光纤回音壁模式激光产生长度的实验与理论研究

The study on the produced length of whispering-gallery-mode fiber laser

采用沿光纤轴向光抽运消逝场激励增益的方式,获得了沿光纤轴向较长范围的回音壁模式激光辐射.研究了这种激光器的激光产生长度与抽运能量间的关系.实验发现当抽运能量刚超过激光产生阈值时,激光产生长度迅速增长;随抽运能量的继续增加,产生长度的增长趋势变缓;产生长度随抽运能量的变化关系决定于增益包层溶液的染料浓度和溶液折射率.根据抽运光沿光纤轴向以受抑全反射方式传播的物理特性,在抽运能量中引入了遵循比尔吸收定律的指数衰减函数,结合消逝场激励增益的回音壁模式激光理论,在分析系统增益和损耗的基础上由激光阈值条件推导出了激光沿光纤轴向的产生长度与抽运能量关系的理论公式,理论计算结果和与实验数据符合甚好.

Long length of whispering-gallery-mode fiber lasing emission along a fiber＇s axis is obtained by using the method of evanescence-wave optically pumped and gain coupled fiber laser.The relationship between produced length of lasing emission and pumping energy has been investigated.With the increasing of pumping energy,it is found from our experiment that the length of whispering-gallery-mode lasing emission along the fiber＇s axis is increased sharply,when the pumping energy is just larger than the threshold energy.However,the increasing trend of the produced length is slow when the pumping energy is much larger than the threshold energy.It was also found from the experiment that both dye concentration and refractive index of cladding gain solution have key affects on the produced length.Based on the characteristic of frustrated totally internal reflection of light traveling along the fiber,and the theory of evanescence-wave pumped and gain coupled fiber laser,an equation determining the produced length of lasing emission has been deduced,the calculated result with the equation matches the experimental data very well.