Multiphoton polymerization (MPP) as one of the direct laser writing techniques is capable of manufacturing three-dimensional (3D) micro-structures with complex shapes and novel functionalities. However, current MPP methods rely on point-by-point or layer-by-layer scanning and therefore are time-consuming. The low fabrication throughput of conventional MPP is the key factor that limits its wider adoption for industrial manufacturing over large surface area. One way to increase the fabrication speed is to turn layer-by-layer process into a volumetric process. An ideal volumetric printing method can fabricate structures with complex 3D geometry by single exposure and should be easy to implement. As a step towards this goal, this dissertation discusses a volumetric fabrication method based on 3D structured light fields. I will discuss the application of zero-order Bessel beams for rapid fabrication of various high-aspect-ratio structures such as polymer fibers and scaffolds. Next, I demonstrate the generation of superposed high-order Bessel beams using a spatial light modulator (SLM). Such beams have multiple foci with long depth of focus and are suitable for parallel fabrication of high-aspect-ratio structures. Furthermore, I investigate optical aberration observed when Bessel beams propagate through tilted interfaces. A method is introduced in which a single phase map on an SLM is used to generate an "elliptical axicon" that compensates for such aberration. Finally, I develop the theory of "helical beams", whose transverse intensity distribution rotates while propagating along the optical axis. Both transverse and longitudinal shape of such beams are tunable. These beams are generated as a superposition of high-order Bessel modes and have a closed-form expression relating the design of the phase mask to the rotation rate of the beam. I demonstrate rapid fabrication of helical microstructures with tunable shape in polymer by single exposure using these beams. This volumetric fabrication technique increases the throughput by orders of magnitude compared to conventional MPP, paving the way for adopting MPP in many industrial applications. The presented technique should have potential applications in other fields such as laser processing of bulk semiconductor/dielectric with increased throughput.

This dissertation focuses on the structural transformations in photo-thermo-refractive (PTR) glass that enable recording phase holograms for efficient transformation of optical beams and high resolution spectroscopy. PTR glass is a multicomponent silicate matrix doped with Ce, Ag, Sn and Sb. It is a holographic phase medium with the ability of permanent refractive index change after UV exposure and thermal development above 500°C due to the precipitation of a NaF crystalline phase. Electronic processes are studied by analyzing the structure of absorption and luminescence bands of PTR glass matrix and its dopants. We analyze the structural transformations in PTR glass from the perspective of induced optical scattering. A high-sensitivity experimental setup for measuring scattering at 90° with respect to a 1-mm diameter probe beam at 405 nm was constructed. A specific algorithm of UV exposures and thermal regimes to reveal the lowest temperature at which inhomogeneities arise was proposed. It was shown that no scattering increase observed in UV exposed PTR glass after thermal processing at temperatures below 450°C. This means that all structural transformations produced by this treatment occurred at atomic scale. Finally, we discuss the low temperature ion exchange method. We describe the theoretical basis of this method and present an experimental layout capable of performing low-temperature ion exchange in the surface of PTR samples. Results of a system that provides measurements of surface refractive index called 'the waveguide method' is presented. It is shown how this system can be used for the characterization of planar optical waveguides created on the surface of PTR glass samples and how their refractive index profile can be calculated by the inverse Wentzel-Kramers-Brillouin (WKB) method.

Lithium niobate has numerous extraordinary features that make it useful for a wide range of applications, particularly in optics. The material's strong electro-optic effect and second-order nonlinearities are two prime examples with applications in optical modulation and wavelength conversion, respectively. The thin-film lithium niobate platform has revitalized the conventional applications of lithium niobate during the last decade. The platform is now one of the most actively investigated subdisciplines in integrated photonics. The waveguides on this innovative platform are high index contrast, resulting in a size reduction of more than 20 times and a bending radius decrease of about two orders of magnitude when compared to traditional counterparts. These ultracompact waveguides facilitate the realization of highly efficient photonic devices, some of which are presented in this work. First, tunable dual-channel integrated Bragg filters with ultra-narrow linewidths are demonstrated. These filters have potential applications in optical communication, sensing, and quantum optics. Next, high-speed Mach-Zehnder electro-optic modulators with an extrapolated 3-dB bandwidth of 170 GHz and low half-wave voltage-length product of 3.3 V.cm are presented. Furthermore, microwave-to-optical converters with integrated antennas and optical waveguides are demonstrated with improved efficiency compared to the currently existing devices for integrated microwave photonics applications. Afterward, fabricated periodically-poled lithium niobate devices are utilized to illustrate nonlinear wavelength translators through cascaded sum- and difference-frequency generations. Finally, further works on these research topics, which are appropriate for future research, are discussed.

