Study On Design Of The Fiber With Multi-peak Brillouin Scattering Spectrum With Close Intensity

In the fiber with a few acoustic excitation modes,the forward light can stimulate multi-mode backward Brillouin scattering light,and the corresponding Brillouin scattering spectrum(BSS)of the fiber shows multiple peaks.The multi peaks of Brillouin scattering light beat with each other in the process of backward propagation,forming the Brillouin Beat Spectrum(BBS)which has only hundreds MHz peak frequency.The peak power of Brillouin beat spectrum can be detected by homodyne Brillouin optical time-domain reflectometry(BOTDR),and the rapid measurement of temperature and strain can be achieved.However,in order to obtain high measurement precision by use of the method,it is necessary to design sensing fiber with close intensity multi-peak Brillouin scattering spectrum.Unfortunately,there is no such optical fiber with the property.In order to improve the sensing precision based on BBS detection,the method for designing the fiber with multi peak BSS with close intensity is studied in this thesis.In the thesis,the optical modes,acoustic modes and corresponding Brillouin scattering spectra of typical solid core fibers and photonic crystal fibers are obtained by finite element analysis.The influence of optical fiber parameters on the shape of BSS is explored.On this basis,new type of solid core fiber and photonic crystal fiber with multi peak BSS with close intensity are designed.The obtained solid core fiber is a fiber with the square law of refractive index.Its core radius is 1.0?m,and the refractive index in the fiber core is 1.485.When the wavelength of the incident light is 1550 nm,the relative power of the three peak BSS of the fiber is 0dB,-10.4dB and-5.1dB,respectively.The designed photonic crystal fiber is a total internal reflection photonic crystal fiber,and it has six layers of distribution.The circular air aperture from inside to outside is 0.76?m?0.80?m?0.76?m?0.76?m?0.76?m and 0.76?m respectively,and the air hole spacing is 1.2?m.When the wavelength of the incident light is 1550 nm,the relative power of the three peak BSS of the fiber is-2.5dB,-1.3dB and 0dB,respectively.