Date of Award
8-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Electrical Engineering
Committee Chair/Advisor
Eric G. Johnson
Committee Member
Judson Ryckman
Committee Member
Richard J. Watkins
Committee Member
Lin Zhu
Abstract
The development and optimization of optical systems will play a pivotal role in the continued exploration and exploitation of the world’s underwater environments. These systems offer advantages in many sectors, and includes applications in areas such as high-speed communication, advanced sensing and imaging, and environmental characterization and monitoring. Underwater environments offer a plethora of challenges, however, and mitigating these obstacles remains an arduous task. In this work, the inherent advantages of structured light are leveraged to optimize optical system performance through non-ideal underwater conditions. Additionally, fundamental relationships between the generation of specified structured modes and their interactions with complex environments are studied, and pertinent environmental information is presented.
An underwater turbulence emulator (UTE) is created to generate stable, repeatable, and reasonable turbulent underwater conditions. The UTE serves as a testbed for all optical propagation experiments described in this work, allowing for the detailed analysis of the interaction between generated structured modes and a dynamic underwater environment. The conditions within the UTE are characterized using optical and thermal methods.
Using a modified Higher Order Bessel Beams Integrated in Time (HOBBIT) system, reliant on an acousto-optic deflector (AOD) and coordinate transform log-polar optics, a probe and control system is demonstrated to exploit optical channels within a turbulent underwater environment. The exploitation of the channels increases system performance in both received optical power and the ability to support a high-speed optical communication link. Further, the system successfully exploits channels in a turbid and turbulent environment. The ability to exploit multiple channels simultaneously is demonstrated, providing relevant information about the density and distribution of the channels within the turbulent environment.
In an effort to experimentally realize unperturbed propagation through a turbulent volume, non-diffracting beams are rapidly generated and manipulated using the HOBBIT generation architecture. Experimental generation of arbitrary non-diffracting modes is shown through the alteration of the angular spectrum around a perfect vortex envelope. Leveraging this rapid and customizable generation method, a circular volume of underwater turbulence is probed with off-axis Bessel-Gauss (BG) beams. Due to the speed of the probing system, instantaneous realizations of the turbulence are scanned, and optimal propagation paths are determined in which the input beam closely matches the output beam, indicating relatively unperturbed transmission through the turbulent volume. It is demonstrated that the beams within these optimal channels are less affected by the turbulence than beams outside of these paths, including reduced levels of beam wander and scintillation comparatively. Within the probed volume of underwater turbulence, the prevalence and persistence of these channels is determined, proving key insights for further exploitation of the environment. The propensity for simultaneous propagation through multiple unperturbed channels is verified through the application of superposition.
Utilizing a non-diffracting beam basis, a rapid probing system determines the OAM content of an underwater turbulent environment through frequency filtering and interferometry techniques. A complex amplitude function around a perfect vortex (PV) envelope is determined. By constraining the power measurement to the on-axis portion of the Fourier transformed field at the exit of the turbulent environment, this turbulence-dependent angular spectrum represents a matched filter of the complex media. The OAM mode spectrum is determined for each angular spectrum measured, allowing insight into the OAM content of the turbulence. Consecutive scans are conducted over a time interval such that the temporal characteristics of the OAM induced by the turbulence can be studied. The results indicate an OAM spectrum that evolves in time as the environment changes, with the average OAM around the PV fluctuating as well.
Recommended Citation
Wiley, Jaxon P., "A Study on the Propagation and Exploitation of Structured Light in Underwater Turbulence" (2025). All Dissertations. 3975.
https://open.clemson.edu/all_dissertations/3975