Date of Award
Doctor of Philosophy (PhD)
School of Materials Science and Engineering
Over half a century ago, the paper entitled “Absence of Diffusion in Certain Random Lattices” was published by P. Anderson and described a metal-to-insulator transition phenomenon where electron diffusion does not occur in disordered semiconductors. This phenomenon is now commonly referred to as “Anderson localization” (AL). Since the AL detailed in Anderson’s paper arose from the wave nature of electrons, similar behavior should be observed in other wave systems, more specifically in optics.
Given the utility of optical fibers, extensive theoretical treatment has been conducted on transverse Anderson localization (TAL, disorder in x- and y-directions, with the z-direction remaining invariant) in such systems. Only recently has it been experimentally observed, paving the way for studies into the influence of fiber material on linear and nonlinear TAL. This Dissertation represents the first materials study of doped silicate transverse Anderson localizing optical fibers (TALOFs) and their corresponding passive and active optical properties.
More specifically, Chapter I reviews microstructured and multicore optical fiber, and methods of their fabrication, in order to develop an understanding of the impact of the core microstructure on waveguide properties. Then, an overview of TALOFs is developed to provide insights into the different materials and fabrication methods used to develop the few TALOFs reported to date. The former fiber systems are well studied; therefore, this research Dissertation will be focused on the novel effects and material influences on the latter (Anderson) systems.
Chapter II begins the development of these novel fibers through in situ phase separation in optical fibers drawn using the molten core method (MCM). Limitations in the resulting fibers were studied, and adaptations to the fabrication method were made to elongate the already formed microphases through development and subsequent use of a two-tier MCM.
Chapter III introduces an alternative fiber fabrication technique, namely the stack-and-draw method, specifically adapted to utilize MCM-derived precursor fibers in the stack. The resulting fibers are characterized to understand the effects of processing on the core microstructure, and ultimately to understand how the core microstructure leads to TAL.
Chapters IV and V investigate the material properties and potential applications of the TALOFs that resulted from the fabrication technique developed in Chapter III. Specifically, Chapter IV investigates both Yb3+ and Er3+ doped TALOFs for solid-state lasing and amplification respectively. The resulting experimental observations and present limitations of these fibers for active applications are discussed.
In Chapter V, the first nonlinear optical TALOFs are explored. Even though the higher refractive index phases possessed an estimated nonlinear refractive index (n2) similar to silica, small modal effective areas were demonstrated due to the strong localization in certain regions of these TALOFs. As a result, nonlinear optical frequency shifts were demonstrated for the first time in a TALOF, attributed to Raman and four-wave mixing (FWM), concomitantly. While not decisive into the underlying nature of TAL in the presence of optical nonlinearities, this suggests that the two are not mutually exclusive.
Finally, Chapter VI summarizes the findings of this Dissertation, discusses the challenges with further fiber development in these TALOFs, and provides examples for future efforts in improving both the fibers themselves, and ultimately the understanding of these fibers.
Tuggle, Matthew Artus, "Material Properties of Anderson Localizing Optical Fiber" (2020). All Dissertations. 2584.