Motion Synchronization of Multiple Piezoelectric Actuators (PEAS) Using the Linear Active Disturbance Rejection Controller (LADRC)

This thesis investigates how the Linear Active Disturbance Rejection Controller (LADRC) can be used with the synchronous strategy for motion synchronization of multiple piezoelectric actuators (PEAs). Both a single PEA system and a three PEA system are used to validate the control system. The investigation consists of a brief introduction of the LADRC, system identication of a single PEA and three PEA system, parameter estimation of the LADRC, implementation of the LADRC for a single PEA and for a three PEA system with the synchronization strategy, a comparison between the LADRC using the synchronization strategy and Linear Quadratic Gaussian (LQG) using the synchronization strategy. The investigation demonstrated that the synchronized LADRC is a viable and simple control solution for the three PEA system, used to control the gap spacing between the mirrors of the Fabry - Perot Spectrometer own by SDCNLab in stratospheric balloon missions

Fourierdomänen modengekoppelte Laser: Aufklärung der Funktionsweise und Erschließung neuer Anwendungsbereiche

Mit der Fourierdomänen Modenkopplung (FDML) wurde vor kurzem ein neuer Operationsmodus für sehr schnell in der Wellenlänge abstimmbare Laser entdeckt, bei dem ein schmalbandiger Spektralfilter resonant zur Lichtumlaufzeit im Resonator abgestimmt wird. Diese FDML-Laser, deren genaue Funktionsweise noch unverstanden ist, gehören zu den schnellsten weit abstimmbaren Lichtquellen und eignen sich besonders für die optische Kohärenztomografie (OCT), die ein junges dreidimensionales Bildgebungsverfahren darstellt. In dieser Arbeit wurden zwei Ziele parallel verfolgt. Zum einen sollten durch Optimierungen und Erweiterungen des Lasers neue Anwendungsmöglichkeiten insbesondere in der OCT ermöglicht, gleichzeitig aber auch neue Erkenntnisse über die genaue Funktionsweise der Fourierdomänen Modenkopplung auf physikalischer Ebene gewonnen werden. In dem eher anwendungsorientierten Teil dieser Arbeit wurde zunächst eine neue Methode entwickelt, mit der es in der OCT mit schnell abstimmbaren Lasern möglich ist, zweidimensionale Schnitte bei einer bestimmten Tiefe, sogenannte en face Schnitte, ohne aufwändige Computerberechnung zu erhalten. Während diese Schnitte bisher nur sehr rechenintensiv durch Nachbearbeitung und Extraktion aus einem vollständig aufgenommenen dreidimensionalen Datensatz gewonnen werden konnten, lassen diese sich nun um ein Vielfaches schneller aufnehmen und darstellen. Weiterhin wurde durch den Eigenbau eines auf Abstimmgeschwindigkeit optimierten Spektralfilters die Aufnahmegeschwindigkeit eines mit einem FDML-Laser betriebenen OCT-Systems um über eine Größenordnung erhöht, so dass dieses nun mit Abstand zu den schnellsten Systemen gehört. Obwohl bei diesen hohen Geschwindigkeiten das Signal-Rausch-Verhältnis durch Schrotrauschen bereits limitiert wird, konnten Aufnahmen sehr hoher Qualität erzeugt werden, was a priori nicht selbstverständlich war. Im Grundlagenteil dieser Arbeit wurde das Verständnis der Operationsweise der Fourierdomänen Modenkopplung erweitert. Da FDML-Laser vollständig aus Glasfaserkomponenten aufgebaut sind und Längen von mehreren Kilometern aufweisen, wurde der Einfluss der Faserdispersion auf sowohl Linienbreite und Rauschverhalten untersucht. Mit einer speziellen dispersionskompensierten Resonatorgeometrie konnte dabei ein einfaches Modell des Einflusses der Dispersion auf die Kohärenzlänge validiert und eine deutliche Erhöhung dieser erreicht werden. Ein umfassenderes Modell der Operationsweise von FDML-Lasern ist wünschenswert, um experimentell schwer zugängliche Fragestellungen beantworten zu können. Auf dem Weg dahin müssen zunächst alle physikalischen Effekte im Resonator, welche zur Lasertätigkeit beitragen, aufgeklärt werden. Hierzu wurde die zeitabhängige Leistung eines FDML-Lasers durch verschiedene Terme in der nichtlinearen Schrödingergleichung modelliert, numerisch ausgewertet und mit experimentellen Daten verglichen. Dadurch konnten wichtige an der Laseroperation beteiligte Prozesse aufgeklärt und eine Basis für weitergehende Simulationen geschaffen werden

