大芯径天文光纤焦比退化因素分析及机制研究

项目名称： 大芯径天文光纤焦比退化因素分析及机制研究

项目编号： No.U1331114

项目类型： 联合基金项目

立项/批准年度： 2014

项目学科： 数理科学和化学

项目作者： 孙伟民

作者单位： 哈尔滨工程大学

项目金额： 60万元

中文摘要： 大芯径天文光纤已经在LAMOST等国内外天文望远镜中得到了广泛地应用，光纤将焦面上收集的星光传输到光谱仪中，进而可以分析其视向速度等参量。星光在光纤中传输时，光纤中焦比退化会引起能量损耗，严重时甚至会引起光斑中心偏移，严重影响星体光谱测量的精确度。本项目致力于研究大芯径天文光纤中模式传播规律，分析由于大芯径光纤弯曲、扭转和材质不匀造成的模式变高、焦比变小的问题。利用模式群理论分析大芯径光纤中数以万计的光纤导模的转化规律，建立大芯径天文光纤扭转、弯曲条件下的焦比退化模型；探索大口径天文光纤中模式相互转化的概率，寻找临界弯曲和扭转条件，以期指导天文光纤的选择、安装和控制；研究不同物理、几何特性的大口径光纤扰模工作机制和优化参数，以期进行后期模式控制。

中文关键词： 大芯径光纤；焦比退化；光纤损耗；环形斑；光纤扰模器

英文摘要： The large-core astronomical fibers were used wildly in many telescopes around the world, such as LAMOST (Large Sky Area Multi-Object Fibre Spectroscopy Telescope). The fibers transmit the star lights from the focal board to the optical spectrometer to analyze the radail velocity of these stars. The focal ratio degradation (FRD) could cause the effective energy loss and even shift of the spot centers. The FRD could seriously influence the accuracy of the measurement of the radius velocity. Firstly we want to investigate on the transmission of light along the large-core astronomical fibers, and to analyze the mode-rising and FRD because of bend, twist and nonuniform of the fibers. Secondly we want to use the mode group theory to analyze the transfer law of the thousands of guide modes according to fiber bend and twist. Thirdly we want to study on the probability of mode transfer law to find the critical conditions of fiber bend and twist. We hope these research results could help astronomers to choose suitable fibers and to find the better installing and controlling conditions. Lastly we want to research on the mode disturbing methods of the astronomical fibers to find a way to control the output fiber modes.

英文关键词： Large-core fibers；focal ratio degradation；fiber loss；ring spot；fiber scrambler