| For over two decades, researchers have applied optical fiber technology to the field of oceanic acoustic sensing. Initially, most fiber-optic-based acoustic sensor array designs focused on the use of Mach-Zehnder-type interferometers as the acoustic sensors. The use of the Sagnac-interferometer for acoustic sensing has been demonstrated successfully in the context of single acoustic sensors, but not in the context of arrays which scale efficiently to high sensor counts.; In this dissertation, we present our efforts to develop large-scale fiber-optic-based acoustic sensor arrays based on the Sagnac-interferometer. We propose a novel design which enables a single Sagnac interferometer to support a large number of sensors, and we provide a detailed analysis of the performance of such an array. Many improvements to this basic design are proposed and demonstrated. The culmination of this design research is an array which has amongst its advantages a passively desensitized Sagnac loop (delay coil), a passive elimination of polarization-induced signal fading on all sensors, and an ability to create multiple outputs with arbitrary bias points. A full-scale demonstration of a 16-sensor Sagnac-based array with distributed erbium-doped fiber amplifiers in the array telemetry is described, providing experimental verification of the operation principle of the array as well as the optical noise theory. Additionally, an analysis of the dynamic range of interferometric sensor arrays (both Mach-Zehnder and Sagnac) is presented, and the dynamic range performance of the two types of arrays is compared for both military and ocean floor mapping applications. The results indicate that, for the military applications, the dynamic range performance of the Sagnac array is significantly better than that of the Mach-Zehnder array. |
