光频率调制法测量动态光栅瞬态反射谱特性

动态光栅的瞬态特性影响了单纵模掺铒光纤激光器的稳定性. 提出一种利用铒离子瞬态效应,通过对写入光施加快速频率调制测量动态光栅瞬态反射谱的新方法. 测量了线性结构动态光栅的瞬态反射谱,研究了注入光功率与端面反射率 对动态光栅响应特性的影响.结果表明, 3 m长的掺铒光纤形成的动态光栅半带宽为30 MHz, 与稳态理论值符合较好.光栅瞬态反射率相对变化随注入光功率增加和端面反射率增加而减小, 在小注入功率或低端面反射率时,最大的反射率相对变化值约为4%. 光栅建立时间随注入光功率增加而减小,当注入光功率大于4倍饱和功率时,建立时间小于1 ms. 使用双波混频过程可解释这一实验规律.

Measurements of transient reflectance spectra of dynamic gratings by optical frequency modulation

The characteristics of dynamic gratings greatly affect the linewidth and mode stability of ultra-narrow linewidth erbium-doped fiber (EDF) lasers. In this paper, we propose a novel method to measure the temporal evolution of the reflectance spectra of the dynamic gratings recorded in EDF based on the transient effect of the erbium ions by applying optical frequency modulation on the written light. The transient reflectance spectra of the linear configuration dynamic gratings are measured, and the influences of the written optical power and the terminal reflectivity on the response characteristics of the gratings are also studied. Experimental results show that the first order zero point frequency of the gratings formed in a 3-m-long erbium doped fiber is 30 MHz which accords with the value obtained from the steady state theory. The relative reflectivity change decreases with the increase of input optical power or terminal reflectivity. The measured maximal changes occur at low input power or terminal reflectivity. The grating building time also decreases with the increase of optical power, and it is less than 1 ms when input power is larger than 4 times the saturable power. This phenomenon can be explained by the process of two-wave mixing.