VTechWorks Repository :: Browsing by Author "Indebetouw, Guy J."

Browsing by Author "Indebetouw, Guy J."

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Characterization of Organic and Inorganic Optoelectronic Semiconductor Devices Using Advanced Spectroscopic Methods
Schroeder, Raoul (Virginia Tech, 2001-12-14)
In this thesis, advanced spectroscopy methods are discussed and applied to gain understanding of the physical properties of organic conjugated molecules, II-VI thin film semiconductors, and vertical cavity surface emitting lasers (VCSEL). Experiments include single photon and two-photon excitation with lasers, with subsequent measurements of the absorption and photoluminescence, as well as photocurrent measurements using tungsten and xenon lamps, measuring the direct current and the alternating current of the devices. The materials are investigated in dissolved form (conjugated polymers), thin films (polymers, II-VI semiconductors), and complex layer structures (hybrid device, VCSEL). The experiments are analyzed and interpreted by newly developed or applied theories for two-photon saturation processes in semiconductors, bandgap shrinkage due to optically induced electron hole pairs, and the principle of detailed balance to describe the photoluminescence in thin film cadmium sulfide.
Code Division Multiplexing of Fiber Optic and Microelectromechanical Systems (MEMS) Sensors
Jacobson, Carl P. (Virginia Tech, 2000-02-22)
Multiplexing has evolved over the years from Emile Baudot's method of transmitting six simultaneous telegraph signals over one wire to the high-speed mixed-signal communications systems that are now commonplace. The evolution started with multiplexing identical information sources, such as plain old telephone service (POTS) devices. Recently, however, methods to combine signals from different information sources, such as telephone and video signals for example, have required new approaches to the development of software and hardware, and fundamental changes in the way we envision the basic block diagrams of communication systems. The importance of multiplexing cannot be overstated. To say that much of the current economic and technological progress worldwide is due in part to mixed-signal communications systems would not be incorrect. Along the vein of advancing the state-of-the-art, this dissertation research addresses a new area of multiplexing by taking a novel approach to network different-type sensors using software and signal processing. Two different sensor types were selected, fiber optics and MEMS, and were networked using code division multiplexing. The experimentation showed that the interconnection of these sensors using code division multiplexing was feasible and that the mixed signal demultiplexing software unique to this research allowed the disparate signals to be discerned. An analysis of an expanded system was performed with the results showing that the ultimate number of sensors that could be multiplexed with this technique ranges from the hundreds into the millions, depending on the specific design parameters used. Predictions about next-next generation systems using the techniques developed in the research are presented.
Color coding of spatial frequencies using incoherent optical processing
Indebetouw, Guy J. (Optical Society of America, 1979-10)
An incoherent optical processing technique for color coding the spatial frequency content of an input is described. Experimental results and comparison with the output of a coherent filtering system are discussed. Possible applications such as texture recognition in aerial imagery or radiography analysis are suggested.
Coupling of orthogonal polarization states in a nonlinear birefringent cavity
Ho, Kwongchoi Caisy; Indebetouw, Guy J. (Optical Society of America, 1990)
We discuss the coupling of orthogonally polarized beams in a nonlinear cavity and show experimentally how this can be used to implement gates or latches in which one polarization state is switched by another. These devices must be reset by interrupting a light beam and thus must dissipate energy to switch down. The possibility of up and down switching with positive pulses only is also discussed.
