Dissertation Title: “VOLUME BRAGG GRATINGS WITH COMPLEX PHASE STRUCTURES A three-dimensional foundation for laser-beam shaping”
The Bragg diffraction is a natural phenomenon that arises from the coherent interference of scattered waves in multilayered structures with a well-defined periodicity. In practice, the physical size of these multilayered structures varies greatly depending on the intended application, from micrometer-thick dielectric mirrors with tens of layers to centimeter-long Bragg gratings with tens of thousands of layers. The scope of this work centers around a unique class of multilayered elements developed in bulk photo-thermo-refractive (PTR) glass – the volume Bragg grating (VBG). The content of this thesis places an emphasis on the volume nature of these Bragg devices, implying a three-dimensional structure whereupon arbitrary spatial phase information can be embedded for laser beam shaping, or the distribution of Bragg periods across each element is instead engineered to yield diffracted light with distinct spatio-temporal properties.
In Chapter 1, operating principles, and fabrication technique of a conventional VBG are introduced. Owning to the principles of Bragg diffraction, the desired spatial and/or spectral phase information can be encoded onto the interference of scattered waves, reflecting from different sections along a grating volume. In Chapter 2, this principle is implemented in the form of phase-shifted volume Bragg gratings, whereby desired phase information is holographically engineered into the relative shift between neighboring Bragg substructures. Unlike other known active or passive phase-shaping tools, these phase-shifted elements can reconstruct the encoded phase profiles over a broad range of wavelengths that meet the Bragg condition of the VBG. On the other hand, the chirped volume Bragg grating, identified by a unique variation in grating periods across its volume, presents an alternative mean upon which phase information can be encoded – i.e., the Bragg-period distribution. Gratings of this kind are addressed in detail through Chapter 3. Due to the adaptability of holographic technique employed for the fabrication of volume gratings, a new class of Bragg elements is explored, capable of inscribing phase information into both (1) the relative shift between local Bragg elements, and (2) the Bragg-period variation across the grating volume. Chapter 4 reports on the construction of these hybrid structures, referred to as the phase-shifted, chirped volume Bragg gratings. Their unique ability to double as distributed feedback lasers, when recorded into the optically active volume of doped PTR glass, is discussed, paving the way for a novel source of light – the chirped distributed feedback laser.
BS: 2016, Engineering Physics, Colorado School of Mines
MS: 2020, Optics and Photonics, University of Central Florida
Committee in Charge:
Ivan B. Divliansky Chair
Leonid B. Glebov Co-chair
Peter J. Delfyett
Kyu Young Han
Arkadiy Lyakh External
Approved for distribution by Ivan B. Divliansky, Committee Chair, on April 28th, 2022.
The public is welcome to attend.