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基于环形腔被动锁模光纤激光器的基本原理,对影响其输出特性的关键因素——耦合输出比(R)作了理论和实验研究。理论仿真结果表明.要得到高质量的脉冲,激光器腔内增益与耦合输出比存在一最佳比值,小信号增益为7.5 dB时,耦合输出比应在30%左右。实验中取3 m长的增益光纤,分别采用5%,10%～40%和60%～90%的耦合输出比搭建环形腔被动锁模光纤激光器。实验结果对比分析表明,耦合输出比对激光器的输出特性有重要影响.R取5%～10%间时脉冲谱宽最宽(可达25.4 nm)且谱宽调谐范围较大(>12 nm),R=10%和30%时脉冲波动幅度最小,R=70%左右时单脉冲能量最大(达3.86 nJ)。另外,取R=30%.可在脉冲幅值波动较小的基础上获得最大的脉冲能量;而R=10%时为保证脉冲波动小、谱宽宽和能量大的平衡点。取3 m长的增益光纤和R=10%的激光器,获得了重复频率15.87 MHz,谱宽25.4 nm,单脉冲能量约0.52 nJ的脉冲激光,这些特性不会受到工作台振动、激光器搬动及普通温度变化等因素的影响,脉冲幅值存在约4%的波动。
Based on the basic principle of ring-mode passively mode-locked fiber laser, theoretical and experimental studies on the key factor affecting the output characteristics, such as the output-to-coupling ratio (R), are carried out. The theoretical simulation results show that there is an optimal ratio between gain and coupling output ratio of laser to get high quality pulse. When the small signal gain is 7.5 dB, the coupling output ratio should be about 30%. In this experiment, a gain fiber with 3 m length was used, and a cavity-locked passively mode-locked fiber laser was constructed using a coupling output ratio of 5%, 10% -40% and 60% -90% respectively. The comparison of the experimental results shows that the coupling output ratio has an important influence on the output characteristics of the laser.The pulse spectrum width is widest (up to 25.4 nm) and the spectrum tuning range is larger (> 12 nm) when 5% ~ 10% The pulsation amplitude is the smallest at R = 10% and 30%, and the single pulse energy is the largest at R = 70% (up to 3.86 nJ). In addition, taking R = 30%, the maximum pulse energy can be obtained on the basis of smaller pulse amplitude fluctuation; while R = 10% is the balance point for ensuring small pulse fluctuation, wide spectrum width and large energy. A pulsed laser with a repetition frequency of 15.87 MHz, a spectral width of 25.4 nm and a single pulse energy of about 0.52 nJ was obtained with a 3 m long gain fiber and a R = 10% laser. These characteristics were not affected by table vibration, laser movement and Ordinary temperature changes and other factors, the pulse amplitude of about 4% fluctuations.