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We use a vortex retarder-based approach to generate few optical cycles light pulses carrying orbital angular momentum (OAM) (known also as twisted light or optical vortex) from a Yb:KGW oscillator pumping a noncollinear optical parametric amplifier generating sub-10 fs linearly polarized light pulses in the near infrared spectral range (central wavelength 850 nm). We characterize such vortices both spatially and temporally by using astigmatic imaging technique and second harmonic generation-based frequency resolved optical gating, respectively. The generation of optical vortices is analyzed, and its structure reconstructed by estimating the spatio-spectral field and Fourier transforming it into the temporal domain. As a proof of concept, we show that we can also generate sub-20 fs light pulses carrying OAM and with arbitrary polarization on the first-order Poincaré sphere.

The ability to utilize resources to meet the need of growing diversity of communication services and user behavior marks the future of cognitive wireless communication systems. Cognitive wireless technologies for vehicular communications, in combination with Orbital Angular Momentum (OAM) modes aim at extending Non-Line-Of-Sight (NLOS) short-distance communications for smart mobility. In this regard, OAM antenna frameworks need to be developed to support these technologies. In this work, we describe a magnetoelectric dipole antenna framework supporting OAM modes. The framework is derived from moment tensors of specific vector spherical harmonic functions synthesized from dipoles. The antenna framework is discussed in terms of OAM generation, and it is validated numerically and experimentally for l = 1 OAM mode, achieving more than 500MHz operation bandwidth at the frequency of operation of 3.5GHz. Also, for l = 1 OAM mode, the null aligns precisely with the anticipated dimensions numerically computed., This work was financially supported by PDR-2014-2022/56-30157-2021-2A, 2021 SGR 01415 Q0818003F and Metropolis PLEC2021-007609 grants of the Generalitat de Catalunya and European Regional Development Fund (FEDER), by CICYT PID2019-107885GB-C31, PID2022-136869NB-C31 and Prueba de Concepto PDC2022-133091-I00 grants of the Agencia Estatal de Investigación (Spain) and Next Generation EU., Peer Reviewed, Postprint (author's final draft)

We introduce a novel class of structured random beams carrying orbital angular momentum on incoherent background. We confirm that such beams maintain their vortex structure in free space and manifest robust behavior against atmospheric turbulence as well., ISBN 9798350326734QC 20231010

A medium and high-frequency antenna array for radar and radio imaging of the ionosphere is planned for installation in Aguadilla, Puerto Rico. Science goals include the study of space weather, radio propagation, meteors, lightning, and plasma physics. Radio imaging is ideal for the study of stimulated ionospheric radio emissions, such as those induced by the Arecibo Observatory high-power HF radio transmitter, which is likely to be restored to operation in the near future. The array will be complemented by a wide variety of instruments fielded by collaborators, and will be a rich source of student projects at all levels.

The protection of confidential data is a fundamental need in the society in which we live. This task becomes more relevant when observing that every day, data traffic increases exponentially, as well as the number of attacks on the telecommunication infra-structure. From the natural sciences, it has been strongly argued that quantum communication has great potential to solve this problem, to such an extent that various governmental and industrial entities believe the protection provided by quantum communications will be an important layer in the field of information security in the next decades. However, integrating quantum technologies both in current optical networks and in industrial systems is not a trivial task, taking into account that a large part of current quantum optical systems are based on bulk optical devices, which could become an important limitation. Throughout this thesis we present an all-in-fiber optical platform that allows a wide range of tasks that aim to take a step forward in terms of generation and detection of photonic states. Among the main features, the generation and detection of photonic quantum states carrying orbital angular momentum stand out. The platform can also be configured for the generation of random numbers from quantum mechanical measurements, a central aspect in future information tasks. Our scheme is based on the use of new space-division-multiplexing (SDM) technologies such as few-mode-fibers and photonic lanterns. Furthermore, our platform can also be scaled to high dimensions, it operates in 1550 nm (telecommunications band) and all the components used for its implementation are commercially available. The results presented in this thesis can be a solid alternative to guarantee the compatibility of new SDM technologies in emerging experiments on optical networks and open up new possibilities for quantum communication., Skydd av konfidentiell information är ett grundläggande behov i det samhälle vi lever i. Denna uppgift blir mer relevant när man observerar att datatrafiken ökar exponentiellt varje dag, liksom antalet attacker på telekommunikationsinfrastrukturen. Från naturvetenskapen har det starkt hävdats att kvantkommunikation har en stor potential att lösa detta problem, i en sådan utsträckning att olika statliga och industriella enheter tror att skyddet som tillhandahålls av kvantkommunikation kommer att vara en viktig del av informationssäkerhet de kommande decennierna. Att implementera kvantteknik både i nuvarande optiska nätverk och i industriella system är dock inte en trivial uppgift, med tanke på att en stor del av nuvarande kvantoptiska system inte är i optiska fiber, vilket kan bli en begränsning. Genom hela denna avhandling presenterar vi en plattform som är helt konstruerad med optiska fiber som tillåter ett brett utbud av uppgifter som syftar till att ta ett steg framåt när det gäller integration med nu-varande optiska nätverk. Bland huvuddragen i denna idé utmärker den skapandet och detekteringen av fotoniska kvanttillstånd i ”Orbital Angular Momentum”, såväl som allmänna överlagringar av rumsliga optiska moder som kan transmitteras inom en optisk fiber. Plattformen kan också konfigureras för generering av slumptal från kvantmekaniska mätningar, vilket är en central aspekt i framtida hantering av information. Vår plattform är baserad på användningen av nya tekniker för ”Space Division Multiplexing” (på Engelska) såsom ”few-mode-fibers” och ”photonic lanterns”. Dessutom kan vår plattform skalas till högre dimensioner, den fungerar i 1550 nm (telekommunikationsbandet) och alla komponenter som används för dess implementering är kommersiellt tillgängliga, därför kan resultaten som presenteras i denna avhandling vara ett robust alternativ för att säkerställa kompatibiliteten av nya framväxande teknologier och experiment med nästa generations optiska nätverk och öpp

