Seawater temperature and salinity sensing based on in-fiber Michelson-Fabry-Perrot hybrid interferometer employing frequency domain decomposition method

Abstract

We propose an in-fiber Michelson-Fabry-Perrot (M-FP) hybrid interferometer for the simultaneous measurement of seawater temperature and salinity. The sensor head consists of two parallel hetero Fabry-Perot (FP) cavities fabricated on the end face of the twin core fiber (TCF). A fiber fusion taper is used to split and recouple the light in the two cores. In this case, the Vernier effect can be obtained which can greatly enhance the sensitivity and solve the problem of temperature cross-sensitivity. Different from the traditional demodulation method based on envelop detection, we employed frequency domain decomposition method (FDDM) to demodulate the sensing signal. The simulation results indicate that the proposed sensor has high sensitivity to salinity and temperature. Thanks to the merits of high sensitivity, ease of fabrication and small footprint, the proposed seawater temperature and salinity sensor would have potential applications in marine science, food industry and ocean ranching.

References

[1] WoosleyR J, HuangF, MilleroF J. Estimating absolute salinity (SA) in the world’s oceans using density and composition[J]. Deep sea research part I: oceanographic research papers, 2014, 93: 14-20

[2] XuM X, ZhangX N, ChaiX, et al.. Design of marine salinity sensor based on boron-doped diamond film electrode[J]. Journal of ocean technology, 2022, 41(02):12-19

[3] ShenL, JiangJ F, WangS, et al.. Fiber laser salinity sensing based on micro-tubule[J]. Journal of optoelectronics·laser, 2022, 33(01):1-8(in Chinese)

[4] WangH, LiangC, BaoX. Salinity concentration sensing based on a tapered dual-core as As₂Se₃-PMMA hybrid fiber[J]. IEEE photonics technology letters, 2021, 33(4):181-184

[5] SamavatiZ, SamavatiA, IsmailA, et al.. Role of outer layer configuration on saline concentration sensitivity of optical fiber probe coated with ZnO/Ag nano-heterostructure[J]. Optics & laser technology, 2021, 136: 106722

[6] ZhaoY, ZhaoJ, WangX, et al.. Femtosecond laser-inscribed fiber-optic sensor for seawater salinity and temperature measurements[J]. Sensors and actuators B: chemical, 2022, 353: 131134

[7] ZhaoJ, ZhaoY, CaiL. Hybrid fiber-optic sensor for seawater temperature and salinity simultaneous measurements[J]. Journal of lightwave technology, 2022, 40(3):880-886

[8] WangY, TongR, ZhaoK, et al.. Optical fiber sensor based on SPR and MZI for seawater salinity and temperature measurement[J]. Optics & laser technology, 2023, 162: 109315

[9] LiZ, LiL, ZhangY, et al.. Highly-sensitive fiber-optic FP salinity sensor based on Vernier effect[J]. Optical fiber technology, 2022, 74: 103148

[10] WangL, GengY, LiX, et al.. High-resolution optical fiber salinity sensor with self-referenced parallel Fabry-Perot fiber microcavity[J]. IEEE sensors journal, 2022, 23(1):337-343

[11] NiuH L, WangW, ShenJ X, et al.. Composite double-cavity fiber Fabry-Perot salinity sensor based on hollow core fiber[J]. Optical instruments, 2021, 43(3):72-77

[12] QuanX, FryE S. Empirical equation for the index of re-fraction of seawater[J]. Applied optics, 1995, 34(18):3477-3480