Kim Yong Hyun, Song Kwang Yong
Department of Physics, Chung-Ang University, Seoul 06974, Korea.
Sensors (Basel). 2021 Mar 19;21(6):2168. doi: 10.3390/s21062168.
Brillouin scattering is a dominant inelastic scattering observed in optical fibers, where the energy and momentum transfer between photons and acoustic phonons takes place. Narrowband reflection (or gain and loss) spectra appear in the spontaneous (or stimulated) Brillouin scattering, and their linear dependence of the spectral shift on ambient temperature and strain variations is the operation principle of distributed Brillouin sensors, which have been developed for several decades. In few-mode optical fibers (FMF's) where higher-order spatial modes are guided in addition to the fundamental mode, two different optical modes can be coupled by the process of stimulated Brillouin scattering (SBS), as observed in the phenomena called intermodal SBS (two photons + one acoustic phonon) and intermodal Brillouin dynamic grating (four photons + one acoustic phonon; BDG). These intermodal scattering processes show unique reflection (or gain and loss) spectra depending on the spatial mode structure of FMF, which are useful not only for the direct measurement of polarization and modal birefringence in the fiber, but also for the measurement of environmental variables like strain, temperature, and pressure affecting the birefringence. In this paper, we present a technical review on recent development of distributed Brillouin sensors on the platform of FMF's.
布里渊散射是光纤中一种主要的非弹性散射，其中光子与声子之间会发生能量和动量转移。在自发（或受激）布里渊散射中会出现窄带反射（或增益和损耗）光谱，其光谱频移对环境温度和应变变化的线性依赖性是分布式布里渊传感器的工作原理，这种传感器已经发展了几十年。在少模光纤（FMF）中，除了基模外还会传导高阶空间模式，两种不同的光学模式可以通过受激布里渊散射（SBS）过程耦合，如在称为模间SBS（两个光子 + 一个声子）和模间布里渊动态光栅（四个光子 + 一个声子；BDG）的现象中所观察到的。这些模间散射过程根据FMF的空间模式结构显示出独特的反射（或增益和损耗）光谱，这不仅有助于直接测量光纤中的偏振和模式双折射，还可用于测量影响双折射的应变、温度和压力等环境变量。在本文中，我们对基于FMF平台的分布式布里渊传感器的最新进展进行技术综述。
