Vijay Kumar

National Institute of Technology, Warangal | NITW · Department of Physics

Machine learning has emerged as a powerful tool for physicists for building empirical models from the data. We exploit two convolutional networks, namely Alexnet and a wavelet scattering network for the classification of orbital angular momentum (OAM) beams. We present a comparative study of these two methods for the classification of 16 OAM modes...

A deep learning assisted scheme for classification of noisy LG modes is proposed. This model is noise and alignment independent and will increase the accuracy and fidelity of OAM mode detection systems.

Orbital angular momentum (OAM) beams have the potential to increase the information-carrying capacity because of the extra degrees of freedom associated with them. Traditional methods for mode detection and de-multiplexing are complex and require expensive optical hardware. We propose a very simple and cost-effective deep learning based model for d...

The recognition of orbital angular momentum (OAM) in light beams holds significant importance in optical communication. The majority of current OAM recognition techniques are highly sensitive to stringent alignment issues. The speckle-based OAM recognition method reported in J. Opt. Soc. Am. A 39 , 759 ( 2022 ) JOAOD6 1084-7529 10.1364/JOSAA.446352...

Orbital angular momentum (OAM)-carrying beams have gained significant attention in recent years due to their unique properties and potential to improve spectral efficiency and data transmission rates in optical communication systems. However, fully exploiting the capabilities of the entire OAM mode spectrum remains challenging. The emergence of AI...

The recognition of orbital angular momentum (OAM) in light beams holds significant importance in optical communication. The majority of current OAM recognition techniques are highly sensitive to stringent alignment issues. The speckle-based OAM recognition method reported in [J. Opt. Soc. Am. A 39, 759 (2022)] is alignment-free in the transverse di...

The recognition of orbital angular momentum (OAM) in light beams holds significant importance in optical communication. The majority of current OAM recognition techniques are highly sensitive to stringent alignment issues. The speckle-based OAM recognition method reported in [J. Opt. Soc. Am. A 39, 759 (2022)] is alignment-free in the transverse di...

In this Letter, we introduce a novel, to the best of our knowledge, structured light recognition technique based on the 1D speckle information to reduce the computational cost. Compared to the 2D speckle-based recognition [J. Opt. Soc. Am. A 39, 759 (2022)10.1364/JOSAA.446352], the proposed 1D speckle-based method utilizes only a 1D array (1× n pix...

We report an experimental proof of concept for speckle-based one-to-three non-line-of-sight (NLOS) free space optical (FSO) communication channels employing structured light shift-keying. A 3-bit gray image of resolution ${{100}} \times {{100}}$ 100 × 100 pixels is encoded in Laguerre–Gaussian or Hermite–Gaussian beams and decoded using their respe...

Intensity degenerate orbital angular momentum (OAM) modes are impossible to recognize by direct visual inspection even using available machine learning techniques. We are reporting speckle-learned convolutional neural network (CNN) for the recognition of intensity degenerate Laguerre-Gaussian (LGp, l) modes, intensity degenerate LG superposition mo...

Speckle-based deep learning approach for the classification of partially coherent vortex beams is presented. Remarkably, this approach achieved 100% classification accuracy.

The evolution of the OAM speckle fields from the Fresnel to Fraunhofer region has been studied for the classification of OAM beams using 1D-CNN.

We present a deep learning model that recognizes multiplexed superposed Laguerre Gaussian beams through their astigmatic transformed far-field speckle patterns with an accuracy of 99%.

This is the summary of our work published in "Optics in 2022", a special issue of Optics & Photonics News.

Orbital angular momentum (OAM) modes have addressed the bandwidth issues with high information capacity by employing mode-division-multiplexing. State-of-the-art terabits/sec speed was achieved by using OAM modes. By establishing OAM modes into multicasting communication channel applications, single channel advantages can be inculcated in multiple...

We present a deep learning model for speckle-based Orbital Angular Momentum Shift-Keying (OAM-SK) for optical Communication. A Convolutional Neural Network (CNN) is trained to recognize intensity degenerate OAM modes through their astigmatic transformed far-field intensity speckle patterns. For robustness, the CNN is trained with noisy OAM modes in...

Here I presented a deep learning model that recognizes Perfect Optical Vortices through their astigmatic transformed speckle patterns in the presence of Gaussian White Noise with an accuracy of > 97% for SNR of 0dB.

We present a deep learning model that recognizes Perfect Optical Vortices through their astigmatic transformed speckle patterns in the presence of Gaussian White Noise with an accuracy of > 97% for SNR of 0dB.

