Applications of Brillouin Dynamic Grating to Distributed Fiber Sensors

In the process of stimulated Brillouin scattering (SBS), acoustic waves are generated by the interference of counter-propagating optical waves via electrostriction effect. These acoustic waves not only stimulate the Brillouin scattering process, but can also play a role of moving Bragg reflector for another optical wave when a proper phase-matching condition is satisfied between the interacting optical waves. Brillouin dynamic grating (BDG) represents this secondary role of the acoustic wave, which shows a unique reflection spectrum, called BDG spectrum. The BDG spectrum generally shows higher sensitivity to the change of physical variables, such as temperature and strain than ordinary Brillouin gain spectrum (BGS), and also provides information on the waveguide parameters, such as polarization or modal birefringence with high accuracy. This paper reviews the operation principle of BDG under various conditions and the research progresses on its application to distributed fiber sensors.