Designs for Zero Polarization-Mode Dispersion And Polarization-Maintaining Fibers
Baghdadi, Jihad Abdul-Hadi III (Virginia Tech, 1998-05-08)
This dissertation addresses several aspects pertaining to polarization in optical fibers and optical waveguide devices. In particular, the analysis and design of fibers that maintain polarization over long lengths, provide zero polarization-mode dispersion, and function as polarizers or mode filters are presented. First, optimum designs for high-birefringence as well as single-polarization single-mode fibers are studied. For high-birefringence fibers, several index profiles were obtained that provided high birefringence while achieving zero or very small dispersion in 1.3 μm and 1.55 μm windows. Also, few index profiles were found that resulted in single-polarization single-mode operation with zero or very small dispersion at about 1.3 μm and 1.55 μm. A wavelength range of 100 nm to 500 nm was achieved for truly single-mode operation. Second, a comprehensive analysis of polarization-mode dispersion in a multiple-clad fiber due to ellipticity of fiber cross-section is carried out. The analysis results are then used to design large effective area single-mode dispersion-shifted fiber that provides zero polarization-mode dispersion at the wavelength 1.55 μm. Effective area on the order of 122 μm² with mode-field diameter of about 10 μm have been attained for this design. Tolerance analysis on the transmission parameters due to ±1% and ±2% variations in the radii of the fiber layers is carried out. Finally, a wedge-shape dielectric waveguides bounded by conducting planes is introduced and analyzed. Conductor and dielectric losses for the fundamental mode in waveguides with wedge angle of π/n; n ≥ 1, and 2π/3 as a special case with noninteger azimuthal number have been evaluated. These waveguides generally support fewer number of modes for smaller wedge angles and the modes cannot be of TM type. They find applications as mode filters and polarizers..
Development of Novel Optical Fiber Interferometric Sensors with High Sensitivity for Acoustic Emission Detection
Deng, Jiangdong (Virginia Tech, 2004-10-12)
For the purpose of developing a new highly-sensitive and reliable fiber optical acoustic sensor capable of real-time on-line detection of acoustic emissions in power transformers, this dissertation presents the comprehensive research work on the theory, modeling, design, instrumentation, noise analysis, and performance evaluation of a diaphragm-based optical fiber acoustic (DOFIA) sensor system. The optical interference theory and the diaphragm dynamic vibration analysis form the two foundation stones of the diaphragm-based optical fiber interferomtric acoustic (DOFIA) sensor. Combining these two principles, the pressure sensitivity and frequency response of the acoustic sensor system is analyzed quantitatively, which provides guidance for the practical design for the DOFIA sensor probe and system. To meet all the technical requirements for partial discharge detection, semiconductor process technologies are applied, for the first time to our knowledge, in fabricating the micro-caved diaphragm (MCD) used for the DOFIA sensor probe. The novel controlled thermal bonding method was proposed, designed, and developed to fabricate high performance DOFIA sensor probes with excellent mechanical strength and temperature stability. In addition, the signal processing unit is designed and implemented with high gain, wide band response, and ultra low noise. A systematic noise analysis is also presented to provide a better understanding of the performance limitations of the DOFIA sensor system. Based on the system noise analysis results, optimization measures are proposed to improve the system performance. Extensive experiments, including the field testing in a power transformer, have also been conducted to systematically evaluate the performance of the instrumentation systems and the sensor probes. These results clearly demonstrated the feasibility of the developed DOFIA sensor for the detection of partial discharges inside electrical power transformers, with unique advantages of non-electrically conducting, high sensitivity, high frequency response, and immunity to the electro-magnetic interference (EMI).
Distortion-free imaging through inhomogeneities by selective spatial-filtering
Indebetouw, Guy J. (Optical Society of America, 1990-08)
Distortion-free imaging through a system with aberrations is possible for a certain class of input. The input spatial spectrum must be restricted to spatial frequencies which are equally affected by the aberrations (i.e., which experience identical phase shifts mod2-pi). We demonstrate experimentally that if the aberrations can be localized in the pupil plane, an arbitrary input can be prefiltered to produce a distribution which is imaged without distortion by an aberrant system. Equivalently, the output of the system can be postfiltered to select the information which was imaged without distortion.
