have recently been proposed and demonstrated based on interferometry, phase retrieval, spatial coherence analysis, which limit their applicability in the presence of significant perturbations or long-distance propagation. In this study, we propose and experimentally demonstrate an efficient method for measuring both the magnitude and sign of the topological charge (TC) of OOV beams using the auto-correlation distribution after scattering through a rough surface. We generated the OOV beams using partially blocked computer-generated holograms. Although the rings or zero points present in the auto-correlation are broken, the number of rings is equal to the TC. Further, we have utilized the radius of the first ring and its divergence with propagation distance, which can be easily observed for all orders, for finding the TC of higher orders. We can measure the sign of the topological charge solely through intensity measurements using the rotation of the autocorrelation profile with the help of blocking parameter. Furthermore, we demonstrate that the characteristics of OOV beams derived from our proposed method align well with the propagation characteristics of unobstructed OV beams. The results confirm the efficacy of optical vortex beams for free-space optical communication.

The study introduces a novel asymmetric optical cryptosystem that utilizes bright C-point polarization singularity speckle (BCPSS) patterns as security keys while offering multiuser capabilities. The C-point singular beams, with spatially varying polarization distributions, are created by superposing optical vortex modes of different magnitudes into an orthogonal polarization basis. This complex light beam is then scattered through a rough surface to generate the BCPSS patterns. These generated speckle patterns inherit some unique properties due to the vectorial light field and the randomness of the rough surface, which make them nearly impossible to duplicate. To generate a complex image, the BCPSS phase mask is used to further modify the original image after it has been phase encoded. The final encrypted image is then obtained by processing the intermediate complex image using two-dimensional non-separable linear canonical transform (2D-NS-LCT) and polar decomposition. The 2D-NS-LCT has ten independent parameters which expends the key space, improving its resistance to various attacks. The implementation of polar decomposition in the proposed cryptosystem enables us to have two private keys, helping in multiuser functionality. The proposed method is also validated by testing it against various potential attacks, including contamination and plaintext attacks. Numerical simulations confirm the authenticity and reliability of the proposed cryptosystem.

Memristive devices represent a promising future for memory and computing technologies, offering non-volatile storage, high-speed switching, and analog capabilities. In this study, we report the fabrication and evaluation of HfO2 thin films deposited on SiO2 -layered Si (100) substrate using a simple, cost-effective chemical solution method. The HfO2 thin films with thicknesses ranging from 79 to 316 nm were investigated to assess their impact on the structural, electrical, and ferroelectric properties. The XRD analysis revealed that the thin films exhibit the tetragonal phase of HfO2 with ferroelectric properties at room temperature, which was confirmed through the P–E hysteresis loops. The influence of film thickness on resistive switching behavior was revealed, providing insights into optimizing HfO2-based memristive devices for reliable and efficient memory applications. The HfO2 film with an intermittent thickness exhibits superior performance, with as high ON/OFF ratio of ~ 977, attributed to its stability, balance between vacancy mobility and defect clustering, ensuring reliable switching. The switching mechanism follows the Schottky conduction model, which is linked to improved crystallinity, reduced defect density, and minimized strain effects.

Praseodymium (Pr) and Bismuth (Bi) co-doped Yttrium Iron Garnet (PrxBiY2-xFe₅O₁₂, where x = 0.1, 0.25, 0.5, and 1.0) nanoparticles were synthesized via a self-combustion-assisted sol-gel method. Structural analysis confirmed the formation of a pure cubic Y₃Fe₅O₁₂ (YIG) phase without any secondary phases. Morphological characterization and energy dispersive spectroscopy (EDS) confirmed the successful incorporation of Pr³⁺ and Bi3+ ions into the YIG ferrite structure. Optical measurements showed a decreased optical band gap attributed to new energy levels introduced by Pr³⁺ doping. Magnetic characterization exhibited typical ferrimagnetic behaviour, with reduced saturation magnetization, coercive field, and anisotropy constant as Pr³⁺ content increased, indicating disruption in magnetic alignment. While challenges remain in balancing enhanced dielectric properties with reduced magnetic alignment and ensuring stability for practical applications, the composition with x = 0.25 demonstrated balanced magneto-dielectric properties. This makes it a promising candidate for multifunctional microwave applications such as filters and resonators.

Smart manufacturing, or Industry 4.0, integrates technologies such as the Internet of Things (IoT), artificial intelligence (AI), and cloud computing to transform production, enhancing productivity and flexibility. However, IoT devices often rely on conventional batteries, which have drawbacks like toxicity, short lifespan, and the need for frequent replacement. Magneto-mechano-electric (MME) generators offer a sustainable alternative for powering IoT devices and wearable electronics by harvesting energy from stray magnetic fields. Recent advancements in MME generators include the use of multiferroic composites in cantilever structures, combining magnetostrictive, piezoelectric, and triboelectric materials with permanent magnets. These innovations focus on optimizing crystallographic orientation, minimizing energy conversion losses, and utilizing flexible micro-fiber materials and magnetic flux concentration. Hybrid energy conversion principles and magnetic shape memory alloys, which deform under magnetic fields, further enhance energy harvesting capabilities. This review explores the design and development of MME generators, emphasizing strategies to improve efficiency and integrate hybrid energy harvesting technologies. It also highlights challenges and future prospects for achieving self-powered IoT sensors and wearable devices.

There has been considerable interest in the nonlinear optical phenomenon in recent years, particularly in two-dimensional materials. Here, we study the optical polarization quantities namely ellipticity and Faraday rotation for the monolayer 1T ′ -WTe 2 two-dimensional (2D) material. We develop a new general approach based on many-body perturbation theory to compute polarization quantities via the second harmonic susceptibility of the material. We find that the nonlinear second-harmonic longitudinal and transverse responses are tunable with the inclination angle made by the out-of-plane field with an axis vertical to the 2D plane. This field breaks the inversion symmetry of the system which is an essential condition for the behavior of the second harmonic susceptibility. Such tunable behavior gives significant variation to the Faraday rotation and ellipticity. Our findings provide valuable information for future experiments on the optical phenomenon in 2D materials.

