Optical Fibre Sensors for high Sensitivity Gas Detection

近红外(IR)可调谐半导体激光光谱(TDLS)技术在许多气体传感领域已经成为一种强有力的技术手段。特别是，对于在困难或危险的环境/位置中的远程(有时是多点)应用，光纤TDLS的兴趣正在增长。该项目的总体目标是将光纤TDLS的灵敏度提高三到四个数量级，使其能够应用于检测微量气体，如毒素、神经毒气或其他可能构成安全威胁的物质和爆炸物或其他危险化学品分解产物的蒸气。将采取双重方式。第一种是一种风险相对较低的方法，通过仔细的光学设计和增强的光学和电子信号处理来消除标准具条纹并提高信噪比，从而在近红外系统中获得两到三个数量级的增强。在第二种更激进的方法中，我们将研究在远程气室使用导波、非线性连续波参数差频(DFG)装置，从近红外泵浦和光纤传输的信号波中产生中红外闲置波长。这将第一次使更强的中红外基波吸收线(以2/3个数量级)能够通过光纤使用TDLS进行寻址。基本DFG技术的一种变体/单谐振光参量振荡器-将在近红外中享受信号调制(TDLS技术)、光纤传输、恢复和检测的所有好处，同时利用与中红外更强的基波吸收线相关的灵敏度增益。预计灵敏度将远低于十亿分之几的水平。

Near infra-red (IR) tuneable diode laser spectroscopy (TDLS) has become a powerful technique in many areas of gas sensing. In particular, interest in TDLS over optical fibre is growing for remote (sometimes multi-point) applications in difficult or hazardous environments / locations. The overall aim of this project is to enhance the sensitivity of TDLS over optical fibre by three to four orders of magnitude to enable its application to the detection of trace gases such as toxins, nerve gases or other species that may represent a security threat and vapour by products of the decomposition of explosives or other hazardous chemicals. A dual approach will be adopted. The first is a relatively low risk approach to gaining two to three orders of magnitude enhancements in the near IR system through careful optical design and enhanced optical and electronic signal processing to eliminate etalon fringes and improve the signal to noise ratios. In the second, more radical, approach we will investigate the use of guided wave, non-linear CW parametric difference frequency generation (DFG) devices at the remote gas cell to generate mid IR idler wavelengths from near IR pump and signal waves transmitted over optical fibre. This will enable, for the first time, the much stronger (by 2 / 3 orders of magnitude) mid IR fundamental absorption lines to be addressed using TDLS over optical fibre. A variation of the basic DFG technique / the singly resonant optical parametric oscillator - will enjoy all the benefits of signal modulation (TDLS techniques), optical fibre transmission, recovery and detection in the near IR, whilst exploiting the sensitivity gains associated with the much stronger fundamental absorption lines of the mid IR. Sensitivities well below the part per billion level are anticipated.