This chapter documents progress in the extensive area of supercontinuum (SC) generation research devoted to applications in telecommunications, including research into the different mechanisms of spectral broadening and their interplay, SC generation in various media and the most promising SC applications in fibre-based and free-space telecom

Real-life communications applications necessitate the development of antennas with different patterns and radiation characteristics. Antennas that can produce the beam scanning in a conical sweep can be advantageous for applications such as spaceborne wind scatterometers weather radars. This work presents the synthesis, prototyping and measurements of threeantennas that can produce the conical beam scanning: The 3D-printed shaped and materialoptimized lenses, the flat-layered meta-lenses, and the transmitarray antennas. The synthesis of the 3D-printed lens and meta-lens inhomogeneity requires the use of a software package hybridizing the computational electromagnetics method of Geometrical optics (GO) with the optimization strategy of Particle Swarm Optimization (PSO). Additionally, a new synthesis algorithm is presented for the design of transmitarrays that can produce the conical beam sweep based on the optimization of the feed location and a modified transmitarray phase compensation. Novel implementation and fabrication methods based on additive manufacturing and metamaterial structures are presented for the realization of the proposed antennas. In the last part of this work, Orbital Angular Momentum (OAM) beams for antenna applications are investigated. The theory and mathematical formulations of the far-field properties of OAM beams using the antenna aperture field method are presented in a systematic and comprehensive manner. Transmitarray antennas are proposed to generate circularly-polarized (CP) OAM beams with cone-shaped radiation patterns. Antennas with cone-shaped patterns can be advantageous for applications such as geosynchronous satellite based navigation and guidance systems that serve moving vehicles and ceiling-mounted indoor wireless systems. An ultra-thin “S-ring” transmitarray unit cell is introduced to support CP that can provide arbitrary CP phase compensation by proper rotation of the elements. The synthesis, prototyping and measurement valid

A high-power 1310 nm VECSEL with orbital angular momentum would be very beneficial to optical communications because it would allow for orbital angular momentum to be used as a multiplexing technique, drastically increasing the bandwidth of optical communications[5]. Two main initial design parameters were investigated for the design of such a laser; material of the quantum well structure and thermal management techniques, along with other secondary design parameters. An initial assessment of the best option was given along with secondary choices depending on the circumstances. A Live ABCD Matrix Beam profile simulation program in Matlab was discussed, including the theory, how the code was made, and the inputs and outputs of this program. This program was specifically designed for the V cavity VECSEL and thus can also be used for the high-power 1310 nm VECSEL with orbital angular momentum. It can be used to have instant feedback and an increased ability to troubleshoot any issues or constraints that present themselves moving forward during the design and creation process for this VECSEL. Finally, there was an investigation into the simulation of an astigmatic mode converter at an angle to analyze whether or not this would be able to compensate for spatial walk-off. The theory of an Astigmatic Mode Converter and how to code one is investigated. Once the creation of the code had been explained, the spatial walk-off was input into the simulated beam. Lastly, the AMC's angle was incrementally changed, and results were analyzed to determine the effect on distortion.

Within the last few decades, the spatial degree of freedom of light has gained significant attention in the form of photonic orbital angular momentum (OAM). The use of OAM for remote sensing has been of significant interest due to its inherent orthogonality that can be used for spatial frequency filtering, coherence filtering, and as both an active or passive sensing modality. Beams with OAM also contain interesting propagation properties that have potential to be more robust than non-OAM counterparts. One application of remote sensing is using OAM to measure the strength of optical phase distortions through random media that can contain turbulence or particulate matter. There has been significant work done on the subject, but there have been difficulties at creating an applicable OAM based sensing technique employed for use in an outdoor environment. This work develops an active OAM sensing modality denoted as Optical Heterodyne Detection of Orthogonal OAM Modes (OHDOOM) to reduce the optical receiver hardware based on a beatnote signal for the first time. The beatnote signal is then hypothesized to return information about the propagation environment by measuring the crosstalk between OAM modes due to channel perturbations. OHDOOM results through an emulated turbulent medium show that our method is highly sensitive to weak and strong turbulence depending on the transmitted OAM mode. Within a turbid medium, OHDOOM is believed to be sensitive to particles larger than the wavelength and insensitive to smaller particles. Experimental results agree well with simulated environmental conditions using wave optic simulations (WOS) implementing phase screens. A WOS for a turbulent medium is derived from turbulent phase statistics based on refractive index fluctuations. However, for the first time, a turbid medium's phase statistics are derived from a solution to the radiative transfer equation within the paraxial approximation.