In this paper, a new nonlinear optical multi-image authentication scheme is proposed based on Kramers-Kronig digital holography and orthogonal triangular decomposition or QR decomposition. Here, the complex light field carrying the information of multiple images is modulated by random phase masks and propagated at certain distance. Afterwards, the QR decomposition is applied to the complex wavefront to generate the private keys and to add the non-linearity in the scheme. Next, the product of orthogonal matrix and upper triangular matrix is processed further. The obtained output is modulated by different phase masks and interfered with reference beam to record the encrypted image. For decryption, the Kramer-Kronig relation is utilized to extract the plaintext images directly with only the positive frequency part. A series of numerical simulations are conducted to validate the efficacy and robustness of proposed image authentication scheme.

In this paper, we propose an optical asymmetric phase image encryption method in which the vectorial light field is used to encode the data. In transverse plane, the vectorial light field has spatially varying polarization distributions where we are allowed to have a greater number of degrees of freedom. In this scheme, the input image is first phase encoded and then modulated by a phase encrypting key, synthesized from the speckles obtained by the scattering of Hermite-Gaussian beams. The modulated image is further processed using fractional Fourier transform with a specific order (α). A pixel scrambling operator is utilized to increase the randomness to further enhance the security and singular value decomposition approach is employed to add the nonlinearity in the encryption process. Now, the stokes parameters, i.e. S1 and S2 are calculated using the light intensities correspond to different polarizations. S1 is used as the encrypted image for transmission and S2 is reserved as one of the private decryption keys. The robustness of the proposed technique is tested against various existing attacks, such as known plaintext attack, chosen plaintext attack, and contamination attacks. Numerically simulated results validate the effectiveness and efficiency of the proposed method.

Computational methods have been established as cornerstones in optical imaging and holography in recent years. Every year, the dependence of optical imaging and holography on computational methods is increasing significantly to the extent that optical methods and components are being completely and efficiently replaced with computational methods at low cost. This roadmap reviews the current scenario in four major areas namely incoherent digital holography, quantitative phase imaging, imaging through scattering layers, and super-resolution imaging. In addition to registering the perspectives of the modern-day architects of the above research areas, the roadmap also reports some of the latest studies on the topic. Computational codes and pseudocodes are presented for computational methods in a plug-and-play fashion for readers to not only read and understand but also practice the latest algorithms with their data. We believe that this roadmap will be a valuable tool for analyzing the current trends in computational methods to predict and prepare the future of computational methods in optical imaging and holography.

In this paper, we propose a new asymmetric optical cryptosystem for phase image encoding with the utilization of speckles generated by scattering the Hermite Gaussian beams (HGBs) through a rough surface. These speckle patterns are unique and almost impossible to clone as one cannot mimic the physical process. The generalized Schur decomposition, named as, QZ decomposition, approach is used to generate unique private keys for decrypting the encoded data. The plaintext image is first phase-encoded and then modulated with the pattern obtained by the convolution of HGBs and random phase masks. The modulated image is then Fresnel propagated for a distance of z1, and the QZ decomposition operation is performed on the complex wavefront to generate the private keys. Afterward, the gyrator transforms with a rotational angle (α), and the phase truncation is used to further process the information. The phase truncation and phase reservation (PT/PR) will result in another phase private key, which will be utilized for decryption. A non-linear power function is introduced to modify the amplitude part after PT/PR operation and the resultant is modulated using an HGB amplitude mask to get an intermediate wavefront. Finally, the encrypted image is obtained by Fresnel propagating the intermediate wavefront with a distance of z2. The effectiveness and validity of the proposed method are tested and verified through numerical simulations. A series of potential attacks such as contamination and plaintext attacks have been tried and tested to further check the robustness of the proposed method. The results confirm the efficacy of the proposed method.

Magneto-mechano-electric (MME) generators efficiently harness ubiquitous stray magnetic fields and convert them into electricity, capturing significant attention for powering innumerable wireless sensors. In this study, lead-free 0-3 particulate magnetoelectric (ME) nano-composite ceramics, specifically x(Ba0.85Ca0.15Zr0.1Ti0.9O3)-(1-x)Ni0.5Zn0.5Fe2O4 [x(BCT-BZT)–(1-x)NZFO], were synthesized using the sol-gel method. Subsequently, a flexible MME generator was designed, incorporating the optimized ME composite. Structural parameter calculations indicated higher tetragonal distortion of 0.4% in 0.4(BCT-BZT)-0.6NZFO, possibly due to uniform particulate distribution. The ME composites displayed uniform dual-phase microstructures, with 0.4(BCT-BZT)-0.6NZFO showing a higher NZFO concentration. The maximum values of the magnetodielectric (MD) and ME coupling coefficients have been determined to be -3.6% and 2.55 mV cm -1 Oe-1, respectively, for an x = 0.4 composite. The MME generator is designed using an optimized 0.4(BCT-BZT)-0.6NZFO ME composite with film thickness of 34 μm. This MME generator harvests a sinusoidal wave with a maximum output peak-to-peak voltage of 4.1 V when exposed to a weak AC magnetic field of 10 Oe at a frequency of 50 Hz. Additionally, the device demonstrates an exceptional optimal DC power density of 3.89 μW cm-3. The lead-free 0-3 particulate ME composite enables effective magnetic energy harnessing. As a result, it holds great promise as an efficient autonomous power supply for various Internet of Things based applications.

