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1
Chang, Cheng-Chun. "Coupled-waveguide Fabry-Perot resonator". Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-10062009-020056/.
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Tran, Tuan A. "Extrinsic Fabry-Perot interferometer for surface acoustic wave measurement". Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10242009-020318/.
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3
Neal, Kerry Ann. "A confocal Fabry-Perot interferometer for use in LIDAR receivers". Thesis, Montana State University, 2009. http://etd.lib.montana.edu/etd/2009/neal/NealK1209.pdf.
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A series of crop rotations were evaluated for their impacts on soil-borne populations of root lesion nematodes, Pratylenchus neglectus. Population changes, measured as the ratio of P. neglectus adults counted at harvest to those counted at planting time, was recorded under a series of two-year rotations alternating winter wheat with either fallow, barley, pea, lentil, canola, and camelina. Fallow, barley, pea, and camelina were found to have a neutral effect on nematode populations (p < 0.001). Winter wheat and canola caused significant increases in populations, while lentils caused significant decreases (p < 0.001). Populations were sustained through winter following winter wheat and barley, but not canola, camelina, pea, lentil, or fallow treatments (p < 0.001). In addition to the rotation study, cultivars of barley and canola were evaluated for their resistance to P. neglectus. Greenhouse trials for barley showed significant differences among 19 cultivars tested (p < 0.001), with a 5-fold difference in P. neglectus multiplication separating the least- from the most resistant. Separation among cultivars was not found with canola (p = 0.20). The information gathered in this study will help Montana wheat growers better understand the impacts of their crop selections on this important pest.
4
Dhawan, Rajat R. "The split-cavity cross-coupled extrinsic fiber interferometer". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-12052009-020307/.
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Zeakes, Jason S. "Extrinsic Fabry-Perot Interferometric hydrogen gas sensor". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06162009-063525/.
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Conkey, Andrew P. "Vibration sensors utilizing fiber fabry-perot interferometers and permanent magnets". Thesis, [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-1541.
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Gross, Mason A. "An investigation of nonlinear fabry-perot structures and modulators". Diss., Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/14954.
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Corbett, Kerry. "Modelling and experiments on the behaviour of injection current modulated multimode semiconductor lasers". Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phc7891.pdf.
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Bibliography: p. 215-231. This thesis investigates the behaviour of semiconductor lasers under large amplitude sinusoidal current modulations. It focuses directly on the behaviour of Faby-Perot lasers under direct modulation of the injection current.
9
Bhatia, Vikram. "Signal processing techniques for optical fiber sensors using white light interferometry". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09192009-040440/.
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10
Walmsley, Byron Alan. "Micromechanical investigation of MEMS-based short-wave infrared tunable Fabry-Perot filters". University of Western Australia. School of Mechanical Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0188.
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[Truncated abstract] This study investigates the mechanical and physical properties of low-temperature (100-300 ?C) plasma enhanced chemical vapour deposited (PECVD) silicon nitride (SiNxHy) thin films for the fabrication of short-wave infrared tunable Fabry-Perot filters with high fill factor, high cavity finesse and low actuation voltages. It has been the intensions of this work to fabricate a tunable filter that can be monolithically integrated with temperature-sensitive substrates, namely mercury cadmium telluride (Hg(1-x)CdxTe) photoconductors and photodiodes. A range of methods have been utilised to determine the Young's modulus (E), residual stress ([sigma]0), density ([rho]) and Poisson's ratio ([nu]) of PECVD SiNxHy thin films. In order to understand how E, [sigma]0, [rho] and [nu] are affected by process conditions, a range of SiNxHy thin films deposited with varying chuck temperatures, RF powers and chamber pressures were measured. The resonance method was used to determine E and [nu] of SiNxHy thin films deposited under varying process conditions. The resonance method involves exciting the bending and torsional vibration modes of a microcantilever beam fabricated from a film. The E and G values can be extracted directly from the bending and torsional vibration modes and the [nu] value can be determined from the calculated E and G values. The density of the films was determined using the quartz crystal microbalance method. In order to determine the validity of the resonance method, finite element modelling was used to determine its dependence on microcantilever beam dimensions. ... Increasing the temperature also increases the tensile residual stress of the films. This study also reveals that increasing the RF power and decreasing the chamber pressure increases E and [rho], as well as increasing the compressive residual stress of the films. The theoretical design and analysis, as well as the fabrication of a new surface micromachined short-wave infrared tunable Fabry-Perot filter for adaptive infrared photon detectors is also presented in this study. The proposed structure, termed the suspension filter, uses broad spectral range, high reflectivity distributed Bragg reflector (DBR) mirrors, resulting in very high finesse filters. The device utilises multiple sacrificial layers to define the resonant cavity spacer and the separation of the top mirror from the supporting flexures. The flexures were fabricated from low-temperature (PECVD) SiNxHy thin films. Separation of the top mirror from the supporting flexures allows for improved fill-factors (up to 79%), as well as increased tuning range. Theoretical optical and electromechanical results shows large wavelength tuning ranges (1.5-2.5 [mu]m) at low actuation voltages (<30 V) are possible using the proposed design, whilst still maintaining a high cavity finesse. Optical characterisation of fixed filter micro-cavities on Si substrates show transmissions of ~60% with small line widths (35 nm) are achievable using the proposed mirror system. Mirror displacement versus applied bias voltage curves obtained from a released filter fabricated on Si show a stable mirror displacement of 620 nm was achieved, whilst theoretical results suggested the required 750 nm mirror displacement is possible using the proposed design.
11
Shillig, Tyler. "Multi-point temperature sensing in gas turbines using fiber-based intrinsic Fabry-Perot interferometers". Thesis, Virginia Tech, 2012. http://hdl.handle.net/10919/33612.
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Due to their compact size, sensitivity, and ability to be multiplexed, intrinsic Fabry-Perot interferometers (IFPIs) are excellent candidates for almost any multi-point temperature or strain application, and it is well-known that using a single-mode lead-in fiber, a multi-mode fiber section as the Fabry-Perot cavity, and an additional single-mode fiber as the tail results in a structure that generates strong interference fringes while remaining robust. Though the basic principles behind these sensors are understood, to the best of the authorâ s knowledge there hasnâ t been a thorough investigation into the design and fabrication of a chain of multiplexed IFPI sensors for industrial use in an environment where serious issues associated with the size of the test coupon, sensor placement, and mechanical reinforcement of the fiber could arise. This thesis details the preparation and results of this investigation. It turns out that fabricating a sensor chain with appropriate sensor spacing and excellent temperature response characteristics proved a significant challenge, and issues addressed include inter-sensor interference, high-temperature mechanical reinforcement for bare fiber sections, and high bending losses. After overcoming these problems, a final sensor chain was fabricated and characterized. This chain was then subjected to a battery of tests at the National Energy Technology Laboratory (NETL), where four multiplexed sensors were installed on a 2â x2â coupon in a simulated gas turbine environment. Final results are presented and analyzed. The work that went into developing this chain lays the foundation for future efforts in developing quasi-distributed temperature sensors by identifying potential obstacles and fundamental limitations for certain approaches.Master of Science
12
Gigioli, George William Jr. "Optimization and tolerancing of nonlinear Fabry Perot etalons for optical computing systems". Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184537.