The advent of the optical fiber in the second half of the 20th century has had numerous consequences not only for the advancement of telecommunication and information transfer technologies, but also for humanity as a whole. At the time of writing of this thesis, we live in a world that is defined by unprecedented and unparalleled access to information made possible by fiber optic cables that line the ocean beds. As the world becomes increasingly reliant upon the internet, the demand for access is outgrowing the pace at which the capacity of our fiber optic networks can be scaled up. In the past decade, a consensus has emerged among researchers in academia and the industry that we are now approaching the fundamental classical capacity limit of a conventional single mode fiber, namely the Shannon limit. This has spurred interest in multimode fibers that allow for hundreds of spatial modes to co-propagate, potentially allowing for at least an order of magnitude increase in capacity per fiber. While multiplexing in the spatial domain has the potential to offer significantly higher capacities, linear and nonlinear mixing between the spatial modes of a fiber are expected to play an important role in determining the capacity and performance of spatially multiplexed telecommunication systems. So far, multimode fibers have mostly been relegated to low-power short- distance links, as a result of which nonlinear propagation effects in the presence of multiple spatial modes has received relatively little attention. This thesis adds to a growing body of literature that is increasingly interested in uncovering the physics of multimodal propagation in the nonlinear regime. Although the need for spatial multiplexing is important factor driving research interest in this topic, experiments in recent years have revealed a plethora of complex spatiotemporal non- linear phenomena occurring in multimode fibers, including Kerr-induced beam self-cleaning, parametric instability processes a

Orbital angular momentum (OAM) modes have low model interactions during fiber propagation at data center distances, and thus are suitable for ultra-high capacity systems at low digital signal processing. Generating OAM modes using free-space setups is useful for proof-of-concept experiments, but is not a scalable solution. We use an optical phased array (OPA) with two-dimensional antennas for on-chip circularly polarized OAM beam generation. Our previous work demonstrated an OAM multiplexer for lower-order modes. In this work, we demonstrate an OAM multiplexer that supports a record of 46 (23 per polarization) simultaneous spatial modes up to OAM order 11. We also improve the crosstalk performance of our multiplexer. We incorporate an intensity tuning capability that substantially improves the OAM quality by enabling a uniform power distribution across the antennas. The worst-case crosstalk for the supported OAM5 to OAM11 are found experimentally to be better than -12 dB, with OAM10 achieving -17.2 dB.

We propose and numerically verify a design of the photonic integrated circuit for in-plane generation of a 1st azimuthal order vortex mode in dielectric rectangular waveguides. Radiation is introduced into the proposed structure in a standard way through two grating couplers. Applying a mode coupling and specific phase shift, a field with the required amplitude-phase distribution is formed directly in the output waveguide. The geometric dimensions of the device are simulated and optimized to fit the technological parameters of the silicon-on-insulator platform.

In this paper, a communication link based on circular phased array antennas generating orbital angular momentum (OAM) beams at radio frequency is investigated. The presence of a null in the radiation pattern of OAM antennas is the main drawback of them. This problem makes it difficult to establish a telecommunication link using OAM systems and calculate the link budget for such a system. To solve this problem, we have defined two new gain parameters by using Friis Transmission Equation. The new formulas can help to calculate the effective gain of OAM antennas. Also, we have defined the effective OAM gain in detail for the first time in order to evaluate the performance of the OAM links. By using the proposed formulas, a capable and secure link based on the orthogonality of OAM beams can be designed.

Photonic topological insulators (PTIs) represent an area of emerging research into a new class of materials and devices with exciting electromagnetic properties. These materials are capable of supporting directional conducting modes along their surface or edge at frequencies that lie in the material bandgap. The presence of the bandgap ensures that the bulk of the material behaves as an insulator, which allows for a very high degree of energy confinement at the surface. This work briefly details a few variations on PTIs and then proceeds to focus on the creation of interface modes for 3D dielectric structures using only a 1D integration technique to obtain the geometric phase that is required for a material to be classified as topological. This 1D Zak phase allows for a simpler method to create topological waveguides with propagation path bends in fixed directions, along with a directional dependence based on the rotational nature of the fields. A shift towards more traditional forms of PTIs in the latter half of the thesis focuses on the application aspects of topological insulators. The use of metallic spin PTI metasurfaces as antennas been demonstrated with device operation broken down into (1) confined and (2) leaky wave propagation. While the confined mode is best known for its use as energy guiding structures, abrupt truncations can allow for radiation at the aperture with a `self-matched' property, allowing for immunity to the reflection caused due to the aperture impedance mismatch. Operation of the same PTI structure above the light cone in its leaky region enables the use of the PTI metasurface as a leaky wave antenna having an azimuth phase variation, with energy wrapped around in a closed loop propagation path. These waves possess an inherent orbital angular momentum (OAM), and control of the OAM beam charge can be achieved by the manipulating the physical and electrical path lengths. This control is invaluable to switching and multiplexing of different

The radially anisotropic ring-core fiber with cylindrical birefringence is theoretically and numerically investigated as a novel platform for the transmission of vector-vortex beams with unique modal properties. First, we elucidate the parametric conditions where such fiber enables modal substitution in which either the donut-shaped azimuthal TE01 or radial TM01 mode replaces the normal Gaussian-like HE11 mode as the fundamental mode of the waveguide. We also demonstrate that it is possible to significantly engineer the waveguiding properties of the fiber via the addition of small radial birefringence (~10−4 ) so as to make the (hitherto non-degenerate) TE0m and TM0m modes fully degenerate. The latter property is used to create stable vortex modes of high purity (>99%) with the newly degenerate modal pair – a feat not possible with standard few-mode fibers – all without affecting the co-propagating hybrid HE/EH modes that remain available as an independent basis set to produce vortex beams of similarly high purity. These new insights are relevant to the topical fields of mode-division multiplexing (MDM), structured light, fiber modelling and fabrication. With respect to MDM applications, the newly available vortex modes created with the degenerate TE/TM basis set can now be concurrently used with the more common vortex modes created via the HE/EH modal basis set.

