2,229 research outputs found
Disparity map generation based on trapezoidal camera architecture for multiview video
Visual content acquisition is a strategic functional block of any visual system. Despite its wide possibilities,
the arrangement of cameras for the acquisition of good quality visual content for use in multi-view video
remains a huge challenge. This paper presents the mathematical description of trapezoidal camera
architecture and relationships which facilitate the determination of camera position for visual content
acquisition in multi-view video, and depth map generation. The strong point of Trapezoidal Camera
Architecture is that it allows for adaptive camera topology by which points within the scene, especially the
occluded ones can be optically and geometrically viewed from several different viewpoints either on the
edge of the trapezoid or inside it. The concept of maximum independent set, trapezoid characteristics, and
the fact that the positions of cameras (with the exception of few) differ in their vertical coordinate
description could very well be used to address the issue of occlusion which continues to be a major
problem in computer vision with regards to the generation of depth map
Generation and Manipulation of Higher Order Fractional and Integer Bessel Gaussian Beams
Optical orbital angular momentum (OAM) describes orbiting photons, swirling local wave vectors, or spiraling phase distribution depending on what theory we use to explain light. If we consider light as a propagating electromagnetic wave, then light has the freedoms of frequency, magnitude, phase, and polarization. For a monochromatic light, expanding the later three freedoms spatiotemporally, numerous optical modes are solved from Maxwell’s equations and boundary conditions. OAM mode study starts from integer charge because it is in the integer form of the fundamental phase singularity structure.
Fractional OAM mode is the Fourier series of integer OAM modes. The average OAM does not conserve along with propagation for the traditional fractional OAM modes. We propose a new asymmetric fractional Bessel Gaussian mode providing the average OAM conserving along with the propagation.
To better understand the fractional OAM mode or integer OAM mode combination, we study the novel concentric vortex optics. The analytical propagation expression of the concentric vortex beam is derived and analyzed. The concentric vortex beam is essentially the OAM spectrum, with only two integer OAM components. The spectrum coefficiencies are real numbers and approximately power equalized in general cases. The concentric vortex beam is the coherent combination of incomplete Kummer beams. As the inner aperture tuning large, the beam evolves into the Kummer beam with the inner charge number. The aperture decreases, the outer charges Kummer beam dominates.
The proposed asymmetric fractional Bessel Gaussian beam’s Fourier transform is azimuthal Gaussian perfect vortex. We use log-polar coordinate mapping diffractive optics to transform the elliptical Gaussian beam into the desired azimuthal Gaussian perfect vortex beam. The generated asymmetric fractional Bessel Gaussian beam is systematically compared with Kotlyar’s asymmetric Bessel Gaussian beam. It’s found that the proposed beam has a narrower OAM spectrum, preserving average fractional OAM. Furthermore, the log-polar transform’s inherent output lateral shifting problem is addressed for the first time to our knowledge. An improved log-polar design is proposed, and we use five critical metrics to show the new log-polar generated asymmetric Bessel Gaussian beam’s quality is much improved.
The manipulation of the high order asymmetric fractional Bessel Gaussian beam is critical to applications scaling from communication, sensing, filamentation, to micromanipulation. We propose and demonstrate acousto-optical deflector (AOD) HOBBIT (Higher Order Bessel Beams Integrated in Time) system. The system can continuously tune the OAM modes on the order of 400 kHz. This speed beats the fastest spatial light modulator (SLM), and even better, the proposed system could work for high power applications
Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review
Advances in reflectarrays and array lenses with electronic beam-forming
capabilities are enabling a host of new possibilities for these
high-performance, low-cost antenna architectures. This paper reviews enabling
technologies and topologies of reconfigurable reflectarray and array lens
designs, and surveys a range of experimental implementations and achievements
that have been made in this area in recent years. The paper describes the
fundamental design approaches employed in realizing reconfigurable designs, and
explores advanced capabilities of these nascent architectures, such as
multi-band operation, polarization manipulation, frequency agility, and
amplification. Finally, the paper concludes by discussing future challenges and
possibilities for these antennas.Comment: 16 pages, 12 figure
Orbital Angular Momentum Waves: Generation, Detection and Emerging Applications
Orbital angular momentum (OAM) has aroused a widespread interest in many
fields, especially in telecommunications due to its potential for unleashing
new capacity in the severely congested spectrum of commercial communication
systems. Beams carrying OAM have a helical phase front and a field strength
with a singularity along the axial center, which can be used for information
transmission, imaging and particle manipulation. The number of orthogonal OAM
modes in a single beam is theoretically infinite and each mode is an element of
a complete orthogonal basis that can be employed for multiplexing different
signals, thus greatly improving the spectrum efficiency. In this paper, we