Dual Processing Spatially Distributed Integrating Fiber Optic Sensors for Non-intrusive Patient Monitoring
Xu, Xiaohua (Virginia Tech, 2005-04-21)
Given the rapid aging of the worldâ s population, improvements in technology for automation of patient care and documentation are badly needed. This project is based on previous research that demonstrated a â smartâ bed that can non-intrusively monitor a patient in bed and determine a patient's respiration, heart rate and movement without intrusive or restrictive medical measurements. The â smartâ bed is an application of spatially distributed integrating fiber optic sensors. The basic concept is that any patient movement that also moves an optical fiber within a specified area will produce a change in the optical signal. A statistical mode (STM) sensor and a high order mode excitation (HOME) sensor were previously investigated, based on which the author developed the present design including both modal modulation approaches. Development was made in both hardware and software for the combined STM/HOME sensor: a special lens system was installed allowing only the high order modes of the optical fiber to be excited and coupled into the sensor; computer-processing method was used for handling output from the dual STM-HOME sensor, which would offer comprehensive perturbation analysis for more reliable patient monitoring. Experimental results of simulating human body breathing and heartbeats by periodic mechanical perturbations are also presented, and the relative advantage and drawbacks of the two modal modulation approaches are discussed.
Dynamics of Competition using a Bit String Model with Age Structure and Mutations
Astalos, Robert Joseph (Virginia Tech, 2001-04-17)
Using Monte Carlo simulations and analytic methods, we examine the dynamics of inter-species competition using the Penna bit-string model. We begin with a study of the steady state with a single species, then proceed to the dynamics of competition between two species. When the species are not evenly matched in fitness, a simple differential equation provides a satisfactory model of the behavior of the system. However, when the species are equally fit, we show that a model, originally proposed to describe population genetics [Fisher,Wright], is required. When mutations are allowed between the competing species, the dynamics becomes more interesting. The mutation rate becomes a parameter that dictates the steady state behavior. If the two species are not equally fit, the value of the mutation rate determines whether the longer-lived or faster reproducing species is favored. With two species that are equally fit, the steady state varies with mutation rate from a single peaked to a double peaked distribution. This behavior is shown to be well described by an extension to the Fisher-Wright model mentioned above. Finally, we describe the preliminary results of a few new lines of investigation, and suggest ideas for further study of the dynamics of this model.
Effects of Thickness, Morphology and Molecular Structure of Donor and Acceptor Layers in Thermally Interdiffused Polymer Photovoltaics
Gopal, Anamika (Virginia Tech, 2007-04-10)
An in-depth study of concentration gradients in thermally-interdiffused polymer – fullerene photovoltaic devices, with a focus on thickness and heat treatments, is presented in this thesis. Device performance is improved from the bilayer by the creation of a concentration gradient of the donor and acceptor materials throughout the active layer of the device. Concentration gradients are expected to improve device performance by optimizing the charge transfer, transport and collection processes. This is achieved through heat-induced interdiffusion of the two materials at temperatures above the glass transition temperature of the polymer. Investigation of the poly(3-octylthiophene) (P3OT) – C₆₀ system show a three-fold improvement in the external quantum efficiencies (EQE) as compared with bilayer devices. Auger spectroscopy, combined with argon-ion beam milling, serves to record the concentration depth profile and identify concentration gradients in the device through detection of the sulfur in the P3OT backbone. Concentration gradients are optimized to yield the best devices through a thickness variation study conducted on the P3OT – C₆₀ system for fixed thermal interdiffusion conditions at 118 °C for 5 minutes. An optimum thickness of 40 to 60 nm is obtained for the two materials that yields the ideal morphology of a concentration gradient as recorded by Auger spectroscopy. For such devices, the concentration gradient is seen to extend through the device, ending in a thin layer of pure material at each electrode. A monochromatic power conversion efficiency of 2.05% is obtained for 5.3 mW/cm²⁺ illumination at 470 nm. A brief study is also presented to optimize the concentration gradient profile through variations of the thermal