Slavík R, Numkam Fokoua E R, Bukshtab M, Chen Y, Bradley T D, Sandoghchi S R, Petrovich M N, Poletti F, Richardson D J
Opt Lett. 2019 Sep 1;44(17):4367-4370. doi: 10.1364/OL.44.004367.
The output phase and propagation time of an optical signal propagating through a hollow-core optical fiber (HCF) drift with changes in environmental temperature significantly less than in conventional optical fibers. In all earlier experimental studies, however, the simplifying assumption was made that the thermo-optic effect of air was negligible. In this Letter, we present, to the best of our knowledge, the first experimental demonstration that the air inside a HCF core can make an appreciable contribution to the fiber's thermal sensitivity with the performance depending on whether the fiber is open to the atmosphere or sealed at both ends (e.g., spliced to solid fiber pigtails). We measure both the sensitivity of the accumulated phase as well as the signal propagation time for both open and sealed HCF and show that these are opposite in sign. Most importantly, we show that the thermal sensitivity contribution from the air inside an open HCF has the sign opposite to the effect of fiber elongation (which is otherwise the dominant effect responsible for the overall thermal sensitivity of HCF). We then go on to show that these two effects can be used to balance each other out in order to achieve zero thermal sensitivity for both accumulated phase and propagation time. We demonstrate this property experimentally over a large spectral range.
通过空心光纤（HCF）传播的光信号的输出相位和传播时间随环境温度的变化而漂移，其变化程度明显小于传统光纤。然而，在所有早期的实验研究中，都做了一个简化假设，即空气的热光效应可忽略不计。在本信函中，据我们所知，我们首次通过实验证明，HCF纤芯内的空气会对光纤的热灵敏度产生显著影响，其性能取决于光纤是与大气相通还是两端密封（例如，与实心光纤尾纤熔接）。我们测量了开放型和密封型HCF的累积相位灵敏度以及信号传播时间，结果表明二者符号相反。最重要的是，我们表明开放型HCF内空气的热灵敏度贡献与光纤伸长效应的符号相反（否则光纤伸长效应是导致HCF整体热灵敏度的主要因素）。然后我们进一步表明，这两种效应可相互抵消，从而使累积相位和传播时间的热灵敏度均为零。我们在较大光谱范围内通过实验证明了这一特性。
