Browsing by Author "Pieper, Ronald J."
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- Applications of infrared fibers in temperature sensingMatthews, Amy L. (Virginia Tech, 1988-06-05)As attenuation in silica based fibers approaches its ultimate theoretical limit, investigation is in progress to develop new materials which exhibit lower losses than silica. These bulk materials could then be used to fabricate ultralow loss optical fibers which operate farther out in the infrared than do silica fibers. Such infrared fibers could be used in long, repeaterless telecommunications links, the transmission of CO and CO₂ laser power, and in several sensing mechanisms. This thesis presents an overview of these new fibers and how they can be applied in noncontact temperature measurement. Fiber optic temperature sensing is thus reviewed, and an optical fiber pyrometer is discussed.
- Dual channel bidirectional wavelength division multiplexing datalinkTohme, Henri Edouard (Virginia Tech, 1988-06-05)Wavelength division multiplexing two channels on one fiber is one approach that enables us to make use of the extremely large bandwidth of optical fibers. We start with an analysis of optical fibers, sources, detectors, filters and wavelength division ,multiplexers. Then, using the knowledge from the experimental data, we design a 20 km bidirectional WDM datalink. The design is backed up with theory and measurements. Fiber to the home is one of many applications that makes use of such a design.
- Exact solution for four-order acousto-optic Bragg diffraction with arbitrary initial conditionsPieper, Ronald J.; Koslover, Deborah; Poon, Ting-Chung (Optical Society of America, 2009-03-01)An exact solution to the four-order acousto-optic (AO) Bragg diffraction problem with arbitrary initial conditions compatible with exact Bragg angle incident light is developed. The solution, obtained by solving a 4th-order differential equation, is formalized into a transition matrix operator predicting diffracted light orders at the exit of the AO cell in terms of the same diffracted light orders at the entrance. It is shown that the transition matrix is unitary and that this unitary matrix condition is sufficient to guarantee energy conservation. A comparison of analytical solutions with numerical predictions validates the formalism. Although not directly related to the approach used to obtain the solution, it was discovered that all four generated eigenvalues from the four-order AO differential matrix operator are expressed simply in terms of Euclid's Divine Proportion. (C) 2009 Optical Society of America
- Extending the depth of focus using digital image filteringHu, Guang-hua (Virginia Tech, 1987-04-15)Two types of image processing methods capable of forming a composite image from a set of image slices which have in-focus as well as out-of-focus segments are discussed. The first type is based on space domain operations and has been discussed in the literature. The second type, to be introduced, is based on the intuitive concept that the spectral energy distribution of a focused object is biased towards lower frequencies after blurring. This approach requires digital image filtering in the spatial frequency domain. A comparison among methods of both types is made using a quantitative uÌ delity criterion.
- High resolution optical time domain reflectometry and its applicationsZimmermann, Bernd D. (Virginia Polytechnic Institute and State University, 1988-01-15)High resolution Optical Time Domain Reflectometry (OTDR) measurements have recently allowed spatial resolutions of less than one millimeter. These capabilities indicate that OTDR techniques may be suitable for non-conventional applications such as the determination of fiber strain. This thesis presents an investigation of how high resolution OTDR techniques can be used in such applications. The concept of fiber segmentation via partially reflective optical splices for local strain measurements is discussed both from a theoretical and practical standpoint. Experimental results demonstrating the feasibility of such local strain measurements are also given. Another part of this investigation considers the practical details of the proposed strain measurement technique, addressing such topics as launching conditions, and environmental factors. Possible applications of the local strain measurement techniques, such as two- and three-dimensional stress analysis, and strain determination of fiber optic cables, are also presented. These applications also include the development of small, easy to manufacture elastomeric optical splices, which were shown to yield acceptable performance < 0.2 dB losses) for multimode fibers.
