Theoretical Analysis And Application Of Forward And Backward Stimulated Brillouin Scattering In Optical Fibers

The stimulated Brillouin scattering?SBS?effect in fiber is a kind of very important nonlinear effect.Usually,the SBS effect is harmful in optical fiber communication.When the SBS effect occurs in fibers,a few Stokes lights with new frequencies will be generated,so there is a large loss for pump light.However,according to the characteristics of the SBS effect,it can also be used in other useful ways.Now the SBS effect has been used for fiber laser,fiber amplifier,fiber sensing,laser gyroscope and so on.The SBS effect has important applications on different fields.Therefore,it is necessary to investigate the SBS process theoretically and experimentally.On the one hand,it is necessary to avoid the occurrence of the SBS in some fields,especially on long-distance optical transmission.On the other hand,we also hope to make better use of the SBS effect to achieve the results we need,such as new lasing generation,fiber sensing and light velocity control.In this paper,numerical simulation are carried out for the forward and backward Brillouin scattering in optical fibers.In addition,the backward SBS effect is studied experimentally.The main contents are as follows:Firstly,the finite element method is used to analyze the forward Brillouin scattering effect in the fiber.The influences on the forward SBS by the fiber core size is studied in the step-index fiber and the photonic crystal fiber,respectively.In the step-index fiber,there are several forward Brillouin scattering peaks with the Brillouin frequency shifts from 20 to 800 MHz,and changing the core diameter does not affect the Brillouin frequency shifts.While in photonic crystal fibers,the core diameter has a great influence on the Brillouin frequency shift,and the Brillouin frequency shift decreases as the core diameter increases.Secondly,the characteristics of the backward Brillouin gain spectrum in the chalcogenide photonic crystal fiber are simulated numerically.The effects by the fiber size and optical mode field on the Brillouin gain spectrum are studied.For the As₂Se₃photonic crystal fiber,there is only one peak in Brillouin gain spectra with large core,while for the small core,there are two peaks in Brillouin gain spectra.When the core diameter is large,the Brillouin frequency shift varies few with the core diameter.When the core diameter is small,the Brillouin frequency shift will be increased significantly with the core diameter increasing.Thirdly,using the Brillouin scattering effect and the four-wave mixing effect in the fiber,a multi-wavelength laser output device is designed.Through the experimental exploration,the characteristics of the output are explored with respect to the pump power,the amplification power and the free oscillation in the cavity.When the pump wavelength is 1565 nm,the maximum output of the laser can be obtained with the EDFA output of 483.0 mW.The number of output wavelength exceeds 110.