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Growth characterisation of In_xGa_1-xAs/GaAs/AlAs vertical-cavity surface-emitting laser structure using photomodulated reflectance

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IEE PROCEEDINGS-OPTOELECTRONICS 2001年第1期148卷 49-53页

作者： Choulis, SA Hosea, TJC Univ Surrey Dept Phys Guildford GU2 5XH Surrey England

Of crucial importance for vertical-cavity surface-emitting lasers (VCSELs) is the energy separation of the Fabry-Perot cavity mode and peak of the gain spectrum of the quantum-well (QW) active region. Since this is affected by growth variations, nondestructive characterisation of VCSEL wafers is usually required prior to full processing, to check that structures have been grown to specification. It is shown that photomodulated reflectance (PR) spectroscopy is useful for prefabrication testing of VCSEL wafers, for the example of a near-infrared ln(x)Ga(1-x)As/ GaAs/AlAs VCSEL. By varying either the probe position on the wafer or the temperature, PR was used to study the interaction between the cavity mode and both the ground-state QW exciton and all the higher-order QW transitions. Firstly, a growth-induced shift across the wafer was exploited to tune the cavity-mode wavelength through resonance with all the QW excitonic transitions at room temperature. Secondly, by cooling from room to liquid-helium temperatures, each QW transition was blue-shifted into resonance with the cavity mode. In both methods, the PR signal was enhanced at such resonances, which could provide a sensitive way of locating 'sweet spots' on a nonuniform VCSEL wafer (where operating devices might be fabricated). Since PR can detect all the QW transitions, it is able, by comparing the measured and predicted transition energies, to provide much information about the QW cavity and growth.

关键词： photoreflectance aluminium compounds prefabrication testing Vacuum deposition quantum well lasers Design of specific laser systems Laser resonators and cavities optical testing growth variations III-V semiconductors growth characterisation gain spectrum temperature Materials testing Nondestructive testing: optical methods QW cavity optical fabrication InGaAs-GaAs-AlAs probe position Testing photomodulated reflectance nonuniform VCSEL wafer VCSEL Production facilities and engineering gallium arsenide optical testing techniques ground-state QW exciton nondestructive characterisation InxGa1-xAs/GaAs/AlAs vertical-cavity surface-emitting laser structure cavity mode near-infrared InxGa1-xAs/GaAs/AlAs VCSEL blue-shift growth-induced shift Fabry-Perot resonators resonance transition energies molecular beam epitaxial growth nondestructive testing excitons ground states 9 to 325 K QW excitonic transitions liquid-helium temperatures operating devices higher-order QW transitions sweet spots QW transitions spectral line shift semiconductor growth Other optical properties of condensed matter Surface treatment and coating techniques Fabry-Perot cavity mode Engineering materials semiconductor device testing Lasing action in semiconductors indium compounds Optoelectronics manufacturing Semiconductor lasers laser cavity resonators optical fabrication, surface grinding VCSEL wafers surface emitting lasers quantum-well active region energy separation cavity-mode wavelength room temperature

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Capturing, processing and rendering real-world scenes

Capturing, processing and rendering real-world scenes

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conference on Videometrics and optical Methods for 3D Shape Measurement

作者： Nyland, LS Lastra, A McAllister, DK Popescu, V Mccue, C Fuchs, H Univ N Carolina Chapel Hill NC 27515 USA

ISBN: (纸本)0819439878

While photographs vividly capture a scene from a single viewpoint, it is our goal to capture a scene in such a way that a viewer can freely move to any viewpoint, just as he or she would in an actual scene. We have built a prototype system to quickly digitize a scene using a laser rangefinder and a high-resolution digital camera that accurately captures a panorama of high-resolution range and color information. With real-world scenes, we have provided data to fuel research in many areas, including representation, registration, data fusion, polygonization, rendering, simplification, and reillumination. The real-world scene data can be used for many purposes, including immersive environments, immersive training, re-engineering and engineering verification, renovation, crime-scene and accident capture and reconstruction, archaeology and historic preservation, sports and entertainment, surveillance, remote tourism and remote sales. We will describe our acquisition system, the necessary processing to merge data from the multiple input devices and positions. We will also describe (and show) high quality rendering using the data we have collected. Issues about specific rendering accelerators and algorithms will also be presented. We will conclude by describing future uses and methods of collection for real-world scene data.

关键词： Software prototyping

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Intelligent multi-fiber interface module for high bit-rate interprocessor data transfer

Intelligent multi-fiber interface module for high bit-rate i...