The pathway toward the tailored synthesis of materials starts with precise characterization of the conformational properties and dynamics of individual molecules. Electron spin resonance (ESR)-based scanning tunneling microscopy can potentially address molecular structure with unprecedented resolution. Here, we determine the fine structure and geometry of an individual titanium-hydride molecule, utilizing a combination of a newly developed millikelvin ESR scanning tunneling microscope in a vector magnetic field and ab initio approaches. We demonstrate a strikingly large anisotropy of the g tensor, unusual for a spin doublet ground state, resulting from a nontrivial orbital angular momentum stemming from the molecular ground state. We quantify the relationship between the resultant fine structure, hindered rotational modes, and orbital excitations. Our model system provides avenues to determine the structure and dynamics of individual molecules. © 2021 American Physical Society.

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We propose and demonstrate a novel vortex Airy beam which is a superposition of an Airy beam and its laterally sheared beam with a pi/2 phase shift. This new-type of vortex Airy beam exhibits stable propagation dynamics, wherein its singular point closely follows its main lobe, unlike conventional vortex Airy beams. Notably, the orbital angular mode purity of this new vortex Airy beam is up to 10% better than that of a conventional vortex Airy beam. We anticipate that this new type of vortex Airy beam, which combines the characteristics of an optical vortex and a diffraction-free Airy beam, will facilitate new directions in applications such as microscopy, material processing and nonlinear optics.

Orbital angular momentum (OAM) carried by vortex beams has seen an explosion of interest across fields and this is particularly true in attosecond physics. Given that twisted electrons have been shown to be sensitive to the chirality of molecules, exploring this sensitivity on the attosecond scale is a particularly exciting prospect. The OAM of photoelectrons has been theoretically studied discussing ways to measure and understand the ionization via an analytic formalism. This opens up the possibility of using the photoelectron OAM as an imaging tool. However, in most of the earlier studies the effects of the initial state on the photoelectron OAM have been neglected. In this project, using an analytic formalism to produce chiral hydrogen states, we have investigated how the photoelectron OAM in strong field ionization can be used to image molecular chirality.

Light carrying orbital angular momentum constitutes an important resource for both classical and quantum information technologies. Its inherently unbounded nature can be exploited to generate high-dimensional quantum states or for channel multiplexing in classical and quantum communication in order to significantly boost the data capacity and the secret key rate, respectively. While the big potentials of light owning orbital angular momentum have been widely ascertained, its technological deployment is still limited by the difficulties deriving from the fabrication of integrated and scalable photonic devices able to generate and manipulate it. Here, we present a photonic integrated chip able to excite orbital angular momentum modes in an 800 m long ring-core fiber, allowing us to perform parallel quantum key distribution using 2 and 3 different modes simultaneously. The experiment sets the first steps towards quantum orbital angular momentum division multiplexing enabled by a compact and light-weight silicon chip, and further pushes the development of integrated scalable devices supporting orbital angular momentum modes.

An orbital angular momentum directional modulation (OAM-DM) signal is proposed for communication and guidance integration. This signal is transmitted by a uniform circular antenna array (UCA). We divide the array into odd and even antenna groups. Each group is excited by differential coded digital modulation waveform to send different signal constellations in different directions. In order to improve the performance of angle estimation, we have designed specific phase shift sequences to obtain the different OAM modes. Mode detection can eliminate multiple value ambiguity of elevation and azimuth angles. The single antenna receiver can demodulate the OAM-DM signal to communicate, detect OAM modes and estimate angles in different directions. Finally, we assess the effectiveness of the proposed approach via numerical simulation.

Рассмотрена мультиспиральная фазовая пластинка, у которой имеется множество центров сингулярности фазы, расположенных в произвольных точках в плоскости пластинки. Получены замкнутые выражения для топологического заряда вихревого поля в начальной плоскости сразу за обычной спиральной фазовой пластинкой и нормированного на мощность пучка орбитального углового момента. Топологический заряд в начальной плоскости равен сумме топологических зарядов каждой сингулярности, если их центры находятся внутри круглой апертуры конечного радиуса. Если часть центров сингулярности фазы лежит на границе круглой диафрагмы, ограничивающей обычную спиральную фазовую пластинку, то их топологический заряд в сумме нужно поделить на 2. Орбитальный угловой момент зависит от расположения центров сингулярности: чем дальше от центра пластинки расположен центр сингулярности, тем меньше вклад в орбитальный угловой момент. Если все центры сингулярности лежат на границе, ограничивающей мультиспиральную фазовую пластинку диафрагмы, то орбитальный угловой момент пучка равен нулю, хотя топологический заряд пучка в этом случае будет отличен от нуля. We investigate a multispiral phase plate (MSPP) with multiple centers of phase singularity arbitrarily located in the MSPP plane. Equations to describe the topological charge of an optical vortex in the initial plane immediately behind the MSPP and orbital angular momentum (OAM) normalized relative to the beam power are derived. The topological charge in the initial plane is found as a sum of the topological charges of all singularities if their centers are located inside a finite-radius circular aperture. If the phase singularity centers are partially located on the boundary of a circular diaphragm limiting the MSPP, the total topological charge is found as the sum of all singularities divided by 2. Total OAM that the vortex carries depends on the location of the singularity centers: the farther from the center of the plate the singularity center is located

