Mode modulation accelerometer

An analysis to determine the mode loss in a heavily damped multimode optical fiber subjected to forced and controlled vibrations was performed. The results of the analysis concluded that an optical fiber could be used to sense acceleration. The experimental configuration was modeled as a heavily damped large diameter rigid fiber element that .was modified in the number of guided modes that it was capable of supporting via the introduction of microbends. The mode loss was detected as a modulation of optical power propagating through the fiber. The measured RMS voltage was compared to the results of an analytical model that predicted the mode loss. The analysis was performed on four different fiber configurations: (1) a 40.48 mm unweighted fiber, (2) a 40.48 mm weighted fiber, (3) a 91.28 mm unweighted fiber, and (4) a 91.28 mm weighted fiber. The data for the 40.48 mm unweighted fiber configuration was in greatest agreement with the theory. The remaining experimental configurations exhibited harmonic oscillations as determined by FFT analysis and thus showed propagation results that were not always in agreement with the model. It was determined that the unweighted 40.48 mm fiber provides valid acceleration measurements between 30 Hz and 540 Hz with an acceleration range of .58 g to 5.01 g