Simultaneous Measurement of Pressure and Temperature in Seawater with PDMS Sealed Microfiber Mach-Zehnder Interferometer

Simultaneous measurement of pressure and temperature in seawater is realized based on polydimethylsiloxane (PDMS) sealed microfiber Mach-Zehnder interferometer (MZI). Benefitting from the high thermal-optic coefficient and large elasticity of PDMS, high sensitivity and robust structure can be obtained. In theoretical modeling, significant enhanced pressure response in fiber is observed clearly, and pressure or temperature sensitivities are calculated theoretically. In experiment, PDMS sealed MZI is fabricated by a two-step sealing method. Using this MZI, sensitivity of 13.31 nm/MPa for pressure sensing and -7.41 nm/°C for temperature sensing are demonstrated, respectively, which are about one order higher than bare fiber MZIs (without PDMS sealing). To verify the accuracy of sensor, several tests under arbitrarily pressure and temperature are performed with average errors of 4.38% and 1.44%, respectively. In addition, effects of encapsulation on avoiding cross-sensitivity with salinity, PDMS thickness on pressure sensitivity, response time, repeatability, time stability, and polarization of the sensor are also evaluated by experiment. Sensors demonstrated here show advantages of low cost, simple fabrication, robust and compact structure, high-pressure resistance, high sensitivity, good repeatability, and long-term stability.