Abstract A compact refractive index (RI) sensor, based on the Mach-Zehnder Interferometer (MZI), has been developed and experimentally evaluated for the highly sensitive detection and quantification of gases (Helium, Methane, and Carbon Dioxide). The RI sensor utilizes a variety of fibre types: Single Mode Fibre (SMF), Photonic Crystal Fibre (PCF), and Hollow-Core Photonic Crystal Fibre (HC-PCF). In order to fabricate the MZI sensors, a short length of sensing fibre was positioned between a lead-in and a lead-out single mode fibre (SMF) with an air gap at each interface. Three types of sensors were fabricated using this configuration employing 4 mm stub of: (i) PCF, (ii) 10 µm HC-PCF, and (iii) 20 µm HC-PCF as the sensing elements. The performance of these sensors, for detecting and measuring the quantity of gas present, were compared. The transmission spectrum of MZI sensors are formed by interference between the cladding and core modes. These transmission signals correspond to the frequency components in the sensor’s Fast Fourier Transform (FFT) spectrum. The effect of gap distance on the number and amplitude distribution of the modes was examined in an effort to optimize the design elements. The resulting fiber sensors can measure the RI of a gas-filled cavity and they showed high-sensitivity to helium, methane, and carbon dioxide. The highest RI sensitivity of 3210 nm/RIU was demonstrated in the RI range of 1.0000347-to-1.000449 by a sensor with a 4 mm long sensing stub element of 10 µm HC-PCF. Cyclic tests with the group of gases demonstrated that the measurements are highly repeatable. The measurement response and recovery times for all sensors were determined, and it was concluded that the 20 µm HC-PCF sensor has the fastest response/recovery time and the PCF sensor has the slowest. This research illustrates that the sensors fabricated by the proposed method have potential for improving the ability to detect and quantify pure gases. Additionally, the sensors are highly sensitive to low percentages of CO2, making them suitable for greenhouse gas measurement.

中文翻译：

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光子晶体光纤结构对Mach-Zehnder干涉仪光纤气体传感器性能的影响

摘要 一种基于马赫-曾德干涉仪 (MZI) 的紧凑型折射率 (RI) 传感器已被开发和实验评估，用于气体（氦气、甲烷和二氧化碳）的高灵敏度检测和量化。RI 传感器使用多种光纤类型：单模光纤 (SMF)、光子晶体光纤 (PCF) 和空心光子晶体光纤 (HC-PCF)。为了制造 MZI 传感器，将一小段传感光纤放置在引入和引出单模光纤 (SMF) 之间，每个接口处都有气隙。使用这种配置制造了三种类型的传感器，采用 4 mm 短截线：(i) PCF、(ii) 10 µm HC-PCF 和 (iii) 20 µm HC-PCF 作为传感元件。比较了这些传感器用于检测和测量存在的气体量的性能。MZI 传感器的传输光谱是由包层模式和纤芯模式之间的干扰形成的。这些传输信号对应于传感器的快速傅立叶变换 (FFT) 频谱中的频率分量。为了优化设计元素，研究了间隙距离对模式数量和幅度分布的影响。由此产生的光纤传感器可以测量充气腔的 RI，并且它们对氦气、甲烷和二氧化碳表现出高灵敏度。在 1.0000347 至 1.000449 的 RI 范围内，具有 4 mm 长的 10 µm HC-PCF 传感短截线元件的传感器证明了 3210 nm/RIU 的最高 RI 灵敏度。对一组气体进行的循环测试表明，测量结果具有高度可重复性。确定所有传感器的测量响应和恢复时间，并得出结论，20 µm HC-PCF 传感器的响应/恢复时间最快，而 PCF 传感器最慢。这项研究表明，由所提出的方法制造的传感器具有提高检测和量化纯气体能力的潜力。此外，传感器对低百分比的 CO2 高度敏感，使其适用于温室气体测量。