Compact optical fiber refractive index differential sensor for salinity measurements

Design and initial tests of a compact differential refractometer of deviation type are described. The use of optical fiber instrumentation for detection of the beam deviation profited in a compact device for remote sensing. For the industrial application a reflection type of type differential refractometer was designed. The laser is launched into the refractometer cell through the single mode fiber and SELFOC to illuminate a detector in form of a gaussian beam. The detection system consists of the in-line arranged multimode fibers. The deviation of the beam due to salinity of water is evaluated from light intensifies detected by four sequentially arranged fibers. Analog digital conversion and numerical computation of the signal results in the accuracy in determination of salinity better than 0.5%. The salinity measurement range starts from the lowest concentrations through seawater up to coal mine salt water.