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Since the discovery of optical bistability a considerable amount of research activity has been aimed toward the realization of general-purpose all-optical computers. The basic premise for most of this work is the widely held notion that a reliable optical switch can be fabricated from a piece of optically bistable material. To date only a very small number of published articles have addressed the subject of the engineering issues (that is, the optimization and tolerancing) of these optical switches. This dissertation is a systematic treatment of these issues. From the starting point of Maxwell's equations a simple model of optically bistable Fabry-Perot etalons is outlined, in which the material is assumed to be a pure Kerr medium having linear absorption. This model allows for a relatively straightforward optical switch optimization procedure. The procedure is applicable for optimizing any number of switch parameters. The emphasis in this dissertation is on the optimization of the contrast of the switch's output signals, with the other parameters (switching energy, tolerance sensitivity) assuming a secondary yet critical role. Following the optimization of the optical switch is a tolerance analysis which addresses the manufacturability and noise immunity of the optimized switch. In the first part of this analysis equations describing the propagation of errors through a large scale system of like devices are derived from the truth tables of the switches themselves. From these equations worst case tolerances are established on the optical switch's transfer function parameters. In the second part of the tolerance analysis the bistability model is used to arrive at tolerances on the physical parameters of the switch. These tolerances are what determine the manufacturability of the optical switches. The major conclusion of the dissertation is that, within the range of validity of the model and the other simplifying assumptions, optically bistable Fabry-Perot etalons cannot be used reliably as logic gates in large-scale computing systems.
13
Hansbrough, Andrew K. "Application of a Fabry-Perot interferometer for measuring machining forces in turning operations". Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-02132009-172658/.
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Medhi, Gautam. "Intracavity laser absorption spectroscopy using quantum cascade laser and Fabry-Perot interferometer". Doctoral diss., University of Central Florida, 2011. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/4800.
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Intracavity Laser Absorption Spectroscopy (ICLAS) at IR wavelengths offers an opportunity for spectral sensing of low vapor pressure compounds. We report here an ICLAS system design based on a quantum cascade laser (QCL) at THz (69.9 micrometers]) and IR wavelengths (9.38 and 8.1 micrometers]) with an open external cavity. The sensitivity of such a system is potentially very high due to extraordinarily long effective optical paths that can be achieved in an active cavity. Sensitivity estimation by numerical solution of the laser rate equations for the THz QCL ICLAS system is determined. Experimental development of the external cavity QCL is demonstrated for the two IR wavelengths, as supported by appearance of fine mode structure in the laser spectrum. The 8.1 micrometers] wavelength exhibits a dramatic change in the output spectrum caused by the weak intracavity absorption of acetone. Numerical solution of the laser rate equations yields a sensitivity estimation of acetone partial pressure of 165 mTorr corresponding to ~ 200 ppm. The system is also found sensitive to the humidity in the laboratory air with an absorption coefficient of just 3 x 10[super -7] cm[super -1] indicating a sensitivity of 111 ppm. Reported also is the design of a compact integrated data acquisition and control system. Potential applications include military and commercial sensing for threat compounds such as explosives, chemical gases, biological aerosols, drugs, banned or invasive organisms, bio-medical breath analysis, and terrestrial or planetary atmospheric science.ID: 030646266; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 87-95).
Ph.D.
Doctorate
Physics
Sciences
Physics
15
Ho, Kwongchoi Caisy. "Possibility of positive-pulse switching in systems of nonlinear Fabry-Perot cavities". Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39427.
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The conventional way of using a nonlinear Fabry-Perot cavity as an optical memory requires a negative pulse input to reset the state of the cavity. The possibility of using positive pulses to turn a system of nonlinear Fabry-Perot cavities on and off is studied and it was found that positive pulse switching is possible in a system of two coupled nonlinear cavities.
First, Korpel and Lohmann's proposal of using polarization switching in a single nonlinear birefringent cavity was studied. After a detailed investigation of their proposal it was found that positive pulse switching in a single nonlinear Fabry-Perot cavity is not possible. One of the reasons is that the eigen-polarization states of the output of a nonlinear Fabry-Perot cavity cannot be switched independently. Although it is not possible to switch a single nonlinear Fabry-Perot cavity with positive pulses we were able to use the coupling of the eigen-polarization states to implement other kinds of optical switches which were demonstrated experimentally. The cross-talk effect in a metallic Fabry-Perot cavity was also studied.
Next, a steady state model of a system of two coupled nonlinear Fabry-Perot cavities was developed and it was found that positive pulse switching is possible in such a system. The output can be turned on and off either by pulses sent into different cavities or by pulses of different magnitudes sent into one cavity.
Finally, the dynamic behavior of the coupled cavities system was modeled by extending Goldstone and Garmire's model of a single cavity with one input to a system of two coupled cavities with two inputs. We verified by numerical calculations that positive pulse switching is also possible in the dynamic regime.Ph. D.
16
Forbis, David L. "Optical sensing as a means of monitoring health of multicomputer networks". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-11242009-020318/.
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Wardill, P. "Dynamics of the thermosphere over Mawson, Antarctica /". Title page, contents and abstract only, 1988. http://web4.library.adelaide.edu.au/theses/09PH/09phw265.pdf.
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Malak, Karam Maurine. "A contribution to photonic MEMS : study of optical resonators and interferometers based on all-silicon Bragg reflectors". Phd thesis, Université Paris-Est, 2011. http://tel.archives-ouvertes.fr/tel-00769408.
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This research work has been conducted to introduce a novel class of Fabry-Perot (FP) resonators : curved FP cavity based on coating-free Bragg mirrors of cylindrical shape, obtained by silicon micromachining. Another specificity is the rather large cavity lengths (L>200 µm) combined with high quality factor Q (up to 104), for the purpose of applications requiring cavity enhanced absorption spectroscopy, in which the product Q.L is a figure of merit. In this contest, the basic architecture has been modeled analytically to know the high order transverse modes supported by such cavities. Hence, the experimental conditions which lead to preferential excitation (or rejection) of these modes have been tested experimentally leading to the validation of our theoretical model and to a better understanding of the cavity behaviour. A second architecture, based on the curved FP together with a fiber rod lens has been developed for the purpose of providing stable designs. It was also modeled, fabricated and characterized leading to the expected performance improvements. On another side, a highlight on one of the potential applications that we identified for the curved cavities is presented by inserting the cavity into an electro-mechanical system. It consists of exciting and measuring tiny vibration through opto-mechanical coupling in a MEMS mechanical resonator embedding an FP cavity.Finally, as a complement to our study on resonators, we started exploring applications of optical interferometers based on similar micromachined silicon Bragg mirrors. For this purpose, an optical measurement microsystem was designed, fabricated and characterized ; it consists of an optical probe for surface profilometry in confined environments, based on an all-silicon Michelson interferometer
19
Bhatnagar, Mohit. "Multiplexing of interferometric fiber optic sensors for smart structure applications using spread spectrum techniques". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-12052009-020246/.
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Sanderson, James M. "Epoxy matrix composite strain sensing and cure monitoring". Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-01102009-063758/.
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21
Shen, Fabin. "UV-Induced Intrinsic Fabry-Perot Interferometric Fiber Sensors and Their Multiplexing for Quasi-Distributed Temperature and Strain Sensing". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/28053.
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Distributed temperature and strain sensing is demanded for a wide range of applications including real-time monitoring of industrial processes, health monitoring of civil infrastructures, etc. Optical fiber distributed sensors have attracted tremendous research interests in the past decade to meet the requirements of such applications.
This research presents a multiplexed sensor array for distributed temperature and strain sensing that can multiplex a large number of UV-induced sensors along a single fiber. The objective of this research is to develop a quasi-distributed sensing technology that will greatly increase the multiplexing capacity of a sensor network and can measure temperature and strain with a high accuracy and high resolution.
