Salinity sensor based on the back reflection on a fiber collimator

A new optical salinity sensor was proposed, which was designed by an optical collimator, based on a two-channel back reflection technique, and especially suitable for the long distance measurement of salinity (salinity was demonstrated by different concentrations of sodium chloride in de-ionized water). To demonstrate the performance of this new sensor, a comparative experiment was conducted. The experimental system was based on the structure of two Fresnel-back-reflection channels, one of which was designed with the measuring sensor, and the other was a fiber end with protective cladding. The main innovation and advantages of this sensor were that the common collimator could be directly used as a salinity sensor. Especially, the experimental results showed the signal to noise ratio(SNR) of this measuring method by using the collimator-sensor was at least 6.11 dB more than the common method by using fiber-sensor and the equivalent extended measurement distance of the system was at least extended by 30 km. The experimental results also show the temperature influence was estimated to be 0.005 16 dB/℃, which meant the temperature has little influence on the measurement, and also the influences resulted from fluctuation of light source and environment can be effectively eliminated.