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European conference on optical Communication (ECOC)

作者： N.A. Riza Z. Yaqoob Photonic Information Processing Systems Laboratory Nuonics Inc. Orlando FL USA Photonic Information Processing Systems Laboratory School of Optics CREOL UCF Orlando FL USA

ISBN: (纸本)0780367057

An intelligent multi-fiber interface module (IMIM) is proposed for a multi-Gigabit inter-processor data transfer using wavelength division multiplexing (WDM). The IMIM features ultrafast nanosecond rate dataflow path reconfiguration speeds between multiple fibers of an optical data bus and parallel processors arranged in ring architecture. The IMIM exploits an arrayed-waveguide grating device and wavelength tuning in a compact non-coupler design.

关键词： optical transmitters High speed optical techniques Ultrafast optics Tunable circuits and devices optical fiber devices Laser tuning optical fiber cables Wavelength division multiplexing optical interconnections optical tuning

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Design of high-encryption wireless network with distributed host management and dynamic key generation

Design of high-encryption wireless network with distributed ...

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conference on Optoelectronic and Wireless Data Management, processing, Storage, and Retrieval

作者： Weber, R Univ Colorado Boulder CO 80309 USA

ISBN: (纸本)0819442585

The widespread deployment of wireless networks using the 802.11(b) standard across the country presents a rebirth of age-old network security problems along with a number of new ones. The wireless network, much like a shared network using broadcast devices such as network hubs, travels across a shared medium. Because of the structure any member of the wireless network can observe and intercept data being sent or received by other members. Unlike 'wired' networks there is no means to isolate traffic from other network members. The second security issue for wireless networks is the transmission of data 'clear text' so that if it is intercepted it can be read and used. Wireless networks bring about another problem that compounds the first two concerns that all shared networks must deal with, that is, anyone within the transmission range of the wireless network can join. No longer must a person enter a building to infiltrate a business network, they need only park across the street. The first implementation of network security for wireless was the WEP (Wired Equivalent Privacy) protocol. WEP attempts to make a wireless network at least as secure as a switched 'wired' network. The WEP protocol intends to secure the traffic integrity with the use of a RC4 cipher and a CSC-32 checksum. In the passphrase used for the RC4 encryption is also used as a form of access control. There are several critical faults in the WEP implementation that allow both passive data acquisition and active data modification. At 11 Mbit, capturing approximately 5 hours of clear text data can guarantee the capture of two packets with the same initialization vector (IV). Once the packets are used to get the clear text packet, that information can be used to decrypt any packets with the same IV. Since the IV's are only 24 bits the decryption of entire network becomes only an exercise in patience, with a 24 hours of continuous monitoring the WEP encryption can be defeated completely and a simple approx

关键词： Network security Standards development Error control coding information security Computer security Databases Local area networks Data acquisition Software development Operating systems

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Computing with interference: all-optical single-query 50-element database search

Computing with interference: all-optical single-query 50-ele...

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Quantum Electronics and Laser Science conference (QELS)

作者： C. Dorrer P. Londero M. Anderson S. Wallentowitz I.A. Walmsley The Institute of Optics University of Rochester Rochester NY United States

Summary form only given. Quantum information processing relies on interference and entanglement. Certain quantum algorithms have been demonstrated using interference alone. These have been criticized on the grounds that the number of resources they require does not scale favorably with the size of the database. Nonetheless it has been argued that algorithms implemented entirely using interference may be more efficient than algorithms implemented on classical particle-based machines.

关键词： Interference Databases optical computing Ultrafast optics optical signal processing optical solitons Adaptive optics Analog computers optical devices Quantum computing

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Perspectives and limits of optical information processing

Perspectives and limits of optical information processing

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Quantum Electronics and Laser Science conference (QELS)

作者： K. Wagner Department of ECE Optoelectronic Computing Systems Center University of Colorado Boulder CO USA

Summary form only given. . In this talk we will compare the development of the analog optical signal processing approaches to the Moore's law exponential growth of digital microelectronic techniques and show an example in array processing where optics will continue to have a substantial advantage in computational throughput for the foreseeable future.

关键词： information processing optical computing Ultrafast optics optical signal processing optical solitons Adaptive optics Analog computers optical devices Quantum computing optical fiber networks

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A portable device for optically recognizing Braille. I. Hardware development

A portable device for optically recognizing Braille. I. Hard...