This paper introduces a robust and automated method for detecting grain boundaries and estimating particle sizes in microstructural images using OpenCV-based image processing techniques. The approach leverages high-resolution image analysis to enhance clarity and precision in boundary detection through a series of preprocessing steps, including image format conversion, cropping, brightness/contrast adjustments, and sharpening. Following this, Gaussian blurring and thresholding are applied to separate particles, with contour detection used to accurately identify grain boundaries. Particle sizes are then calculated by converting pixel dimensions to micrometers, enabling precise measurements. To improve the reliability of the results, statistical techniques like outlier removal and clustering are employed to refine the size distribution. Additionally, texture analysis is performed using the Gray Level Co-occurrence Matrix (GLCM), and k-means clustering is applied to segment regions based on texture similarity. This comprehensive method provides material scientists with a highly accurate, efficient tool for grain size analysis and boundary detection, offering significant improvements in both speed and precision compared to traditional manual techniques.

Pulsed power and power electronics systems used in electric vehicles (EVs) demand high-speed charging and discharging capabilities, as well as a long lifespan for energy storage. To meet these requirements, ferroelectric dielectric capacitors are essential. We prepared lead-free ferroelectric ceramics with varying compositions of (1 − x)Ba0.7Sr0.3TiO3–(x)BiMg0.5Ti0.5O3 (BST–BMT) (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1) using a solid-state-reaction method. To analyze the crystallinity and structural parameters, we examined the X-ray diffraction (XRD) patterns using the pseudo-Voigt function in the FullProf software. Additionally, Raman spectrum analysis confirmed the presence of ceramic structural distortion caused by microstrain and doping. Microstructure images of the ceramic samples showed an increase in grain size from 1 to 2.4 μm and an improved distribution of grain sizes with increasing doping levels. We investigated the dielectric properties of the BST–BMT ceramic capacitors across a wide range of frequencies and temperatures. Interestingly, as the BMT content increased, the previously saturated ferroelectric (FE) curve for x = 0.01 gradually shifted towards a narrower relaxor ferroelectric (RFE) curve for x = 0.1. The most favorable effective energy storage density was observed with a BMT doping concentration of x = 0.04, which coincided with exceptionally high-energy efficiency (η ~ 91%) under a field strength of 50 kV/cm and a relatively high dielectric normalized energy storage density of 3.71 µJV−1 cm−2 due to structural modifications that causes relaxor ferroelectric behavior. More interestingly, the energy storage performance of 0.96BST–0.04BMT displays a fatigue free characteristic enduring through numerous switching cycles. We also calculated the optical bandgap (Eg) values from UV–Vis spectra and compared them with the increase in BMT concentration. The Eg value for all ceramics was approximately 3.2 eV, similar to the pure BST ceramic sample. Additionally, the resistive switching behavior demonstrated by our bulk ceramic capacitors is not commonly observed in other bulk ceramics.

Extracting the grain size from the microscopic images is a rigorous task involving much human expertise and manual effort. While calculating the grain size, we will be utilizing a finite number of particles which may lead to an uncertainty in the measurement. To avoid this difficulty, we utilize a simple mathematical tool, the auto-correlation function, to determine the grain size. The random particle distribution and the finite width Gaussian histogram of particle size has motivated us to utilize the auto-correlation function, which has been extensively studied for finding the size of random optical patterns. The finite width of the correlation function provides the grain size, and the difference in correlation length along two mutually independent directions provides information about the asymmetry present in the particle distribution, i.e., the deviation from a spherical shape. The results may find applications in material, pharmaceutical, chemical, and biological studies where extracting the grain size is essential.

The integration of magnetoelectric (ME) principles using magneto-mechano-electrical (MME) generators enables the construction of self-powered wireless sensor networks (WSNs) for mechanical energy harvesting. In this study, we propose a lead-free, flexible MME generator that incorporates poly(vinylidene fluoride) (PVDF)/Ba0.85Ca0.15Ti0.9Zr0.1O3 (BCZT) fiber composites and Metglas. This generator produces a robust output voltage even in the presence of stray magnetic fields, without requiring a magnetic bias field. We prepared flexible PVDF/BCZT fiber composites by electrospinning the components at various proportions, and a magnetostrictive Metglas layer was incorporated during the ME composite fabrication process. Under resonance conditions (50 Hz), the optimized ME composition yielded a maximum ME voltage of 472 V cm−1 Oe−1 without a magnetic DC bias field. This significant improvement is attributed to the interfacial interactions between the surface of inorganic BCZT nanoparticles and dipoles within the PVDF polymer matrix, as well as the high permeability of Metglas. Additionally, the flexible MME generator proposed in this study produced an open-circuit voltage of 14.8 V and an approximate power density of 4.7 µW cm−3 under an AC magnetic field of 10 Oe with a frequency of 50 Hz. We demonstrate that our MME device can be used to monitor the health of a muffle furnace by tapping into the magnetic field noise coming from its electronic cables. The as-developed lead-free flexible MME generator shows potential for advanced applications in self-powered WSN and energy harvesting technologies.

Piezoelectric materials play a crucial role in energy harvesting applications, efficiently capturing renewable energy from sources like human activities and vibrations. Oxygen vacancies, common imperfections in these materials, significantly influence their overall effectiveness. In our study, Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) powder was calcined under different conditions (air and vacuum) to investigate their impact on crystal structure, microstructure, electrical properties, and energy harvesting performance. X-ray diffraction (XRD) and Rietveld analysis confirmed varied phases in vacuum calcined BCZT with a smaller particle size. X-ray photoelectron spectroscopy (XPS) revealed lower oxygen vacancy concentration for vacuum-calcined samples. The vacuum calcined BCZT ceramics demonstrated a remarkable 580% enhancement in the figure of merit (FOM) when contrasted with traditional ceramics, highlighting superior dielectric and piezoelectric characteristics. In mechanical energy harvesting, BCZT ceramics, protected by polyimide with Cu/Ag electrodes, outperformed conventional ceramics, generating a higher open-circuit voltage (10.61 V) and peak-to-peak power (1.510 mW/cm3). This energy harvester maintained stable output through 7000 cycles, suggesting its potential for powering miniature electronics.

