Advanced optical fiber sensors for measuring seawater salinity and pressure

The measurement of ocean salinity and pressure is crucial for studying changes in the marine environment, climate prediction, and the development of ocean resources. This study introduces two advanced optical fiber sensors designed for marine applications. One sensor is a surface plasmon resonance (SPR) reflection probe based on plastic optical fiber, used for measuring seawater salinity. Using thermal evaporation deposition technology, multimode optical fiber SPR reflection probes with Au and Ag coatings were fabricated, achieving sensitivities of 2321.42 nm/RIU and 2640 nm/RIU, respectively. The other sensor is a fiber Bragg gratings (FBG)-based seawater pressure sensor that employs a coupling technique between an elastic diaphragm and FBG. The FBG is embedded at the diaphragm and fixed within a chamber, providing precise temperature compensation and avoiding issues related to chirp effects and low sensitivity caused by metal packaging. Within the pressure range of 0 to 300 kPa, this sensor demonstrates a sensitivity of 19.65 pm/kPa. Both sensors exhibited excellent performance in seawater salinity and pressure testing, offering advanced technological means for marine environmental monitoring.