parameters. The dependence of the concentration gradient on the interdiffusion time and temperature is investigated. The merits of heat treatment on the crystallinity of P3OT and the overall device performance are also discussed. It is shown in some case that devices with annealed P3OT layers show almost twice the EQE as non-annealed P3OT layer devices. Potential alternatives for C₆₀ in interdiffused devices with P3OT have been presented. [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), a well-investigated acceptor for blend devices, is studied as an acceptor in concentration gradient devices. A method for spin-coating uniform bilayers of P3OT and PCBM, without solution damage to either layer, is presented. A thermal variation study of the interdiffusion conditions on this system indicated higher interdiffusion temperatures and times are preferred for P3OT – PCBM systems. For interdiffusion at 150 °C for ten minutes, EQE values approaching 35 % at 500 nm are obtained. Auger spectroscopy studies on this system yielded the same conclusions about the concentration gradient device morphology that gives optimum device output. 1:1 and 1:2 blends of P3OT – PCBM are also studied. The influence of various thermal treatments on these devices is described. The endohedral fullerene Sc₃N@C₈₀ is introduced as a new acceptor material. The endohedral fullerene consists of Sc₃N cluster enclosed in a C₈₀ cage. An order of magnitude increase is seen in device performance upon sublimation of these molecules on a P3OT layer confirming its effectiveness as an acceptor. Preliminary studies done on this system indicated the need for greater thermal treatment to produce optimum concentration gradients. An in depth study for varying temperatures and times is presented. The best device performance was seen for interdiffusion at 160 °C for 25 minutes. The endohedral fullerene devices also show a long-term deterioration and so best result are presented from a set of devices fabricated within the same time period. The study of these three donor-acceptor systems confirms that the conclusions on the thickness dependence and device performance study conducted for the P3OT – C₆₀ system extend to other acceptors. A model of EQE for varying thicknesses based on absorption in the interdiffused concentration gradient regions is also presented. This model effectively highlights the influence of P3OT layer thickness on the trends observed in the EQE. It did not, however, reproduce the experimental thickness variation results for varying C₆₀ thicknesses. Incorporation of the effects of the electric field intensity distribution is expected to correct for this. Suggestions have been given on how this might be achieved.
Extended Depth-of-focus in a Laser Scanning System Employing a Synthesized Difference-of-Gaussians Pupil
Kourakos, Alexander William (Virginia Tech, 1999-05-11)
Traditional laser scanning systems, such as those used for microscopy, typically image objects of finite thickness. If the depth-of-focus of such systems is low, as is the case when a simple clear pupil is used, the object must be very thin or the image will be distorted. Several methods have been developed to deal with this problem. A microscope with a thin annular pupil has a very high depth-of-focus and can image the entire thickness of a sample, but most of the laser light is blocked, and the image shows poor contrast and high noise. In confocal laser microscopy, the depth-of-focus problem is eliminated by using a small aperture to discard information from all but one thin plane of the sample. However, such a system requires scanning passes at many different depths to yield an image of the entire thickness of the sample, which is a time-consuming process and is highly sensitive to registration errors. In this thesis, a novel type of scanning system is considered. The sample is simultaneously scanned with a combination of two Gaussian laser beams of different widths and slightly different temporal frequencies. Information from scanning with the two beams is recorded with a photodetector, separated electronically, and processed to form an image. This image is similar to one formed by a system using a difference-of-Gaussians pupil, except no light has been blocked or wasted. Also, the entire sample can be scanned in one pass. The depth-of-focus characteristics of this synthesized difference-of-Gaussians pupil are examined and compared with those of well-known
Fabry-Perot filters used for optical preprocessing
Indebetouw, Guy J.; Case, S. K. (Optical Society of America, 1981-10)
A Fabry-Perot etalon placed in the object plane of a coherent optical processing system can be used as a variable bandpass preprocessing filter. Use of this filter leads to improved correlation signals in a matched spatial filter system. Experimental results are shown and compared with results obtained by two other preprocessing methods.
