Shi Bo, Sakr Hesham, Hayes John, Wei Xuhao, Numkam Fokoua Eric, Ding Meng, Feng Zitong, Marra Giuseppe, Poletti Francesco, Richardson David J, Slavík Radan
Opt Lett. 2021 Oct 15;46(20):5177-5180. doi: 10.1364/OL.438302.
The optical phase accumulated when light propagates through an optical fiber changes with temperature. It has been shown by various authors that this thermal phase sensitivity is significantly smaller in hollow core fibers (HCFs) than in standard single-mode fibers (SSMFs). However, there have been considerable differences in the level of sensitivity reduction claimed, with factors in the range ×3 to ×20 improvement for HCFs relative to SSMFs reported. Here we show experimentally that this large variation is likely attributable to the influence of fiber coating, which is exacerbated in HCFs with a relatively thin silica glass outer wall (e.g., the wall thickness is typically just 20 µm in a 125 µm diameter HCF). Further, we show that the coating also causes the optical phase stability to suffer from relaxation effects, which have not been previously discussed in the HCF literature, to the best of our knowledge. In addition to demonstrating these relaxation effects experimentally, we analyze them through numerical simulations. Our results strongly suggest that they originate from the viscoelastic properties of the coating. To minimize the adverse effects of the coating, we have fabricated a HCF with a relatively thick wall (∼50µ) and a very thin coating (10 µm). This results in an almost 30-fold reduction in HCF thermal phase sensitivity relative to SSMFs - a significantly lower sensitivity than in previous reports. Moreover, our thinly coated HCF exhibits no discernable relaxation effects while maintaining good mechanical properties.
光在光纤中传播时积累的光学相位会随温度变化。许多作者已经表明，这种热相位灵敏度在空心光纤（HCF）中比在标准单模光纤（SSMF）中要小得多。然而，在声称的灵敏度降低水平上存在相当大的差异，据报道，相对于SSMF，HCF的改善因子在3倍至20倍之间。在这里，我们通过实验表明，这种巨大的变化可能归因于光纤涂层的影响，在具有相对较薄二氧化硅玻璃外壁的HCF中（例如，在直径为125μm的HCF中，壁厚通常仅为20μm），这种影响会加剧。此外，我们表明涂层还会导致光学相位稳定性受到弛豫效应的影响，据我们所知，这在HCF文献中尚未被讨论过。除了通过实验证明这些弛豫效应外，我们还通过数值模拟对其进行了分析。我们的结果强烈表明，它们源于涂层的粘弹性特性。为了尽量减少涂层的不利影响，我们制造了一种壁厚相对较厚（约50μm）且涂层非常薄（10μm）的HCF。这使得HCF的热相位灵敏度相对于SSMF降低了近30倍——比以前的报告中的灵敏度要低得多。此外，我们的薄涂层HCF在保持良好机械性能的同时，没有表现出明显的弛豫效应。