UV-induced intrinsic Fabry-Perot interferometric (IFPI) optical fiber sensors, which have low reflectance and low power loss, are good candidates for multiplexed sensors networks. Partial reflectors are constructed by irradiating photosensitive fiber with a UV laser beam. A pair of reflectors will form a Fabry-Perot interferometer that can be used for temperature and strain sensing. A sensor fabrication system based on a pulsed excimer laser and a shadow mask is developed.
A spectrum-based measurement system is presented to measure the interference fringes of IFPI sensors. A swept coherent light source is used as the light source. The spectral responses of the IFPI sensors at different wavelengths are measured. A frequency division multiplexing (FDM) scheme is proposed. Multiple sensors with different optical path differences (OPD) have different sub-carrier frequencies in the measured spectrum of the IFPI sensors. The multiplexing capacity of the sensor system and the crosstalk between sensors are analyzed.
Frequency estimation based digital signal processing algorithms are developed to determine the absolute OPDs of the IFPI sensors. Digital filters are used to select individual frequency components and filter out the noise. The frequency and phase of the filtered signal are estimated by means of peak finding and phase linear regression methods. The performance of the signal processing algorithms is analyzed.
Experimental results for temperature and strain measurement are demonstrated. The discrimination of the temperature and strain cross sensitivity is investigated. Experimental results show that UV-induced IFPI sensors in a FDM scheme have good measurement accuracy for temperature and strain sensing and potentially have a large multiplexing capacity.Ph. D.
22
Yiu, H. I. "High latitude thermosphere meso-scale studies and long-term database investigations with the new Scanning Doppler Imager and Fabry-Perot Interferometers". Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1431715/.
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The SCANning Doppler Imager, SCANDI, is a new all-sky development on the network of UCL Fabry Perot Interferometers, FPI, in the Arctic region. It is able to provide high temporal and spatial resolution measurements on the upper atmosphere, in scales of minutes and tens of kilometres. This is a step change from the single look direction provided by a standard FPI. SCANDI’s mechanics, control-software, data analysis and calibration methods are presented. This includes details on techniques that are specific to the instrument’s all-sky capability. The meso-scale data are of particular interest to developments in atmospheric models, which look for increasingly small-scale structures. An ionospheric cusp study utilising SCANDI is able to provide direct neutral measurements at high spatial resolution. It indicates Joule heating is likely to be one of the main sources which contributes to atmospheric cusp density upwelling. The neutral cusp results also complement the CHAMP satellite density data and are able to demonstrate the neutral thermosphere has a considerable meso-scale structure reflecting its response to the cusp dynamics. The temperature variation over the recent solar-cycle in years 1999-2009 is analysed, which covers the extended solar minimum of cycle 23/24. It is also the longest continual period of FPI observation from a single site that has been analysed. The dataset demonstrates that the polar cap neutral temperature is unaffected by the unusually low solar activity, possibly because of high latitude geomagnetic contributions. The difference between measurements and MSIS model results are explored, which demonstrate MSIS unexpectedly over-estimated the neutral temperature by 200 K at this solar maximum. It indicates MSIS is unable to recreate the low temperatures in this unusually weak solar cycle. A new technique was also developed for the study of FPI long term neutral temperature by modelling the red and green-line emission profiles. It is demonstrated that the FPI-measured temperature can be lowered by ∼50K because of variations in the width of the emission height profile and peak altitude. This needs to be considered in long-term temperature trend analysis, especially where looking for trends of as small as a few Kelvin.
23
Joshi, Pratik Prasad. "Ion-neutral coupling in the geomagnetically disturbed mid-latitude ionosphere as observed by SuperDARN HF radars and NATION Fabry-Perot Interferometers". Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/56561.
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The earth's ionosphere-thermosphere region is a coupled environment which is governed by interactions between the overlapping neutral constituents and ionospheric plasma. The mid-latitude thermosphere-ionosphere system is very complex owing to its sensitivity to both the polar and equatorial processes. The mid-latitudes is also a relatively unexplored and less understood region primarily due to the paucity of observing instruments that have traditionally been available. However, the past 9 years of mid-latitude expansion of the Super Dual Auroral Radar Network (SuperDARN) has provided new access to continuous large-scale observations of the sub-auroral ionosphere. On the other hand, the past 3 years of mid-latitude expansion of the North American Thermosphere Ionosphere Observation Network (NATION) Fabry-Perot interferometer array, has created a critical resource for measuring the thermospheric neutral winds. The overlap of these two observing networks in the mid-east North American sector has resulted in a strong ground-based large-scale platform for co-located study of mid-latitude thermosphere-ionosphere dynamics for the first time. The coupling between ions and neutrals is a very important process for controlling the thermospheric dynamics. Ion-neutral coupling at high latitudes has been studied in many previous papers, but there have been very few studies focused on the mid-latitude region. Hence, in this work we have studied the ion-neutral coupling mechanisms and timescales at mid-latitudes during disturbed geomagnetic conditions by using the co-located observations from the SuperDARN-NATION array. The study has focused on the main phase as well as the late recovery phase of a geomagnetic storm which occurred on October 2-3, 2013. Ion drag is known to drive the neutral circulation during the main phase of storm at auroral latitudes, while the neutral wind disturbance dynamo mechanism is known to generate ionospheric electric fields and currents during the recovery phase. By using the methods of ion-neutral momentum exchange theory and time lagged correlation analysis, we analyzed the timescales at which the ion-neutral coupling operates. The ions are observed to drive the neutral winds on a timescale of ~ 84 minutes in the storm main phase which is significantly faster than expected from the driving due to local ion-drag alone (~ 124 minutes). This suggests that along with ion-drag, other local and non-local storm-time influences like Joule heating are also playing an important part in driving the neutral winds. On the other hand, in the late recovery phase, the neutral winds are found to be strongly coupled with the ions and maintain the ion convection without any significant time delay which is consistent with effect of the 'disturbance dynamo' or 'neutral-flywheel' persisting well into the late recovery phase. The timescales and underlying physics understood through this work serve as an important contribution to our knowledge of ion-neutral coupling processes at the middle latitudes. Looking forward, the expansion of co-located SuperDARN-NATION coverage at mid-latitudes, and developments in the tools of large-scale visualization through FPI wind field mapping and SuperDARN convection maps, has created a very strong basis for using the results and analysis tools developed in this work for large-scale ion-neutral coupling characterization in future.Master of Science
24
Dawkins, Samuel T. "Sapphire room temperature optical frequency reference : design, construction and application". University of Western Australia. School of Physics, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0200.
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A pair of high-stability optical frequency references has been developed. The devices are based on room temperature Fabry-Perot cavities with mirrors spaced apart by a hollow single-crystal sapphire element. The sapphire element delivers mechanical sti ness that provides improved immunity to vibrational perturbations compared with the more common spacers made from ultra-low expansion glass. The system is housed in an vacuum chamber designed to provide isolation from environmental perturbations through the use of an active thermal control system, suspension legs and a unique beam alignment system. The dimensional stability of the Fabry-Perot was translated into a highly stable laser frequency by frequency locking a 1064nm Nd:YAG laser to the centre of a mode of the cavity. This frequency lock was implemented by the Pound-Drever-Hall scheme. By careful design, this control system was able to hold the frequency of the laser to within parts in 1016 of the frequency of the fundamental cavity mode. The minimum fractional frequency stability of the laser frequency was measured at 2.1x10[-]14 for integration times of 0.8 s, limited by the residual instability of the Fabry-Perot cavity. The experimental methods used to measure the performance of the system have also been considered in depth. For example, the most common way of characterizing the frequency stability of a frequency standard is the Allan variance. It is demonstrated that, without care, data taken with modern frequency counters can produce erroneous and distorted results when their output is supplied to this algorithm. The method to avoid or account for these errors is also presented. The Fabry-Perot cavity performance is limited on long timescales by residual temperature uctuations, which can be ameliorated in future by enhancing the design of the thermal control system. At short timescales, the system is limited by vibration-induced uctuations together with a white noise source, that is yet to be identi ed, but may relate to fundamental thermodynamic temperature uctuations of the sapphire spacer. This system was used to measure the stability of an optical signal synthesised from a cryogenic microwave sapphire oscillator using an wide-band optical frequency comb. This was the rst demonstration of a multiplication of an ultra-stable signal from the microwave frequency domain into the optical frequency domain, without loss of delity at the level of 2x10[-]14.
