A compact multifunctional fiber sensor for simultaneous underwater measurement of salinity, temperature and strain

In this paper, a compact multifunctional optical fiber sensor based on single mode fiber-photonic crystal fiber-no core fiber-photonic crystal fiber-single mode fiber-polarization maintaining fiber Bragg grating (SPNPS-PMFBG) has been proposed. By monitoring the wavelength and output power of the two resonance peaks of PMFBG, simultaneous measurement of salinity, temperature and strain can be realized. In our experiment under water, the sum output power of the two resonance peaks in 0–7 wt% salinity shows a good linear relationship and repeatability, and the sensitivity is −0.58 dB/wt% with 3 s response time. In addition, the measured temperature wavelength sensitivities at two resonance peaks are 0.042 nm/°C and 0.040 pm/°C, and the output power sensitivities are approximate to 0.079 dB/°C and 0.081 dB/°C, respectively. Further, the strain wavelength sensitivities are 0.535 nm/1000 με, and the output power sensitivities are 0.65 dB/1000 με and 0.70 dB/1000 με.