Piezoelectric energy harvesting has recently gained attention due to its high power density and potential for self-powered sensor networks. This study investigates the effects of dopants on Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics, examining Strontium (Sr2+), Zinc (Zn2+), and praseodymium (Pr3+/4+) ions at different sites and their impact on structural, dielectric, and electrical properties. X-ray diffraction and Rietveld analysis reveal a coexistence of tetragonal and rhombohedral/orthorhombic phases, with a predominant tetragonal phase, confirmed by Raman analysis. Energy-dispersive X-ray spectroscopy ensures chemical homogeneity. The density measurements indicate a dense microstructure with a relative density of 90–95 %. Dielectric analysis shows a relaxor-like behavior in AB-site doped BCZT ceramics, validated by polarization-electric field hysteresis loops. B-site doped BCZT ceramics exhibit ultra-low leakage currents, approximately 103 times lower than undoped BCZT. An optimized biocompatible flexible film-based energy harvester, incorporating A-site doped BCZT ceramic particles, demonstrated impressive energy harvesting capabilities. A simple finger tapping generated ∼80.2 V and ∼18.2 nA, with an average peak-to-peak power density of 7.6 µW-cm−3. These results highlight the significant potential of dopant inclusion in BCZT ceramics, marking a major advancement in doping strategies for piezoelectric energy harvesting in miniature electronics.

In the modern era, the secure transmission and storage of information are among the utmost priorities. Optical security protocols have demonstrated significant advantages over digital counterparts, i.e., a high speed, a complex degree of freedom, physical parameters as keys (i.e., phase, wavelength, polarization, quantum properties of photons, multiplexing, etc.) and multi-dimension processing capabilities. This paper provides a comprehensive overview of optical cryptosystems developed over the years. We have also analyzed the trend in the growth of optical image encryption methods since their inception in 1995 based on the data collected from various literature libraries such as Google Scholar, IEEE Library and Science Direct Database. The security algorithms developed in the literature are focused on two major aspects, i.e., symmetric and asymmetric cryptosystems. A summary of state-of-the-art works is described based on these two aspects. Current challenges and future perspectives of the field are also discussed.

Data protection via encryption continues to be a key concern in the constantly changing field of digital security. This study investigates a novel method of pixel displacement picture encryption via a modified Caesar cipher algorithm. The proposed method ensures enhanced security by shifting pixel values according to a random key matrix, obscuring image content from unauthorized access. Unlike traditional Caesar cipher applications, which are often criticized for their simplicity and vulnerability, this pixel-wise encryption method leverages the power of modular arithmetic to transform grayscale image data into a format resilient to common cryptographic attacks and concerns. Since the encryption strength is largely dependent on the key's unpredictability and secrecy, key management is essential to this strategy. This technique offers a trivial alternative suitable for specific low resource applications where efficiency is Paramount. The paper also discusses the implications of this method in the broader context of confidentiality, data integrity, and authentication, which are crucial elements in the modern digital security paradigm.

Mechanical energy harvesting and energy storage through lead-free piezoelectric materials is an inevitable source of eco-friendly sustainable powering of electronic devices. Herein, we have synthesized amphoteric rare-earth element praseodymium (Pr) modified Ba0.85Ca0.15Ti0.9Zr0.1O3(BCZT) ceramics, with a cost-effective solid-state-reaction based two-step sintering method for the controlled grain growth. Their crystalline structures and surface morphology were investigated by using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The dielectric and ferroelectric properties of the ceramic capacitors were investigated and correlated with structural parameters. In the vicinity of the monotonic phase transition region, with the coexistence of orthorhombic and tetragonal symmetry, the Pr ion addition in BCZT improves the tetragonal phase, which widens its energy harvesting and storage arena. The appreciable energy harvesting ability was found for an optimized energy harvester with a composition of 0.04 wt% Pr added BCZT ceramic, with an open-circuit voltage of about 5.1 V (corresponding power density of 1.213 mW/cm3) from a simple finger tapping and bring about output voltage stability with a maximum output voltage of about 9 V over 10,000 cycles when periodic force is applied by a machine tapping. Furthermore, this optimized Pr added BCZT ceramic capacitor is capable of storing a substantial recoverable energy density of 81.9 mJ/cm3with a considerable energy storage efficiency of 76.4%. These upshots offer a head start in implementing these ceramic capacitors for effective energy harvesting and energy storage applications for powering futuristic miniature electronics.

Interferenceless coded aperture correlation holography (I-COACH) is one of the simplest incoherent holography techniques. In I-COACH, the light from an object is modulated by a coded mask, and the resulting intensity distribution is recorded. The 3D image of the object is reconstructed by processing the object intensity distribution with the pre-recorded 3D point spread intensity distributions. The first version of I-COACH was implemented using a scattering phase mask, which makes its implementation challenging in light-sensitive experiments. The I-COACH technique gradually evolved with the advancement in the engineering of coded phase masks that retain randomness but improve the concentration of light in smaller areas in the image sensor. In this direction, I-COACH was demonstrated using weakly scattered intensity patterns, dot patterns and recently using accelerating Airy patterns, and the case with accelerating Airy patterns exhibited the highest SNR. In this study, we propose and demonstrate I-COACH with an ensemble of self-rotating beams. Unlike accelerating Airy beams, self-rotating beams exhibit a better energy concentration. In the case of self-rotating beams, the uniqueness of the intensity distributions with depth is attributed to the rotation of the intensity pattern as opposed to the shifts of the Airy patterns, making the intensity distribution stable along depths. A significant improvement in SNR was observed in optical experiments.