25
Conde, Mark. "Spectroscopic observations of the [lambda]630 nm thermospheric emission from Mawson, Antarctica, under daylight, twilight and night-time observing conditions /". Title page, contents and summary only, 1990. http://web4.library.adelaide.edu.au/theses/09PH/09phc745.pdf.
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Meller, Scott A. "Extrinsic Fabry-Perot Interferometer System Using Wavelength Modulated Source". Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36516.
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Interferometric optical fiber sensors have proved many orders of magnitude more sensitive than their electrical counterparts, but they suffer from limitations in signal demodulation caused by phase ambiguity and complex fringe counting when the output phase difference exceeds one fringe period. Various signal demodulation methods have been developed to overcome some of the these drawbacks with limited success. This thesis proposes a new measurement system for the extrinsic Fabry-Perot interferometer (EFPI) sensor. Using a wavelength modulated source and a novel extended-gap EFPI, some of the limitations of interferometric signal demodulation are overcome. By scanning the output wavelength of a multilongitudinal mode laser diode through current modulation, the EFPI sensor signal is scanned through multiple fringes. Gap movement is then unambiguously determined by monitoring the phase of the multiple fringe pattern.Master of Science
27
Hoffman, David Swick. "Confocal Fabry-Perot interferometer based high spectral resolution LIDAR". Diss., Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/hoffman/HoffmanD1212.pdf.
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A high spectral resolution lidar (HSRL), which has been developed at Montana State University, utilizes a confocal Fabry-Perot interferometer (CFP) to separate aerosol and molecular lidar returns for the purpose of atmospheric aerosol observation. The CFP is actively frequency locked to the laser-transmitter via a novel frequency modulation based technique. 532 nm second harmonic light from a frequency doubled Nd:YAG injectionseeded, pulsed laser is directed vertically into the atmosphere. Light backscattered by the atmosphere is collected using a commercial Schmidt-Cassegrain telescope. The secondharmonic return signal is mode matched into a tunable CFP interferometer with a free spectral range of 7.5 GHz and a finesse of 50.7 (312) at 532 nm (1064 nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected by the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to those from a co-located solar radiometer, demonstrating the successful operation of the instrument. The HSRL presented in this dissertation provides an important means to study atmospheric aerosols, which are the largest source of uncertainty in current global climate models. Additionally, the novel frequency locking technique allows for the future development of multi-wavelength HSRL instruments, and the robustness of the frequency locked optical filter allows for the deployment of future air and space based HSRL instruments.
28
Xie, Zhaoxia. "Two applications of the Fabry-Perot interferometric sensor". [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1019.
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Wavering, Thomas A. "Optical Path Length Multiplexing of Optical Fiber Sensors". Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36037.
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Optical fiber sensor multiplexing reduces cost per sensor by designing a system that minimizes the expensive system components (sources, spectrometers, etc.) needed for a set number of sensors. The market for multiplexed optical sensors is growing as fiberoptic sensors are finding application in automated factories, mines, offshore platforms, air, sea, land, and space vehicles, energy distribution systems, medical patient surveillance systems, etc. Optical path length multiplexing (OPLM) is a modification to traditional white-light interferometry techniques to multiplex extrinsic Fabry-Perot interferometers and optical path length two-mode sensors. Additionally, OPLM techniques can be used to design an optical fiber sensor to detect pressure/force/acceleration and temperature simultaneously at a single point. While power losses and operating range restrictions limit the broadscale applicability of OPLM, it provides a way to easily double or quadruple the number of sensors by modifying the demodulation algorithm. The exciting aspect of OPLM is that no additional hardware is needed to multiplex a few sensors. In this way OPLM works with conventional technology and algorithms to drastically increase their efficiency. [1]Master of Science
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Gan, Haiyong. "Electro-optic Polymer Based Fabry-Perot Interferometer Devices for Optoelectronic Applications". Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195839.
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Fabry-Perot interferometer (FPI) devices are designed based on the electro-optic (EO) activities of nonlinear optical (NLO) polymer materials for tunable optical filters (TOFs) and spatial light modulators (SLMs). The performance of the EO polymer based FPI devices is theoretically modeled with first order approximation on the FPI cavity interface phase dispersion. NLO materials including TCBD coupled hybrid sol-gel, AJL8/amorphous polycarbonate (APC), and AJLS102/APC are incorporated in FPI structures with distributed Bragg reflector mirrors and transparent conducting oxide electrodes for TOFs. High finesse (over 200), low drive voltage (10 dB isolation ratio with 5 V), and fast settling time (about sub-millisecond) are achieved. The physical origin of the large tunabilities is explored and the contributions from EO effect and inverse piezoelectric effect are analyzed. EO polymer SWOHF3ME/APC is employed in FPI devices with simplified structures for SLMs. Modulation beyond megahertz level is achieved with constant modulation ratio from DC frequency to high operation speed. The operation speed can be potentially over gigahertz with improved device and drive circuit design. When the EO polymer based SLM is configured to work at near the resonance band of the NLO material, the spectral tunability is increased due to resonance enhanced EO activity and the SLM performance is significantly improved. The EO polymer based FPI devices can be further optimized and are promising candidates for many optoelectronic applications.
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Zhang, Yan. "Miniature fiber-optic multicavity Fabry-Perot interferometric biosensor". Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/30104.
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Fiber-optic Fabry-Perot interferometric (FFPI) sensors have been widely used due to their high sensitivity, ease of fabrication, miniature size, and capability for multiplexing. However, direct measurement of self-assembled thin films, receptor immobilization process or biological reaction is limited in the FFPI technique due to the difficulty of forming Fabry-Perot cavities by the thin film itself. Novel methods are needed to provide an accurate and reliable measurement for monitoring the thin-film growth in the nanometer range and under various conditions.
In this work, two types of fiber-optic multicavity Fabry-Perot interferometric (MFPI) sensors with built-in temperature compensation were designed and fabricated for thin-film measurement, with applications in chemical and biological sensing. Both the tubing-based MFPI sensor and microgap MFPI sensor provide simple, yet high performance solutions for thin-film sensing. The temperature dependence of the sensing cavity is compensated by extracting the temperature information from a second multiplexed cavity. This provides the opportunity to examine the thin-film characteristics under different environment temperatures.
To demonstrate the potential of this structure for practical applications, immunosensors were fabricated and tested using these structures. Self-assembled polyelectrolytes served as a precursor film for immobilization of antibodies to ensure they retain their biological activity. This not only provides a convenient method for protein immobilization but also presents the possibility of increasing the binding capacity and sensitivity by incorporating multilayers of antibodies into polyelectrolyte layers. The steady-state measurement demonstrated the surface concentration and binding ratio of the immunoreaction. Analysis of the kinetic binding profile provided a fast and effective way to measure antigen concentration. Monitoring the immunoreaction between commercially available immunoglobulin G (IgG) and anti-IgG demonstrated the feasibility of using the MFPI sensing system for immunosensing applications.Ph. D.
