Diagnosis of diseases through exhalation is a new, noninvasive method. In this study, a new photonic crystal fiber (PCF) has been proposed for detecting ammonia gas in breath. The spectroscopy system contains a tunable laser source, a monochromator that sets the wavelength at the absorption line of ammonia gas, a PCF used as a cell gas, a detector, and a computer to monitor and show the results. The gas sensing attributes of photonic crystal fiber are analyzed through the Finite Element Method (FEM). According to the simulated result, the high relative sensitivity of 63.18% is obtained when the core is filled by ammonia gas at 1.544 µm wavelength. The effect of water vapor on ammonia gas is investigated. It is shown that with the addition of respiratory moisture, the sensor still has high sensitivity and less confinement loss. Therefore, it is almost insensitive to moisture. These results illustrate the high performance of the sensor designed and that it can be helpful for medical applications, especially in diagnosing renal failure.

通过呼气诊断疾病是一种新的无创方法。在这项研究中，已提出了一种新的光子晶体光纤（PCF）用于检测呼吸中的氨气。光谱系统包含一个可调激光源，一个在氨气吸收线上设置波长的单色仪，一个用作池气体的PCF，一个检测器以及一台用于监视和显示结果的计算机。通过有限元方法（FEM）分析了光子晶体光纤的气敏特性。根据模拟结果，当纤芯中填充波长为1.544 µm的氨气时，可获得63.18％的较高相对灵敏度。研究了水蒸气对氨气的影响。结果表明，随着呼吸水分的增加，该传感器仍然具有较高的灵敏度和较小的限制损失。所以，它几乎对水分不敏感。这些结果说明了所设计传感器的高性能，并且对于医疗应用特别是在诊断肾衰竭中可能会有所帮助。