In this paper, we propose a new multiuser nonlinear optical cryptosystem using fractional-order vortex speckle (FOVS) patterns as security keys. In conventional optical cryptosystems, mostly random phase masks are used as the security keys which are prone to various attacks such as brute force attack. In the current study, the FOVSs are generated optically by the scattering of the fractional-order vortex beam, known for azimuthal phase and helical wavefronts, through a ground glass diffuser. FOVSs have a remarkable property that makes them almost impossible to replicate. In the input plane, the amplitude image is first phase encoded and then modulated with the FOVS phase mask to obtain the complex image. This complex image is further processed to obtain the encrypted image using the proposed method. Two private security keys are obtained through polar decomposition which enables the multi-user capability in the cryptosystem. The robustness of the proposed method is tested against existing attacks such as the contamination attack and known-plaintext attack. Numerical simulations confirm the validity and feasibility of the proposed method.

Many researchers have been interested in finding elements that help in calculating the orbital angular momentum (OAM) of perturbed vortex beams i.e., after propagating through turbulence in recent years. In this work, we realized a method that utilizes the area of spatial auto-correlation function of scattered optical vortices for finding the topological charge. We have also established an analogy between the area of the intensity auto-correlation profile of the partially coherent vortices and the radii of the related coherent ring-shaped vortex beam transverse profiles which helps us finding the topological charge in a simpler way. This method is independent of the beam waist of Gaussian laser beam for generating the vortex beams. Our experimental results are in good agreement with the theoretically obtained results. These results may find applications in free space optical communication and ghost imaging with vortex beams.

Yttrium iron garnet (YIG; Y3Fe5O12) is an important material in the field of electronics because of its unique magnetic properties. This makes it ideal for use in devices such as microwave filters, amplifiers, sensors, and even magnetic storage devices. It is also used in spintronics, which is the study of the spin of electrons and how it can be manipulated for storage and computation. Additionally, it is highly stable and has low losses when exposed to electromagnetic fields, making it useful in applications such as controlling electric properties with magnetic fields or vice-versa, and magnetic resonance imaging (MRI). Herein, we have prepared YIG and Bi-doped YIG (Bi: YIG: Y2Bi1Fe5O12) nanoparticles (NPs) using the sol–gel auto-combustion method. The obtained garnet powders were sintered at 950 °C both in an air and vacuum environment. We have explored the structural, electrical, optical, magnetic, and magneto-electric (ME) properties of Bi-doped YIG sintered in a vacuum (YBIG-V) and compared it with YIG and Bi-doped YIG sintered in the air (YBIG-A). We found the enhancement in dielectric response, magnetic properties, and the reduction in leakage current for the YBIG-V ceramics than for YBIG-A, YIG ceramics. We have studied the magneto-electric (ME) coupling at room temperature and found that YBIG-V ceramics show the better coupling strength with a maximum coupling coefficient, αME of 354.3 mV/cm-Oe. The dielectric response of these samples significantly varies with the applied magnetic field, which will be positive in Bi-doped YIG ceramics and negative in pure YIG ceramics. Compared to YBIG-A, YBIG-V samples have better variation in dielectric response with the magnetic field, due to which they may be utilized for magnetic field sensing applications. We also observed that the resonance frequency varies with the applied magnetic field, which may be another parameter for field sensing applications. We attribute the enhancement of these properties in YBIG-V sample to the reduction in the average oxygen valency which is 1.63 for YBIG-A and 1.58 for YBIG-V. These values have been determined with the help of X-ray photoelectron emission spectroscopy data.

In this paper, we propose a new asymmetric cryptosystem for phase image encryption, using the physically unclonable functions (PUFs) as security keys. For encryption, the original amplitude image is first converted into a phase image and modulated with a PUF to obtain a complex image. This complex image is then illuminated with a plane wave, and the complex wavefront at a distance d is recorded. The real part of the complex wavefront is further processed to obtain the encrypted image and the imaginary part is kept as the private key. The polar decomposition approach is utilized to generate two more private security keys and to enable the multi-user capability in the cryptosystem. Numerical simulations confirm the feasibility of the proposed method.

We introduce a modified sintering approach to investigate the microstructure, dielectric, and resistive switching (RS) properties of bulk Ba0.7Sr0.3TiO3 (BST) ceramics. The ceramics were prepared using a solid-state-reaction method, and then sintered using modified double-step sintering (DS) processes, as well as conventional single-step sintering (CSS) at different peak temperatures (1250°C and 1350°C). To find the phase purity, lattice parameters, and tetragonality of the samples, x-ray diffraction patterns were fitted with the pseudo-Voigt function in the FullProf software. With the help of the software, bond angles and bond lengths were found for all the ceramics. Furthermore, Raman spectrum analysis was performed to confirm the samples' structural variations. The microstructure images of the samples show that the grain size was reduced and the grain size distribution was improved for the DS-processed ceramics as compared to the CSS-processed ceramics. The dielectric properties of the BST ceramic capacitors were investigated in a wide range of frequencies and temperatures. All the BST ceramics displayed humps at near-room temperature, corresponding to tetragonal–cubic phase transitions, and a small shift in transition temperature towards higher temperature regions for the DS ceramics compared with the CSS ceramics was observed due to structural modification by a grain size effect. The metal–insulator–metal (MIM) structures, so-called memristors, were designed with these dielectric ceramics. A bipolar RS behavior was observed in these MIM structures which were confirmed through current–voltage (I–V) characteristics. The improved RS in these structures is the result of the migration and redistribution of cations, such as oxygen ions and oxygen vacancies ,as well as the ferroelectric domain orientation.

