1,720,961 research outputs found
Integrated optical phased arrays for three-dimensional display applications
No full textThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2020Cataloged from student-submitted PDF of thesis.Includes bibliographical references (pages 154-164).The compatibility of silicon photonic platforms with complementary metal-oxide-semiconductor (CMOS) fabrication processes has facilitated a surge in the development of silicon-based integrated optical phased arrays (OPAs) for light detection and ranging (LiDAR) and free-space communications. However, silicon is limited to operating at infrared wavelengths since its bandgap prevents visible light transmission. The development of integrated OPAs for arbitrary complex wavefront synthesis in the visible spectrum would enable the expansion of this technology into a multitude of new applications spaces such as optical trapping, imaging through scattering media, underwater LiDAR, optogenetic stimulation, and three-dimensional (3D) displays. Silicon nitride, a CMOS-compatible material that is transparent in the visible spectrum, may be used as the waveguiding material in phased array systems designed for the above applications.In this work, we develop large-scale visible light integrated OPA systems fabricated in a silicon-nitride-based platform for 3D display applications. We begin by presenting the first demonstrations of visible light integrated OPAs. Building on this, we demonstrate a chip-scale architecture for autostereoscopic image projection using a system of multiple integrated OPAs to reconstruct virtual light fields. Specically, we generate a static virtual 3D image with horizontal parallax and a viewing angle of 5. Next, we present an architecture for realizing a transparent near-eye direct-view augmented/mixed reality (AR/MR) display using a system of integrated OPAs to directly project holographic images onto the user's retina. This display architecture was developed to address the deficiencies in current AR/MR headsets with respect to brightness, field of view (FOV), and the vergence-accommodation conflict, which causes eye fatigue.Here, we present a passive demonstration of the display as well as a number of key photonic components required to realize a system for 3D video.by Manan Raval.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Scienc
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Nanophotonic visible light phased arrays
No full textThesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.Cataloged from PDF version of thesis.Includes bibliographical references (pages 81-85).Previously demonstrated integrated optical phased arrays have primarily been implemented in silicon-based platforms and have therefore been limited to operation at infrared wavelengths, where silicon provides low-loss transmission. Developing integrated optical phased arrays for visible wavelengths would enable the exploration of new applications for this technology, such as autostereoscopic displays and neuronal targeting for optogenetics. The work presented in this thesis involves the development of visible light integrated optical phased array components and systems with a focus on autostereoscopic image projection applications. Practical 3D microdisplay applications will require (1) large-aperture phased array systems for diffraction minimization, (2) integrated phase modulation for implementing dynamically reconfigurable phased array antenna elements, and (3) a phased array system architecture for accurately encoding the light field of virtual objects. Integrated photonic architectures for all three aforementioned goals are investigated in this thesis. With respect to the first goal, a 1x1 mm2 aperture visible light phased array with a near diffraction limited far-field spot size is demonstrated. With respect to the second goal, the design of an integrated phase modulator based on the electro-optic tuning of a nematic liquid crystal waveguide cladding layer is developed and a near-x phase shift is demonstrated in a fabricated device. Finally, an autostereoscopic image projection system comprised of multiple tiled phased arrays configured to project a virtual image with parallax in one dimension within an 8.58° field of view is demonstrated.by Manan Raval.S.M
Design and Fabrication of GaAs/AlGaAs Slot Waveguards
Get PDFWe present the theoretical simulation and experimental results of a slot waveguide structure and a strip-to-slot waveguide coupler implemented in the GaAs/AlGaAs system. Although there have been many demonstrations of slot waveguides in silicon and silicon nitride, there has been limited work devoted to demonstrating this device in a III-V semiconductor material system. Implementing slot waveguides in a III-V material system such as GaAs/AlGaAs would provide the advantage of monolithic integration with active photonic components such as lasers and photodetectors. Slot waveguides have been widely studied for biosensing applications because of their ability to confine a significant portion of the electric field in an air slot, thereby increasing the spatial overlap of the optical mode with surrounding analytes. Monolithic integration in the III-V system would therefore enable the development of photonic lab-on-a-chip biosensing platforms. Due to the low refractive index contrast in the GaAs/AlGaAs relative to that of the silicon-on-insulator (SOI) material system, AlGaAs material composition, epitaxial waveguide layer thicknesses, and slot etch depth must be optimized to realize low-loss propagation in the slot waveguide. Specifically, we demonstrate elevated and suspended slot waveguide structures. The first is formed by etching into the underlying AlGaAs cladding layer and the second is formed by etching away the underlying AlGaAs cladding. These structures are fabricated and tested at a wavelength of 1550 nm.Submitted by Janice Progen ([email protected]) on 2014-10-24T15:54:53Z
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Previous issue date: 2014-05Ope
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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