High sensitivity open-cavity Mach-Zehnder interferometer based on no-core fiber for seawater salinity measurement

In this paper, an open-cavity Mach-Zehnder interferometer (MZI) based on no-core fiber (NCF) for salinity measurement in seawater is proposed and experimentally demonstrated. The sensor is fabricated by splicing a short section of NCF in a large offset between two sections of NCF. Therefore, when the input light is transmitted to the offset fusion point, it is divided into two parts, one part is transmitted in the offset NCF and the other part is transmitted in the solution under detection. Since the interaction between transmitted light and solution is large, high RI sensitivity can be realized. In the experiment, the sensitivity of salinity and temperature of the sensor are measured about 3.444 nm/% and 0.798 nm/℃ respectively by tracking the shift of interference dips. The seawater salinity sensor demonstrated in this paper has the advantages of corrosion resistance, low cost, high sensitivity and compact size, which would play an important role in marine environment monitoring or other micro-sample detection in the biological field.