A study on first-order polarization correlation in propagating vector speckle fields is carried out. Vector speckle field, generated by scattering of Poincare beam, is propagated through a spherical and a cylindrical lens. The first-order polarization correlation was experimentally constructed from intensity images of vector speckle fields at vario...

We present a speckle-based deep learning approach for orbital angular momentum (OAM) mode classification. In this method, we have simulated the speckle fields of the Laguerre–Gauss (LG), Hermite–Gauss (HG), and superposition modes by multiplying these modes with a random phase function and then taking the Fourier transform. The intensity images of...

The experimental proof-of-concept for 1-D CNN empowered speckle-based non-line-of-sight communication using Hermite-Gaussian modes is presented and achieved an average classification accuracy >96%. © 2022 The Author(s)

Classification of Hermite-Gaussian modes using a randomly picked 1D cross-line array across the 2D speckle pattern of the respective modes is proposed. Less than one-by-thousandth of the image data is utilized for classification.

Here I presented a deep learning assisted scheme for the classification of noisy LG modes. This model is noise and alignment independent and will increase the accuracy and fidelity of OAM mode detection systems.

Polarization correlations are analyzed in propagating vector speckle field generated by scattering of Poincaré beam. Dynamical charge inversion of the correlation vortex is observed when the speckles propagate through a cylindrical lens.

Far-field slit diffraction of circular optical-vortex (OV) beams is efficient for measurement of the topological charge (TC) magnitude but does not reveal its sign. We show that this is because in the common diffraction schemes the diffraction plane coincides with the incident OV waist plane. Based on the examples of Laguerre–Gaussian incident beam...

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 be...

Far-field slit-diffraction of circular optical-vortex (OV) beams is efficient for measurement of the topological charge (TC) magnitude but does not reveal its sign. We show that this is because in the common diffraction schemes the diffraction plane coincides with the incident OV waist plane. With explicit involvement of the incident beam spherical...

Nonlinear behaviour of gold micro disks patterned Ruby film has been investigated via Z-scan technique. Open Z-scan was performed for Ruby and Ruby/gold thin film using 532 nm Laser source. Two-photon absorption (TPA) and Saturable absorption (SA) have been observed in pure Ruby and Ruby/gold thin film respectively. The expression for normalized tr...

Orbital angular momentum (OAM) has emerged as an important parameter to store, control and transport information using light. Recognizing optical beams that carry OAM at the nanoscale and their interaction with sub-wavelength nanostructures has turned out to be a vital task in nanophotonic signal processing and communication. The current platforms...

Spin-orbit interactions are subwavelength phenomena that can potentially lead to numerous device-related applications in nanophotonics. Here, we report the spin-Hall effect in the forward scattering of Hermite-Gaussian (HG) and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarize...

Spin-orbit interactions are subwavelength phenomena that can potentially lead to numerous device-related applications in nanophotonics. Here, we report the spin-Hall effect in the forward scattering of Hermite–Gaussian (HG) and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarize...

Higher order statistical correlations of the optical vector speckle field, formed due to scattering of a vector-vortex beam, are explored. Here, we report on the experimental construction of the Stokes parameters covariance matrix, consisting of all possible spatial Stokes parameters correlation functions. We also propose and experimentally realize...

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...

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 Poinca...

We generate orbital angular momentum entangled states by spontaneous parametric down-conversion with a pump as a superposition of optical vortices. The generated entangled states are tuned by controlling the mixing of vortices in the superposition. This method of tuning the entanglement has applications in quantum key distribution.

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

We present newly conceived liquid-crystal-based retardation waveplates in which the optic axis distribution has a “superelliptically” symmetric azimuthal structure with a topological charge q superimposed. Such devices, named superelliptical q-plates, act as polarization-to-spatial modes converters that can be used to produce optical beams having p...

Topological structure of monstar in π-symmetric fields with index Ic = +1/2 and three radial lines ending at C-point is an intermediate structure having properties of lemon and star. We experimentally realized monstar pattern in polarization ellipse orientation via three different routes, from lemon pattern using topologically-invariant squeezing a...

Tunable lemon-dipole-star topological transformations are achieved when structured light beam propagates through a uniaxial crystal under the influence of transverse electric field. The results are understood by mapping the transformations on a higher-order Poincaré sphere.

Topological approach to study complex optical field is reported here. Fundamental topological structures lemon, star, monstar and spiral, node, saddle are experimentally realized in optical parameter fields.

