aun zaidi

Transformers in Speech Processing: A Survey

arXiv (Cornell University), Mar 21, 2023

Generalized polarization holography using metasurfaces

Practical Holography XXXVII: Displays, Materials, and Applications

Evolution of Total Angular Momentum and Berry Phase in 3D Structured Light

Conference on Lasers and Electro-Optics

Vector beams can be structured to change their polarization state and topological charge locally ... more

Supplementary document for Generalized polarization transformations with metasurfaces - 5503468.pdf

format_quoteJones Matrix representation uses Pauli matrices to describe polarizing system dynamics through sequential retardance and diattenuation.format_quote

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Polarization-dependent holography with metasurfaces

High Contrast Metastructures X, 2021

Metasurfaces may be structured with anisotropic constituent elements, leading to form birefringen... more Metasurfaces may be structured with anisotropic constituent elements, leading to form birefringence. In recent years, these devices have enabled a variety of new polarization-dependent optical elements. The most general of these are holograms; a wide variety of polarization-dependent holograms have been demonstrated with metasurfaces, including those that can be switched by an arbitrarily specified basis of (in general) elliptical polarization states. In this presentation, we will thoroughly review work of this nature. In doing so, we will show that the design freedom afforded by form-birefringent metasurfaces to produce polarization-dependent holograms has not been fully exploited: metasurfaces may be used to produce what we dub “Jones matrix holograms”, in which the polarization response is not limited to an orthogonal basis of polarization states. Examples of these are shown.

Total Angular Momentum Management of Three Dimensional Vortices with a Single Plate

Conference on Lasers and Electro-Optics, 2020

We present compact planar devices that enable light’s spin and orbital angular momenta to evolve,... more

Electron beam-induced tunable radiation from silicon-only structures in the near-infrared

Conference on Lasers and Electro-Optics, 2018

We experimentally demonstrate the generation of tunable radiation from silicon-only periodic stru... more

Manipulating Smith-Purcell radiation polarization with metasurfaces

Conference on Lasers and Electro-Optics, 2018

Swift electrons moving closely to a periodic structure can generate far-field radiation. The radi... more

Giant higher-order multipoles enable strong intrinsic chirality in planar nanostructures

Frontiers in Optics 2017, 2017

We demonstrate near-unity circular dichroism and polarization rotation exceeding 100,000°/mm in p... more

Towards compact and snapshot channeled Mueller matrix imaging

Optics Letters, 2021

A polarization transformation can be fully described by a 4 × 4 matrix, known as the Mueller matr... more A polarization transformation can be fully described by a 4 × 4 matrix, known as the Mueller matrix. To fully image an object’s polarization response, one needs to compute the Mueller matrix at each pixel of the image. Standard divison-of-time Mueller matrix imaging, because of its sequential nature, is ill-suited to applications requiring immediate and real-time imaging and is also bulky owing to multiple moving parts. In this work, we propose a new method for compact, snapshot Mueller matrix imaging, based on structured polarization illumination, and division-of-focal plane imaging, which can, in a single-shot, fully capture the Mueller matrix information of a band-limited signal.

Polarization-controlled holography using dielectric metasurfaces

Practical Holography XXXV: Displays, Materials, and Applications, 2021

Metasurfaces are arrays of artificially engineered subwavelength nanostructures. Owing to the str... more Metasurfaces are arrays of artificially engineered subwavelength nanostructures. Owing to the strong form birefringence of these nanostructures, metasurfaces provide a fascinating platform to realize novel polarization optics. Recently, we propose and implement a general design strategy for polarization-dependent holograms with metasurfaces, using Fourier optics and phase retrieval principles applied to the Jones calculus. We use this to design metasurface holograms with arbitrarily chosen polarization responses. We fabricate these gratings (for operation at visible wavelengths) and test them with Mueller matrix polarimetry, showing agreement with design.

Parallel polarization state generation and measurement with a single metasurface (Conference Presentation)

High Contrast Metastructures VIII, 2019

In polarimetry, that is, a measurement of the four-component polarization Stokes vector, a measur... more In polarimetry, that is, a measurement of the four-component polarization Stokes vector, a measurement must either consist of four (or more) sequential intensity measurements, sacrificing time resolution, or contain four separate light paths each with separate polarization optics, increasing bulk, cost, and system complexity. Similar issues present difficulty across polarization optics technology. Metasurfaces, nanophotonic arrays of phase shifting elements, have emerged as a novel platform for polarization optics. These individual phase shifters can be designed with a characteristic anisotropy, and are thus imbued with tunable shape birefringence. A metasurface, then, can function as a subwavelength spaced array of nanoscale waveplates. I will describe how, through relatively simple optimization methods, a metasurface producing arbitrarily specified polarization states (when illuminated with light of a known polarization) can be designed. This functionality is equivalent to a traditional diffraction grating with individual waveplate optics on each order; here, all the necessary polarization optics can be integrated into a flat, ultrathin optical element. Moreover, such a metasurface can be used in a reverse configuration as a parallel snapshot polarimeter with no need for additional polarization optics (save for a single polarizer). I present a detailed experimental characterization of both concepts in the visible spectral region and a comparison of the performance of the metasurface to a commercially available rotating waveplate polarimeter. With no bulk birefringent crystal optics, a parallel, full-polarization state measurement can be made with an integrated, scalable, and inexpensive device. Given its diffractive nature, the design naturally extends to spectropolarimetry and polarization imaging.

