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仿真说明了单模光纤(SMF)中瑞利散射(RS)的机理,指出纤芯掺杂的不均匀性以及拉丝过程引起的光纤几何尺寸的随机变化是光纤中RS产生的主要原因,并以此为基础制作了损耗为0.54 d B/km的散射光纤.在通信波段,5 km该散射光纤的瑞利背向散射(RBS)强度高于相同长度的SMF-28近5 d B.在基于RBS单模随机激光器的数值模拟中,大量的具有随机幅度和相位的纵模在经历不平坦增益的多次放大之后,只有在增益最大点附近的模式能够克服损耗成为输出模式.实验中以掺铒光纤作为增益介质,500 m散射光纤提供随机反馈,窄带布拉格光纤光栅(FBG)作为波长选择器件,得到线宽约3.5 k Hz、对比度近50 d B的单模激光输出.与采用相同长度SMF-28的随机激光器相比,其阈值电流降低了80 m A,相同抽运条件下的最大输出功率提高了3 d Bm.该单模窄线宽随机激光器的输出波长的调谐特性仅由FBG的中心波长决定.
The mechanism of Rayleigh scattering (RS) in single-mode optical fiber (SMF) is described. It is pointed out that the variation of fiber doping inhomogeneity and the random change of fiber geometry caused by the drawing process are the main causes of RS in optical fiber. Based on this, a scattering optical fiber with a loss of 0.54 d B / km was fabricated.The Rayleigh backscatter (RBS) intensity of this scattering fiber was 5 km higher than that of SMF-28 with the same length at 5 km in the communication band, In the numerical simulation of RBS single-mode stochastic laser, only a large number of longitudinal modes with random amplitude and phase undergo multiple amplification of uneven gain, only the mode near the maximum gain can overcome the loss and become the output mode.In the experiment, Erbium fiber as a gain medium, 500 m scattered fiber provides random feedback, narrow band Bragg fiber grating (FBG) as a wavelength-selective device, get a linewidth of about 3.5 k Hz, single-mode laser output contrast nearly 50 d B. With the same length SMF -28, the threshold current is reduced by 80 m A, and the maximum output power is increased by 3 d Bm under the same pumping conditions.The tuning characteristics of the output wavelength of the single-mode narrow-line laser are only limited by the FBG center Long decided.