Simultaneous measurement of salinity and temperature using a Sagnac interferometer based on concatenated polarization-maintaining fiber tapers

This paper presents a systematic review of the research available on salinity optic fiber sensors (OFSs) for seawater based on the refractive index (RI) measurement principle for the actual measurement demand of seawater salinity in marine environmental monitoring, the definition of seawater salinity and the correspondence between the seawater RI and salinity. To further investigate the progress of in situ measurements of absolute salinity by OFSs, the sensing mechanisms, research progress and measurement performance indices of various existing fiber optic salinity sensors are summarized. According to the Thermodynamic Equation of Seawater-2010 (TEOS-10), absolute salinity is recommended for sensor calibration and measurement. Comprehensive domestic and international research progress shows that fiber-optic RI sensors are ideal for real-time, in situ measurement of the absolute salinity of seawater and have excellent potential for application in long-term in situ measurements in the deep ocean. Finally, based on marine environmental monitoring applications, a development plan and the technical requirements of salinity OFSs are proposed to provide references for researchers engaged in related industries.

Section: Salinity Ofssmentioning

confidence: 99%

“…( b ) The proposed seawater−filled PCF [ 67 ]. ( c ) Schematic diagram of the performance test system for the proposed SI based on concatenated panda PMF tapers [ 68 ]. Reprinted with permission from Ref.…”

Section: Salinity Ofssmentioning

confidence: 99%

Review of Seawater Fiber Optic Salinity Sensors Based on the Refractive Index Detection Principle

Wang

Shi

et al. 2023

“…Taking the sensing of sodium nitrate in seawater, for example, an ultrahigh sensitivity of 14.95 pm/ppm is realized, whose equivalent sensitivity is about 1.26 × 10 5 nm/RIU for RI sensing. In addition, by combining an in-line MMZI with tapered SF or Sagnac loop, simultaneous measurements of temperature and salinity are also achieved ( Figure 4 e) [ 104 , 105 ].…”

Section: Ofs For Multi-parameter Sensing and Measurement In Tspmentioning

confidence: 99%

Review of Optical Fiber Sensors for Temperature, Salinity, and Pressure Sensing and Measurement in Seawater

Liang

Wang

Zhang

et al. 2022

Temperature, salinity, and pressure (TSP) are essential parameters for the ocean. Optical fiber sensors (OFSs) have rapidly come into focus as an ocean detection technology in recent years due to their advantages of electromagnetic interference, light weight, low cost, and no waterproof requirement. In this paper, the most recently developed TSP sensors for single parameter and multi-parameter TSP sensing and measurement based on different OFSs are reviewed. In addition, from the practical point of view, encapsulation methods that protect fibers and maintain the normal operation of OFSs in seawater, and the response time of the OFS, are addressed. Finally, we discuss the prospects and challenges of OFSs used in marine environments and provide some clues for future work.

“…Fiber optic technology for salinity measurement has recently attracted extensive attention due to the advantages of high sensitivity, low cost, anti-electromagnetic interference, and strong stability [ 3 ]. In the last few years, various fiber optic salinity sensors have been proposed, including fiber Bragg grating (FBG) [ 4 ], Fabry–Perot interferometer [ 5 ], MZI [ 6 , 7 , 8 ], Sagnac interference loop [ 9 ], surface plasmon resonance (SPR) [ 2 ], etc. Because different sensing structures have distinctive advantages, combining different methods can give full play to the advantages of the whole sensing system and has become a new research hotspot.…”

Section: Introductionmentioning

confidence: 99%

Salinity and Temperature Dual-Parameter Sensor Based on Fiber Ring Laser with Tapered Side-Hole Fiber Embedded in Sagnac Interferometer

Zhao

Lin

et al. 2022

This paper presented a new kind of salinity and temperature dual-parameter sensor based on a fiber ring laser (FRL) with tapered side-hole fiber (SHF) embedded in a Sagnac interferometer. The sensing structure is majorly composed of tapered SHF located in the middle of SHF inside the Sagnac interferometer loop structure. The influences of the SHF’s diameters of different tapered in the Sagnac interferometer loop on the FRL sensing system are studied. The presence of air holes in the SHF makes the cladding mode easier to excite, and the interaction between the cladding mode with its surroundings is enhanced, thus having higher salinity sensitivity. Besides, the unique advantages of high resolution, narrower linewidth, and high signal-to-noise ratio (SNR) of fiber laser make the measurement results more accurate. In this experiment, the SHF with different taper diameters was made, and it was found that reducing the diameter of the taper waist diameter could further improve the salinity sensitivity. When the waist diameter was 9.70 μm, the maximum salinity sensitivity of 0.2867 nm/‰ was achieved. Temperature sensing experiments were also carried out. The maximum temperature sensitivity of the FRL sensing system was −0.3041 nm/°C at the temperature range from 20 to 30 °C. The sensor has the characteristics of easy manufacture, good selectivity, and high sensitivity, proving the feasibility of simultaneous measurement of seawater salinity and temperature.