Measurement of concentration and temperature using a fiber loop ring-down technique with core-offset structure

Cavity Ring-Down Spectroscopy: Recent Technological Advancements, Techniques, and Applications

“…The introduction of optical fibers as the ring-down cavity has added a compact and versatile version to the otherwise bulky CRDS systems. , To trap light inside the fiber, typically fiber couplers are used with high coupling ratios (∼99:1), where the fiber is arranged either in a loop format or in a linear fashion . Alternatively, fiber Bragg gratings (FBG) or high-reflective thin-films can also be used on two sides of the fiber to construct a fiber resonator.…”

“…The fiber as well as the couplers contributes toward various losses such as the fiber’s transmission loss, insertion, and coupling losses, etc., which can significantly reduce the inherent ring-down time of the resonator. To recompense these losses, amplifiers such as erbium-doped fiber amplifiers (EDFA) are utilized, which provide a gain for maintaining the signal strength. , The sensing region is usually composed of a normal or tapered fiber but might consist of other components such as a gas cell, FBG, or a variable attenuator . Flexibility of incorporating different sensor elements is also one of the major advantages of fiber-based CRDS techniques.…”

“…The gain measurement using fiber-based CRDS did not require any preinformation on material constants of the fiber, which is usually the case with other methods, and the technique can be utilized for other microresonator systems. Apart from the above applications, fiber-based CRDS has been exploited for applications like temperature , and chemical sensing , as well. It can be noted from the above discussion that essentially the near-infrared (IR) region has been utilized for fiber-based CRDS applications.…”

“…To recompense these losses, amplifiers such as erbium-doped fiber amplifiers (EDFA) are utilized, which provide a gain for maintaining the signal strength. 40,43 The sensing region is usually composed of a normal or tapered fiber 39 but might consist of other components such as a gas cell, 44 FBG, 41 or a variable attenuator. 45 Flexibility of incorporating different sensor elements is also one of the major advantages of fiberbased CRDS techniques.…”

Refractive index Mach–Zehnder interferometer sensor based on tapered no-core fiber

“…In recent years, optical Mach-Zehnder interferometer (MZI) sensors have attracted increasing attention due to their high sensitivities and simple structures. More and more novel structures are used in optical MZI sensors, such as core offset fusion [1], twisting [2], coating [3], etching [4], and tapering [5][6][7]. Various parameters can be measured by optical sensors, such as temperature [8], humidity [9], refractive index [10][11][12], liquid level [13], strain [14], and so on.…”