- Longitudinal misalignment based strain sensorAndrews, Jeffrey Pratt (Virginia Tech, 1989-06-04)A practical fiber optic strain sensor has been developed to measure strains in the range of 0.0 to 2.0 percent strain with a resolution ranging between 10 and 100 microstrain depending on sensor design choices. This intensity based sensor measures strain by monitoring strain induced longitudinal misalignment in a novel fiber interconnection. This interconnection is created by aligning fibers within a segment of hollow core fiber. Related splice loss mechanisms are investigated for their effect on resolution. The effect of gauge length and launch conditions are also investigated.
- Modal interference techniques for strain detection in few-mode optical fibersDuncan, Bradley Dean (Virginia Tech, 1988-04-30)Interference between the modes of an optical fiber results in specific intensity patterns which can be modulated as a function of disturbances in the optical fiber system. These modulation effects are a direct result of the difference in propagation constants of the constituent modes. In this presentation it is shown how the modulated intensity patterns created by the interference of specific mode groups in few-mode optical fibers (V < 5.0) can be used to detect strain. A detailed discussion of the modal phenomena responsible for the observed strain induced pattern modulation is given and it is shown that strain detection sensitivities on the order of 10-9 can be expected. Data taken during the evaluation of an actual experimental strain detection system based on the developed theory is also presented.
- Novel microbend loss fiber optic hydrophones for direction sensingVengsarkar, Ashish Madhukar (Virginia Tech, 1988-08-05)Dual purpose fiber optic microbend loss sensors have been developed for measurement of underwater acoustic wave amplitudes and for detection of the direction of wave propagation. Cylindrical sensing elements with external threads have fibers wound around them. Axial slots, cut along the length of the cylinder and deeper than the threads, provide the microbends. Three different construction schemes for cylindrical sensing elements are built. The dual purpose hydrophones are characterized for frequencies ranging from 15 kHz to 75 kHz. Based on the results, an improved design that uses the wavelength dependence of microbend loss in a single mode fiber is proposed.
- Optical fiber modal domain sensors for dynamic strain measurementBennett, K. D. (Kimberly Dean) (Virginia Tech, 1990-01-03)Modern engineering structures often incorporate new materials and complex designs for which existing techniques for nondestructive evaluation prove inadequate, especially for dynamic and in-service measurements. At the same time, optical fiber sensors have been identified as an ideal candidate for embedded and attached measurements of material parameters such as strain, temperature, or state of damage. In particular, sensors based on optical fiber modal interference phenomena have been shown to be capable of highly sensitive detection of static and dynamic strain. This work reviews known applications of modal domain sensing to measurement science to date, and discusses the principles behind the method. A general expression for the intensity distribution emerging from a multimode fiber is formulated, covering both few mode and highly multimode fibers, and new expressions for their sensitivity to both radial and axial strain are derived. Optimized multimode fibers are seen to show an intrinsic phase sensitivity which rivals or even surpasses that of the single mode interferometer, especially in the case of applied radial strain. The use of modal domain sensors for real-time ultrasonic wave transduction is described as a particular application to NDE, with experimental results being presented with regard to acoustic emission monitoring as well as the detection and analysis of shock waves due to impact. Finally, optimization schemes and alternatives for such sensors are addressed, and recommendations for future work are raised.
- A real time embedded controller for smart structuresAhrens, Christian P. (Virginia Tech, 1989-08-05)This thesis presents a simple Real Time Embedded Control System (RTECS) in an application of Intelligent Structure Monitoring. Research in smart structures, especially the area of vibration suppression, has warranted the investigation of advanced computing environments. Real time PC computing power has limited development of high order control algorithms. The system discussed allows for implementation of l/O intensive algorithms and provides capability for advanced system development. In an application of Modal Domain Sensing for Vibration Control, RTECS is compared to a PC AT based system for overall functionality and speed. Using a model development procedure, the system is optimized for efficient operation and speed. This includes minimizing the computational overhead associated with I/O. A comparison shows an order of magnitude I increase in system speed with larger speed increases discussed. The results provide an avenue for high order control system design. This leads to more accurate device modeling and a higher level of system control. RTECS employs a novel RISC microcontroller capable of 15 MIPs continuous performance and burst rates of 40 MIPs. Advanced CMOS circuits are integrated on a single printed circuit board measuring 100 mm by 160 mm and require only 1 Watt of power. An operating system written in Forth provides the flexibility for high speed operation in short development cycles.
