Investigation On Slow Light Based On Stimulated Brillouin Scattering In Few-mode Fibers

In this dissertation,the characteristics of optical fields and acoustic fields based on stimulated Brillouin scattering in few-mode fibers are investigated by full vectorial finite element method.The characteristics of slow light of different modes in few-mode fibers under different conditions are obtained by coupling theory of optical wave and acoustic wave.And the influences of doping concentration,temperature and strain on slow light based on stimulated Brillouin scattering in few-mode fibers are also demonstrated.The main contents and conclusions are as follows:1.Under the steady-state small signal solution,the expression of time delay of slow light in few-mode fibers is derived by the acousto-optic coupling equation based on stimulated Brillouin scattering,and the theory of slow light is demonstrated.The slow light of different mode pairs?pump-stokes?in the few mode fiber are presented by full vectorial finite element method.The influences of the pump power,effective transmission length on the Brillouin threshold,time delay and pulse broadening factor of different mode pairs in the few mode fiber are also simulated.The simulation results show that the characteristics of tunable slow light of different mode pairs in the few mode fiber are different.Brillouin threshold decreases as the effective fiber length increasing,but increases with the mode order increasing.The larger time delay and pulse broadening factor of different modes are achieved as pump power and effective transmission length increasing,and the time delay and pulse broadening factor of intramodal stimulated Brillouin scattering are greater than intermodal stimulated Brillouin scattering for a given input pump power.The time delay ofLP₀₁-LP₀₁,LP₁₁-LP₁₁andLP₀₁-LP₁₁mode pairs are respectively 643.7 ns,362.6 ns and 213.2 ns at a given input pump power of 0.5 W and the effective fiber length of 1 km,pulse broadening factors are1.346,1.207 and 1.126,separately.The few mode fiber with larger delay and smaller pulse deformation is obtained by analyzing the characteristics of slow light based on stimulated Brillouin scattering in the few mode fiber.This conclusion theoretically points out a feasible research direction for designing slow-light devices and improving transmission capacity.2.The influences of doping concentration on the characteristics of slow light based on stimulated Brillouin scattering in the few mode fiber are investigated theoretically,and the variation of the effective mode area,Brillouin threshold,time delay and pulse broadening factor ofLP₀₁mode andLP₁₁mode under different doping conditions are simulated.The results show that different doping concentrations have different effects on the characteristics of slow light of different modes,which has a stronger influence on theLP₁₁ mode compared with theLP₀₁mode.The effective mode area and Brillouin threshold ofLP₀₁mode andLP₁₁mode decrease as doping concentration increasing,but the time delay and pulse broadening factor increase as doping concentration increasing at a given pump power.The time delay of theLP₀₁mode is greater than that of theLP₁₁ mode,but the time delay of the LP₁₁mode is more sensitive to doping concentration.The tunable time delay of different modes can be obtained by changing the doping concentration at a given condition.This work has an important theoretical significance for the research of optical buffer devices.3.The effects of temperature and strain on the characteristics of slow light of LP₀₁mode andLP₁₁ mode in the few mode fiber are investigated.The variation of the effective refractive index,effective mode area,Brillouin threshold,time delay and pulse broadening factor of each mode are simulated when temperature varies from-20°C to 80°C and strain varies from 0??to 2000??.The results show that the characteristics of slow light ofLP₀₁mode andLP₁₁mode vary significantly with the temperature and strain,andLP₁₁mode is more sensitive to the variation of temperature and strain.The effective mode area and Brillouin threshold ofLP₀₁mode andLP₁₁mode decrease as temperature and strain increasing,but the time delay and pulse broadening factor increase as temperature and strain increasing at a given pump power.The conclusion has a theoretical reference for designing the temperature and stress sensor of the few mode fiber based on stimulated Brillouin scattering.