Polarization mode dispersion (PMD) is stochastic in nature and continues evolving in an unpredictable manner according to the changing environment. Nonlinear birefringence in multichannel systems alters the polarization states of the bits, so that they vary from one bit to the next in a way that is difficult to predict. These are the two major signal-impairment effects that are inherent in optical fibre transmission links which can seriously degrade network performance. It is therefore extremely challenging to compensate for both linear and nonlinear birefringence in multichannel systems. The purpose of this thesis is to investigate the interaction between PMD and nonlinear induced birefringence in a fibre with consideration of mode coupling. A sound knowledge of this interaction is necessary in designing a linear and nonlinear polarization mode dispersion compensator for WDM systems, as was successfully carried out in this study. The investigation shows that the effect of nonlinear birefringence alone depolarizes the signal, while in high PMD links where polarization mode coupling is high, the nonlinear birefringence effect couples with second-order PMD such that it may reduce the penalty and improve the signal DOP. Further investigation shows that when nonlinear birefringence becomes significant, asymmetry arises between the two principal axes of the fibre, such that it is only one axis which experiences the effect of nonlinear birefringence. It is found out that along this vii axis, there exists a critical point in pump power where the nonlinear birefringence cancels PMD in the link and improves the signal. An adaptive compensator to cancel PMD and nonlinear birefringence was designed based on feedforward DOP-monitoring signal. The compensator was tested both at laboratory level and on the Telkom buried fibre link and found to be functioning as intended. It was able to adaptively track and compensate PMD in the link in less than a second. The compensator was able to cancel PMD in the link up to a maximum of 30 ps. The compensator improved the DOP of the worst signal by more than 100 percent.

Coherent anti-Stokes Raman scattering microscopy is a versatile technique for label-free imaging and spectroscopy of systems of biophysical interest. Due to the coherent nature of the generated signals, CARS images and spectra can often be difficult to interpret. In this thesis, we document how distortions and enhancements can be produced in CARS hyperspectroscopy as a result of the instrument, geometrical optical effects, or unique molecular states, and discuss how these effects may be suppressed or exploited in various CARS applications.

Nanophotonics is a booming field of research with the promise of chip-scale devices which harness the tremendous potency of light. In this regard, surface plasmons have shown great potential for confining and manipulating light at extreme sub-wavelength scales. Advances in fabrication technology have enabled the scientific community to realize metasurfaces with unconventional properties that push the limits of possible applications of light. This thesis is comprised of computational and experimental studies on plasmonic metasurfaces. The computational study presents efficient design principles for plasmonic half-wave plates using L-shaped nanoantennas. These principles can be used to design waveplates at an operating wavelength of choice and for specific application requirements. The impact of this study goes beyond the efficient design of waveplates: it provides useful insights into the Physics of L-shaped nanoantenna arrays which have been proposed as building blocks for plasmonic metasurfaces. The experimental work investigates the interaction of a plasmonic metasurface, composed of dipole antenna arrays, with an epsilon-near-zero (ENZ) material. This work thus forms a bridge between plasmonics and ENZ materials science, which is a rapidly advancing field in its own right. The first experimental study investigates the exciting unconventional response of plasmonic dipole antennas when placed on a thin indium tin oxide (ITO) film near its ENZ wavelength of 1417 nm. The antenna-on-ITO system has split resonances whose spectral positions are largely independent of the antenna dimensions. The resonance splitting occurs due to coupling between the antenna resonance and the ENZ mode of the ITO film. This coupling results in field intensity enhancements on the order of a 100 in the ITO film. The second experimental study demonstrates, using the z-scan method, that this large field enhancement in the antenna-on-ITO structure further enhances the already strong nonlinearity of ITO around its ENZ wavelength. In particular, the antenna-on-ITO structure exhibits an extremely large nonlinear absorption coefficient, which is two orders of magnitude larger than that of a bare ITO film, and three to five orders of magnitude larger than that of many other nonlinear materials. This thesis thus constitutes a beautiful blend of three thriving areas of research: plasmonics, ENZ materials science and nonlinear optics. The findings reported here have the potential to contribute to all of these fields, and thus have relevance to a broad spectrum of optical scientists.