Singularities, where physical quantities are indeterminate and cannot be defined are an integral part of nature. Catastrophe optics deals with the unusual behaviour in the amplitude. Singular optics on the other hand is a study of optical fields with phase and polarization singularities. These singularities may or may not be meaningful, but it inva...

Optical singularities of index I u = ± 1 / 2 associated with lemon, monstar, and star topological structures in π -symmetric fields and singularities of index I c = ± 1 associated with radial, circulation (elliptic), spiral, node, and saddle structures in 2 π -symmetric vector fields are studied in detail here. The topological structures in the pol...

Polarization-singularity C points, a form of line singularities, are the vectorial counterparts of the optical vortices of spatial modes and fundamental optical features of polarization-spatial modes. Their generation in tailored beams has been limited to so-called “lemon” and “star” C points that contain symmetric dislocations in state-of-polariza...

Polarization-singularity C-points, a form of line singularities, are the vectorial counterparts of the optical vortices of spatial modes and fundamental optical features of polarization-spatial modes. Their generation in tailored beams has been limited to lemon and star C-points that contain symmetric dislocations in state-of-polarization patterns....

Polarization structured optical beams have half-integer topological structures: star, lemon, monstar in π-symmetric polarization ellipse orientation tensor field and integer-index topological structures: saddle, spiral, node in 2π-symmetric Poynting vector field. Topological approach to study the polarization structured optical beams is carried out...

Tunable lemon-dipole-star topological transformations are achieved when structured light beam propagates through a uniaxial crystal under the influence of transverse electric field. The results are understood by mapping the transformations on a higher-order Poincaré sphere.Optics and Photonics

Poynting vector density of polarization singular field with well defined polarization structure such as lemon or star is experimentally measured using polarization interference and found to have unique features in contrast to constituent scalar fields.

Experimental measurements of the nonplanar phase of scalar optical beams is achieved using polarization singularities and Stokes parameters. The product of beam intensity and its phase gradient is calculated to get the Poynting vector distribution in the beam cross section. Using these we propose a scheme and experimentally obtain generic fundament...

To construct a Poincare sphere equivalent representation for the polarization singular states: lemon, star and monstar.

Space-variant inhomogeneously polarized field formed due to superposition of orthogonally polarized Gaussian .LG00/ and Laguerre–Gaussian .LG01/ beams results in polarization singular beams with different morphology structures such as lemon, star and dipole patterns around the C-point in the beam cross-section. The Pancharatnam–Berry phase plays a...

The theoretical formalism and experimental measurements to form and transform between the three morphologies of the polarization singular patterns—star, lemon and monstar—are presented here. The monstar is statistically rare in isotropic random fields but its controllable realization is achieved by tuning the field anisotropy in three-beam interfer...

Spin-orbit interaction in optical fiber leads to the breaking of the degeneracy in the propagation constants resulting in partial vortices. We present our experimental results on the energy exchange between the two partial vortices in a step-index two-mode fiber as a function of input wavelength.

Interference of fiber eigen vector modes of different phase and spatial variation of polarization gives rise to different types of polarization singularities – isolated C-point surrounded by star / lemon type polarization morphology patterns, a dipole or two C-points of same index – in 2D polarization fields. In this context, fiber modal decomposit...

Polarization singularities formed due to superposition of orthogonally polarized fundamental and higher order modes evolve as it propagates in a two-mode fiber and is used to study the vector waveguide modes and their dispersion.

We report the formation and annihilation of vectorial topological dipole mediated by plasmons in structure-free metal surfaces using a polarization singular optical beam. The measured far-field behavior is due to the strong angular and polarization dependence of the reflection coefficient and the phase shift experienced by the spatially inhomogeneo...

Excitation of surface plasmons using a polarization singular optical beam results in the formation of vectorial topological dipole due to the strong angular and polarization dependence of the reflection coefficient and phase shift.

We present here controlled generation of asymmetric optical vector-vortex beams using a two-mode optical fiber and study the dynamic evolution of the transverse energy flow (TEF) when focused through a spherical lens. The dependence of the TEF on various factors such as the vortex charge, vortex anisotropy and polarization structure around the vort...

Experimental measurements of the twirl and changes in the anisotropy of the constant intensity ellipse, and the rotation of the polarization singular lemon pattern a generalized vector-vortex beam experiences around the two foci due to the converging and diverging conical waves and in between, are presented and interpreted as being due to the unive...

Optical vortex beams with tunable anisotropy is generated using a two-mode optical fiber and its propagation characteristics are measured and analyzed. The transverse energy circulation in such beams is found to be proportional to the strength of anisotropy with maximum circulation for isotropic vortex beam.