Разработан и реализован экспериментально метод измерения спектров амплитуд и начальных фаз и топологического заряда пучков Лагерра–Гаусса в базисе мод Эрмита–Гаусса. Теоретически обоснован и воплощён на эксперименте метод измерения топологического заряда невозмущённых пучков Лагерра–Гаусса с различными значениями радиальных и азимутальных чисел посредством астигматического преобразования на цилиндрической линзе. Показано, что измеренные спектры мод Эрмита–Гаусса позволяют определить орбитальный угловой момент и топологический заряд, а также осуществить цифровую сортировку мод Эрмита–Гаусса с последующим восстановлением реального сингулярного пучка. We developed and implemented an intensity moments technique for measuring amplitude and initial phase spectra, the topological charge (TC) and orbital angular momentum (OAM) of the Laguerre-Gauss (LG) beams decomposed into the basis of Hermite-Gaussian (HG) modes. A rigorous theoretical justification is given for measuring the TC of unperturbed LG beams with different values of radial and azimuthal numbers by means of an astigmatic transformation on a cylindrical lens. We have shown that the measured amplitude and phase spectra of the HG modes make it possible to find the orbital OAM and TC, as well as digitally sorting the HG modes and then restoring the initial singular beam.

The helical phase structure of a twisted light beam has attracted big interest in both fundamental science and practical applications. A facile metasurface approach to generate and manipulate ring vortex beams is reported and experimentally demonstrated. The generation of ring vortex beams is realized by combining the functionalities of an axicon, a vortex beam generator and a beam deflector onto a single reflective metasurface, which consists of nanorods with spatially variant orientations sitting on a silicon dioxide layer in the middle and a gold layer at the bottom. By controlling the polarization state of the incident light, the superposition of ring vortex beams is continuously tuned. The unique property of the developed device renders this technology very attractive for polarization detection and quantum science related applications. © 2020 The Authors. Published by Wiley-VCH GmbH

In this article, a novel electrically controlled optical broadband phase shifter (ECO-BPS) is proposed and experimentally investigated for broadband microwave orbital angular momentum (OAM) mode generation. Based on the proposed ECO-BPS and a 17-element circular antenna array, the effect of the phase error on the OAM mode quality is studied by comparing the OAM modes respectively synthesized by three phase schemes: ideal phase shifts, ECO-BPS phase shifts, and optical true time delay phase shifts. In addition, the crosstalk caused by the phase error in applications of OAM modes multiplexing is investigated in a Dammann vortex grating based OAM modes demultiplexing system. All numerical simulation results demonstrate the feasibility of the ECO-BPS in broadband microwave OAM applications.

An orbital angular momentum directional modulation (OAM-DM) signal is proposed for communication and guidance integration. This signal is transmitted by a uniform circular antenna array (UCA). We divide the array into odd and even antenna groups. Each group is excited by differential coded digital modulation waveform to send different signal constellations in different directions. In order to improve the performance of angle estimation, we have designed specific phase shift sequences to obtain the different OAM modes. Mode detection can eliminate multiple value ambiguity of elevation and azimuth angles. The single antenna receiver can demodulate the OAM-DM signal to communicate, detect OAM modes and estimate angles in different directions. Finally, we assess the effectiveness of the proposed approach via numerical simulation.

An orbital angular momentum directional modulation (OAM-DM) signal is proposed for communication and guidance integration. This signal is transmitted by a uniform circular antenna array (UCA). We divide the array into odd and even antenna groups. Each group is excited by differential coded digital modulation waveform to send different signal constellations in different directions. In order to improve the performance of angle estimation, we have designed specific phase shift sequences to obtain the different OAM modes. Mode detection can eliminate multiple value ambiguity of elevation and azimuth angles. The single antenna receiver can demodulate the OAM-DM signal to communicate, detect OAM modes and estimate angles in different directions. Finally, we assess the effectiveness of the proposed approach via numerical simulation.

Spin and orbital angular momenta of light have been a subject of fundamental interest since long ago, classically associated with circular polarization and wave vector. In recent years, extraordinary spin angular momenta in structured electromagnetic waves have been investigated, mostly in subwavelength evanescent fields at the nanoscale. Here we present an in-depth theoretical analysis of the transverse spin density and related momentum induced by mode confinement inside waveguides, with alternating spin layers governed by guided mode spatial symmetry, different from and indeed richer than that in the evanescent region outside. Furthermore, hybrid guided modes with intrinsic helicity exhibit in addition longitudinal spin density. Such fundamental features are manifested through fascinating phenomenology relevant to spin-orbit coupling in nanophotonic waveguides. Thus, guided light intrinsically carrying a wealth of spin momenta holds promise of superb devices to control spin-orbit interaction within confined geometries throughout the electromagnetic spectra.

At first sight, any rotation generates some angular momentum (it is true for a solid body). But these characteristics (rotation and orbital angular momentum) are rather different for optics and mechanics. In optics there are the situation when the rotation is important. On the other hand, there are the cases where the nonzero orbital angular momentum is necessary. The main goal of this article is to investigate a relationship between a rotation under propagation of spiral beam and its angular momentum.It can be done the following conclusion: there is no any relation between rotation under propagation of spiral beam and its OAM.

