In situsalinity measurements in seawater with a fibre-optic probe

Abstract

We have successfully proved the feasibility of an optical salinity meter for marine applications in a two-week measurement campaign, carried out for the realization of in situ salinity measurements in seawater. An optical instrument (optode), in which the main element is a fibre-optic refractive-index sensor based on surface plasmon resonance (SPR), has been developed for that purpose, and has been especially designed to be able to operate in realistic conditions. The performance of the optode has been evaluated on an oceanographic ship in the Baltic Sea, close to the Vistula estuarine area. The obtained results (in different tests, such as depth-profiling, towing and stationary measurements) show good correlation with the data provided by a commercial probe. Although the device is currently a part of a more complex measuring platform and uses an axial spectrograph as detector, the output power measurement used and the simplicity of its conception allow us to conceive a closed, extremely compact set-up which can be in principle commercially competitive with existing sensors.

Surface Plasmon Resonance‐Based Fiber Optic Sensors: Principle, Probe Designs, and Some Applications

“…Surface plasmon resonance-based fiber optic sensors have also been reported for other chemical species. These include measurements of salinity in water [22,37], refractive indices of alcohols [17], BSA [34], vapor and liquid analyses [18]. In addition a single-mode waveguide surface plasmon resonance sensor has been developed for biomolecular interaction analysis [47].…”

“…The additional advantage of optical fiber is that the SPR probe can be miniaturized which can be advantageous for samples which are available in minute quantity or are costly. Due to these advantages the surface plasmon resonance-based optical fiber sensors have drawn a lot of attention [10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Both experimental and theoretical investigations have been reported in literature on the SPRbased fiber optic sensors.…”

Tapered optical fibre sensor for detection of hydrocarbon spills in seawater

“…Used as a refractometer without any deposited layers, silica tapers present the limitation that they are unable to measure indices lower than the value of silica refractive index. The coating of tapers with metallic and dielectric layers permits to overcome these limitations, thus increasing the measurable range of indices and being able to apply to other fields, such as the seawater salinity measurement [10][11][12] .…”

Salinity sensor based on polyimide-coated photonic crystal fiber

“…In addition to the unique features reported in [1][2][3], PCFs also possess the advantages of conventional optical fibers in sensing applications such as EMI immunity, compact size, corrosion resistance, light weight, multiplexing capability, etc. Optical fiber sensors are also attractive for in situ monitoring of different physical, chemical, and biological parameters, e.g., strain [4,5], temperature [6], refractive index [7], pH [8], relative humidity [9,10], and water salinity [11][12][13][14][15][16][17][18]. Salinity sensors play an important role in manufacturing process control and protection of ecosystems.…”

“…Salinity sensors play an important role in manufacturing process control and protection of ecosystems. Fiber optic salinity sensors have been reported based on salinity sensitive hydrogel/polyimide-coated fiber Bragg gratings (FBG) [11,12], surface Plasmon resonance effect [13,14], and refractive index detection with long-period fiber gratings [15,16], etched FBG [17], and femtosecond laser micro-machined Fabry-Pérot interferometer [18] to derive salinity response. However, these salinity sensors have relatively low sensitivity and/or exhibit large temperature cross sensitivity which degrades the sensor performance.…”