High Speed Fiber Optic Spectrometer
Wang, Yongxin (Virginia Tech, 2007-12-10)
This dissertation presents the structure, operational principle and mathematical model of a novel high speed fiber optic spectrometer (HSFOS). In addition, the performance analysis is conducted and preliminary experimental results are listed and discussed. Such a spectrometer is highly desired by the ever-increasing applications of fiber optic sensors. In the recent decades, a variety of fiber optic sensors have been proposed, built and tested. Compared to their electronic counterparts, fiber optic sensors although still under development, are preferred more by certain industrial and medical applications which benefit from their unique properties such as immunity to electromagnetic interference, ability to withstand harsh environments and composition of purely dielectric materials. In recent years, new fiber optic sensors have been designed for applications where high response frequency up to a few hundred KHz is required while advantages of high accuracy and large dynamic range must be maintained. The bottle neck then emerged in the signal demodulation part of the sensor system. The quadrature phase detection could achieve high demodulation speed but with small dynamic range, medium accuracy and measurement ambiguity. The white light interferometry could provide a solution for high accuracy and large dynamic range measurement without ambiguity because of its absolute measurement nature. However the signal demodulation speed is limited due to the low spectrum acquisition rate of the existing spectrometers. The new HSFOS utilizes time domain dispersion of the sampled incoming light by dispersive fiber rather than the spatial dispersion employed by traditional spectrometers. In addition the signal that represents the spectrum of the light is naturally a serial signal which can be detected by a single detector and recorded by a high speed data acquisition device. Theoretical study of the operation principle is made and a mathematical model for the spectrometer is developed based on Marcuse's previous work. One major difference of the new derivation is that the propagation constant is expanded about the center circular frequency of each monochromatic light pulse instead of the center frequency of the chromatic light pulse which makes the physical picture of the chromatic light pulse evolution in a dispersive fiber clearer and facilitates both the analytical and numerical analysis. The profile of the dispersed chromatic light pulse could be treated as the superposition of all the dispersed monochromatic light pulses. Another major difference is the Taylor's series of the propagation constant is not truncated as it is in those previous work, which improves the accuracy of the model. Moreover, an approximate model is made which could further reduce the computation tasks in numerical simulations. Performance analysis for accuracy, resolution, speed and noise are conducted through numerical simulations based on the model and the experimental results. The sources of two different errors and their effects on accuracy are discussed respectively. The effects on spectral resolution by the properties of the modulation pulse and the fiber dispersion are studied. The results indicate that by using a rectangle modulation pulse under certain conditions, the resolution can be improved. The speed analysis gives that the spectrum acquisition rate can reach 1 million frames per second when the spectral width is less than 100 nm. In the noise analysis, the erbium-doped fiber amplifier (EDFA) is determined to be the dominant noise source. But by using two EDFAs, the overall signal to noise ratio is improved by 9.2 dB. The preliminary experimental results for FP sensor and FBG sensor signal demodulation are presented. The HSFOS for FP sensor signal demodulation achieves 15 nm resolution. By using the oversampling method, the HSFOS for FBG sensor signal demodulation achieves 0.05 nm spectral positioning resolution.
High Temperature High Bandwidth Fiber Optic Pressure Sensors
Xu, Juncheng (Virginia Tech, 2005-12-15)
Pressure measurements are required in various industrial applications, including extremely harsh environments such as turbine engines, power plants and material-processing systems. Conventional sensors are often difficult to apply due to the high temperatures, highly corrosive agents or electromagnetic interference (EMI) noise that may be present in those environments. Fiber optic pressure sensors have been developed for years and proved themselves successfully in such harsh environments. Especially, diaphragm based fiber optic pressure sensors have been shown to possess advantages of high sensitivity, wide bandwidth, high operation temperature, immunity to EMI, lightweight and long life. Static and dynamic pressure measurements at various locations of a gas turbine engine are highly desirable to improve its operation and reliability. However, the operating environment, in which temperatures may exceed 600 °C and pressures may reach 100 psi (690 kPa) with about 1 psi (6.9kPa) variation, is a great challenge to currently available sensors. To meet these requirements, a novel type of fiber optic engine pressure sensor has been developed. This pressure sensor functions as a diaphragm based extrinsic Fabry-Pérot interferometric sensor. One of the unique features of this sensor is the all silica structure, allowing a much higher operating temperature to be achieved with an extremely low temperature dependence. In addition, the flexible nature of the sensor design such as wide sensitivity selection, and passive or adaptive temperature compensation, makes the sensor suitable for a variety of applications An automatically controlled CO₂ laser-based sensor fabrication system was developed and implemented. Several novel bonding methods were proposed and investigated to improve the sensor mechanical ruggedness and reduce its temperature dependence. An engine sensor testing system was designed and instrumented. The system generates known static and dynamic pressures in a temperature-controlled environment, which was used to calibrate the sensor. Several sensor signal demodulation schemes were used for different testing purposes including a white-light interferometry system, a tunable laser based component test system (CTS), and a self-calibrated interferometric-intensity based (SCIIB) system. All of these sensor systems are immune to light source power fluctuations, which offer high reliability and stability. The fiber optic pressure sensor was tested in a F-109 turbofan engine. The testing results prove the sensor performance and the packaging ruggedization. Preliminary laboratory and field test results have shown great potential to meet not only the needs for reliable and precise pressure measurement of turbine engines but also for any other pressure measurements especially requiring high bandwidth and high temperature capability.
