The Study Of Brillouin Scattering Sensing Mechanism Based On Microfiber

Brillouin optical fiber sensing technology uses the phenomenon of Brillouin scattering in optical fiber to detect the environmental parameters.The Brillouin scattering effect in optical fiber can be used to detect the safety of national defense,tunnel mining,industrial control,medicine and health,factory building and so on.With the improvement of fiber preparation technology in recent years,the preparation technology of micro-nano fiber is more and more mature,and its fiber diameter can reach the magnitude of micron or nanometer.In the process of Stimulated Brillouin scattering in micro-nano fiber,the boundary effect makes the photon and phonon strongly constrained and highly overlapped in space,which generates two new acoustic waves,surface acoustic waves and hybrid acoustic waves.Multi-peak Brillouin gain spectrum with large gain is detected in micro-nano fiber.Therefore,the study of surface acoustic wave and hybrid acoustic wave Brillouin scattering in micro-nano fiber is beneficial to promote the innovative detection in the field of Brillouin fiber sensing.In this paper,a temperature and strain sensing method based on surface acoustic waves and hybrid acoustic waves Brillouin scattering in micro-nano fiber is proposed.The characteristic frequencies of the surface acoustic modes and the hybrid acoustic modes were solved by the elastodynamic equation including electrostrictive stress.The distribution of optical field and acoustic field in micro-nano fiber was simulated by finite element method,and then the Brillouin gain spectrum characteristics under different diameters were analyzed.According to the influence of temperature and strain on material properties,the temperature and strain sensitivity of surface acoustic mode and hybrid acoustic mode were simulated numerically.In addition,a method of simultaneous sensing of temperature and strain was proposed.The main achievements are as follows:（1）The theoretical analysis model of surface acoustic wave and hybrid acoustic wave Brillouin scattering is established,and the finite element analysis method is used to solve the energy distribution of light field,acoustic field displacement and density distribution under 1μm diameter.（2）Numerical simulation of Brillouin gain spectrum at 1～1.3μm diameter.The Brillouin gain spectrum has a multi-peak structure due to the multiple surface acoustic modes and hybrid acoustic modes excited by stimulated Brillouin scattering in micro-nano fibers.In addition,micro-nano fiber has a smaller effective acousto-optic area and a larger Brillouin gain than single-mode fiber.The surface acoustic wave Brillouin gain is 7.2324 W^-1m^-1,and the hybrid acoustic wave Brillouin gain is 37.6959 W^-1m^-1,which is much higher than the 0.4 W^-1m^-1Brillouin gain in single-mode fiber.（3）The temperature and strain sensitivity of the surface acoustic modes and the hybrid acoustic modes at the diameter of 1～1.3μm were simulated numerically.The results show that the temperature and strain sensitivities of the hybrid acoustic modes are up to 1.082 MHz/℃ and 0.0289 MHz/με,respectively,which is suitable for micro-nano fiber sensing application of high temperature and strain resolutions.The temperature and strain sensitivities of the surface acoustic modes are less affected by the fiber diameter,and the temperature and strain sensitivity vary from 0.05 to 0.25 MHz/℃/μm and 0.1 to 0.5 k Hz/με/μm.It can be found that that surface acoustic wave Brillouin scattering for temperature and strain sensing would put less stress on manufacturing constraints for optical microfibers.（4）A method for simultaneous sensing of temperature and strain using a combination of surface acoustic mode and hybrid acoustic mode is proposed.The temperature and strain errors in the sensing process are as low as 0.30～0.34℃ and 14.47～16.25με.