Study On Brillouin Scattering In Micro-scaled Optical Fibers And Its Application On Refratlve Index Sensing

Brillouin scattering in optical fibers is a non-linear effect introduced by the interaction between acoustic field and optical field.By analyzing Brillouin spectrum characteristics,temperature,strain,vibration and other parameters can be measured accordingly.Distributed sensing can be realized through the relationship between time and space,so it has great advantages in the field of structural health monitoring.However,in conventional sensors,single-mode optical fibers are used as sensing media.The optical field is limited inside the core area,and it can not interact with the environmental media.It greatly limits the application of Brillouin scattering based sensor.Micro/nano fiber is a kind of micro structured optical fiber whose diameter is close to the wavelength of light.It has a relatively strong evanescent field and provides a potential for the interaction between light and external media.The study of Brillouin scattering spectrum characteristics in micro/nano optical fibers is of great significance for expanding the application field of distributed sensors.In this paper,characteristics of Brillouin scattering spectrum in micro/nano optical fibers are studied theoretically,and the optical field distribution and acoustic field dispersion curves with different fiber diameters are simulated.The feasibility of refractive index sensing using Brillouin scattering in a micro/nano optical fibers is analyzed.The influence of transmitted constant of acoustic modes to the sensitivity of the sensor is studied.Finally,the refractive index sensing experiment is carried out by using micro-nano optical fibers with diameter of 2?m,and the method for solving the cross-sensitivity problem of the sensor is studied.The experimental results indicate that the measured frequency of Brillouin peaks introduce in a micro/nano optical fiber with a diameter of 2?m is in agreement with the theoretical simulation results.The Brillouin frequency shift has a linearly dependence on the external refractive index in the refractive index range of 1.33-1.37.Brillouin peak with center frequency of 9.4 GHz has the highest sensitivity of 1619MHz/RIU.Since the temperature,strain and refractive index coefficient for each Brillouin peak is different,the cross sensitivity problem can be solved accordingly.