Homodyne scanning holography
Rosen, Joseph; Indebetouw, Guy J.; Brooker, Gary (Optical Society of America, 2006)
We have developed a modified version of a scanning holography microscope in which the Fresnel Zone Plates (FZP) are created by a homodyne rather than a heterodyne interferometer. Therefore, during the scanning the projected pattern on the specimen is frozen rather than varied as previously. In each scanning period the system produces an on-axis Fresnel hologram. The twin image problem is solved by a linear combination of at least three holograms taken with three FZPs with different phase values. (c) 2006 Optical Society of America.
Horizontal-parallax-only electronic holography
Poon, Ting-Chung; Akin, T.; Indebetouw, Guy J.; Kim, Taegeun (Optical Society of America, 2005-04-01)
The principle of optical scanning holography (OSH) is proposed to acquire horizontal-parallax-only (HPO) holographic information electronically. We first briefly summarize the results of OSH and then discuss how HPO-electronic holographic information can be acquired using OSH. Finally we provide simulations to illustrate and clarify the proposed idea. Although many ideas of HPO-holography have been proposed and studied, to the best of our knowledge, this is the first proposed electronic technique to acquire HPO-holographic information. (C) 2005 Optical Society of America.
Image transfer via color-coded projections
Indebetouw, Guy J. (Optical Society of America, 1983-07)
A technique is proposed whereby a 2-D distribution is transmitted via a set of 1-D projections. The color-coded projections are produced by illuminating the object with the dispersed spectrum of a white light source. They are transmitted serially and reconstructed by backprojection.
Imaging with Fresnel zone pupil masks: extended depth of field
Indebetouw, Guy J.; Bai, Hanxian (Optical Society of America, 1984-12)
Fresnel zone plates are used as pupil apertures to extend the depth of field of an incoherent imaging system. The defocused optical transfer function is evaluated approximately, and the results are confirmed by experiments and by subjective evaluations of the images of a test chart. With a pupil having four zones, for example, the resolution limit at four depths of field out of focus is improved by a factor of 10.
Incoherent Bandpass Spatial-Filtering with Longitudinal Periodicity
Poon, Ting-Chung; Indebetouw, Guy J. (Optical Society of America, 1990-09-01)
We explore the possibility of realizing bandpass filtering with longitudinal periodicity in incoherent systems. The necessary condition for spatial filtering to be longitudinally periodic is derived. Results indicate that bandpass filtering with longitudinal periodicity can be achieved in a two-pupil system with Fresnel zone plates with a small opening ratio as the pupils.
Incoherent Spatial-Filtering with A Scanning Heterodyne System
Indebetouw, Guy J.; Poon, Ting-Chung (Optical Society of America, 1984-01-01)
Imaging systems with two pupils in the receiving optics have been used to synthesize bipolar point spread functions in incoherent image processing. We describe a two-pupil system using a scanning illumination technique and compare its attributes with more conventional techniques. Experimental examples using two-pupil interaction and an acoustooptic frequency offset for the direct 2-D bandpass filtering of diffusely reflecting objects are presented.

Browsing by Author "Indebetouw, Guy J."

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