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Huo, Wei. "Controlled Fabrication System of Fabry-Perot Optical Fiber Sensors". Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/10033.
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The use of optical fiber sensors is increasing widely in industry, civil, medicine, defense and research. Among different categories of these sensors is the Extrinsic Fabry-Perot interferometer (EFPI) sensor which is inherently simple and requires only modest amount of interface electronics. These advantages make it suitable for many practical applications. Investigating a cost-effective, reliable and repeatable method for optical fiber sensor fabrication is challenging work. In this thesis, a system for controlled fabrication of Fabry-Perot optical fiber sensors is developed and presented as the first attempt for the long-term goal of automated EFPI sensor fabrication. The sensor fabrication control system presented here implements a real-time control of a carbon dioxide (CO₂) laser as sensor bonding power, an optical fiber white light interferometric subsystem for real-time monitoring and measurement of the air gap separation in the Fabry-Perot sensor probe, and real-time control of a piezoelectric (PZT) motion subsystem for sensor alignment. The design of optoelectronic hardware and computer software is included. A large number of sensors are fabricated using this system and are tested under high temperature and high pressure. This system as a prototype system shows the potential in automated sensor fabrication.Master of Science
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Vargas-Rodríguez, Everardo. "Optical gas sensors based on correlation spectroscopy using a Fabry-Perot interferometer". Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/50199/.
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In this work we present an analysis of gas sensors based on correlation spectroscopy with a Fabry-Perot interferometer (FPI). In this technique the spectral FPI transmission fringe pattern is matched with ro-vibrational absorption lines. To produce the cross correlation principle the FPI fringe pattern must be shifted along the frequency axis. Hence as the spectral FPI fringes are equidistant and symmetric therefore the ro-vibrational absorption lines of the target molecule must be almost equidistant. Well resolved ro-vibrational lines with Lorentzian line shapes and with almost equidistant spectral separation are characteristics of most diatomic and linear molecules, i.e. CO2, CO, N2O, and some specific absorptions bands of symmetric top and spherical top molecules eg. NH3, CH4 at one atmosphere pressure. In this work we review two general sensor designs, in the first the FPI it is illuminated with a collimated beam and in the second design the FPI it is illuminated by a converging beam. In the collimated beam design all the rays reaching the FPI have the same angle of incidence whilst in converging beam the incident rays have different angles of incidence. Hence the spectral FPI fringe pattern it is affected by the different angles of incidence and therefore it is essential to consider these effects during the evaluation of the sensor response. A novel analytical method based on the Fourier transform which gives a good insight of the gas sensor design based on correlation spectroscopy with a FPI it is presented which we call the convolution method. The method provides a simple way to evaluate much faster the sensor response, and using the Fourier transform characteristics the functions involved in the mathematical model of the sensor response the optimal cavity length of the FPI can be directly determined and it is shown that if the sensor signal will be recovered by a Phase Sensitivity Detector the optimum mirror reflectivity is 0.41 regardless of the other parameters. Moreover using the convolution method the optimal FPI mirror reflectivity can be quickly evaluated. The method also gives us guidance on selecting the best bandpass filter for the application. In this work we also review the effects of the blackbody converging beam and some possible solutions to minimize the effect of the degraded FPI fringe pattern are proposed. In this case it is important to consider the spurious FPI fringe patterns produced by reflection within the mirrors substrates of FPI mirrors. Finally based on all these knowledge we describe a full methodology to simulate the sensor response. It is important to mention that in our methodology we not use 'fitting parameters’ to adjust the simulated results with experimental measurements. Our experimental measurements strongly support the simulated sensor response obtained with our methodology. Therefore the methodology can be applied to design other gas sensors based on cross correlation spectroscopy with a FPI as a modulator. Moreover it is shown that these sensors present an almost negligible sensitivity to molecules other than the target. Finally based on our simulated and experimental results we can conclude that this sensor design configuration is viable to fabricate commercial gas sensors if the FPI and the detector are integrated within a MEMS structure.
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Liu, Quan. "Enhanced Emission of a Single Quantum Emitter Coupled to a Microcavity and a Nanocavity". Thesis, Troyes, 2021. http://www.theses.fr/2021TROY0029.
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Le développement de techniques basées sur une seule molécule au cours des dernières décennies a permis de sélectionner, de suivre et de mesurer directement une molécule individuelle. Dans cette thèse, la dynamique structurelle d'un seul émetteur quantique, servi par l'hypéricine, est caractérisée. En utilisant la microscopie à balayage confocale combinée à des modes laser polarisés radialement / azimutalement, une réorientation tridimensionnelle du moment dipolaire de transition d'une seule molécule est observée. Pour quantifier les propriétés temporelles de la tautomérie, la fonction d'autocorrélation des photons est utilisée pour extraire les fluctuations d'intensité. Les résultats montrent l'influence distincte de l'environnement local, comme la matrice PVA et l'effet de deutération. L'environnement photonique local d'une molécule est modifié par la microcavité / nanocavité. Un changement significatif du taux d'émission radiatif et des spectres de fluorescence est discuté. Il nous permet de mesurer le rendement quantique absolu en utilisant une microcavité accordable. Les résultats montrent la possibilité de contrôler la tautomérisation en modifiant l'environnement photonique. Par la suite, la dissociation moléculaire est discutée par des spectres Raman améliorés en surface à molécule unique bénéficiant de l'amélioration en champ proche de la nanocavité. Une stratégie d'optimisation expérimentale rapide vers une amélioration optimale de la fluorescence est décriteThe development of single molecule-based techniques in the last decades has enabled directly selecting, tracking, and measuring an individual molecule. In this thesis, the structural dynamics of a single quantum emitter, served by hypericin, is characterized. By using confocal scanning microscopy combined with radially/azimuthally polarized laser modes, three-dimensional reorientation of the transition dipole moment of a single molecule is observed. To quantify the temporal properties of the tautomerism, photon autocorrelation function is used to extract the intensity fluctuations. The results show the distinct influence of the local environment, such as PVA matrix and deuteration effect. The local photonic environment of a molecule is modified by the microcavity/nanocavity. A significant change of the radiative emission rate and of the fluorescence spectra is discussed. It allows us to measure the absolute quantum yield by using a tunable microcavity. The results show the possibility of controlling tautomerization by changing the photonic environment. Subsequently, molecular dissociation is discussed by single molecule surface-enhanced Raman spectra profiting from near field enhancement of nanocavity. A fast experimental optimization strategy towards optimal fluorescence enhancement is outlined
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Ivanov, Georgi Pavlov. "Fabry-Perot Sapphire Temperature Sensor for Use in Coal Gasification". Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/32931.
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Sapphire fiber based temperature sensors are exceptional in their ability to operate at temperatures above 1000ºC and as high as 1800ºC. Sapphire fiber technology is emerging and the fiber is available commercially. Sapphire fiber has a high loss, is highly multi-mode and does not have a solid cladding, but it is nonetheless very useful in high temperature applications. Of the available interferometer configurations, Fabry-Perot interferometers are distinguished in their high accuracy and great isolation from sources of error.
