In the literatures of investigating the coupling mechanism between laser diodes and fibers, Gaussian beam profile was used to describe the propagation of laser beams. But the real laser diode beams exist astigmatism. In order to understand the distributions of real laser diode beams, we used single-mode fiber interferometer to measure the near-field intensity and phase distributions of laser diodes. The nanometer aperture of taper fiber was used to scan through the horizontal and vertical directions across the maximal intensity point of the planes which were perpendicular to propagation axis to measure the intensity and phase distributions of laser diodes. In the measurement of phase distributions, these two single-mode fibers produced interference fringes through accepting laser beams. When the taper fiber scanned the optical field and the reference fiber kept a fixed distance from a laser diode for a stationary phase, the interference fringes shifted because of the phase difference of laser diodes change. In the measurement, in order to improve the stability of interference fringes and consider the aperture of taper fiber, we altered some experiment frameworks. There were four types of experimental framework. According to the experiment results of the near-field measurements, the measured beam widths along the horizontal and vertical directions at the laser diode facet were 4.11 £gm and 1.57 £gm respectively. The measured wavefront radius curvature were 6.59 £gm and 2.96 £gm in horizontal axis and vertical axis respectively. After Gaussian beam fitting, the beam widths along the horizontal and vertical directions at the laser diode facet were 4.04 £gm and 0.83 £gm respectively. The difference in beam widths between measured values and Gaussian fitting were 0.07 £gm and 0.74 £gm. The measured beam widths and the Gaussian beam curve fitting had similar results. We could see that the beam spread tendency in the z-axis for the laser beam which propagated in the z direction. In the phase distribution measurement, the measured wavefront radius curvatures and the theoretically calculated Gaussian beam values had a slight difference. The calculated wavefront radius curvatures at the laser diode facet were 11921.51 £gm and 3.48 £gm in horizontal axis and vertical axis respectively. They were 1809 times and 1.2 times of the measured values. The aperture of taper fiber was expanded because of the energy of laser beams, which also caused the spatial resolution degeneration. Moreover, the wavefront radius curvature in horizontal direction was biggish so the measurement framework also limited the ability of the phase distribution measurement. The above points were the reasons to cause the error of the phase distribution measurement. Furthermore, the measurement of the laser diode facet is under investigation.

The objective of this thesis was to develop applications of monolithic fiber devices and actively controlled fibers. A special twin-core fiber known as a ‘Gemini’ fiber was used to construct equal arm-length fiber interferometers, impervious to temperature and mechanical perturbations. A broadband add/drop multiplexer was constructed by inscribing fiber Bragg gratings in the arms of a Gemini Mach-Zehnder interferometer. A broadband interferometric nanosecond switch was constructed from a micro-structured Gemini fiber with incorporated metal electrodes. Additionally, a Michelson fiber interferometer was built from an asymmetric twin-core fiber and used as a high-temperature sensor. While the device could be readily used to measure temperatures below 300 °C, an annealing process was required to extend the range up to 700 °C. The work included development, construction and evaluation of the components along with numerical simulations to estimate their behaviors and to understand the underlying processes. The thesis also explored the use of electrically controlled fibers for filtering in the microwave domain. An ultra-narrow phase-shifted fiber Bragg grating inscribed in a fiber with internal electrodes was used as a scanning filter to measure modulation frequencies applied to an optical carrier. A similar grating was used inside a dual-wavelength fiber laser cavity, to generated tunable microwave beat frequencies. The studied monolithic fiber interferometers and actively controlled fibers provide excellent building blocks in such varied field as in microwave photonics, telecommunications, sensors, and high-speed switching, and will allow for further applications in the future. / Syftet med denna avhandling var att utveckla tillämpningar av monolitiska fiber komponenter samt aktivt kontrollerbara fiber. En speciell tvillingkärnefiber, även kallad ’Geminifiber’ användes för att konstruera fiber interferometrar med identisk armlängd som ej påverkas av termiska och mekaniska variationer. En bredbanding utbytarmultiplexor konstruerades genom att skriva in fiber Bragg gitter inuti grenarna på en Gemini Mach-Zehnder interferometer. Geminifibrer med interna metallelektroder användes för att konstruera en bredbandig nanosekundsnabb interferometrisk fiberomkopplare. Därtill användes en tvillingkärnefiber som en hög-temperatursensor. Även om komponenten direkt kan användas upp till 300 °C, måste den värmebehandlas för att kunna användas upp till 700 °C. Arbetet har innefattat utveckling, konstruktion och utvärdering av komponenterna parallellt med numeriska simuleringar för att analysera deras beteenden samt få insikt om de underliggande fysikaliska processerna. Avhandlingen behandlar även tillämpningar av en elektriskt styrbar fiber för att filtrera radiofrekvenser. Ett ultrasmalt fasskiftat fiber Bragg gitter skrevs in i en fiber med interna elektroder och användes som ett svepande filter för att mäta modulationsfrekvensen på en optisk bärfrekvens. Ett liknande gitter användes inuti en laserkavitet för att generera två olika våglängder samtidigt. Dessa två våglängder användes sedan för att generera en svävningsfrekvens i mikrovågsbandet. De undersökta monolitiska fiberinterferometrarna och de aktivt styrbara fibrerna erbjuder en utmärkt byggsten inom så pass skiljda områden som Mikrovågsfotonik, Telekommunikation, Sensorer samt Höghastighets-omkopplare och bör kunna användas inom många olika tillämpningar i framtiden. / <p>QC 20130226</p>

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This diploma thesis solves possibilities of utilization optical fiber as sensor. At the beginning, basic division of this sensors is desribed, their principles and usage. Then the thesis is focused on distributed sensors based on the interference of the light, interferometers. This optic fiber interferometers are described, mainly their modifications for detection and localization of vibrations along optical fiber. Significant part of the thesis deals with dual Mach--Zehnder interferometer. This interferometer is theoreticaly desribed and simulated in Matlab. Further the thesis deals with development of two aplication in Matlab software. One application is for simulation and theoretical computation of dual Mach--Zehnder interferometer. Second application serves for signal processing of acquired data that are measured on this interferometer. At the end of the thesis, dual Mach--Zehnder interferometer is designed and build in laboratory enviroment and executed measurement and localization of vibrations using this interferometer.