Development of a dynamic strain distributed fiber optic sensor

In the 1990's, most of the research in the area of distributed fiber optic sensing focused on increasing the overall sensing length and improving spatial resolution. For applications like civil structural monitoring and aerospace vehicle sensing, current centimeter resolutions and kilometer ranges yield much useful information but lack the acquisition speed to produce dynamic strain. The time it takes to make a typical measurement using current Brillouin technology is several minutes and hence the results are instantaneous but not instantly available, rendering them not useful for dynamic measurements.; This thesis provides a method for reducing the measurement time, while at the same time maintaining the range characteristics of previous studies. The testing procedure entails covering the entire strain profile of the fiber in one measurement by sending multiple equally spaced wavelengths in the form of a frequency domain comb over a short time interval. This was accomplished by carefully controlling the signal bandwidth, pulse width and using coherent heterodyne detection for the first time for a two laser Brillouin sensing system.; The Mathematical formulation and simulation model of Brillouin interaction was first developed in Matlab. Temperature and Strain experiments were performed using the direct detection stepped frequency Brillouin Optical Time Domain Analysis (BOTDA) sensor system as well as the new Coherent Parallel Receiver (CPR) configuration. The CPR results showed the expected sinusoidal strain profile for a 12 s periodic strain cycle. The strain distribution for the entire fiber was obtained in 128 mus, thereby demonstrating for first time the potential to measure dynamic strains up to 3.9 kHz.