The Experimental Study Of Brillouin Sensing In An All-solid Photonic Bandgap Fiber

Brillouin scattering is an inelastic scattering phenomenon of nonlinear effect in a fiber,which results from the coupled effect of light and sound waves propagating through the fiber.The scattering effect should be suppressed in long distance communications. However, it is a hottopic in senging field because of its high sensitivity on the temperature and stress of the fiber.Many papers have reported that Brillouin frequency shift and Brillouin intensity show lineardependence on temperature and strain, which means a lot to the engineering test field. Comparedto conventional sensors, fiber can perform sensing and information transmission simulataneously,and it is light, low cost, portable and confidential, which makes fiber very convenient for thefield of structure healthy test and some special fields such as submarine cable test. ThereforeBrillouin scattering has been attracting a lot of scholars’ interest. At the same time, as adevelopment of new sensors, various fibers with different optical properties have been studiedand developed in which different Brillouin scattering phenomenon have been observed.This thesis studies a specialty fiber-all solid bandgap photonic crystal fiber. We not onlypresent the fundamental theory but also do some experiments. We have proposed two differentprocessing of the fiber: taper and etched long-period fiber grating (LPFG) for which we haveperformed the temperature and stress measurements respectively. The idea of taper has beenachieved by using a splice machine through changing the discharge time and intensity. TheLPFG has been fabricated in the laboratory. Both of the two methods excite the Brillouinresonance peaks in the cladding as we have expected.Based on the experimental results, we have found that these two methods both excite fourBrillouin resonance peaks, of which three are from cladding modes, one from the fundamentalmode in the core. The core mode and cladding modes have different dependences upontemperature and strain, making it possible to get the temperature and strain coefficients bysolving the coupled equations. It is an effecient solution to solve the cross-sensitivity problem forsimultaneous measurement of temperature and strain upon the fiber.