Multichannel continuous-wave fiber cavity ringdown gas sensing utilizing frequency-shifted interferometry

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

“…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 frequency shift is usually introduced by an acousto-optic modulator (AOM), while a balanced detector is used to subtract the two interference signals to remove noise and effects of outside disturbances. The resultant FFT signal is converted to distance, which provides the CRD signals in the spatial domain. ,, This circumvents the need for fast detectors and fast data acquisition systems, making the system cost-effective.…”

“…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.…”

“…The resultant FFT signal is converted to distance, which provides the CRD signals in the spatial domain. 44,46,47 This circumvents the need for fast detectors and fast data acquisition systems, making the system costeffective.…”

Multipoint Fiber Loop Ringdown Sensors for Large Strain Measurement Using Frequency-Shifted Interferometry

“…In addition, differential detection is used to eliminate the direct current (DC) noise of the interference signal and thus the SNR is further improved, which provides the sensing system with high stability. Since its advent, it has been used in magnetic field [18], pressure [19], and gas concentration detection [20,21,22]. However, no reports have been found on strain sensing using FSI-FLRD.…”