Simulation of complex phenomena in optical fibres Simulation of complex phenomena in optical fibres
Simulation of complex phenomena in optical fibres Simulation of complex phenomena in optical fibres
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光纤中复杂现象的模拟 光纤中复杂现象的模拟
DOI：
10.1111/j.1365-2966.2012.21776.x
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发表时间：
2012
影响因子：
4.8
通讯作者：
Allington-Smith J
中科院分区：
文献类型：
--
作者：
Allington-Smith J
光纤对于许多类型的高度复用和精确的光谱学是必不可少的。正在建设的新一代多纤维仪器的成功调查宇宙学中的基本问题，如暗能量的性质，需要准确的建模的纤维系统，以实现其信噪比（SNR）的目标。尽管它们的结构简单，但纤维表现出意想不到的行为，包括光学扩展量的不守恒（焦比退化，FRD）和模态噪声。此外，新的光纤几何形状（非圆形或锥形）已变得可用于改善加扰特性，加扰特性与模式噪声一起限制了精密光谱学中可实现的SNR。这些问题通常通过对候选纤维及其终端进行广泛测试来解决，但这些测试既困难又耗时。通过射线跟踪和波分析建模是可能的商业软件包，但这些不解决更复杂的功能，特别是FRD。我们使用相位跟踪射线跟踪方法来提供一个实际的描述FRD来自我们以前的实验工作对圆形纤维，并将其应用到非标准的纤维。这使得加扰和FRD之间的关系首次被量化。我们发现，扰频主要影响近场图案的形状，但对重心的影响可以忽略不计。FRD有助于均匀化近场图案，但不会使其完全均匀。具有多边形横截面的纤维在不放大FRD的情况下改善了扰乱。椭圆形光纤与锥形光纤相结合，可以提供一种有效的图像切片方法，以提高分辨率和吞吐量的乘积，但结果对照明的细节很敏感。我们还研究了接近极限数值孔径的光纤的性能，因为这可能会影响一些主焦点光纤仪器的SNR的均匀性。
Optical fibres are essential for many types of highly multiplexed and precision spectroscopy. The success of the new generation of multifibre instruments under construction to investigate fundamental problems in cosmology, such as the nature of dark energy, requires accurate modellization of the fibre system to achieve their signal-to-noise ratio (SNR) goals. Despite their simple construction, fibres exhibit unexpected behaviour including non-conservation of etendue (focal ratio degradation, FRD) and modal noise. Furthermore, new fibre geometries (non-circular or tapered) have become available to improve the scrambling properties that, together with modal noise, limit the achievable SNR in precision spectroscopy. These issues have often been addressed by extensive tests on candidate fibres and their terminations, but these are difficult and time-consuming. Modelling by ray tracing and wave analysis is possible with commercial software packages, but these do not address the more complex features, in particular FRD.We use a phase-tracking ray-tracing method to provide a practical description of FRD derived from our previous experimental work on circular fibres and apply it to non-standard fibres. This allows the relationship between scrambling and FRD to be quantified for the first time. We find that scrambling primarily affects the shape of the near-field pattern but has negligible effect on the barycentre. FRD helps to homogenize the near-field pattern but does not make it completely uniform. Fibres with polygonal cross-section improve scrambling without amplifying the FRD. Elliptical fibres, in conjunction with tapering, may offer an efficient means of image slicing to improve the product of resolving power and throughput, but the result is sensitive to the details of illumination. We also investigated the performance of fibres close to the limiting numerical aperture since this may affect the uniformity of the SNR for some prime focus fibre instrumentation.