Continuous-Wave Fiber Cavity Ringdown Pressure Sensing Based on Frequency-Shifted Interferometry

Abstract

We present a continuous-wave fiber cavity ringdown (FCRD) pressure-sensing method based on frequency-shifted interferometry (FSI). Compared with traditional CRD or FCRD techniques, this FSI-FCRD scheme deduces pressure by measuring the decay rate of continuous light exiting the fiber ringdown cavity (RDC) in the spatial domain (i.e., the CRD distance), without the requirement for optical pulsation and fast electronics. By using a section of fiber with the buffer layer stripped in the fiber RDC as the sensor head, pressures were measured within the range from 0 to 10.4 MPa. The sensitivity of 0.02356/(km∙MPa) was obtained with a measurement error of 0.1%, and the corresponding pressure resolution was 0.05 MPa. It was found that the measurement sensitivity can be improved by enlarging the interaction length of the sensor head. The results show the proposed sensor has the advantages of simple structure, low cost, high sensitivity, and high stability in pressure detection.

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

“…That is, a poor stability is not caused by the FSI-FLRD technique itself. Actually, it has been verified that the FSI-FLRD can obtain better stability [19] because the differential detection and common-path interference have been employed to eliminate the impact of external disturbances in this technique. According to Equation (7), the calculated detection limits for the two sensing points were 0.0123 dB and 0.0360 dB, respectively.…”

“…Equation (7) shows that the detection limit is determined by the baseline stability of the ringdown distance δdi/d¯i and the number of roundtrips h . In the FSI-FLRD technique, differential detection is used for improving the SNR and stability, and also the ringdown distance is immune to the power fluctuation of CW light source, therefore, FSI-FLRD has better baseline stability and a higher detection limit under the same condition compared with the conventional FLRD techniques [19].…”

“…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.…”

Optical Sensor Using Space-Domain Active Fiber Cavity Ringdown Technique

“…Compared with the conventional FCRD method, this new scheme was more cost-effective because it utilizes a low-cost CW laser and slow detector without the need of expensive pulsed laser and fast electronics. Due to its excellent characteristics, such as low cost and high stability, the space-domain passive FCRD technique has attracted more and more interests and been widely used for many sensing applications, such as gas detection [22], pressure [23], magnetic field sensing [24] and so on.…”

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

“…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.…”