Development of the distributed Brillouin sensor with high spatial and frequency resolution

This thesis includes studies of improving the performance of the distributed fiber optic sensor based on Brillouin scattering, especially focusing on spatial resolution and frequency resolution.;High spatial and frequency resolution Brillouin sensor with phase locking technique has been studied. A theoretical model dealing with laser source phase locking has been derived. Simulation and experimental results have been used to prove the ability of improving the spatial and frequency resolution with phase locking technique.;Improving the spatial and frequency resolution with different pulse pair technique has been explored. This technique can obtain high spatial resolution (<1m) and high frequency resolution (<35MHz linewidth) simultaneously along several kilometer long sensing fiber, which is a promising candidate in the field of structure health monitoring. The ultimate measurement accuracy with different pulse pair Brillouin optical time domain analysis technique has been investigated and it is determined by the combination of the system bandwidth, system signal-to-noise ratio, absolute pulse width, pulse width difference, and the rise/fall time of the pulse.;A Brillouin optical time domain analysis sensor based on optical differential parametric amplification technique has been proposed and realized to obtain high spatial and frequency resolution at the same time without increasing the measurement time. Anew theoretical model dealing with optical differential parametric amplification technique has been derived. An experiment is successfully realized to validate the proposal in a polarization maintaining fiber with a spatial resolution of 0.5 m and a strain accuracy of 6 muepsilon.;A novel distributed Brillouin sensor based on offset locking of two distributed feedback lasers has been developed. With offset locking technique, the beat frequency of two lasers can not only be locked together but also be tuned over a wide range of more than 1GHz. Moreover, a lock-in amplifier has been applied to lock the bias drift of the electro optic modulator, which ensures the probe pulse stability and constant signal-to-noise ratio during the sensing measurement. With the offset locking based distributed Brillouin sensor, a 1m spatial resolution and 0.5°C temperature resolution has been achieved.