各向同性与各向异性动态光栅特性研究

发布时间：2018-04-22 05:37

本文选题：光学非线性 + 掺铒光纤　；参考：《国防科学技术大学》2015年硕士论文

【摘要】：掺铒光纤动态光栅具有超窄带宽、实时光控与自适应特性,在光纤激光器、光纤信息技术等领域有重要应用价值,从而引起了广泛的关注。在传统的应用中需要两束同频、同偏振光场在掺铒光纤中形成驻波,通过饱和吸收效应形成吸收型各向同性动态光栅。实际应用中存在着光栅效率较低,易受偏振态影响等问题,从而影响光纤器件性能、造成光纤激光器不稳定。近年来的报道表明:增益型动态光栅可能有更高的光栅效率。同时本课题组独立发现了利用法拉第旋镜,可使两束偏振正交光场在普通非双折射掺铒光纤中产生各向异性动态光栅的新现象,其产生机理值得深入研究。本文将针对这两种动态光栅展开研究。同时在光频率调制法的基础上发展了“强弱光交替”法,可用于测量动态光栅的瞬态特性。本文的研究内容和结果包括:(1)在考虑泵浦光的情况下,推导出掺铒光纤中统一的四波混合非线性微分方程,可用于描述泵浦或非泵浦下的动态光栅特性。对统一的非线性微分方程进行了数值分析,发现了在一定强度的泵浦光下掺铒光纤中可同时存在增益型和吸收型动态光栅,并在实验中测到这一现象。对各向同性动态光栅的特性随写入光强、泵浦光强变化的规律进行了系统的实验研究并与仿真结果对比,结果表明:新的非线性微分方程在一定程度上可用于描述增益型动态光栅的反射谱特性。(2)在光频率调制法的基础上,提出将“强弱光交替”法用于测量动态光栅特征时间。对此方法进行测试,测得的数据与理论相符,验证了此方法的有效性。(3)结合光频率调制法和“强弱光交替法”,将各向异性动态光栅与各向同性动态光栅进行了系统的对比研究。实验结果表明,各向异性动态光栅在特征时间、带宽方面与各向同性动态光栅相似,但其反射谱的最大相对变化约为2.5%,比各向同性动态光栅低约1/2。
[Abstract]:Erbium-doped fiber dynamic gratings (EDGs) have been widely used in many fields such as fiber lasers, fiber information technology and so on, because of their ultra-narrow bandwidth, real-time optical control and adaptive characteristics. In the traditional application, two beams of the same frequency are needed, the same polarized light field forms standing wave in erbium-doped fiber, and the absorption isotropic dynamic grating is formed by saturated absorption effect. In practical application, there are some problems such as low efficiency of grating and easy to be affected by polarization state, which affects the performance of fiber devices and results in instability of fiber laser. It has been reported in recent years that the gain dynamic grating may have higher grating efficiency. At the same time, our team has independently discovered that using Faraday rotating mirror can make two beams of polarization orthogonal light field produce anisotropic dynamic grating in ordinary non-birefringent erbium-doped fiber, and its mechanism is worthy of further study. In this paper, the two kinds of dynamic gratings will be studied. At the same time, based on the optical frequency modulation method, the "strong and weak light alternating" method is developed, which can be used to measure the transient characteristics of the dynamic grating. The research contents and results of this paper include: (1) under the consideration of pump light, a unified four-wave nonlinear differential equation of mixing in erbium-doped fiber is derived, which can be used to describe the dynamic grating characteristics under pump or non-pumping. The unified nonlinear differential equations are numerically analyzed. It is found that there are both gain and absorption dynamic gratings in erbium-doped fiber under a certain intensity of pumping light, and this phenomenon is measured in experiments. The characteristics of the isotropic dynamic grating with the writing intensity and the pump intensity are studied experimentally and compared with the simulation results. The results show that the new nonlinear differential equation can be used to describe the reflectance spectrum characteristics of the gain dynamic grating to some extent. On the basis of the optical frequency modulation method, the "strong and weak light alternating light" method is proposed to measure the characteristic time of the dynamic grating. This method is tested and the measured data are in agreement with the theory. The validity of the method is verified by combining the optical frequency modulation method with the "strong and weak light alternating method". The comparison between anisotropic dynamic grating and isotropic dynamic grating is carried out. The experimental results show that the anisotropic dynamic grating is similar to the isotropic dynamic grating in characteristic time and bandwidth, but the maximum relative variation of the reflectance spectrum is about 2.5, which is about 1 / 2 lower than that of the isotropic dynamic grating.
【学位授予单位】：国防科学技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN25

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