In this thesis, improvements are reported to an existing design to enhance its reliability and to reduce possible modes of failure. The existing high temperature sensor design has shown a lot of potential in the past by continuously measuring the temperature in a coal gasifier for 7 months, but its true potential has not yet been realized. The goal of this work and the work of many others is to extend the working life and reliability of high-temperature optical sapphire temperature sensors in harsh environments by exploring a solid cladding for sapphire fiber, improved fringe visibility sapphire wafers and a new sensor design. This project is supported by the National Energy and Technology Laboratory of the Department of Energy.Master of Science
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Choi, Gi-Hyuk. "A study of the variability of dynamics and temperatures near the mesopause from observations of the hydroxyl (OH) Meinel band emissions". Thesis, University College London (University of London), 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244222.
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Lee, Kyung-Woo. "Fiber Fabry-Perot interferometer (FFPI) sensor using vertical cavity surface emitting laser (VCSEL)". Diss., Texas A&M University, 2005. http://hdl.handle.net/1969.1/4221.
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This research represents the first effort to apply vertical cavity surface emitting lasers (VCSELs) to the monitoring of interferometric fiber optic sensors. Modulation of the drive current causes thermal tuning of the laser light frequency. Reflection of this frequency-modulated light from a fiber Fabry-Perot interferometer (FFPI) sensor produces fringe patterns which can be used to measure the optical path difference of the sensor. Spectral characteristics were measured for 850nm VCSELs to determine the combination of dc bias current, modulation current amplitude and modulation frequency for which single mode VCSEL operation and regular fringe patterns are achieved. The response characteristics of FFPI sensors were determined experimentally for square, triangular, saw-tooth waveforms at frequencies from 10kHz to 100kHz. The dependence of VCSEL frequency on the dc bias current was determined from spectral measurements to be ~165GHz/mA. An independent measurement of this quantity based on counting fringes from the FFPI sensor as the laser modulated was in good agreement with this value. The effect of optical feedback into the laser was also studied. By observing the fringe shift as the FFPI sensor was heated, a fractional change in optical length with temperature of 6.95 X 10-6/ðC was determined in good agreement with previous measurements on a 1300nm single mode fiber. The performance of 850nm VCSEL/FFPI systems was compared with their counterparts using 1300nm distributed feedback (DFB) lasers. The results of these experiments show that the 850nm VCSEL/FFPI combination gives regular fringe patterns at much lower bias current and modulating current amplitudes than their 1300nm DFB/FFPI counterparts.
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Cheung, Chi Shing. "An investigation of chirped fibre Bragg gratings Fabry-Perot interferometer for sensing applications". Thesis, Cranfield University, 2005. http://hdl.handle.net/1826/904.
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Fibre interferometer configurations such as the Michelson and Fabry-Perot (FP) have
been formed using uniformed and chirped Fibre Bragg Gratings (FBG) acting as
partial reflectors. As well as increasing the dynamic range of the interferometer,
chirped FBGs are dispersive elements which can allow tuning of the response of the
interferometers to measurements such as strain and temperature. In a chirped FBG,
the resonance condition of the FBG varies along the FBG’s length. Each wavelength
is reflected from different portion of the FBG, which imparts a different group delay
to the different components of the incident light. The implication of the wavelength
dependence resonance position is that there is a large movement of the resonance
position when the incident wavelength is changed. A chirped FBG FP can be
configured in which the large movement of the reflection positions in the respective
FBGs forming the cavity changes in such a way that the sensitivity of the cavity can
be enhanced or reduced. The FP filter response can be tailored through the extent of chirp.
In this project a theoretical model of the in fibre interferometers formed using chirped FBGs is presented. The model indicates that it is possible to form FP cavities with
varying sensitivity to strain and temperature by appropriate choice of chirp parameters and cavity length. An experimental demonstration of a chirped FBG FP cavity with reduced sensitivity to strain. This scheme offers flexibility in determining the
sensitivity of the FP sensor to strain, not only through the gauge length but also via
the parameters of the chirped FBG pairs, allowing the use of long or short gauge
length sensors. It is possible to configure the system to exhibit enhanced sensitivity to strain or alternatively, to have reduced or even zero strain sensitivity. This ability to tailor the sensitivity of the FP via the FBG parameters will enhance the capabilities of FP sensor system.
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Varu, H. S. "The optical modelling and design of Fabry Perot Interferometer sensors for ultrasound detection". Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1447253/.
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The work in this thesis documents the optical modelling and design of Fabry Perot Interferometer (FPI) sensors for the detection of ultrasonic waves. The ultrasonic waves modulate the optical phase of the beam through a change in the cavity spacing of the FPI sensor. The optical sensitivity is defined as the change in the reflected light per unit change in the cavity thickness. An optical model to simulate Interferometer Transfer Functions (ITFs) for a Gaussian beam propagating in a Fabry Perot Interferometer is implemented. An understanding of the Gaussian beam phase propagation in a Fabry Perot Interferometer is presented to help in explaining the shape of ITFs simulated. The model is experimentally validated. The model is applied as a design tool for the purpose of optimising FPI sensors. This is achieved by choosing the beam radii, mirror reflectivities and cavity spacing’s which lead to high optical sensitivity. A FPI sensor with high optical sensitivity and pressure linearity is achieved. A high pressure linearity can be achieved by creating a highly asymmetric ITF, by a combination of a highly diverging beam and aperturing the reflected beam. The understanding presented in this work helps in designing optimised FPI sensors for ultrasound detection, as well as in providing a general understanding of the effects of Gaussian beams or other types of divergent beams illuminating FPIs.
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Aruliah, Anasuya Lohini. "The synoptic variability of thermospheric and meospheric winds observed using a Fabry-Perot interferometer". Thesis, University College London (University of London), 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360048.
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Oh, Ki Dong. "Optical Fiber Fabry-Perot Interferometer based Sensor Instrumentation System for Low Magnetic Field Measurement". Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/29687.
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This dissertation proposes a miniaturized optical fiber based sensor system for the measurement of 3-dimensional vector magnetic fields. The operation of the sensor system is based on the detection of magnetostrictive dimensional changes in the sensor gage using a modified extrinsic Fabry-Perot Interferometer configuration. Because of the magnetostrictive reflector the gap length depends on the magnetic fields applied to the sensor. Since the diameter of the magnetostrictive sensor gage is 125 micrometer which is the same as that of the input/output fiber, the sensor is simply constructed by inserting the sensor gage and the input/output fiber into a small glass tube. The glass tube serves as both an aligner for the sensor gage and input/out fiber, and a passive temperature compensator. In addition, it also enhances the mechanical strength and compactness of the sensor. This sensor design shows 98 percent suppression of the thermally induced sensor output changes. The linear output of the sensor system is enhanced by transverse field annealing which increases magnetostrictive induction in the ferromagnetic sensor gage material and controls the sensor gage geometry. A 5-times increase in sensor sensitivity is obtained with the transverse field annealing and the use of a new magnetostrictive material. A modified sensor gage endface demonstrates 92 percent of fringe visibility, which further improves the performance of the interferometer. The signal fading in the interferometric sensors at the peak or bottom of a fringe is reduced by using a quadrature signal demodulation method. The system has been shown to have a resolution better than 100 nT over a measurement range from 100 to 40,000 nT. This research is supported financially by the Phillips Laboratory of the U.S. Air Force.Ph. D.
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Huang, Zhengyu. "Quasi-Distributed Intrinsic Fabry-Perot Interferometric Fiber Sensor for Temperature and Strain Sensing". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/26247.