The spin-orbital-entangled Kramers doublet, known as the Jeff=1/2 pseudospin driven by large spin-orbit coupling (SOC), appears in layered iridates and α-RuCl3, manifesting a relativistic Mott insulating phase. Such entanglement, however, seems barely attainable in 3d transition metal oxides, where the SOC is small and the orbital angular momentum is easily quenched. Based on the density-functional-theory calculations, we report the CuAl2O4 spinel as the possible example of a Jeff=1/2 Mott insulator in 3d transition metal compounds. With the help of strong electron correlations, the Jeff=1/2 state can survive the competition with an orbital-momentum-quenched S=1/2 state in the d9 configuration of CuO4 tetrahedron. From the dynamical mean-field theory calculations, the electron-addition spectra probing unoccupied states are well described by the jeff=1/2 hole state, whereas electron-removal spectra have a rich multiplet structure. The fully relativistic entity found in CuAl2O4 provides insight into the untapped regime where the spin-orbital-entangled Kramers pair coexists with strong electron correlation. © 2019 American Physical Society.

Spatial multiplexing using orbital angular momentum (OAM) modes is an efficient means of scaling up the capacity of fiber-optic communications systems; integrated multiplexers are crucial enablers of this approach. OAM modes are circularly polarized when propagating in a fiber, however, OAM generators previously demonstrated in silicon photonics use locally linearly polarized emitters. Coupling from multiplexers to fibers in those solutions results in extra loss and complexity. Moreover, many of those solutions are based on resonator structures with strong wavelength dependence, and are thus incompatible with wavelength-division multiplexing (WDM). We experimentally demonstrate on-chip generation and multiplexing of OAM modes using an array of circularly polarized 2D antennas with wide wavelength coverage. The proposed device was implemented on the standard 220-nm silicon-on-insulator platform. Optical vortex beams with OAM orders ranging from -3 to +3 in both left and right circular polarization states were generated from the same aperture across a wavelength range of 1540 nm to 1557 nm. This device could serve as a multiplexer or demultiplexer for up to 12 information bearing channels coupling into an

The orbital angular momentum revolutionized optical communications, like an OAM beam of light need not be interrupted for the transfer ofdata, provides immunity to electromagnetic interference, allows increase bandwidth, rate and transmission capacity information, making theprocess more efficient. Supported by the ability to encode information on OAM modes of light, is necessary the development of a decoder thatintegrate to hardware systems, solve the problem of current techniques, which main disadvantage is to require the use of additional energysources, increasing the implementation cost, and make it less compact. The purpose of this report is towards modelling an optoelectronicdecoder system which discriminates the orbital angular momentum mode in the beam, associated with transmitted information and translates itfrom the selected transmission channel (i.e. outdoor atmosphere) to a recognizable information. Current methodology proposed for thispurpose, integrates the use of thin films of nanometric order, whose design features allows interaction with OAM beams that, can bedistinguish its topological charge., El momento angular orbital ha revolucionado la visión sobre las comunicaciones ópticas, ya que un haz de luz OAM no necesita interrumpirsepara el traspaso de datos, confiere inmunidad a la interferencia electromagnética, permite un aumento en el ancho de banda, la tasa detransmisión y la capacidad de información, haciendo más eficiente este proceso. Sustentados en la posibilidad de codificar información en losdiferentes modos del haz de luz, se hacen necesarios los sistemas de decodificación, que integren al hardware del sistema, una forma para ladetección, solucionando el problema de las técnicas actuales, cuya principal desventaja es requerir de la utilización de fuentes de energíaadicionales, que incrementan el costo de implementación, y la hacen menos compacta. La finalidad del trabajo va encaminada hacia laformulación de un sistema opto-electrónico decodificador que discrimine el modo del momento angular del haz, asociado a la informacióntransmitida y la traduzca, desde el canal de transmisión escogido (por ejemplo, el aire libre) a información reconocible. La metodología actualque se sigue para este fin, integra el uso de películas de espesor de orden nanométrico, que de acuerdo con la interacción con un haz OAM,permite distinguir su carga topológica.

El momento angular orbital ha revolucionado la visión sobre las comunicaciones ópticas, ya que un haz de luz MAO no necesita interrumpirse para el traspaso de datos, confiere inmunidad a la interferencia electromagnética, permite un aumento en el ancho de banda, la tasa de transmisión y la capacidad de información. Sustentados en la posibilidad de codificar información en los diferentes modos del haz de luz, se presentan métodos y desarrollos asociados con la formulación e implementación de una arquitectura de decodificación, usando filtros espaciales de orden nanométrico. Se introduce una mejora a las técnicas de detección de la carga topológica de un haz MAO. Aquí, se reduce al análisis de la difracción por un borde recto y una abertura triangular equilátera. Además, se suprime el uso de óptica adicional necesaria en otras técnicas y reduce el costo de implementación. Con este propósito, teoría física de haces MAO, argumentos para la selección y diseño de componentes del decodificador, junto con detalles experimentales, muestran la viabilidad del método propuesto para decodificar información, The orbital angular momentum revolutionized optical communications, since an OAM beam of light does not need to be interrupted for the transfer of data, provides immunity to electromagnetic interference, allows increase bandwidth, rate and transmission capacity information. Supported by the ability to encode information on OAM modes of light, methods and developments associated with the formulation and implementation of a data decoding architecture are shown, which uses spatial filters at nanoscale order. An Improvement to techniques for detecting the topological charge of an OAM beam is introduced. Here is reduced to the diffraction of OAM beam by a straight edge and a triangular equilateral aperture analysis; due that the use of additional optics is suppressed which would be necessary for other techniques and decreases the cost of implementation. For this purpose, physics theory of OAM beams, arguments for selecting and design components of the decoder are presented, as well as experimental details, discussions and results, showing the feasibility of the proposed method for decoding information