Electromagnetic waves carry information in multiple degrees of freedom, such as amplitude, phase, polarization, coherence, etc. When light encounters physical matter, its properties generally fluctuate in the spatial or the temporal domain. If the structure of matter is complex, these fluctuations may appear random at first glance. However, information about the light-matter interaction can still be recovered from such noise-like signals under certain conditions. Optical sensing or imaging tasks of different approaches can be taken depending on the specific physical problem. In this dissertation, we provide original solutions to several sensing problems based on measurements of intensity fluctuations. First, we will discuss how temporal intensity fluctuations can be used to infer the structural evolution of dynamic scattering media. Then, we will introduce a new and efficient experimental approach for retrieving this dynamic information from complex media in a geometry-independent manner and across a broad range of scattering regimes. In addition, using the process of protein polymerization/depolymerization as an example, we will demonstrate how temporal fluctuations of scattered light can be used to quantify the dynamics of a thermal hysteresis process. The second part of the thesis will discuss the characteristics of intensity fluctuations in both spatial and temporal domains. We will theoretically propose and experimentally demonstrate the statistical nonstationarity of intensity fluctuations in strong scattering media where the mechanisms of recurrent scattering and the near field coupling compete. Furthermore, we will present an experimental procedure for simultaneously assessing the mechanical and optical properties of complex media experiencing structural phase transitions.

Advances in integrated photonic devices require low loss, easy-to-integrate solutions for chip-to-chip and chip-to-fiber interfacing. Among the most common solutions are traditional lenses. However, circular lenses require additional mounting mechanisms to ensure proper alignment. Additionally, the beam routing functionality cannot be added to the traditional lenses unless they are combined with mirrors and operate in the reflection mode. In this dissertation, we investigate lens-embedded photonic crystals (LEPCs) as a solution to flat and multifunctional lenses. The concept is demonstrated by creating self-collimating lattices containing a gradient refractive index lens (GRIN-LEPC), a binary-shaped lens (B-LEPC), and a Fresnel-type binary-shaped lens (F-B-LEPC). The devices are fabricated in a photopolymer by multi-photon lithography with the lattice spacing chosen for operation around the telecom wavelength of 1550 nm. Both the experimentally observed optical behaviors and simulations show that the device behaves like a thin lens, even though the device is considerably thick. The thickness of a B-LEPC was reduced threefold by wrapping phase in the style of a Fresnel lens. Embedding a faster-varying phase profile enables tighter focusing, and NA = 0.59 was demonstrated experimentally. Furthermore, we demonstrate experimentally that a Fresnel lens can also be combined into a bender, so one PC performs both bending and focusing functions, further reducing the footprint of the PC devices. We also explored a hexagonal lattice and demonstrated wide-angle and broad-band self-collimation. The PCs are fabricated using the same material and method as that of the LEPCs. Optical characterization shows that the device strongly self-collimates light at near-infrared wavelengths that span from 1360 nm to 1610 nm. Self-collimation forces light to flow along the extrusion-direction of the lattice without diffractive spreading, even when light couples into the device at high oblique angles. Numerical simulations corroborate the experimental findings.

No description available.