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Nonlinear optics is the study of interactions of materials with intense light beams made possible by the invention of laser. Arguably the most trivial but technologically most important nonlinear optical effect is the intensity-dependent nonlinear refraction: an intense light beam can temporarily and reversibly change the refractive index of a material. However, the changes to the refractive index of a material due to the presence of a strong laser beam are very weak---maximum on the order of $10^{-3}$---and tend to be a small fraction of the linear refractive index. It must be noted that at optical frequencies vacuum has a refractive index of 1 and glass has a refractive index of 1.5. Thus, one of the foundational assumptions of nonlinear optics is that the nonlinear optical changes to material properties are always a small perturbation to the linear response. In the 58-year history of nonlinear optics, one of the overarching themes of research has been to find ways to increase the efficiency of nonlinear interactions. This thesis is a collection of six manuscripts motivated by our experimental finding that at least in a certain class of materials the above long-standing view of nonlinear optics does not necessarily hold true. We have found that in a material with low refractive index, known as an epsilon-near-zero material or ENZ material, the nonlinear changes to the refractive index can be a few times larger than the linear refractive index, i.e. the nonlinear response becomes the dominant response of the material in the presence of an intense optical beam. We believe that the results presented in this thesis collectively make a convincing case that ENZ materials are a promising platform for nonlinear nano-optics.

Taking inspiration from a variety of creatures found in nature, this thesis demonstrates a new class of materials designed for light capture and guidance. Through the facile method of waveguide self-inscription developed herein, the arrangement of these self-generated light channels can be influenced to produce complex architectures. Inspired by the arrangement of ommatidia found in arthropodal eyes, this was first demonstrated through the fabrication of a radial arrangement of waveguides. This resulted in a thin, polymer film which demonstrated a continuous, panoramic field of view (FOV) able to successfully control the light of a light emitting diode (LED). Moving to more complex architecture, waveguides self-generated in a conical geometry were fabricated. More closely reminiscent of the geometry seen in arthropodal eyes, this waveguide architecture demonstrated a seamless omnidirectional FOV and enhanced imaging capabilities in conjunction with a CMOS camera chip. Lastly, using the method of waveguide self-inscription with an electroactive hydrogel precursor, remote controllable light guiding architectures, as inspired by deep sea creatures, are designed and fabricated. The application of an electric field, in conjunction with the stimuli-responsive waveguides, allows for precise control of the waveguide structures and therefore control over the waveguided light. / Thesis / Doctor of Philosophy (PhD)

archives@tulane.edu / The sharing of quantum resources between multiple parties allows for the creation of quantum networks. Traditional four-wave mixing creates twin correlated beams of light. More complex four-wave mixing schemes can create a multitude of correlated beams for use in quantum communication, helping pave the way toward future quantum networks. These correlations can be seen in the intensity-difference squeezing between output modes. In this dissertation, we examine a variety of multi-mode quantum systems. I begin in chapters 2 and 3 by using the noise figure, which compares the signal-to-noise ratios of output modes to input modes, to calculate intensity-difference squeezing and make predictions about phase-sensitivity. In chapter two, I analyze a dual-pump four-wave mixing system yielding three output modes for cases in which a single seed, two asymmetric seeds, and two symmetric seeds are used. In chapter 3, I perform similar calculations for three different cascaded four-wave mixing configurations. Various intensity-difference squeezing combinations are compared for two variations of two cascaded four-wave mixing cells and for three cascaded four-wave mixing cells. Chapter 4 describes a dual pump four-wave mixing scheme with four output modes created experimentally and chapter 5 shows that when only one input mode is seeded this process is phase-insensitive. Interestingly, I find that when only two of the input modes are seeded the system becomes phase-sensitive. Finally, in chapter 6, I describe the simulated and experimental results of using a deep neural network to improve the bit error rates in a classical free-space optical on-off keying scheme, that will eventually be expanded into the quantum regime. / 1 / Sara K Wyllie

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Laser filamentation is a highly complex and dynamic nonlinear process that is sensitive to many physical parameters. The basic properties that define a filament consist of (i) a narrow, high intensity core that persists for distances much greater than the Rayleigh distance, (ii) a low density plasma channel existing within the filament core, and (iii) a supercontinuum generated over the course of filamentation. However, there remain many questions pertaining to how these basic properties are affected by changes in the conditions in which the filaments are formed; that is the premise of the work presented in this dissertation. To examine the effects of anomalous dispersion and of different multi-photon ionization regimes, filaments were formed in solids with different laser wavelengths. The results provided a better understanding of supercontinuum generation in the anomalous dispersion regime, and of how multi-photon ionization can affect the formation of filaments. Three different experiments were carried out on filamentation in air. The first was an investigation into the effects of geometrical focusing. A simplified theoretical model was derived to determine the transition of filamentation in the linear-focusing and nonlinear- focusing regimes. The second examined the effects of polarization on supercontinuum generation, where a polarization-dependent anomalous spectral broadening phenomenon due to molecular effects was identified. The third involved the characterization of filaments in the ultraviolet. The combination of physical mechanisms responsible for filamentation in the ultraviolet was found to be different from that in the near infrared.