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The motivation of this research is to meet the growing demand for the measurand high-resolution, high-spatial resolution, attenuation insensitive and low-cost quasi-distributed temperature and strain sensors that can reliably work under harsh environment or in extended structures. There are two main drives for distributed fiber sensor research. The first is to lower cost-per-sensor so that the fiber sensors may become price-competitive against electrical sensors in order to gain widespread acceptance. The second is to obtain spatial distribution of the measurand.
This dissertation presents detailed research on the design, modeling, analysis, system implementation, sensor fabrication, performance evaluation, sensor field test and noise analysis of a quasi-distributed intrinsic Fabry-Perot interferometric (IFPI) fiber sensor suitable for temperature and strain measurement. For the first time to our knowledge, an IFPI sensor using a different type of fiber spliced in between two single-mode fibers is proposed and tested. The proposed sensor has high measurement accuracy, excellent repeatability, a large working range and a low insertion-loss. It requests no annealing after the sensor is made, and the sensor is calibration-free. The sensor fabrication is low-cost and has a high yield rate. The goal for this research is to bring this sensor to a level where it will become commercially viable for quasi-distributed sensing applications.Ph. D.
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Ma, Cheng. "Modeling and Signal Processing of Low-Finesse Fabry-Perot Interferometric Fiber Optic Sensors". Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/77225.
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This dissertation addresses several theoretical issues in low-finesse fiber optic Fabry-Perot Interferometric (FPI) sensors. The work is divided into two levels: modeling of the sensors, and signal processing based on White-Light-Interferometry (WLI).
In the first chapter, the technical background of the low-finesse FPI sensor is briefly reviewed and the problems to be solved are highlighted.
A model for low finesse Extrinsic FPI (EFPI) is developed in Chapter 2. The theory is experimentally proven using both single-mode and multimode fiber based EFPIs. The fringe visibility and the additional phase in the spectrum are found to be strongly influenced by the optical path difference (OPD), the output spatial power distribution and the working wavelength; however they are not directly related to the light coherence.
In Chapter 3, the Single-Multi-Single-mode Intrinsic FPI (SMS-IFPI) is theoretically and experimentally studied. Reflectivity, cavity refocusing, and the additional phase in the sensor spectrum are modeled. The multiplexing capacity of the sensor is dramatically increased by promoting light refocusing. Similar to EFPIs, wave-front distortion generates an additional phase in the interference spectrogram. The resultant non-constant phase plays an important role in causing abrupt jumps in the demodulated OPD.
WLI-based signal processing of the low-finesse FP sensor is studied in Chapter 4. The lower bounds of the OPD estimation are calculated, the bounds are applied to evaluate OPD demodulation algorithms. Two types of algorithms (TYPE I & II) are studied and compared. The TYPE I estimations suffice if the requirement for resolution is relatively low. TYPE II estimation has dramatically reduced error, however, at the expense of potential demodulation jumps. If the additional phase is reliably dependent on OPD, it can be calibrated to minimize the occurrence of such jumps.
In Chapter 5, the work is summarized and suggestions for future studies are given.Ph. D.
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Zhao, Xin. "Study of Multimode Extrinsic Fabry-Perot Interferometric Fiber Optic Sensor on Biosensing". Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/34534.
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The electrostatic self-assembly (ESA) method presents an effective application in the field of biosensing due to the uniform nanoscale structure. In previous research, a single mode fiber (SMF) sensor system had been investigated for the thin-film measurement due to the high fringe visibility. However, compared with a SMF sensor system, a multimode fiber (MMF) sensor system is lower-cost and has larger sensing area (the fiber core), providing the potential for higher sensing efficiency.
In this thesis, a multimode fiber-optic sensor has been developed based on extrinsic Fabry-Perot interferometry (EFPI) for the measurement of optical thickness in self-assembled thin film layers as well as for the immunosensing test. The sensor was fabricated by connecting a multimode fiber (MMF) and a silica wafer. A Fabry-Perot cavity was formed by the reflections from the two interfaces of the wafer. The negatively charged silica wafer could be used as the substrate for the thin film immobilization scheme. The sensor is incorporated into the white-light interferometric system. By monitoring the optical cavity length increment, the self-assembled thin film thickness was measured; the immunoreaction between immunoglobulin G (IgG) and anti-IgG was investigated.
Master of Science
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Al-Mamun, Mohammad Shah. "Development of a Miniature, Fiber-optic Temperature Compensated Pressure Sensor". Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/71308.
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Since the invention of Laser (in 1960) and low loss optical fiber (in 1966) [1], extensive research in fiber-optic sensing technology has made it a well-defined and matured field [1]. The measurement of physical parameters (such as temperature and pressure) in extremely harsh environment is one of the most intriguing challenges of this field, and is highly valued in the automobile industry, aerospace research, industrial process monitoring, etc. [2]. Although the semiconductor based sensors can operate at around 500oC, sapphire fiber sensors were demonstrated at even higher temperatures [3].
In this research, a novel sensor structure is proposed that can measure both pressure and temperature simultaneously. This work effort consists of design, fabrication, calibration, and laboratory testing of a novel structured temperature compensated pressure sensor. The aim of this research is to demonstrate an accurate temperature measurement, and pressure measurement using a composite Fabry-Perot interferometer. One interferometer measures the temperature and the other accurately measures pressure after temperature compensation using the temperature data from the first sensor.Master of Science
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Han, Ming. "Theoretical and Experimental Study of Low-Finesse Extrinsic Fabry-Perot Interferometric Fiber Optic Sensors". Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27825.
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In this report, detailed and systematic theoretical and experimental study of low-finesse extrinsic Fabry-Perot interferometric (EFPI) fiber optic sensors together with their signal processing methods for white-light systems are presented. The work aims to provide a better understanding of the operational principle of EFPI fiber optic sensors, and is useful and important in the design, optimization, fabrication and application of single mode fiber(SMF) EFPI (SMF-EFPI) and multimode fiber (MMF) EFPI (MMF-EFPI) sensor systems. The cases for SMF-EFPI and MMF-EFPI sensors are separately considered.
In the analysis of SMF-EFPI sensors, the light transmitted in the fiber is approximated by a Gaussian beam and the obtained spectral transfer function of the sensors includes an extra phase shift due to the light coupling in the fiber end-face. This extra phase shift has not been addressed by previous researchers and is of great importance for high accuracy and high resolution signal processing of white-light SMF-EFPI systems. Fringe visibility degradation due to gap-length increase and sensor imperfections is studied. The results indicate that the fringe visibility of a SMF-EFPI sensor is relatively insensitive to the gap-length change and sensor imperfections.
Based on the spectral fringe pattern predicated by the theory of SMF-EFPI sensors, a novel curve fitting signal processing method (Type 1 curve-fitting method) is presented for white-light SMF-EFPI sensor systems. Other spectral domain signal processing methods including the wavelength-tracking, the Type 2-3 curve fitting, Fourier transform, and two-point interrogation methods are reviewed and systematically analyzed. Experiments were carried out to compare the performances of these signal processing methods. The results have shown that the Type 1 curve fitting method achieves high accuracy, high resolution, large dynamic range, and the capability of absolute measurement at the same time, while others either have less resolution, or are not capable of absolute measurement.