Liquid crystals (LCs) are self-assembled soft materials composed of certain anisotropic molecules with orientational orders. Their widespread applications include information displays and photonic devices, such as spatial light modulators for laser beam steering and tunable-focus lens, where achieving desired LC alignment is pivotal. In general, LC alignment is influenced by several factors, including chemical bonding, dipolar interactions, van der Waals interactions, surface topographies, and steric factors. Here, we focus on three alignment techniques for aligning rod-like LC molecules and highlights the photonic devices enabled by these techniques: 1) Two-photon polymerization direct-laser writing-induced alignment, 2) Weigert effect-based reversible photoalignment, and 3) electric field-assisted alignment in polymer-dispersed liquid crystal (PDLC) systems. With the help of advanced two-photon polymerization systems, nano-grooves with arbitrary orientations can be easily created on a variety of surfaces. The geometric topography helps align the LC molecules parallel to the groove direction. Alignment on a planar surface, on a curvilinear surface, and even in the bulk can be realized. Based on the patterning ability, three photonic devices are highlighted: a switchable geometric phase microlens array, a tunable compound microlens array, and a polarization-independent phase modulator. For Weigert effect-based reversible photoalignment, how to achieve space-variant linear polarization field is crucial. Here, two approaches are investigated: the direct projection method and the counter-propagating wave interference exposure method. Using the direct projection method, an LC Dammann grating with pixelized binary phase profile is achieved. Such a method relies on a spatial light modulator and is convenient for creating pixelized alignment that has abrupt changes from pixel to pixel. On the other hand, the interference exposure method can generate continuously and smoothly changing LC alignment. By such a method, two miniature high-quality microlens arrays are fabricated and further assembled into a planar telescope. Further characterizations reveal the high optical quality of the fabricated devices, which not only ensures their adoption in practical applications, but proves the powerful planar alignment patterning capability of the photoalignment materials. For a traditional PDLC system, the LC alignment is random from droplet to droplet, and the operation voltage of the active PDLC is too high to be employed in practical applications. Here, we establish a method to perfectly align LC droplets in a PDLC system and use it as a passive film. The well-aligned passive PDLCs exhibit polarization- and angle-dependent light scattering that can be engineered through composition tuning. Two kinds of selective scattering films are demonstrated: The first kind scatters obliquely incident light but is highly transparent for normally incident light, and the second kind scatters normally incident light but is more transparent for obliquely incident light.

Propagation of electromagnetic radiation through atmospheric turbulence has been a subject of study for over eight decades. With ever expanding applications of lasers, more attention has been paid recently to the interaction between atmospheric turbulence and laser beams propagating over greater and greater distances. For applications in communication, directed energy weapons and wireless power transmission the focused laser beam geometry is of particular interest. To increase understanding of the interaction between atmospheric turbulence and propagating laser beams a series of field campaigns were designed and conducted. These field campaigns provided a focused beam configuration propagated over different ranges and at different intensities of atmospheric turbulence. Collimated laser data was also collected to corroborate the findings. These field campaigns generated temperature spectral data that did not agree with existing temperature spectral models near the ground. Given the relationship between temperature spectral models and refractive index, a previously unexplored refractive index spectral model is examined. The unexplored refractive index spectral model provides a better fit to experimental temperature spectral data. Existing second order weak and strong fluctuation theory is modified to accommodate a novel refractive index spectral model. The results from the modified second order weak and strong fluctuation theory are compared to field campaign laser data and to split step wave optics simulations.

Many of the features of photonic devices, including some of the most ubiquitous components such as resonators and waveguides, are usually thought to be intrinsically dependent on their geometry and constitutive materials. As such, the behaviour of an optical field interacting with such devices is dictated by the boundary conditions imposed upon the field. For instance, the resonant wavelengths and linewidths of a planar cavity are expected to be set by the mirrors' reflectivity, cavity length, and refractive index. Henceforth, satisfying a longitudinal phase-matching condition allows for incident light to resonate with the cavity. As another example, consider the planar waveguide; the field is confined along one transverse dimension, but diffracts along the other unbounded dimension. We have recently introduced several strategies for challenging these long-held intuitions that may be collected under the moniker 'space-time (ST) photonics', whereby the response of a photonic device is tailored post-fabrication in useful ways by sculpting the spatio-temporal structure of the incident optical field. In fact, introducing a prescribed relationship between the spatial frequencies and the temporal frequencies can help overcome the constraints imposed by the boundary conditions. We refer to such pulsed beam configurations as ST wave packets. In one scenario, introducing carefully designed angular dispersion into a pulsed field allows the realization of omni-resonance: the pulse traverses the cavity without spectral filtering even if the pulse bandwidth is larger than the cavity resonant linewidth after the entire bandwidth resonates with it. A similar strategy enables a new class of planar waveguide modes we refer to as 'hybrid guided ST modes' where the field is confined along the unbounded dimension through ST coupling. Crucially, the spatio-temporal structure introduced into the field along the unbounded dimension enables overturning the impact of the boundary conditions along the other dimension. For example, the modal size, index, and dispersion can all be engineered independently of the thickness and refractive index of the planar waveguide; i.e., the impact of the boundary conditions is overturned.

No description available.