- Resolution-Dependent Depth Of Focus For an Incoherent Imaging-SystemPieper, Ronald J.; Park, Jinwoo; Poon, Ting-Chung (Optical Society of America, 1988-11-01)Through the application of the Rayleigh criterion for a two-point resolution, the dependence of the depth of focus on the resolution in the image is determined for a rectangular, a Gaussian, and an annular lens aperture. These solutions are posed in terms of the normalized parameters, obviating the need for the specification of the actual physical lengths. A general approach applicable to any aperture topology is discussed.
- Soliton Propagation in nonlinear optical fibers: theory and applicationGoy, David A. (Virginia Tech, 1987-12-17)A survey of research in nonlinear optical fibers is given. Important background concepts are introduced and explained. Present and future applications of nonlinear optical fibers arc reviewed. A mathematical model of a nonlinear optical fiber is developed using a coupled-mode theory approach, and methods of solving nonlinear partial differential equations arc discussed. A detailed history of research in the field is given, and recommendations for future research are made.
- Telephone Voice Alert: system planning and designFinch, Steven W. (Virginia Tech, 1989-08-05)The Telephone Voice Alert is divided into six parts: the ring detector, controller, voice memory, synthesizer, speaker, and power supply subsystems. These all interact together to produce a voice signal whenever a ring signal is detected. By beginning from the system function and analyzing the components as we break the system into subsystems, we find that the trade-off between system cost and system "effectiveness" minimizes to prove Configuration A (digital voice reproduction) a more effective means. Further testing and development is necessary, however, as the design must be "fine-tuned" in order to insure proper function.
- Temperature insensitive fiber optic interferometer and applicationsMurphy, Kent A. (Virginia Tech, 1989-10-05)A method of modifying a uÌ ber optic fused biconical tapered coupler to produce a relatively temperature insensitive Michelson interferometer is presented. The modification was accomplished by cleaving the coupler after the minimum taper region and polishing, perpendicular to the endface, to a point just short of the interaction region. This allows one of the two fiber cores, which are within micrometers of each other with their claddings fused together, to be coated at its endface with a reflecting material. This reflecting core serves as the reference arm, while the other core serves as the sensing arm. Variations in the method of fabrication of the sensor are described. Because of the close proximity and short length of the reference and sensing arms, the interferometer is temperature insensitive. The miniaturized Michelson interferometer is characterized and its limitations are discussed. A surface acoustic wave detection scheme is successfully demonstrated. Results of a magnetic field sensor using the miniaturized Michelson interferometer and a magnetostrictive material are presented.
- A vector model for analysis, decomposition and segmentation of texturesHays, Peter Sipe (Virginia Tech, 1990-06-08)A model, which assumes tonal decomposition of textures, is proposed for texture analysis and segmentation. The model is based on an interpretation in which the tones form an orthogonal basis in a vector space of possible textures. Three methods for texture segmentation, which employ a texture indicator developed from this concept, are demonstrated. Application of the vector model requires the use of a priori information of the tonal frequencies present and the tonal amplitude distributions. A proposed algorithm, which uses only a priori knowledge of the spatial frequencies to extract the tonal amplitudes i.e. texture vectors, is discussed. Examp1es illustrating the application of this concept are presented. Finally a preliminary discussion of the problems associated with determining the tonal frequencies is presented
- Visibility-Dependent Depth Of Focus For Incoherent Sinusoidal SourcesPieper, Ronald J.; Raj, Kannan; Poon, Ting-Chung (Optical Society of America, 1992-05-01)A visibility-dependent depth of focus is developed for incoherent sinusoidal sources. This analysis is based on a derived relationship between the visibility and the optical transfer function (OTF). The formalism developed is general for any aperture topology and arbitrary orientation of sinusoidal sources. To illustrate the application of the method the cases of an annular aperture and a Gaussian aperture are analyzed. It is found that as the level of defect of defocus increases, the maximum visibility for which a particular spatial frequency can be resolved decreases.