Study On The Properties Of Stimulated Brillouin Scattering In SiO₂ And As₂S₃ Fibers With Small Core Diameters

Stimulated Brillouin scattering(SBS)is a typical nonlinear phenomenon with many evident advantages,such as low threshold power,high conversion efficiency,and ultra-narrow gain linewidth.Combining these advantages,the Brillouin fiber laser has been applied in many fields.The multi-wavelength brillouin fiber laser has become one of the most competitive light sources in dense wavelength division multiplexing(DWDM)system because it can transmit multiple light waves simultaneously in a single fiber.As the gain medium of Brillouin fiber lasers,the composition and performance parameters of the fiber have been optimized.Multimode fiber requires higher incident power to generate SBS effect than single-mode fiber,while ordinary single-mode silica fiber(SMF)requires high pump power and long fiber length to effectively stimulate the SBS effect due to low nonlinear coefficient.However,high pump power tends to lead to complicated device management,reduced system stability and increased energy consumption,etc.,and relatively long gain fibers are not conducive to device miniaturization.In recent years,researchers have begun to explore the SBS effect and its applications based on novel optical fibers with high non-linearity.The effective method to reduce the threshold power is to reduce the effective mode field area(A_eff)of the fiber,and the effective method to increase the non-linearity is to look for novel fibers with high refractive index and low A_eff.In this paper,we choosed both the SiO₂ fibers and highly nonlinear As₂S₃ fiber with small core diameter as the objects of study and compared their SBS effects.The main research contents and innovations of this paper include:(1)We mainly build Brillouin fiber lasers with F-P cavity based on SiO₂ fibers,and then compare the Brillouin characteristic parameters of three kinds of SiO₂ fibers with different core diameters(8.8,5 and 3mm),including the Brillouin threshold P_th,Frequency shiftnand linewidth(35)n.The results show that the fiber with small core diameter can effectively reduce P_th and broaden(35)n,and the influence of core diameter onnis much smaller than that of core doping.(2)Comsol software is used to perform finite element simulation on the effects of the A_eff,acousto-optic overlap integral I,and threshold gain factor G_th on P_th.The results show that small core fiber with higher numerical aperture(NA)can effectively reduce P_th at relatively short length.(3)A multi-wavelength Brillouin fiber laser is constructed using an As₂S₃ fiber with a small core diameter of 5mm.By optimizing the coupling scheme,the non-linear fiber that matches the NA and A_eff of the As₂S₃ fiber is selected,which is coupled to a SMF to form a mode field adapter(MFA),and then coupled with the As₂S₃ fiber to build a low-loss cavity.Finally,a low-loss coupling result with an insertion loss of 0.5 d B and a coupling loss of 2.4 d B was obtained.(4)The output power and the number of Stokes channel of Brillouin fiber laser based on As₂S₃ fiber with small core diameter are compared with and without cavity feedback.The results show that by using customized MFA for coupling,the laser conversion efficiency with cavity feedback(42.6%)is much higher than the laser conversion efficiency without cavity feedback(26.4%)and the number of Stokes channels has more than doubled.Therefore,laser with cavity feedback can effectively improve the multi-wavelength laser output effect.Finally,at a pump power of 2.5 W,the laser with high power output of more than 1 W and number of 20multi-wavelength laser output is achieved.These results provide a scientific reference for low-threshold Brillouin fiber lasers based on special fibers.