comprehensively summarize and compare the methods for generation and detection
of optical OAM, radio OAM and acoustic OAM. Then, we represent the applications
and technical challenges of OAM in communications, including free-space optical
communications, optical fiber communications, radio communications and acoustic
communications. To complete our survey, we also discuss the state of art of
particle manipulation and target imaging with OAM beams
Image-based rendering and synthesis
Multiview imaging (MVI) is currently the focus of some research as it has a wide range of applications and opens up research in other topics and applications, including virtual view synthesis for three-dimensional (3D) television (3DTV) and entertainment. However, a large amount of storage is needed by multiview systems and are difficult to construct. The concept behind allowing 3D scenes and objects to be visualized in a realistic way without full 3D model reconstruction is image-based rendering (IBR). Using images as the primary substrate, IBR has many potential applications including for video games, virtual travel and others. The technique creates new views of scenes which are reconstructed from a collection of densely sampled images or videos. The IBR concept has different classification such as knowing 3D models and the lighting conditions and be rendered using conventional graphic techniques. Another is lightfield or lumigraph rendering which depends on dense sampling with no or very little geometry for rendering without recovering the exact 3D-models.published_or_final_versio
Large scale broadband antenna array systems
Broadband antenna arrays have become increasingly popular for various imaging applications, such as radio telescopes and radar, where high sensitivity and resolution are required. High sensitivity requires the development of large scale broadband arrays capable of imaging distant sources at many different wavelengths, in addition to overcoming noise and jamming signals. The design of large scale broadband antenna arrays requires large number antennas, increasing the cost and complexity of the overall system. Moreover, noise sources often vary, depending on their wavelengths and angular locations. This increases the overall design complexity particularly for broadband applications where the performance depends not only on the required bandwidth, but also on the frequency band.This thesis provides a study of broadband antenna array systems for large scale applications. The study investigates different tradeoffs associated with designing such systems and drives a novel design approach to optimize both their cost and performance for a wide range of applications. In addition, the thesis includes measurements of a suitable array to validate the computational predictions. Moreover, the thesis also demonstrates how this study can be utilized to optimize a broadband antenna array system suitable for a low frequency radio telescope.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Harnessing optical micro-combs for microwave photonics
In the past decade, optical frequency combs generated by high-Q
micro-resonators, or micro-combs, which feature compact device footprints, high
energy efficiency, and high-repetition-rates in broad optical bandwidths, have
led to a revolution in a wide range of fields including metrology, mode-locked
lasers, telecommunications, RF photonics, spectroscopy, sensing, and quantum
optics. Among these, an application that has attracted great interest is the
use of micro-combs for RF photonics, where they offer enhanced functionalities
as well as reduced size and power consumption over other approaches. This
article reviews the recent advances in this emerging field. We provide an
overview of the main achievements that have been obtained to date, and
highlight the strong potential of micro-combs for RF photonics applications. We
also discuss some of the open challenges and limitations that need to be met
for practical applications.Comment: 32 Pages, 13 Figures, 172 Reference
Electromagnetic Absorbers Based on Frequency Selective Surfaces
Frequency Selective Surfaces (FSSs) are bidimensional
arrays of particles arranged in a periodic manner.
These surfaces can be lossless or lossy, depending on the
manufacturing process. They can be fabricated by using metallic or
controlled-resistance surface deposition. Lossy surfaces can be also
obtained through the integration of lumped components on a
metallic surface. The use of FSSs has fostered new research lines in
the design of electromagnetic absorbing surfaces, bringing
improvements both in terms of bandwidth/thickness ratio
maximization and in terms of customizability of the absorbing
bandwidth (narrowband, multi-band, wideband, ultra-wideband) for
specific applications. Artificial impedance surfaces (or HighImpedance
Surfaces, - HIS) are thin resonant cavities synthesized
by printing a periodic frequency selective surface on the top of a
grounded dielectric slab. By proper tailoring of the geometrical and
electrical properties of the FSS as well as the substrate, several
electrically-thin absorbing designs can be obtained. Ultranarrowband
absorbers with extremely stable angular behavior, often
addressed as metamaterial absorbers, can be realized by exploiting
only dielectric losses of commercial substrates. Narrowband,
wideband and ultra-wideband configurations are instead
implemented by also resorting to ohmic losses in a non-conductive
FSS. A thorough review of the available absorbers will be presented
together with multi-band and tunable design techniques.
Manufacturing processes and practical examples will be also
addressed, and the most interesting fields of application of the
presented structures will be described
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