A Multichannel Spatial-Domain Fiber Cavity Ringdown Pressure Sensor

We propose and demonstrate a multichannel spatial-domain fiber cavity ringdown (FCRD) pressure sensing scheme based on frequency-shifted interferometry (FSI). In contrast to existing multichannel FCRD techniques, multichannel FSI-FCRD measures intensity decay rates of continuous-wave (CW) light from different fiber ringdown cavities (RDCs) in the spatial domain, rather than those of pulse light in the time domain. It shares one CW light source, one slow detector and one slow data collector, which greatly reduces the system cost. We experimentally investigated a dual-channel FSI-FCRD pressure sensing system. The locations and pressures applied of the two FCRDs were obtained by measuring the corresponding ringdown distances. The measurement sensitivities were 0.030 (km
^-1
· MPa
^-1
) and 0.042 (km
^-1
· MPa
^-1
), with the minimum detectable pressure of 0.126 MPa and 0.403 MPa, respectively. By power budge analysis, the maximum sensor number was predicted to be 37 over a 50-km distance under the same experimental settings. The experimental and simulated results show that the proposed scheme has the advantages of low cost, high sensitivity, good linear response and good stability, which can enhance the multiplexing capacity and meet the requirements for multipoint measurement.