In Appl. Opt. 55, 4720-4728 (2016), authors demonstrated the vulnerability of Linear Canonical Transform (LCT)-based optical encryption system. One of the primary reasons for this is the predictable nature of the security keys (i.e., simulated random keys) used in the encryption process. To alleviate, in this work, we are presenting a Physically Unclonable Function (PUF) for producing a robust encryption key for the digital implementations of any optical encoding systems. We note a correlation function of the scattered perfect optical vortex (POV) beams is utilized to generate the encryption keys. To the best of our knowledge, this is the first report on properly utilizing a scattered POV for the optical encryption systems. To validate the generated keys, the standard Linear Canonical Transform-based Double Random Phase Encoding (LCT-DRPE) technique is used. Experimental and simulation result validates the proposed key generation method as an effective alternative to the digital encryption keys.

We have generated and propagated both diffracting and non-diffracting speckles using the scattering of perfect optical vortices. The diffracting speckles have been realized in the near field and non-diffracting speckles have been realized in the far field, i.e. after taking the Fourier transform of near-field speckles using a simple convex lens. We found that the experimental results are in good agreement with the theoretical results. These results may find applications in classical cryptography and communication as we have both varying and non-varying random field patterns with propagation distance.

We study correlations in the speckle patterns generated by the scattering of perfect optical vortex (POV) beams and use them to produce a new class of coherence functions, namely Bessel coherence functions. Higher (zeroth) order Bessel coherence functions have been realized in cross (auto)-correlation between the speckle patterns generated by the scattering of perfect vortex beams of different orders. We have also studied the propagation of produced Bessel coherence functions and characterized their divergence with respect to the radius of their first ring for different orders m = 0-4. We observe that the divergence varies linearly with the order of the coherence function. We provide the exact analytical expression for the auto-correlation, as well as cross-correlation functions for speckle patterns. Our experimental results are in good agreement with the analytical results.

Ruby is one of the best solids for generation of slow light at room temperature. Ultraslow light propagation to ∼2.8 m/s has been demonstrated experimentally in ruby rod of length 7.6 cm. The systematic variation of optical delay with the modulation frequency, laser power and depth of focus has been studied. Fine tuning from ∼12 ms to ∼20 ms has been achieved by using laser power and depth of focus as a knob, at a modulation frequency of 1.8 Hz. These studies suggest that ruby rod may find potential applications in developing the tunable optical delay-based devices.

Spatially incoherent light can result from nonlinear processes where a group of photons are emitted in entangled states of spatial modes, which results in an incoherent mixture of constituting spatial modes when the photons are assessed one by one. In this paper we explore a method which uses a tilted lens to probe the orbital angular momentum (OAM) spectrum of such a mixture. We examine the general case where the photons are in mixtures of both different OAM and radial modes, resulting in a 2-dimensional random distribution that creates a more difficult challenge compared to mixtures of OAM only.

We investigate the methods to obtain maximum correlated photon pairs generated in Type I spontaneous parametric down conversion (SPDC) with focused pump beam. We study the effect of pump focusing on the photon collection efficiency of signal and idler modes. The correlated photon pair collection efficiency decreases asymptotically with input pump beam focusing parameter [1]. The results obtained here are expected to be useful in designing appropriate optical fibers for generating efficient entangled photon sources for quantum information applications.

Polarization speckle is a fine granular light pattern having spatially varying random polarization profile. We generate these speckle patterns by using the scattering of Poincaré beams, a special class of vector vortex beams, through a ground glass plate. Here, the Poincaré beams are generated using a polarization sensitive spatial light modulator displaying an on-axis hologram corresponding to an optical vortex phase profile. The different inhomogeneities of the rough surface experience different polarizations, which control the ability for scattered waves to interfere at the detection plane and causes a spatially varying polarization profile. We experimentally determined the spatial variation of local degree of polarization and orientation of the polarization ellipse for these speckle patterns from the Stokes analysis. We also determined the size of scalar speckles using the auto-correlation function of Stokes parameter S0 and the size of polarization speckles using the sum of auto-correlation functions of remaining three Stokes parameters. We found that the change in scalar speckle size with the index of the vector beam is very small and of the order of 1 pixel size of the camera but the size of polarization speckles decreases with the increase in index of the vector beam.

We here demonstrate on both theoretical and experimental bases a method to recover the topological structure of a monochromatic optical field that has suffered diffuse transmission. This method consists of two steps: first, a linearly polarized sample beam is mixed with a coaxial Gaussian beam in orthogonal polarization states resulting in a Poincaré beam; second, a polarization-related spatial correlation function is considered and measured for the overall speckle field arising by optical diffusion. The singularities of the sample beam turn out to be imaged into the correlation function of the vector speckle field.

We address the possibility of using even/odd states of orbital angular momentum (OAM) of photons for the quantum information tasks. Single photon qubit states and two photon entangled states in even/odd basis of OAM are considered. We present a method for the tomography and general projective measurement in even/odd basis. With the general projective measurement, we show the Bell violation and quantum cryptography with Bell's inequality. We also describe hyper and hybrid entanglement of even/odd OAM states along with polarization, which can be applied in the implementation of quantum protocols like super dense coding.

Photon modes have an important role in characterizing the quantum sources of light. The two main pre-detection factors affecting the biphoton mode coupling in SPDC are the pump beam focusing parameter and the crystal thickness. We present the numerical and experimental results on the effect of pump focusing on conditional down-converted photon modes for a Type-I BBO crystal. We experimentally verify that biphoton coupling efficiency decreases asymptotically with pump beam focusing parameter. We attribute this behaviour to (a) the asymmetry in the spatial distribution of down-converted photons with the pump beam focusing parameter and (b) the ellipticity of biphoton modes introduced due to the focusing of the pump beam. We also show the ellipticity experimentally as well as quantify it with the focusing parameter. These results may be useful in selecting optimum conditions for generating efficient fiber coupled sources of heralded single photons and entangled photons for quantum information applications.

