基于增强瑞利反馈的单模窄线宽随机激光器

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 dB/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 dB. 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 kHz、对比度近50 dB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 mA, 相同抽运条件下的最大输出功率提高了3 dBm. 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.

Single-mode narrow linewidth random fiber laser with enhanced feedback from Rayleigh scattering

The origin of Rayleigh scattering in fiber waveguides is numerically demonstrated, which indicates that the inhomogeneous doping and diameter variations during drawing are the two dominant reasons. And the scattering fiber with a loss as high as 0.54 dB/km is successfully fabricated based on such principles. The overall Rayleigh backscattering intensity of 5 km scattering fiber is 5 dB higher than that of SMF-28 with the same length in telecommunication window. The principle of single-mode random fiber laser is also studied. The emission spectrum is the superposition of a large number of random modes with arbitrary amplitudes and phases, among which only the highest gain modes can lasing through gain competition. In experiment, a single-mode erbium-doped fiber linear laser with a narrow linewidth of 3.5 kHz and a high contrast of 50 dB is achieved by combining with 500 m scattering fiber as the random feedback. The threshold pump current is reduced by 80 mA and the max output power is increased by 3 dBm for the proposed laser compared with those of the laser with 500 m SMF-28 as the feedback. The tunabiltiy of the proposed laser is determined mainly by the fiber Bragg grating.