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The objective of this thesis was to explore the usefulness of all-fiber modulators for laser applications. The modulators were all based on refractive index change achieved in the core of the studied fiber- components, exploiting either the elasto-optic effect or the electro-optic effect. This was realized with the aid of electrodes inside the fiber cladding close to the core that provided either thermal stress in the core, or an electric field across the core. The electrodes consisted of low melting-point alloys, such as BiSn and AuSn, which were pushed into the hole-fiber, in the liquid state, which then solidified to form solid electrodes filling the entire hole. Together with an analyzer such as a polarizer or an interferometer the achieved refractive index modulation in the core could then be translated into an amplitude modulation of the guided light, which was subsequently utilized for switching fiber-lasers to generate cavity dumped, Q-switched, or mode-locked pulses. The fast rise/fall-time of a few nanoseconds for the elasto-optic devices was due to the fast thermal expansion of the electrodes. The maximum repetition rate, however, was limited to a few tens of kHz, due to the slow thermal processes for dissipation of the applied energy. The electro-optic fiber components, which displayed similar rise/fall-times on the other hand, showed a much higher cut-off frequency of 16 MHz. The electro-optic, all-fiber switch was also employed to select single pulses at 1 MHz repetition rate out of a 7 MHz train of pulses. Additionally, simulations using the finite element method were performed in order to gain insight and to explain the underlying processes of the observed response of a long-period grating written in a 2-hole fiber with electrodes, when applying HV-pulses to one of these. The thesis shows that the studied fiber-components show great potential of becoming complementary devices with high damage threshold for all-fiber laser applications in the future. / <p>QC 20121129</p>

Optical confinement and manipulation of matter, or optical trapping, is widely adopted at micro-scales as a research tool in disciplines of biology, engineering, and physics. Microfluidic systems arc attractive from the standpoint of low sample volumes, laminar flow, and viscous damping and offer an ideal environment for trapping of miniaturized objects and microorganisms. Various trapping configurations are presented in this thesis using a custom fabricated consumer-grade optofluidic chip and are of significant scientific and practical importance. Microfluidics and fiber optics are integrated in-plane to achieve several flow-dependent particle trapping mechanisms on-chip. Each mechanism results from a combination of fluid drag and optical scattering forces. Parallel and offset fibers, orthogonally oriented to the flow, show cyclic cross-stream particle transit with flow-dependent particle trajectories and loss. Upstream-angled fibers with flow result in circulatory particle trajectories. Asymmetric angled fibers result in continuous particle circulation whereas symmetry with respect to the flow axis enables both stable trapping and circulation modes. Stable trapping of single particles, self-guided multi-particle arrays and stacked particle assemblies are demonstrated with a single upstream-oriented fiber. Size tuning of trapped multiple particle assemblies is also presented. The planar interaction of fluid drag and optical forces results in novel possibilities for cost-effective on-chip diagnostics, mixing, flow rate monitoring, and cell analysis. An opto-hydrodynamic theory is adopted to verify experimentally observed particle array dynamics in a dual-beam fiber-optic trap. When applied to dielectric microsphere particles, the theory confirms the inhomogeneous self-organization and the spontaneous emergence of self-sustained oscillations in particle arrays. In the presence of small-scale symmetry-breaking, self-sustained oscillations are shown to occur spontaneously from an exchange between the optical scattering and the gradient optical forces, in the absence of inertia that is central to the dynamics of ion traps. Experimental results show non-uniform equilibrium particle spacing and spontaneous self-sustained oscillation for large particle numbers. Self-organization and oscillation is of general interest to other systems involving multi-particle optical interactions.

Fiber optic sensors are designed to measure various parameters. The distributed fiber optics sensor has been a very promising candidate for the structural health monitoring. In this thesis, we characterized LEAF (Large Effective Area Fiber) fiber’s Brillouin scattering spectrum and investigated its potentiality for the distributed Brillouin temperature and strain sensor. Optical fibers with complex refractive index profiles are applied to improve the Brillouin threshold by varying the Brillouin linewidth. As LEAF fiber has a modified refractive index profile, we investigated its Brillouin linewidth’s dependence on the square of the pump light’s frequency. We verified the Brillouin frequency’s variation with input SOP experimentally for LEAF fiber in the spontaneous regime. This sets a limitation for the frequency resolution of distributed Brillouin sensors. We also realized a simultaneous temperature and strain sensor with LEAF fiber applying the Brillouin optical time domain analysis. Based on the direct detection of LEAF beat frequencies, a simultaneous strain and temperature sensor was demonstrated.

The objective of the proposed research is to investigate the performance of advanced modulation formats, specifically modified duobinary return-to zero (MD-RZ) modulation scheme and its long-haul repeaterless transmission over standard single mode fiber (SMF). This research also focuses on phase modulation formats like differential phase shift keying (DPSK) and differential quadrature phase shift keying (DQPSK), specifically free spectral range (FSR) optimization and wavelength offset tolerance in direct detection of these phase modulated systems. In this research we present a novel and cost effective technique to generate a modified duobinary return-to-zero (MD-RZ) signal. Next, we attained experimental results for single channel and WDM repeaterless transmission using these MD-RZ signals. A numerical comparison is also drawn with other conventional MD-RZ transmitters. MD-RZ transmission characteristics are also studied numerically for 40 Gb/s WDM signals and compared with other two leading constant intensity phase modulated formats like DPSK and DQPSK. We also have presented experimental results for FSR optimization of DQPSK de-modulator for ultra-high data-rate systems in the presence of strong optical filtering. Choice of an optimal FSR beyond 1-bit delay in Mach-Zehnder delay interferometer (MZ-DI) helps relieving some of the degradations due to strong optical filtering. Wavelength offset tolerance is also experimentally measured and numerically investigated for DPSK and DQPSK modulation formats with different transmitter schemes employing intensity or phase modulators to achieve required phase shifts.

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed March 31, 2008) Includes bibliographical references (p. 33-36).

Thesis (Ph.D.)--Tufts University, 1992. / Submitted to the Dept. of Electrical Engineering. Includes bibliographical references. Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph.D.)--Tufts University, 2001. / Adviser: Chris Davis. Submitted to the Dept. of Electrical Engineering. Includes bibliographical references (leaves 94-101). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (M.S.)--University of Nevada, Reno, 2007. / "May 2007." Includes bibliographical references (leaves 69-70). Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2007]. 1 microfilm reel ; 35 mm.

Thesis (Ph.D.) in Civil Engineering--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 138-145).