% Very different from SMF-EFPI sensors, MMF-EFPI sensors with high fringe visibility usually are more difficult to obtain in practice because the fringe visibility of a MMF-EFPI sensor is much more sensitive to gap-length change and sensor head imperfections. %Previously, only geometric-optics are available to analyze MMF-EFPI sensors which approximate the light in MMF as rays propagating in different directions. Geometric-optics theory has fundenmental limitations because it is approximate and only valid for limited conditions. Moreover, geometric-optics theory is not capable of poviding the exact fringe pattern which is important in the signal processing of white light MMF-EFPI sensor systems. In this report,
Previous mathematical models for MMF-EFPI sensors are all based on geometric optics; therefore their applications have many limitations. In this report, a modal theory is developed that can be used in any situations and is more accurate. The mathematical description of the spectral fringes of MMF-EFPI sensors is obtained by the modal theory. Effect on the fringe visibility of system parameters, including the sensor head structure, the fiber parameters, and the mode power distribution in the MMF of the MMF-EFPI sensors, is analyzed. Experiments were carried out to validate the theory. Fundamental mechanism that causes the degradation of the fringe visibility in MMF-EFPI sensors are revealed. It is shown that, in some situations at which the fringe visibility is important and difficult to achieve, a simple method of launching the light into the MMF-EFPI sensor system from the output of a SMF could be used to improve the fringe visibility and to ease the fabrication difficulties of MMF-EFPI sensors.
Signal processing methods that are well-understood in white-light SMF-EFPI sensor systems may exhibit new aspects when they are applied to white-light MMF-EFPI sensor systems. This report reveals that the variations of mode power distribution (MPD) in the MMF could cause phase variations of the spectral fringes from a MMF-EFPI sensor and introduce measurement errors for a signal processing method in which the phase information is used. This MPD effect on the wavelength-tracking method in white-light MMF-EFPI sensors is theoretically analyzed. The fringe phases changes caused by MPD variations were experimentally observed and thus the MFD effect is validated.Ph. D.
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Liu, Huanhuan. "A novel optical bio-chemical sensor based on hybrid nanostructures of Bowtie nanoantennas and Fabry-Perot Interferometer". Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-01064196.
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Nowadays, the increasing concern for environmental analysis and food quality control, as well as medical needs such as fast diagnosis in case of emergency events, leads to a growing need for new generations of chemical and biological sensors. These devices should have high sensitivity and reliability, perform specific detection of molecules and enable multiple parallel sensing, while being cheap, portable, fast and easy to use. Thus, a general trend tends towards bio-chemical sensors which are on-chip integrated, label-free, and compatible with standard micro-technologies. Photonic dielectric devices based on porous silicon and metallic nanostructures based on plasmon resonances are good candidates to fulfill the above requirements. Porous silicon is a biocompatible material, with a huge specific surface providing a sensitivity enhancement by several orders of magnitude compared to bulk materials; furthermore, its refractive index and thickness can be easily tuned, enabling for the realization of a large variety of photonic designs. Metallic nanostructures provide high confinement and strong field enhancement in sub-wavelength regions, leading to high sensitivities; combined with fluorescence or other sensing mechanisms such as Raman or IR spectroscopy, they have already demonstrated increased sensing potential. The realization of a hybrid device combining both elements would be highly interesting, since it could yield the advantages of both elements, and the photonic structure could shape the plasmonic resonance to develop ultrasensitive devices with narrow resonance linewidth and increased sensing depth. In this context, we realized and studied a novel hybrid photonic / plasmonic device exploiting the coupling between the surface plasmon resonance of a bowtie nano - antenna (NAs) array and the photonic modes of porous silicon (PSi) interferometer. We designed and fabricated a NAs array with resonance wavelength ~ 1.3μm on a homogeneous PSi interferometer. A thin spacing silica layer with controllable density protects the pores of PSi layer and provides a smooth surface for the fabrication of NAs. The coupling mechanisms of two elements - NA array and interferometer, are studied with 2 models, which are interferometer approach and resonator approach. The interferometer approach is focused on studying the influence of NAs array as a homogeneous layer on the fringes shift of the interferometer. For resonator approach, the coupled mode theory is applied. With these models, strong coupling between both elements are discovered: splitting. In the case of viii smaller environment variation, the hybrid device gains 5-10 fold sensitivity enhancement vs. 2 elements alone. The controllable SiO2 layer allows us to sense the index variation within PSi interferometer. This opens a route towards double parallel sensing. The development of the theoretical models under different environment is ongoing, which is expected to utilize the strong coupling for the sensing. A further investigation of the sensing potential of the hybrid device would be expected. And the 2 elements constituting the hybrid structure - the interferometer and the NA array - could be modified in order to enlarge the study to a wider family of devices with greater properties and performances. This work was performed within the framework of the program "Groups of Five Ecoles Centrales" between China Scholarship Council (CSC) and Lyon Institute of Nanotechnologies (INL, CNRS UMR 5270). The project has been supported by the Nanolyon technology platform at INL.
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Fattaccioli, Dominique. "Etudes theoriques sur les interferometres pour la detection des ondes de gravitation". Paris 6, 1987. http://www.theses.fr/1987PA066366.
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D'une part, nous caracterisons la reponse des interferometres de michelson a une onde de gravitation en derivant analytiquement les expressions de leurs fonctions de transfert et de leurs fonctions de green et en explicitant la dependance de celles-ci envers les parametres de l'onde de gravitation, ce travail etant a la base de toute methode d'analyse des donnees d'une grande antenne interferometrique. D'autre part, nous etudions certaines limitations de ces instruments de haute precision que sont les interferometres, dans le but de definir les specifications technologiques des differents elements optiques les constituant qui devront etre satisfaites pour la detection des ondes de gravitation
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Boulanger, Jean-Luc. "Detection interferometrique des ondes de gravitation : dynamique des fabry-perot pendulaires, evaluation des reseaux d'antennes". Paris 6, 1988. http://www.theses.fr/1988PA066099.
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Ce travail comporte deux parties qui s'inscrivent dans le cadre general de la detection interferometrique des ondes de gravitation. Certains detecteurs utilisent des cavites fabry-perot pendulaires dont nous etudions la dynamique dans la 1ere partie. Nous discutons sur le plan theorique et numerique l'effet des retards, dus au temps de propagation de la lumiere entre les deux miroirs. Nous montrons que les cavites utilisees pour les detecteurs d'ondes gravitationnelles presentent generalement des regimes dynamiques instables. Nous presentons quelques resultats experimentaux concernant l'alignement d'une cavite fabry-perot pendulaire au moyen de moteurs magnetiques. Dans la 2eme partie, une methode d'analyse statistique nous permet d'evaluer l'efficacite d'un reseau d'antennes gravitationnelles. Nous donnons une estimation du nombre de signaux gravitationnels detectables par differents reseaux, ainsi que du nombre de signaux detectables en coincidence par plusierus antennes. Nous comparons enfin la directivite des reseaux
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Wang, Xingwei. "Optical Fiber Tip Pressure Sensor". Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/35490.
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Miniature pressure sensors which can endure harsh environments are a highly sought after goal in industrial, medical and research fields. Microelectromechanical systems (MEMS) are the current methods to fabricate such small sensors. However, they suffer from low sensitivity and poor mechanical properties.
To fulfill the need for robust and reliable miniature pressure sensors that can operate under high temperatures, a novel type of optical fiber tip sensor only 125μm in diameter is presented in this thesis. The essential element is a piece of hollow fiber which connects the fiber end and a diaphragm to form a Fabry-Pérot cavity. The all-fused-silica structure fabricated directly on a fiber tip has little temperature dependence and can function very well with high resolution and accuracy at temperatures up to 600ï °C. In addition to its miniature size, its advantages include superior mechanical properties, biocompatibility, immunity to electromagnetic interference, disposability and cost-effective fabrication.
The principle of operation, design analysis, fabrication implementation and performance evaluation of the sensor are discussed in detail in the following chapters.
Master of Science