An investigation of an optical fibre amplifier loop for intra-cavity and ring-down cavity loss measurements

Abstract

We present the design and initial investigation of a fibre optical system which may be used both for intra-cavity and for ring-down measurements of absorption losses. The system consists of a fibre loop containing a length of erbium-doped fibre pumped at 980 nm, with gain adjustment below or above threshold for the two types of operation. The fibre loop is constructed from standard fibre optical components and includes a micro-optical gas cell. The intended application is for measurement of levels of trace gases which possess near-IR absorption lines within the gain bandwidth of the erbium fibre amplifier. We discuss the key issues involved in operation of the system and the level of sensitivity required. Our initial experimental investigations have demonstrated that ring-down times of several microseconds can be obtained, which can be altered through adjustment of the attenuation or gain factor of the loop. Gain control is one of the most important issues and we explain how this may be achieved.

Fiber Ring Laser Intra-cavity Absorption Spectroscopy for Gas Sensing: Analysis and Experiment

“…Optical fiber laser gas sensors based on intra-cavity spectroscopy has attracted considerable interest due to their desirable features: inherent fiber compatibility, narrow linewidth, low detection limit, low noise and compact configuration [1]. High sensitivity Inter-Cavity Absorption Gas Sensor (ICAGS) can be achieved by inserting a gas cell into the fiber laser cavity [2].…”

Cavity-Enhanced Spectroscopy in Condensed Phases: Recent Literature and Remaining Challenges

“…1 pL fluid volumes placed within a 19 μm gap between fibers. Expanding upon the seminal work of Stewart et al [38,39] the work of Andrews et al [29] used an erbium-doped fiber amplifier within the optical loop to provide gain within the fiber to match the undesirable (nonabsorptive) per-pass losses caused by the apparatus. This innovative approach can help account for the high per-pass losses within the fiber loops; however, it can only be applied to certain wavelengths that the amplifier is designed for.…”

Fiber cavity ring down and gain amplification effect

“…Nowadays, CRD spectroscopy is widely used for chemical and molecular analysis in real time [4]. This technology quickly gave rise to the development of fiber optic-based CRD schemes, where a fiber loop is used as resonant cavity [5]. Although its focus is in optical spectroscopy, the CRD technique has also been used to the measurement of physical parameters, such as strain [6], pressure [7], temperature [8], refractive index [9], and biochemical sensing [10].…”