El momento angular orbital ha revolucionado la visión sobre las comunicaciones ópticas, ya que un haz de luz MAO no necesita interrumpirse para el traspaso de datos, confiere inmunidad a la interferencia electromagnética, permite un aumento en el ancho de banda, la tasa de transmisión y la capacidad de información. Sustentados en la posibilidad de codificar información en los diferentes modos del haz de luz, se presentan métodos y desarrollos asociados con la formulación e implementación de una arquitectura de decodificación, usando filtros espaciales de orden nanométrico. Se introduce una mejora a las técnicas de detección de la carga topológica de un haz MAO. Aquí, se reduce al análisis de la difracción por un borde recto y una abertura triangular equilátera. Además, se suprime el uso de óptica adicional necesaria en otras técnicas y reduce el costo de implementación. Con este propósito, teoría física de haces MAO, argumentos para la selección y diseño de componentes del decodificador, junto con detalles experimentales, muestran la viabilidad del método propuesto para decodificar información, The orbital angular momentum revolutionized optical communications, since an OAM beam of light does not need to be interrupted for the transfer of data, provides immunity to electromagnetic interference, allows increase bandwidth, rate and transmission capacity information. Supported by the ability to encode information on OAM modes of light, methods and developments associated with the formulation and implementation of a data decoding architecture are shown, which uses spatial filters at nanoscale order. An Improvement to techniques for detecting the topological charge of an OAM beam is introduced. Here is reduced to the diffraction of OAM beam by a straight edge and a triangular equilateral aperture analysis; due that the use of additional optics is suppressed which would be necessary for other techniques and decreases the cost of implementation. For this purpose, physics theory of OAM beams, arguments for selecting and design components of the decoder are presented, as well as experimental details, discussions and results, showing the feasibility of the proposed method for decoding information

Spatial multiplexing using orbital angular momentum (OAM) modes is an efficient means of scaling up the capacity of fiber-optic communications systems; integrated multiplexers are crucial enablers of this approach. OAM modes are circularly polarized when propagating in a fiber, however, OAM generators previously demonstrated in silicon photonics use locally linearly polarized emitters. Coupling from multiplexers to fibers in those solutions results in extra loss and complexity. Moreover, many of those solutions are based on resonator structures with strong wavelength dependence, and are thus incompatible with wavelength-division multiplexing (WDM). We experimentally demonstrate on-chip generation and multiplexing of OAM modes using an array of circularly polarized 2-D antennas with wide wavelength coverage. The proposed device was implemented on the standard 220-nm silicon-on-insulator platform. Optical vortex beams with OAM orders ranging from −3 to +3 in both left and right circular polarization states were generated from the same aperture across a wavelength range of 1540 to 1557 nm. This device could serve as a multiplexer or demultiplexer for up to 12 information bearing channels coupling into an OAM fiber, and is compatible with WDM multiplexing as well.

Entanglement distribution between distant parties is one of the most important and challenging tasks in quantum communication. Distribution of photonic entangled states using optical fiber links is a fundamental building block towards quantum networks. Among the different degrees of freedom, orbital angular momentum (OAM) is one of the most promising due to its natural capability to encode high dimensional quantum states. In this article, we experimentally demonstrate fiber distribution of hybrid polarization-vector vortex entangled photon pairs. To this end, we exploit a recently developed air-core fiber which supports OAM modes. High fidelity distribution of the entangled states is demonstrated by performing quantum state tomography in the polarization-OAM Hilbert space after fiber propagation, and by violations of Bell inequalities and multipartite entanglement tests. The present results open new scenarios for quantum applications where correlated complex states can be transmitted by exploiting the vectorial nature of light.

A simple formula is obtained to describe the normalized orbital angular momentum (OAM) of a Gaussian beam after passing through a shifter spiral phase plate (SPP). The formula shows that while being equal to the topological charge at the zero off-axis shift, the OAM becomes fractional with increasing shift and it is tending to zero exponentially. Analytic expressions of the complex amplitude of the Gaussian beam having passed through the off-axis SPP show that as the beam propagates, the isolated intensity null moves from the initial point defined by the vector of the SPP's center shift along a straight line perpendicular to the said vector. Using a liquid crystal light modulator, crescent-shaped beams are experimentally generated.