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Australian and New Zealand conference on Intelligent information systems

作者： I. Murray T. Dias School of Electrical and Computer Engineering Curtin University of Technology Bentley WA Australia

This is the first of a pair of papers that describe a prototype portable device for optically scanning embossed Braille and conversion of the scanned text to binary Braille representation. This prototype has been developed in conjunction with the Association for the Blind (WA). An application to convert the literary Braille code to expanded text has also been implemented and is described in part II. The system developed utilises a hand held scanner that captures the embossed Braille image, in real time, via a linear 128-pixel CCD array. A Texas Instruments digital signal processor performs recognition processing.

关键词： optical devices Hardware optical films optical character recognition software Australia Employment Prototypes Real time systems Charge coupled devices Instruments

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Web-based multimedia information retrieval for clinical application research

Web-based multimedia information retrieval for clinical appl...

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Medical Imaging 2001 conference

作者： Cao, XH Hoo, KS Zhang, H Ching, W Zhang, M Wong, STC Univ Calif San Francisco Lab Radiol Informat San Francisco CA 94143 USA

ISBN: (纸本)0819440094

We described a web-based data warehousing method for retrieving and analyzing neurological multimedia information. The web-based method supports convenient access, effective search and retrieval of clinical textual and image data, and on-line analysis. To improve the flexibility and efficiency of multimedia information query and analysis, a three-tier, multimedia data warehouse for epilepsy research has been built. The data warehouse integrates clinical multimedia data related to epilepsy from disparate sources and archives them into a well-defined data model. The middle-ware consists of business logic components such web server, applets and active server page (ASP) scripts for dealing with user authentication and authorization, HTTP request, SQL data access from data warehouse and algorithms to support data analysis. At client side, a web-based graphical user interface (GUI) is used to receive user's query request and display the retrieved textual data. Client-side image processing and display for DICOM format was implemented by Java applets. An image query and display method based on 3D projections has been developed to retrieve and analyze MRI and PET.

关键词： medical multimedia information data warehouse information retrieval World Wide Web

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Towards the automated extraction of accurate 3D models from close range photogrammetric networks

Towards the automated extraction of accurate 3D models from ...

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conference on Videometrics and optical Methods for 3D Shape Measurement

作者： Papadaki, H Robson, S Chapman, D Woodhouse, N UCL Dept Geomat Engn London England

ISBN: (纸本)0819439878

Three-dimensional models are important products of measurement systems in a variety of applications such as archaeology, medicine, architecture and engineering. In order to be appropriate to the end user, such object models must comply with certain accuracy standards. To achieve both accuracy and object coverage with a close range photogrammetric approach often requires a convergent image network in combination with retro reflective targets or some form of projected pattern. Retro-reflective targets alone can only provide sparse data. However, by optimising image acquisition to record both targets and natural surface texture information, proven high accuracy retro reflective target image measurement can be combined with a wealth of automated image analysis algorithms developed by both photogrammetric and machine vision communities. This research is focused on combining photogrammetric and machine vision measurement techniques, through an automated model generation tool based upon dynamic Delaunay triangulation. The model is initialised by a sparse set of retro reflective targets, which form a Delaunay triangulation network known both in image and object space. The original triangles are densified by a multi-image approach, which uses both the image geometry information (through constrained epipolar lines) as well as radiometric properties (patch matching) within relevant triangles. The triangle network is further constrained by edge boundary information to follow the surface of individual objects in the imaged scene. Each set of points produced at various stages of the process is tagged with a unique flag that corresponds to a level of accuracy, determined either through multi-photo intersection or in a more general case through bundle adjustment.

关键词： 3D measurement system object surface digital photogrammetric networks image processing Delaunay triangulation precision reliability engineering standards

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Providing multimedia services to a diverse set of consumer devices

Providing multimedia services to a diverse set of consumer d...

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IEEE International conference on Consumer Electronics (ICCE)

作者： A. Vetro A. Divakaran H. Sun Mitsubishi Electric Research Laboratories Inc. Murray Hill NJ USA

ISBN: (纸本)0780366220

This paper describes an assortment of techniques and a system to adapt multimedia content. The ability to do so allows service providers to offer a wide range of multimedia services to users with various client capabilities. We present a system that is capable of serving a variety of client devices. To do so, we propose novel transcoding and video summarization algorithms. Additionally, we describe a system that invokes these algorithms dynamically as a function of the network, terminal and user information. The impact on the consumer is the added functionality that can be realized and the quality of their service.

关键词： Multimedia systems Network servers Transcoding Bandwidth Signal processing algorithms Image converters Broadcasting Sun Laboratories Signal processing

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