We experimentally generate the Bessel-Gauss coherence functions using the cross-correlations between the two speckle patterns obtained using the perfect optical vortices (POV) of different orders. POV beams are generated using the Fourier transform of Bessel-Gauss beams by displaying the axicon hologram on spatial light modulator. A ground glass plate is used for scattering POV beams and the speckles are recorded. The cross-correlation function of two speckle patterns is Bessel-Gauss functions whose order is given by the difference in the orders of two POV beams used for scattering. The auto-correlation function of these speckles is Bessel-Gauss function of order zero.

We show that there are a number of ways to transform an arbitrary polarization state into another with just two quarter wave plates (QWPs). We have verified this geometrically using the trajectories of the initial and final polarization states corresponding to all the fast axis orientations of a QWP on the Poincaré sphere. The exact analytical expression for the locus of polarization states has also been given, and describes the trajectory. An analytical treatment of the equations obtained through matrix operations corresponding to the transformation supports the geometrical representation. This knowledge can be used to obtain the Mueller matrix by just using QWPs, which has been shown experimentally by exploiting projections of the output states on the input states.

Tunability of work function and optical nonlinearity is carried out by doping Au nanoparticles in TiO2. The work function and optical nonlinearity are found to be inversely related with respect to Au dopant.

We generate the vector vortex or polarization singular beams using a polarization sensitive spatial light modulator displaying an on-axis hologram of an optical vortex. The generated vector beams are characterized by polarimetry and then scattered through a ground glass plate. The polarimetry for scattered light confirms the presence of random spatial polarization distribution, which is known as polarization speckles, although locally every point is completely polarized. Here, we present the structure and characterization of the generated polarization speckles and their statistical properties.

We generate the non-separable state of polarization and orbital angular momentum using a laser beam. The generated state undergoes a cyclic polarization evolution which introduces a Pancharatnam geometric phase to the polarization state and, in turn, a relative phase in the non-separable state. We experimentally study the violation of the Bell-like inequality for different Pancharatnam phases introduced by various cyclic polarization evolutions with linear and circular states as measurement bases. While measuring in linear bases, the Bell-CHSH parameter oscillates with a Pancharatnam phase. One can overcome this dependence by introducing a relative phase in one of the projecting states. However, for measurements in circular bases, the Pancharatnam phase does not affect the Bell-like inequality violation.

Using classical laser beams, we generate a general complex superposition state, cebit, of orbital angular momentum (OAM) of light. We use a nonseparable beam of polarization and OAM generated by a modified Sagnac interferometer for the generation of OAM cebits which can be represented as points on the OAM Poincaré sphere. The general cebit state is represented as a function of the rotation angle of the wave plates so that one can easily generate the required state.

We generate perfect optical vortex (POV) beams, whose intensity distribution is independent of the order, and scatter them through a rough surface. We show that the size of produced speckles is independent of the order of the POV and their Fourier transform gives the random non-diffracting fields. The invariant size of speckles over the free space propagation verifies their non-diffracting or non-diverging nature. The size of speckles can be easily controlled by changing the axicon parameter, used to generate the Bessel-Gauss beams whose Fourier transform provides the POV. These results may be useful in applications of POV for authentication in cryptography.

Vector vortex beams are classified into four types depending upon spatial variation in their polarization vector.We have generated all four of these types of vector vortex beams by using a modified polarization Sagnac interferometer with a vortex lens. Further, we have studied the non-coaxial superposition of two vector vortex beams. It is observed that the superposition of two vector vortex beams with same polarization singularity leads to a beam with another kind of polarization singularity in their interaction region. The results may be of importance in ultrahigh security of the polarization-encrypted data that utilizes vector vortex beams and multiple optical trapping with non-coaxial superposition of vector vortex beams. We verified our experimental results with theory.

Experimental realization of coherence vortex is presented as an application of Poincaré beams. The vortex is realized by constructing the spatial correlation function between the orthogonal polarized field fluctuations of the scattered Poincaré beam.

We generate the vector vortex or polarization singular beams using a polarization sensitive spatial light modulator displaying an on-axis hologram of an optical vortex. The generated vector beams are characterized by polarimetry and then scattered through a ground glass plate. The polarimetry for scattered light confirms the presence of random spatial polarization distribution, which is known as polarization speckles, although locally every point is completely polarized. Here, we present the structure and characterization of the generated polarization speckles and their statistical properties.

We present the intensity correlation studies for speckles corresponding to the scattering of different spatial modes incident on the ground glass plate. We observe that the strength of modulation peak varies with spatial mode.

We demonstrate a stabilized orbital angular momentum (OAM) sorter using polarizing Sagnac interferometer containing a single dove prism. The setup is stable against small misalignments and it is shown to separate complex superposition states too.

We construct a orbital angular momentum (OAM) Poincaré sphere in which we can represent 2-D superposition states of arbitrary OAM. In addition, we represent the mixed states of OAM as non separable states inside the sphere. We also give an experimental set up to generate all points on this sphere.

We generate optical vortices and scatter them through a rough surface. However, the scattered light passing through a lens shows the same vorticity when probed at the Fourier plane. The vorticity is measured using a nonseparable state of polarization and orbital angular momentum of light as it cannot be confirmed by the standard interferometric technique. The observed vorticity is found to be independent of the amount of scattered light collected. Therefore, vortices can be used as information carriers even in the presence of scattering media. The experimental results are well supported by the theoretical results.

We show, both theoretically and experimentally, that the propagation of optical vortices in free space can be analyzed by using the width [w(z)] of the host Gaussian beam and the inner and outer radii of the vortex beam at the source plane (z = 0) as defined in [Opt. Lett. 39, 4364 (2014)]. We also studied the divergence of vortex beams, considered as the rate of change of inner or outer radius with the propagation distance (z), and found that it varies with the order in the same way as that of the inner and outer radii at z = 0. These results may be useful in designing optical fibers for orbital angular momentum modes that play a crucial role in quantum communication.

