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As data consumption continues to grow, the backbone of the internet, comprising single mode fiber (SMF)-based infrastructure, is fundamentally limited by nonlinear optical effects. One strategy to address this bottleneck, space division multiplexing (SDM), utilizes multiple modes in a single fiber as independent data channels. Orbital Angular Momentum (OAM) carrying modes, which have twisting phase fronts tracing out helices as the beams propagate, have recently received tremendous attention as a means of achieving low-crosstalk, digital signal processing (DSP)-free transmission with enhanced capacity. Terabit-scale transmission using 4 OAM modes over 1.1km has been demonstrated, but questions remain – how many OAM modes can fibers support, and how stable is propagation over longer lengths? In this thesis, we investigate angular momentum carrying modes in a novel class of fibers featuring an air core. We find that high-order OAM states, although arising in degenerate pairs, counterintuitively resist mode coupling due to OAM conservation, pointing to a unique stability inherent to OAM modes in fibers. We achieve OAM propagation up to 13.4km lengths, and achieve mode purities greater than 15dB at data-center length-scales. We use these fibers to transmit wavelength-division multiplexed data with 25 GHz channel spacing, 10 GBaud rates and quadrature-phase-shift keyed modulation formats in 12 modes simultaneously, over 1.2km, and over a large number of wavelengths across the C-band (1530-1565nm). However, transmission over every mode in every channel of the C-band was prevented by the accidental degeneracy of OAM states with undesired modes. To achieve a larger ensemble of stable modes over a larger wavelength range, we study new fiber designs that avoid this accidental degeneracy problem. We find that the most scalable modal eigenbasis is a set of states that carry non-integer amounts of average OAM, also called spin-orbit coupled modes in analogy with similar effects observed in atomic physics. We demonstrate excitation and transmission of 24 such modes over device lengths (10m). The achievement of a record number of uncoupled modes in fibers confirms the viability of angular momentum states as data carriers, and potential applications include links in data centers, high capacity optical amplifiers, and quantum communications links. / 2017-09-09T00:00:00Z

A colliding pulse mode-locked (CPM) laser achieves sub-picosecond operation by synchronizing two counter-propagating pulse trains to form a standing wave in a thin absorber jet. When properly aligned, these lasers maintain mode-locking for more than 100 seconds (1010 pulses), but eventually cease mode-locking for short periods of time. This thesis examines the characteristics of these transient events, when CPM mode-locking ceases (dropout) and when it resumes (dropin). The dropout is an apparently rapid event, typically lasting no longer than 5 microseconds or less than 500 pulses. The dropin takes significantly longer time, often has structure, and has a clear power dependency. This thesis uses a variety of statistical methods to search for changes in the nonlinear dynamics prior to the apparent power output change of a dropout, but does not find consistent precursors. Moreover, this thesis uses a fluence mapping method to study ultrashort pulse generation process in a novel bistable medium model. The bistable medium model naturally incorporates various high order perturbations and provides a framework for dynamics study and pulse shape control in ultrafast lasers.

This thesis presents both theoretical and experimental studies of a diffractive beam shaping system for ultrashort high-power laser pulses.;A theoretical model is developed to simulate the reshaped intensity profiles for a 100-fs pulse with various energy levels. Both temporal evolution and spatial intensity distribution of the pulse at the target plane of the beam shaping system are calculated. Numerical simulation shows that after passing through the beam shaping system, the pulse front is significantly curved due to the propagation time delay, and the pulse duration time through the target plane is broadened because of the group velocity dispersion. However, for relatively low energy pulses (on the order of millijoules), although the intensity distribution is changed considerably, the fluence top-hat profile is well maintained. This feature extends the application of this beam shaping system into the regime of ultrashort laser pulses. Theoretical calculation also shows the limit when the top-hat profile starts to degrade. For very high-energy laser pulses (>20 mJ per pulse), the homogeneous fluence profile, as well as the intensity distribution, is destroyed due to the non-linear self phase modulation.;This thesis also presents an experimental study of the beam shaping system for ultrashort high-power laser pulses. A terawatt CPA laser amplification system was built in order to verify the theoretical simulation in experiment. The laser amplification system adopts a multi-pass configuration. The output of this CPA amplifier is operating at 30 Hz repetition rate with a pulse energy of 20 mJ/pulse. The compressed pulse duration is 70 fs, resulting in a pulse peak power of 0.3 TW. Experimental results of the beam shaping system with ultrashort laser pulse input agree with the numerical simulation of the reshaped fluence profiles at various energy levels from 6nJ to 20 mJ. The experimental results confirm the validity of this diffractive beam shaping system for ultrashort pulses with a pulse energy on the order of millijoulses. While millijoule pulses are commonly used in the micromachining technology, the adaptability of this diffractive beam shaping system is greatly improved.

Thesis (doctoral)--Friedrich-Wilhelms-Universität zu Berlin, 1870. / Vita.

Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

Diss.--Wittemberg (J.M. Faulhaber, respondent). / At head of title: Q.D.B.V.

<p> Microspherical photonics emerged in recent years in the context of fundamentally new optical properties of structures formed by coupled dielectric microspheres. These include coupling between whispering gallery modes (WGMs), photonic nanojets, nanojet-induced modes, resonant light pressure and optical super-resolution effects. The bottleneck problem in this area is connected with size disorder of individual microspheres which leads to optical losses and degraded performance of coupled devices. </p><p> In this dissertation novel resonant propulsion of dielectric microspheres is studied with the goal of sorting spheres with identical resonances, which are critical for developing microspherical photonics. First, evanescent field couplers were developed by fixing tapered microfibers in mechanically robust platforms. The tapers with ~1 &micro;m waist diameter were obtained by chemical etching techniques. Using these platforms, WGMs modal numbers, coupling regimes and quality factors were determined for various spheres and compared with theory. Second, the spectroscopic properties of photonic molecules formed by spheres sorted by individual characterization with better than 0.05% uniformity of WGM resonances were studied. It was shown that various spatial configurations of coupled-cavities present relatively stable mode splitting patterns in the fiber transmission spectra which can be used as spectral signatures to distinguish such photonic molecules. The third part of the dissertation is devoted to the observation and study of giant resonant propulsion forces exerted on microspheres in the evanescent microfiber couplers. This effect was observed in suspensions of polystyrene spheres with sufficiently large diameters (D > 10 &micro;m). By integrating optical tweezers for individual sphere manipulation, the wavelength detuning between a tunable laser and WGMs in each of the spheres was precisely controlled. Resonant enhancement of optical forces was directly demonstrated in experiments. The spectral shape, position and magnitude of the observed propulsion force peaks were explained by efficient transfer of light momentum to microspheres under resonant conditions. The peak magnitude of the resonant force is shown to approach total absorption limit imposed by the conservation of momentum. The transverse movement of the spheres during the propulsion process was studied and the existence of a stable radial trap was demonstrated. Giant resonant propulsion forces can be used for large-scale sorting of microspheres with ultrahigh uniform resonant properties.</p>

Thesis (Ph.D.)--University of Washington.

Thèse--Paris. / Bibliography: p. [111]-114.