$Research paper thumbnail of Arbitrary control of Jones matrix properties in a metasurface diffraction grating using matrix Fourier optics$

Arbitrary control of Jones matrix properties in a metasurface diffraction grating using matrix Fourier optics

High Contrast Metastructures X, 2021

Metasurfaces are arrays of artificially engineered subwavelength nanostructures. Owing to the str... more Metasurfaces are arrays of artificially engineered subwavelength nanostructures. Owing to the strong form birefringence of these nanostructures, metasurfaces provide a fascinating platform to realize novel polarization optics. Recently, we proposed a more general design strategy for polarization-dependent metasurfaces using Fourier optics principles applied to the Jones calculus. We use this to design metasurface devices with arbitrarily chosen polarization responses embedded on diffraction orders, such as polarizers, waveplates, and cases that are mixtures of the two. We fabricate these gratings (for operation at visible wavelengths) and test them with Mueller matrix polarimetry, showing agreement with design.

Transvers to longitudinal structuring of light with metasurfaces

High Contrast Metastructures X, 2021

Recent work on beams with light structured along the propagation direction will be presented, whe... more

Smith Purcell Radiation Generation from the VUV to the Near IR: Tunable Emission from Nanophotonic Structures in a Modified SEM

Bulletin of the American Physical Society, 2018

Title : Generation of Wavelength-independent Subwavelength Bessel Beams using Metasurfaces Concise running title : Wavelength-independent Subwavelength Bessel Beams

Bessel beams are of great interest due to their unique non-diffractive properties. Using a conica... more Bessel beams are of great interest due to their unique non-diffractive properties. Using a conical prism or an objective paired with an annular aperture are two typical approaches to generating zeroth order Bessel beams. However, the former approach has a limited numerical aperture (NA), and the latter suffers from low efficiency since most of the incident light is blocked by the aperture. Furthermore, an additional phase-modulating element is needed to generate higher-order Bessel beams, which in turn adds complexity and bulkiness to the system. We overcome these problems using dielectric metasurfaces to realize meta-axicons with additional functionalities not achievable with conventional means. We demonstrate meta-axicons with high NA up to 0.9 capable of generating Bessel beams with full-width at half-maximum about as small as ~λ/3 (λ = 405 nm). Importantly, these Bessel beams have transverse intensity profiles independent of wavelength across the visible spectrum. These meta-axi...

Introducing Berry phase gradients along the optical path via propagation-dependent polarization transformations

Nanophotonics, 2021

As a classical or quantum system undergoes a cyclic evolution governed by slow change in its para... more As a classical or quantum system undergoes a cyclic evolution governed by slow change in its parameter space, it acquires a topological phase factor known as the geometric or Berry phase. One popular manifestation of this phenomenon is the Gouy phase which arises when the radius of curvature of the wavefront changes adiabatically in a cyclic manner, for e.g., when focused by a lens. Here, we report on a new manifestation of the Berry phase in 3D structured light which arises when its polarization state adiabatically evolves along the optical path. We show that such a peculiar evolution of angular momentum, which occurs under free space propagation, is accompanied by an accumulated phase shift that elegantly coincides with Berry’s prediction. Unlike the conventional dynamic phase, which accumulates monotonically with propagation, the Berry phase observed here can be engineered on demand, thereby enabling new possibilities; such as spin-dependent spatial frequency shifts, and modified...

format_quoteAdiabatic evolution of polarization leads to unique additional phase shift, distinct from dynamic phase, showcasing new geometric phase dynamics.format_quote

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Generalized polarization transformations with metasurfaces

Optics Express, 2021

Metasurfaces are arrays of sub-wavelength spaced nanostructures, which can be designed to control... more Metasurfaces are arrays of sub-wavelength spaced nanostructures, which can be designed to control the many degrees-of-freedom of light on an unprecedented scale. In this work, we design meta-gratings where the diffraction orders can perform general, arbitrarily specified, polarization transformation without any reliance on conventional polarization components, such as waveplates and polarizers. We use matrix Fourier optics to design our devices and introduce a novel approach for their optimization. We implement the designs using form-birefringent metasurfaces and quantify their behavior – retardance and diattenuation. Our work is of importance in applications, such as polarization abberation correction in imaging systems, and in experiments requiring novel and compact polarization detection and control.

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Structuring total angular momentum of light along the propagation direction with polarization-controlled meta-optics

Nature Communications, 2021

Recent advances in wavefront shaping have enabled complex classes of Structured Light which carry... more Recent advances in wavefront shaping have enabled complex classes of Structured Light which carry spin and orbital angular momentum, offering new tools for light-matter interaction, communications, and imaging. Controlling both components of angular momentum along the propagation direction can potentially extend such applications to 3D. However, beams of this kind have previously been realized using bench-top setups, requiring multiple interaction with light of a fixed input polarization, thus impeding their widespread applications. Here, we introduce two classes of metasurfaces that lift these constraints, namely: i) polarization-switchable plates that couple any pair of orthogonal polarizations to two vortices in which the magnitude and/or sense of vorticity vary locally with propagation, and ii) versatile plates that can structure both components of angular momentum, spin and orbital, independently, along the optical path while operating on incident light of any polarization. Com...

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Jones matrix holography with metasurfaces

Science Advances, 2021

A new mathematical framework uncovers overlooked possibilities for polarization-dependent metasur... more

format_quoteJones matrix holograms enable designer-specified polarization behavior in far-fields, realized through conventional, dielectric metasurfaces, enhancing previous metasurface design methods.format_quote

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