TiSapphire frequency combs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2011.Cataloged from PDF version of thesis. Vita.Includes bibliographical references (p. 179-186).Femtosecond mode-locked lasers are a unique laser technology due to their broad optical bandwidth and potential for linking the optical and radio frequency domains when these lasers are configured as frequency combs. Ti:Sapphire based mode-locked lasers offer considerable advantages over other laser systems by generating both the broadest optical spectrum and highest fundamental pulse repetition rates directly from the laser cavity. Recent advances in laser diode technology have reduced the cost of pump lasers for Ti:Sapphire based frequency combs considerably, and the recent demonstration of direct diode pumping of a narrowband mode-locked Ti:Sapphire laser suggests that Ti:Sapphire frequency combs may finally be ready to make the transition from an indispensible research tool to a wider set of industrial applications. In this thesis, several applications and fundamental properties of Ti:Sapphire based mode-locked lasers are investigated. To enable more widespread use of Ti:Sapphire based frequency combs, a frequency comb based on an octave spanning 1 GHz Ti:Sapphire laser is demonstrated. The I GHz Ti:Sapphire laser is referenced to a methane stabilized HeNe laser, resulting in a frequency comb with a fractional frequency stability of its optical spectrum of 2x1 0-14 on a 20 second timescale. A recently identified frequency comb application is the calibration of astronomical spectrographs to enable detection of Earth-like planets which are orbiting Sun-like stars. In support of this application, a second frequency comb system was constructed which ultimately was characterized by a 51 GHz pulse repetition rate and 12 nm bandwidth centered at 410 nm. This "astro-comb" system was deployed to the Fred Lawrence Whipple Observatory where preliminary results indicate a 40-fold increase in the spectrograph stability due to calibration by the astro-comb. Finally, the stability of the optical pulse train emitted from femtosecond mode-locked lasers is expected to exhibit the lowest phase noise of any oscillator, with theoretical predictions of phase noise levels below -190 dBc for offset frequencies exceeding 1 kHz. A comparison between the pulse trains of two nearly identical mode-locked lasers resulted in a measured timing error of less than 13 attoseconds measured over the entire Nyquist bandwidth.by Andrew John Benedick.Ph.D

An Assessment of Ground-Based Techniques for Detecting Other Planetary Systems. Volume 2: Position papers

The capabilities of several astronomical interferomenter system concepts are assessed and the effects of the Earth's atmosphere on astrometric precision are examined in detail. Included is an examination of the use of small aperture interferometry to detect planets in binary star systems. It is estimated that, for differential astrometric observation, an amplitude interferometer having two separate telescopes should permit observations of stars as faint as 14th magnitude and a positional accuracy of 0.00005 arc-sec. Instrumental, atmospheric, and photon noise errors that apply to interferometric observation are examined. It is suggested that the effects of atmospheric turbulence may be eliminated with the use of two color refractometer systems. Several sites for future telescopes dedicated to the search for planetary systems are identified

2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

This is the final version. Available on open access from IOP Publishing via the DOI in this recordData availability statement: The data that support the findings of this study are available upon reasonable request from the authors.Photonic technologies offer numerous functionalities that can be used to realize astrophotonic instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large Telescope in Chile that combines the light-gathering power of four 8 m telescopes through a complex photonic interferometer. Fully integrated astrophotonic devices stand to offer critical advantages for instrument development, including extreme miniaturization when operating at the diffraction-limit, as well as integration, superior thermal and mechanical stabilization owing to the small footprint, and high replicability offering significant cost savings. Numerous astrophotonic technologies have been developed to address shortcomings of conventional instruments to date, including for example the development of photonic lanterns to convert from multimode inputs to single mode outputs, complex aperiodic fiber Bragg gratings to filter OH emission from the atmosphere, complex beam combiners to enable long baseline interferometry with for example, ESO Gravity, and laser frequency combs for high precision spectral calibration of spectrometers. Despite these successes, the facility implementation of photonic solutions in astronomical instrumentation is currently limited because of (1) low throughputs from coupling to fibers, coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient integration of photonics with detectors, to name a few. In this roadmap, we identify 24 key areas that need further development. We outline the challenges and advances needed across those areas covering design tools, simulation capabilities, fabrication processes, the need for entirely new components, integration and hybridization and the characterization of devices. To realize these advances the astrophotonics community will have to work cooperatively with industrial partners who have more advanced manufacturing capabilities. With the advances described herein, multi-functional integrated instruments will be realized leading to novel observing capabilities for both ground and space based platforms, enabling new scientific studies and discoveries.National Science Foundation (NSF)NAS

Investigation into Smart Multifunctional Optical System-On-A-Chip Sensor Platform and Its Applications in Optical Wireless Sensor Networks

