Liquid phase sensing applications at 1550 nm are highly desirable due to widely available off-the-shelf components. Generally, liquids at 1550 nm induce a high absorption loss that limits the overall sensor’s sensitivity and detection limit. One solution is to use an active fiber loop in conjunction with cavity ring down spectroscopy to overcome these absorption losses. However, the amplifier inside the fiber loop suffers from inherent gain fluctuations that limit the sensing system’s overall performance. Here, we provide a novel sensor using the wavelength-scanned phase shift-cavity ring down spectroscopy (PS-CRDS) in conjunction with a linear active fiber cavity that potentially offers a more sensitive solution than traditional fiber loop sensors. We use a tapered fiber as a sensing head inside the active cavity built from fiber Bragg gratings. We derive a theoretical phase shift expression for our system and simulate it using the finite element method to determine optimum tapered fiber diameter for glucose sensing in DI water. Compared to a non-amplified system, we find that our amplified system can increase the sensitivity by fourteen times via the amplifier gain tuning. We also conduct experimental measurements using 0-15.5 mM glucose solutions and find them in excellent agreement with our theoretical predictions. Experimentally we obtain the sensor’s sensitivity of 0.768°/mM (1164°/RIU) and detection limit of 0.75 mM ( 4.5×10−44.5\times 10^{-4} RIU) without any temperature stabilization in the system. We anticipate that the present work will find a wide range of sensing applications in fiber cavities, ring resonators, and other microcavity structures.

中文翻译：

---

用于 1550 nm 传感应用的线性和有源光纤腔中的相移腔衰荡光谱


由于现成组件广泛可用，1550 nm 的液相传感应用非常受欢迎。一般来说，1550 nm 处的液体会产生高吸收损耗，从而限制了整个传感器的灵敏度和检测限。一种解决方案是使用有源光纤环路与腔衰荡光谱技术相结合来克服这些吸收损耗。然而，光纤环路内的放大器会受到固有增益波动的影响，从而限制了传感系统的整体性能。在这里，我们提供了一种新型传感器，使用波长扫描相移腔衰荡光谱（PS-CRDS）与线性有源光纤腔相结合，可能提供比传统光纤环路传感器更灵敏的解决方案。我们在由光纤布拉格光栅构建的有源腔内使用锥形光纤作为传感头。我们推导出系统的理论相移表达式，并使用有限元方法对其进行模拟，以确定去离子水中葡萄糖传感的最佳锥形纤维直径。与非放大系统相比，我们发现我们的放大系统可以通过放大器增益调整将灵敏度提高十四倍。我们还使用 0-15.5 mM 葡萄糖溶液进行实验测量，发现它们与我们的理论预测非常一致。通过实验，我们获得了传感器的灵敏度为 0.768°/mM (1164°/RIU)，检测限为 0.75 mM ( 4.5×10−44.5\times 10^{-4} RIU)，而系统中没有任何温度稳定。我们预计目前的工作将在光纤腔、环形谐振器和其他微腔结构中找到广泛的传感应用。