Formation Mechanism Of Brillouin Scattering Slow Light In Optical Fibers

The process of Brillouin Scattering in optical fiber has a promising future in thefield of optical fiber slow light, fiber laser, optical fibre gyro, fiber sensor et al., sinceit’s characterised by lower threshold, long acousto-optic interaction region, flexibleoperation, nontoxicity and easy-to-handle effect. Photonic crystal fiber has become aresearch hotspot in the above areas because of its high nonlinear characteristics and itsflexible structural features. In this thesis, the influence of single-mode fiber parameterson the threshold for Brillouin scattering is investigated and Characteristics of Acousticmodes via Stimulated Brillouin Scattering in photonic crystal fiber are discussed indetail, the main contents are listed as follows:1. Spontaneous Brillouin scattering model is applied for the analysis of the thresholdfor Stimulated Brillouin Scattering in short single-mode fiber at1550nmcommunication window. For short distance transmission (300m) the dependency ofthe threshold exponential gain, Gth, on fiber numerical aperture and fiber length isstudied. The results indicate that in the case of small gain (L1), the threshold gaincoefficient of fiber is not a constant, but have some bearing on the effective numericalaperture and the length of fiber.2. Stimulated Brillouin scattering model is applied for the analysis of the threshold forStimulated Brillouin Scattering in long single-mode fiber at1550nm communicationwindow. With regard to long distance transmission (several kilometers), the dependencyof the threshold exponential gain, Gth, on effective fiber length, fiber length, theeffective core area and the phonon lifetime is analysed and the critical length is defined.3. The wave equation of the acoustic wave for the particle displacement in photoniccrystal fiber is derived based on the knowledge of the elastic mechanics. The resultindicates that both the mixed longitudinal acoustic modes and transverse acoustic modesresonance together produce the acoustic fields, and their coupling forms the hybridacoustic modes.4. The characteristics of acoustic modes and the dependency of the acoustic modescoupling on pump wavelength and the fiber core refractive index in small-core photonic crystal fibers are investigated by effective index method. The simulation results showthat the propagation constant of acoustic modes can be changed by tailoring the pumpwavelength or the core refractive index in the process of Stimulated BrillouinScattering.5. The approximate model of silica rod is applied for analysing the influence of corediameter on Brillouin acoustic modes dispersion in small-core photonic crystal fiber.The results show that the acoustic modes coupling is strengthened and the phasevelocity of the acoustic modes decreases with the increasing of the photonic crystalfiber core diameter and there is also a growing trend of the number of the acousticmodes at the same propagation constant. The phase velocity reduces with the frequencyof the pump wave increases.The work provides some theoretical references for choosing the proper fiber as slowlight medium in short communciation system and long communciation system andexploring the slow light mechanism based on stimulated Brillouin scattering in PCF.