Dual parametric simultaneous measurement of pH and temperature based on optical fiber interference and silanized pH-responsive hydrogel

A no-core and few-mode fiber-based structure coating with polyacrylic acid acrylamide hydrogel is used to realize pH and temperature measurement simultaneously. The proposed structure can be obtained through splicing the no-core fiber, few-mode fiber and no-core fiber (NFN) with a certain length in sequence. Its measurement range can cover 2 to 12 for pH and 20 °C to 90 °C for temperature. Meanwhile, surface silanization of the optical fiber is performed to facilitate the adhesion of the hydrogel and to refine the silanization process. The pH-based transmission-sensitivity is measured to be 0.959 dB/pH and the highest pH-based wavelength-sensitivity is 0.837 nm/pH. The temperature-based wavelength-sensitivities are measured to be 0.01 nm/°C and 0.02 nm/°C, respectively, in two different pH environments of 2 ∼ 5 and 5 ∼ 12, while the temperature-based transmission-sensitivities are measured to be 0.432 dB/°C and 0.356 dB/°C, respectively. The pH response of hydrogel and inherent temperature response of NFN-based Mach-Zehnder interferometer enable the sensor to perform dual parameter measurements for pH and temperature. The dual-parameter matrices are established and validation experiments are carried out. It is demonstrated that the pH and temperature measurement errors can be as low as 0.088 and 1.112°C respectively. This sensor is expected to have broad prospects in environmental monitoring, chemical analysis, and other related fields.