Acoustic metamaterials are artificial materials designed to realize unprecedented properties such as super-resolution imaging, asymmetric wave transport, cloaking, etc. The critical material parameters considered for the design of acoustic metamaterials are mass density and bulk modulus. Previous studies have demonstrated the existence of acoustic metamaterials with negative effective mass density and/or bulk modulus. In this thesis, the realization of acoustic metamaterials with extreme materials parameters including simultaneous zero effective mass density and infinite bulk modulus as well as complex-valued parameters is discussed. Metamaterials with simultaneous zero density and infinite bulk modulus exhibit zero refractive index properties called acoustic double zero index metamaterials in which the propagating sound wave has an infinite phase velocity. This infinite phase velocity results in an infinite wavelength, such that the propagating acoustic wave has a uniform phase inside the metamaterial, which can be used for the realization of acoustic wave tunneling and collimation. Our designed acoustic double zero index metamaterial is induced by a Dirac-like cone dispersion at the Brillouin zone center associated with triply degenerated monopolar and dipolar modes. The monopolar and dipolar modes induce an infinite bulk modulus and a zero mass density, respectively. Meanwhile, the simultaneous zero density and infinite bulk modulus induce a finite acoustic impedance, which can be designed to match with the background medium and enhance the transmission through the boundaries between the metamaterial and the surroundings.On the other hand, metamaterials with complex-valued material parameters are related to the attenuation and amplification of acoustic waves. When the loss and gain inside the metamaterial are exactly balanced, the medium is parity-time (PT) symmetric so that the wave propagation is invariant under PT operator. Such PT symmetric systems contain tw

Correlated light generated from atomic ensembles can have a central role in prominent quantum information protocols, such as long-distance quantum communication. Here we present our studies on three topics involving the generation of correlated light with four-wave mixing (FWM) in a cold atomic ensemble for applications in quantum communications with high capacity. We experimentally investigate the generation of light with seeded FWM in cold cesium atoms and the time correlations of photon pairs generated with spontaneous FWM. We theoretically investigate the correlations in orbital angular momentum of photon pairs generated with spontaneous FWM for a range of experimental geometries. These studies represent foundational work toward the control and measurement of high-dimensional entanglement in the orbital angular momentum degree of freedom photon pairs for use in high-dimensional quantum communication.

We develop an orbital angular momentum (OAM) excitation pump-probe (Pp) spectroscopy and perform experiments on a Bi2Sr2CaCu2O8+delta (Bi2212) superconductor. The OAM modulation for the pump is realized by using a transverse mode conversion technique which allows to modulate the chirality of the optical OAM with a fixed polarization. The result reveals a difference of the OAM-dependent transient reflectivity changes below T (c), indicating that the pump OAM can break the chiral symmetry of the superconducting (SC) state. The OAM dependences of the transient signal imply that the quasi-particle (QP) excitation with OAM enhances the SC with opposite chirality and/or suppress the SC with equal chirality. The temperature dependence of the OAM dynamics shows virtually no pairing fluctuation that usually appears in the QP dynamics observed by conventional Pp, suggesting that the nonequilibrium OAM dynamics is sensitive to the delocalized OAM associated with long range order.

Unlike linearly polarized modes in fiber, modes exploiting orbital angular momentum (OAM) are circularly polarized when propagating in fiber. The use of OAM modes for spatial multiplexing requires efficient, low cost mode generators and multiplexers. We propose such a device based on the standard 220-nm silicon-on-insulator platform, taking multiple single-mode data-modulated signals, and imprinting these signals on right- and left-circularly polarized OAM channels on a single, multiplexed output. The device is designed to easily couple to an OAM fiber with a ring shaped core. This approach treating circular polarization within the multiplexer allows us to avoid the losses associated with filtering out unwanted polarization to create a single polarization. Designing the device to have an output matched to the OAM fiber mode profile also avoids mode size conversion. We describe our design methodology and optimization techniques using a transfer-matrix model and the finite-difference time-domain method. A candidate design is simulated and modal crosstalk is examined, showing that lowcrosstalk OAM multiplexing can be achieved through direct fiberto-chip coupling.

We develop an orbital angular momentum (OAM) excitation pump-probe (Pp) spectroscopy and perform experiments on a Bi2Sr2CaCu2O8+delta (Bi2212) superconductor. The OAM modulation for the pump is realized by using a transverse mode conversion technique which allows to modulate the chirality of the optical OAM with a fixed polarization. The result reveals a difference of the OAM-dependent transient reflectivity changes below T (c), indicating that the pump OAM can break the chiral symmetry of the superconducting (SC) state. The OAM dependences of the transient signal imply that the quasi-particle (QP) excitation with OAM enhances the SC with opposite chirality and/or suppress the SC with equal chirality. The temperature dependence of the OAM dynamics shows virtually no pairing fluctuation that usually appears in the QP dynamics observed by conventional Pp, suggesting that the nonequilibrium OAM dynamics is sensitive to the delocalized OAM associated with long range order.

Quantum communication (QC) represents a key enabler for many quantum applications. However, low information rates and short propagation distances, limit the development of this field and its practical applications. High-dimensional (Hi-D) QC can address these challenges enhancing the information rate and the systems error tolerance. We transmit, for the first time ever, Hi-D quantum states prepared in four orbital angular momentum (OAM) modes in a 1.2 km long OAM-carrying fiber. Furthermore, we successfully implement a real-time decoy-state Hi-D QKD protocol, and demonstrate the highest secret key rate and longest transmission distance of OAM-QKD presented to date

We show that if one cylindrical lens is placed in the Gaussian beam waist and another cylindrical lens is placed at some distance from the first one and rotated by some angle, then the laser beam after the second lens has an orbital angular momentum (OAM). An explicit analytical expression for the OAM of such a beam is obtained. Depending on the inter-lens distance, the OAM can be positive, negative, or zero. Such a laser beam has no isolated intensity nulls with a singular phase and it is not an optical vortex, but has an OAM. By choosing the radius of the beam waist of the source Gaussian beam, the focal lengths of the lenses and the distance between them, it is possible to generate a vortex-free laser beam equivalent to an optical vortex with a topological charge of several hundreds.