This PDF file contains the front matter associated with SPIE Proceedings Volume 12017, including the Title Page, Copyright information, Table of Contents and Conference Committee lists.

The state of spatial coherence of a partially coherent optical source plays the crucial part in free-space evolution of the major properties of the radiated beam, such as its diffraction rate, spectral composition, intensity distribution and polarization/Orbital Angular Momentum (OAM) states. In particular, various effects of source coherence on the beam properties relating to its OAM structure, such as spatial profiling of the vortex core, vortex self focusing, average intensity rotation, etc. have also been illustrated. To account for such coherence effects most efficiently, the treatment of the OAM content in stationary sources and beams with the help of Coherence-OAM (COAM) matrices was recently suggested and is overviewed here. A possible approach to analytical modeling of the COAM matrices is then discussed. A calculus characterizing the OAM transformations, analogous to the Jones-Stokes-Mueller calculi used in polarization optics, was also recently introduced for thin (local) and extended (non-local) devices. Here, we consider the combination of a local and a non-local device to suggest an OAM-resolved imaging system, as a possible application.

The similarity between the 2D Helmholtz equation in elliptical coordinates and the Schr¨odinger equation for the simple mechanical pendulum inspires us to use light to mimic this quantum system. When optical beams are prepared in Mathieu modes, their intensity in the Fourier plane is proportional to the quantum mechanical probability for the pendulum. Previous works have produced a two-dimensional pendulum beam that oscillates as a function of time through the superpositions of Mathieu modes with phases proportional to pendulum energies. Here we create a three-dimensional pendulum wavepacket made of a superposition of Helical Mathieu-Gaussian modes, prepared in such a way that the components of the wave-vectors along the propagation direction are proportional to the pendulum energies. The resulting pattern oscillates or rotates as it propagates, in 3D, with the propagation coordinate playing the role of time. We obtained several different propagating beam patterns for the unbound-rotor and the bound-swinging pendulum cases. We measured the beam intensity as a function of the propagation distance. The integrated beam intensity along elliptical angles plays the role of quantum pendulum probabilities. Our measurements are in excellent agreement with numerical simulations.

We investigate the orbital angular momentum mixing in frequency up-conversion with structured light beams. Phase and polarization vortex beams are coupled in noncollinear second harmonic generation under type-II phase matching. The spatial properties of the second harmonic beam are shaped by the combined features of the input beams. This effect creates a spin-orbit crosstalk allowing for angular momentum transfer between the two degrees of freedom. The information transfer between photonic degrees of freedom encoded on different wavelengths can be useful for connecting different physical platforms in quantum information protocols.

Unlike single photon absorption, the rate of multiphoton absorption processes is dependent on the polarization state of the exciting optical field. Multiphoton absorption spectroscopy is predominantly carried out with an exciting light source which is structured and polarized in a 2D sense in the transverse (x,y) plane, but homogeneous along the direction of propagation (z). Here we study two-photon absorption (TPA) with tightly focused optical vortices, where the spatial confinement generates significant longitudinal components of the electromagnetic fields in the direction of propagation, producing a 3D structured optical field at the focal plane. We discover that the additional polarization degree of freedom in the z direction for 3D structured light produces novel results in TPA compared to the preceding paraxial source excitation.

We explore phase and polarization singularity characteristics including the formation spiral and saddle pattern around V-singularity, due to propagation of converging-diverging beam of light through a tilted-rotated quartz half-waveplate. Such a system modifies the output beam characteristics significantly via coupled linear-circular birefringence experienced by a beam of light due to shape of the path – wave vector dependent Pancharatnam-Berry type geometric phase. Topological characteristics of the output beam for different input beam and waveplate orientation conditions are characterized using spatially-resolved Stokes parameter and weak measurement methods. Understanding the formation and manipulation of topologically structured optical beam using a single piece of optical component can pave the way to its widespread application.

Optical fields possess energy, momentum, and helicity. For the plane waves and paraxial fields of standard, classical optics, the spin angular momentum and optical helicity are well understood, both being proportional to the degree of circular polarization. In contrast, 3D non-paraxial optical fields generated by spatial confinement, such as tight focusing and evanescent waves, may possess spin angular momentum and optical helicity when the degree of 2D-circular polarization is zero. In this work using quantum electrodynamics we highlight two novel properties of non-paraxial optical vortices 1) a non-zero optical helicity (chirality) density for 2D-unpolarized (and 2D-linearly polarized) 3D optical vortices and 2) a longitudinal spin angular momentum density for 2D-linearly polarized 3D optical vortices.

The double ring perfect optical vortex (DR-POV) published in Optics Express in 2020 is an optical beam obtained from the difference between two perfect optical vortices POV. As its predecessor, the DR-POV inherits the shape form invariance from topological charge and possesses a very narrow ring profile. It was proved that the DR-POV can be formed in both the paraxial and tightly focused regimes; however only normalized intensity profiles were presented. In this work we provide complementary data regarding to the field amplitude of the DR-POV to show the complex amplitude interplay when the main lobes approach in both the paraxial and tightly focused regimes.

Understanding the spin-Hall effect of light (SHEL) and in general the spin-shifts (SS) both in the plane of incidence and perpendicular to it are of fundamental and applied research interest. The small polarization changes and hence the beam shifts arising due to light-matter interaction are optically amplified and measured via the weak measurement method. We report here simulation results for the appearance of SS at near-normal (NN) incidence due to focused TM-polarized Gaussian beam reflected at a plane dielectric interface. Measured at the Fourier plane, the cross-polarization component in the output beam shows significant SS due to changes in the state of polarization. The proposed NN incidence configuration has significant experimental advantages as compared to the conventional SHEL / SS measurements and could be used to measure physical parameters and changes in them.