Wireless sensor networks (WSNs) have been widely used in various applications to acquire distributed information through cooperative efforts of sensor nodes. Most of the sensor nodes used in WSNs are based on mechanical or electrical sensing mechanisms, which are susceptible to electromagnetic interference (EMI) and can hardly be used in harsh environments. Although these disadvantages of conventional sensor nodes can be overcome by employing optical sensing methods, traditional optical systems are usually bulky and expensive, which can hardly be implemented in WSNs. Recently, the emerging technologies of silicon photonics and photonic crystal promise a solution of integrating a complete optical system through a complementary metal-oxide-semiconductor (CMOS) process. However, such an integration still remains a challenge. The overall objective of this dissertation work is to develop a smart multifunctional optical system-on-a-chip (SOC) sensor platform capable of both phase modulation and wavelength tuningfor heterogeneous sensing, and implement this platform in a sensor node to achieve an optical WSN for various applications, including those in harsh environments. The contributions of this dissertation work are summarized as follows. i)A smart multifunctional optical SOC sensor platform for heterogeneous sensing has beendeveloped for the first time. This platform can be used to perform phase modulation and demodulation in a low coherence interferometric configuration or wavelength tuning in a spectrum sensing configuration.The multifunctional optical sensor platform is developed through hybrid integration of a light source, an optical modulator, and multiple photodetectors. As the key component of the SOC platform, two types of modulators, namely, the opto-mechanical and electro-optical modulators, are investigated. For the first time, interrogating different types of heterogeneous sensors, including various Fabry-Perot (FP) sensors and fiber Bragg grating (FBG) sensors, with a single SOC sensor platform, is demonstrated. ii)Enhanced understanding of the principles of the multifunctional optical platform withanopto-mechanical modulator has been achieved.As a representative of opto-mechanical modulators, a microelectromechanical systems (MEMS) based FP tunable filter is thoroughly investigated through mechanical and optical modeling. The FP tunable filter is studied for both phase modulation and wavelength tuning, and design guidelines are developed based on the modeling and parametric studies. It is found that the MEMS tunable filter can achieve a large modulation depth, but it suffers from a trade-off between modulation depth and speed. iii) A novel silicon electro-optical modulator based on microring structures for optical phase modulation and wavelength tuning has been designed. To overcome the limitations of the opto-mechanical modulators including low modulation speed and mechanical instability, a CMOS compatible high speed electro-optical silicon modulator is designed, which combines microring and photonic crystal structures for phase modulation in interferometric sensors and makes use of two cascaded microrings for wavelength tuning in sensors that require spectrum domain signal processing. iv)A novel optical SOC WSN node has been developed. The optical SOC sensor platform and the associated electric circuit are integrated with a conventional WSN module to achieve an optical WSN node, enabling optical WSNs for various applications. v) A novel cross-axial dual-cavity FP sensor has been developed for simultaneous pressure and temperature sensing.Across-axial sensor is useful in measuring static pressures without picking up dynamic pressures in the presence of surface flows. The dual-cavity sensing structure is used for both temperature and pressure measurements without the need for another temperature sensor for temperature drift compensation. This sensor can be used in moderate to high temperature environments, which demonstrates the potential of using the optical WSN sensor node in a harsh environment

The 1992 NASA Langley Measurement Technology Conference: Measurement Technology for Aerospace Applications in High-Temperature Environments

An intensive 2-day conference to discuss the current status of measurement technology in the areas of temperature/heat flux, stress/strain, pressure, and flowfield diagnostics for high temperature aerospace applications was held at Langley Research Center, Hampton, Virginia, on April 22 and 23, 1993. Complete texts of the papers presented at the Conference are included in these proceedings

Nonlinear mechanics and nonlinear material properties in micromechanical resonators

Microelectromechanical Systems are ubiquitous in modern technology, with applications ranging from accelerometers in smartphones to ultra-high precision motion stages used for atomically-precise positioning. With the appropriate selection of materials and device design, MEMS resonators with ultra-high quality factors can be fabricated at minimal cost. As the sizes of such resonators decrease, however, their mechanical, electrical, and material properties can no longer be treated as linear, as can be done for larger-scale devices. Unfortunately, adding nonlinear effects to a system changes its dynamics from exactly-solvable to only solvable in specific cases, if at all. Despite (and because of) these added complications, nonlinear effects open up an entirely new world of behaviors that can be measured or taken advantage of to create even more advanced technologies. In our resonators, oscillations are induced and measured using aluminum nitride transducers. I used this mechanism for several separate highly-sensitive experiments. In the first, I demonstrate the incredible sensitivity of these resonators by actuating a mechanical resonant mode using only the force generated by the radiation pressure of a laser at room temperature. In the following three experiments, which use similar mechanisms, I demonstrate information transfer and force measurements by taking advantage of the nonlinear behavior of the resonators. When nonlinear resonators are strongly driven, they exhibit sum and difference frequency generation, in which a large carrier signal can be mixed with a much smaller modulation to produce signals at sum and difference frequencies of the two signals. These sum and difference signals are used to detect information encoded in the modulation signal using optical radiation pressure and acoustic pressure waves. Finally, in my experiments, I probe the nonlinear nature of the piezoelectric material rather than take advantage of the nonlinear resonator behavior. The relative sizes of the linear and nonlinear portions of the piezoelectric constant can be determined because the force applied to the resonator by a transducer is independent of the dielectric constant. This method allowed me to quantify the nonlinear constants