We have considered optical beams with phase singularity and experimentally verified that these beams, although classical, have properties of two-mode entanglement in quantum states. We have observed the violation of Bell's inequality for continuous variables using the Wigner distribution function (WDF) proposed by P. Chowdhury et al. [Phys. Rev. A 88, 013830 (2013)PLRAAN1050-294710.1103/PhysRevA.88.013830]. Our experiment establishes an alternate form of Bell's inequality in terms of the WDF which can be used for classical as well as quantum systems.

We present a scheme to generate three-particle hyper-entanglement utilizing polarization and orbital angular momentum (OAM) of photons. We show that the generated state can be used to teleport a two-qubit state described by the polarization and the OAM. The proposed quantum system has also been used to describe a new efficient quantum key distribution (QKD) protocol. We give a sketch of the experimental arrangement to realize the proposed teleportation and the QKD.

We experimentally show that the non-separability of polarization and orbital angular momentum present in a light beam remains preserved under scattering through a random medium like rotating ground glass. We verify this by measuring the degree of polarization and observing the intensity distribution of the beam when projected to different polarization states, before as well as after the scattering. We extend our study to the non-maximally non-separable states also.

We experimentally demonstrate that the vorticity of light remains preserved even after scattering through a ground glass plate. It shows the robustness of optical vortices along with conservation of orbital angular momentum of light.

We make a source of entangled photons using spontaneous parametric down-conversion (SPDC) in a non-linear crystal and study the spatial distribution of photon pairs obtained through the down-conversion of different modes of light including higher order vortices. We observe that for the Gaussian pump, the thickness of the SPDC ring varies linearly with the radius of pump beam. However, in case of vortex carrying beams, two concentric SPDC rings are formed for beams above a critical radius. The full width at half maximum (FWHM) of SPDC rings increase with increase in the order of optical vortex beams. The presence of a critical beam width for the vortices as well as the observed FWHM of the SPDC rings are supported with our numerical results. © 2014 Elsevier B.V.

Optical vortices, although being classical, have properties of two-mode entanglement present in quantum states. We have experimentally verified the violation of Bell's inequality using Wigner distribution function for such beams.

We construct Poincaré sphere for orbital angular momentum (OAM) states for coherent and partially coherent light beams using a non-separable state generated with modified Sagnac interferometer and a random scatterer.

We experimentally demonstrate that the vorticity of light remains preserved even after scattering through a ground glass plate. It shows the robustness of optical vortices along with conservation of orbital angular momentum of light.

We model scattered optical vortices as partially coherent optical vortices (PCOV) as well as Laguerre Gaussian Schell Model beams. A comparison with our experimental results shows the validity of modelling them as PCOV beams.

We propose a new method for determining the Mueller matrix of an arbitrary optical element and verify it with three known optical elements. This method makes use of two universal SU(2) polarization gadgets to obtain the projection matrix directly from the experiment. It allows us to determine the Mueller matrix without precalibration of the setup, since the generated polarization states are fully determined by the azimuths of the wave plates. We calculate errors in determining the Mueller matrix and compare with other techniques. © 2014 Optical Society of America.

We embed a pair of vortices with different topological charges in a Gaussian beam and study its evolution through an astigmatic optical system, a tilted lens. The propagation dynamics are explained by a closed-form analytical expression. Furthermore, we show that a careful examination of the intensity distribution at a predicted position past the lens can determine the charge present in the beam. To the best of our knowledge, our method is the first noninterferometric technique to measure the charge of an arbitrary vortex pair. Our theoretical results are well supported by experimental observations. © 2014 Optical Society of America.

We have experimentally generated higher order optical vortices and scattered them through a ground glass plate that results in speckle formation. Intensity autocorrelation measurements of speckles show that their size decreases with an increase in the order of the vortex. It implies an increase in the angular diameter of the vortices with their order. The characterization of vortices in terms of their annular bright ring also helps us to understand the se observations. The results may find applications in stellar intensity interferometry and thermal ghost imaging. © 2014 Optical Society of America.

We have studied the spatial intensity distribution of optical vortex beams both theoretically and experimentally. We show that the area of the bright ring present in optical vortex increases with its order along with the inner and outer radii of the vortex beams.

Optical vortices, although being classical, have properties of two-mode entanglement present in quantum states. We have experimentally verified the violation of Bell's inequality using Wigner distribution function for such beams.

We model scattered optical vortices as partially coherent optical vortices (PCOV) as well as Laguerre Gaussian Schell Model beams. A comparison with our experimental results shows the validity of modelling them as PCOV beams.

We construct Poincaré sphere for orbital angular momentum (OAM) states for coherent and partially coherent light beams using a non-separable state generated with modified Sagnac interferometer and a random scatterer.

We have experimentally reproduced ring-shaped beams from the scattered Laguerre-Gaussian and Bessel-Gaussian beams. A rotating ground glass plate is used as a scattering medium, and a plano-convex lens collects the scattered light to generate ring-shaped beams at the Fourier plane. The obtained experimental results are supported with the numerical results and are in good agreement with the theoretical results proposed by Wang et al. [Opt. Express 17, 22366 (2009)]. © 2013 Optical Society of America.

We have experimentally observed the revival of the dark core in the far field intensity distribution in optical vor tices after scattering through rotating ground glass plate. The diameter and darkness of the core is independent of the speed of the rotating ground glass plate. They depend on the spot size and azimuthal index of the beam incident on it. This shows that the spatial coherence of the scattered light is independent of the speed of the rotating ground glass plate. Our experimental results are in good agreement with the numerical results based on the theory given by Wang, Cai and Korotkova (Opt. Exp. 17, 22366 (2009)). © 2013 SPIE.

We show that determination of the orbital angular momentum (OAM) of an optical vortex can be possible using simple convex lens, an ubiquitous optical element found in any optics laboratory.

We show that determination of the orbital angular momentum (OAM) of an optical vortex can be possible using simple convex lens, an ubiquitous optical element found in any optics laboratory. © 2012 OSA.