Femtosecond laser etching C-type fiber optic vernier sensor for seawater temperature and salinity measurements

Abstract

In this work, we demonstrate a dual C-type fiber optic vernier sensor based on femtosecond laser etching for measuring seawater temperature and salinity. The C-type fibers are etched using femtosecond laser microfabrication technology on hollow-core fibers (HCF), including temperature and salinity cavities. The seawater can fully flow into the salinity cavity as a sensing medium, and the polydimethylsiloxane (PDMS) is filled into the temperature cavity as a sensitizing medium. Combined with the vernier effect, dual parameter high sensitivity simultaneous measurement is achieved. Through simulation and experimental testing, the sensor can achieve high sensitivity measurement of seawater salinity and temperature, with sensitivities of −2.69 nm/‰ and −4.54 nm/℃, respectively. In the stability tests of salinity and temperature, the maximum interference wavelength shifts are 0.52 nm and 0.64 nm, respectively. In the repeated measurement experiment, the maximum deviation of sensitivity for salinity cavity and temperature cavity measurements are 0.03 nm/‰ and 0.18 nm/℃, respectively, indicating that the structure has good measurement stability and repeatability. This sensor has the advantages of strong stability, good repeatability, and low cost, which can be used as a new type of sensor to achieve high-sensitivity detection of seawater parameters.