A method for determining the focal ratio degradation of optical fibres for astronomy
A method for determining the focal ratio degradation of optical fibres for astronomy
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DOI：
10.1093/mnras/271.1.1
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发表时间：
1994-11
影响因子：
4.8
通讯作者：
E. Carrasco;I. Parry
中科院分区：
文献类型：
--
作者：
E. Carrasco;I. Parry
我们提出了一种测量光纤焦比退化（FRD）程度并通过单个参数表征其性能的方法，该方法可用于准确模拟光纤在大多数天文光谱应用中的 FRD 性能。通过使用已知的微弯诱导光束扩展理论模型，我们对各种输入光束的光纤远场输出进行了建模，包括准直光束、非准直输入光束和相对于光纤光轴倾斜的非准直笔形光束。该理论用单个参数 D 来表征 FRD。我们通过在实验室观察光纤的远场输出并将其与模型的预测进行比较来测试模型的有效性。对于准直输入光束（激光束）的情况，我们测量了光束扩展作为输入光束角度的函数，并通过找到数据的最佳拟合来确定参数D。通过使用这个 D 值，我们成功地预测了其他实验的结果，其中记录了不同 f 比的输入笔形光束的远场输出光束。因此，我们建议使用理论模型和适当的 D 值可以准确预测任何光纤的完整 FRD 性能，而 D 值可以通过简单的实验确定。最后，我们建议使用单个参数来描述 FRD 将使该领域的工作人员能够以简单、明确的方式比较各种光纤的性能。
We present a method for measuring the degree of focal ratio degradation (FRD) of an optical fibre and characterizing its performance by a single parameter, which can be used to model accurately the fibre's FRD performance in most astronomical spectroscopic applications. By using a known theoretical model for microbending-induced beamspreading, we have modelled the far-field output of an optical fibre for various input beams including collimated beams, uncollimated input beams and uncollimated pencil beams tilted with respect to the fibre's optical axis. This theory characterizes the FRD with a single parameterD. We have tested the validity of our model by observing the far-field output of a fibre in the laboratory and comparing it with the model's predictions. For the case of a collimated input beam (a laser beam), we measured the beamspreading as a function of the input beam angle and determined the parameterDby finding the best fit to the data. By using this value ofD, we successfully predict the results of other experiments where the far-field output beam is recorded for input pencil beams of varyingf-ratio. We therefore propose that the complete FRD performance of any fibre can be accurately predicted using a theoretical model and the appropriate value ofD, which can be determined by a simple experiment. Finally, we suggest that the use of a single parameter to describe FRD will allow workers in the field to compare the performances of various fibres in a simple, well-defined way.