Gas Concentration Sensing Based on Fiber Loop Ring-Down Spectroscopy: A Review

Gas detection plays an important role in many fields, such as atmospheric environment monitoring, biological monitoring, gas leakage monitoring, gas decomposition products detection, and so on. Nowadays, there are many kinds of gas sensors. Compared with normal gas sensors, optical sensors have the advantages of antielectromagnetic interference, high sensitivity, and compact size. Especially in certain extreme conditions, such as in aerospace applications and oil exploration application, optical fiber sensors are more attractive. This article presents a critical review on fiber loop ring-down spectroscopy (FLRDS), which can be used for quantitative detection of concentrations of trace gases. Fiber cavity is the core component of FLRDS system. The principles, loss characteristics, and application ranges of different types of fiber cavities are discussed. This article brings a variety of FLRDS techniques and introduces the basis for each technique, recent developments in methods, and performance limitations in detail. Finally, the existing technical barriers and future prospects of the FLRDS system for gas sensing are presented.

I. Introduction

Gas detection has become an essential matter and a research hotspot in past decades, especially in aerospace, environment monitoring, industrial production, respiratory diagnostics, and so on [1]–[3]. For example, ecology and environment departments monitor atmospheric carbon dioxide and other greenhouse gases to collect atmospheric environmental information; power companies monitor the operation status of equipment by detecting the flammable and explosive small-molecule hydrocarbon gases dissolved in transformer oil; in biomedicine, nitric oxide, ammonia, and so on are detected to achieve respiratory diagnosis.