Machine Learning (ML) has recently been applied to the problem of digital hologram generation with generally positive results due to the generation speed increase that is possible, because of the non-iterative inference step. In this work, a Convolutional Neural Network (CNN) is trained to generate holograms, and its performance is compared to state-of-the-art iterative methods, both in terms of reconstruction quality and computation time. Here, a CNN built on the UNet architecture, capable of hologram generation, is presented. The network is trained on 4096 images of varying spatial frequencies, both generated by hand and from the DIV2K dataset. It is compared to the most common iterative method for hologram generation, namely the Gerchberg-Saxton (GS) algorithm and its modern and improved implementations. In reconstruction quality, the neural network outperforms the original implementation of GS when evaluating Mean Square Error (MSE), geometric error (GE), Structural Similarity Index Measurement (SSIM), and Peak Signal-Noise Ratio (PSNR) of 64 unseen test images. However, on the same test images, the network lacks behind the modern, optimized GS implementations in all error and accuracy measurements. The network does, however, achieve these results at a rate 70-280 times faster than the iterative methods, depending on the particular implementation of the GS algorithm, which corresponds to a possible generation rate of the network of 32 FPS on average.

We have promoted the idea of fabricating a new class of light-actuated microstructures and pioneered their use for so-called Light Robotics (light-driven micro-robotics). A strong scientific desire is to be able to combine advanced topology optimisation, microfabrication, surface functionalization and spatio-temporal light manipulation in full 3D to demonstrate the structure-mediated micro-to-nano coupling paradigm for controlled operation of robotic tools overcoming the diffraction limit while still being optically manoeuvrable and observable. Usually the 3D fabrication of these tiny vehicles for Light Robotics has been based on two-photon photopolymerization. This is inherently a slow, tedious and equipment expensive process leading to relatively soft microscopic polymer-based tools. We will demonstrate a radically different fabrication approach that can lead to much more rigid and useful tools for future Light Robotics undertakings.

In this paper, we present theoretical studies on nonlinear laser trapping of metal/dielectric core/shell nanoparticles using the generalized Lorenz-Mie theory. We discuss the effect of optical nonlinearity under femtosecond pulsed excitation including the effect of Fano-resonance.

Structured light fields are highly susceptible to various aberrations, and so there is a large amount of research into the effects of turbulence on these fields and into methods of mitigating these effects. Much of this research is performed using simulated turbulence. Although simulated turbulence is useful, it is not always sufficient and sometimes a turbulent free-space link is required. Setting up such a link requires several nuanced considerations and potentially time-consuming steps. Tailored for beginners, in this tutorial-style paper we document our practical experience in building structured light free-space links.

Resonant evanescent coupling can be utilized to selectively excite orbital angular momentum (OAM) modes of high angular order supported by a thin circular dielectric rod. Our 2.5-D hybrid-analytical coupled mode model combines the vectorial fields associated with the fundamental TE- and TM-modes of a standard silicon photonics slab waveguide, propagating at oblique angles with respect to the rod axis, and the hybrid modes supported by the rod. One observes an efficient resonant interaction in cases where the common axial wavenumber of the waves in the slab matches the propagation constant of one or more modes of the rod. For certain modes of high angular order, the incident wave is able to transfer its directionality to the field in the fiber, exciting effectively only one of a pair of degenerate OAM modes

Dual beam fiber traps are potentially useful for integrated trapping devices aimed at studying aerosols, and offer opportunities for cavity-enhanced traps. The alignment of such traps is typically seen to be critical. Here we explore the impact of the angular alignment of the optical fibers, and assess trapping viability as a function of misalignment and how particle dynamics change when interacting with displaced fibers. We find that good trapping capability for dual fibers tilted at the same angle, while more complex aerosol dynamics become apparent at higher single fiber tilt angles.

Light propagating along an arbitrary path can carry intrinsic spin (SI) and orbital (OI) and extrinsic orbital (OE) angular momenta (AM) associated respectively with its polarization, helical phase structure and the off-axis trajectory. The coupling of any two of the AM leads to first-order effects which includes spin-to-orbital AM conversion, spin-Hall effect (SHE) and orbital-Hall effect (OHE) of light, widely investigated in different systems and configurations. Moving forward, it is essential to study and understand the interaction and influence of any two AM on the third, leading to second-order effects. Here we investigate the influence of SI and OI on OE by measuring the SHE for different off-axis propagation of linearly polarized optical vortex beam through an inhomogeneous, weakly-anisotropic graded-index rod. The spin-Hall shifts are amplified and measured via optical weak measurement and Stokes parameter. The influence of the orbital Berry phase modifies the spin-Hall shift into a general beam shift, which also significantly modifies the output beam’s spatial structure and orientation. In addition, the influence of the OHE on the SHE results in asymmetric transverse shift. The appearance of X-type beam shift is attributed to orbital Berry phase and the beam shift curve flips with the sign change of topological charge. Interestingly, the measured shift is asymmetric for +/- charge values and right- / left- circular polarization due to orbital-Berry phase

In this paper, the governing parameters of Gaussian to flat top beam shaping are explored in simulation. We show that there exists optimal values for these parameters for a given beam shaping configuration, and that deviation from these values affect both the homogeneity and precision of the output square immensely. By performing a 3D parameter sweep over incident beam waist radius, output square size, and aperture width, we are able to express the best performing parameters in a single parameterized equation.