Simultaneous measurement of underwater temperature and pH based on composite F-P fiber interference sensor coated by SCA-PVA/GO hybrid multilayer structure

Abstract

A composite Fabry-Perot (F-P) fiber optic sensor based on the vernier effect is fabricated, and experiments confirmed that it can be used to simultaneously measure underwater temperature and pH. The fiber optic sensor fabricated with single mode fiber (SMF) − multi mode fiber (MMF) − seven core fiber (SCF) − quartz capillary tube (QCT) − no core fiber (NCF) structures has contained a silane coupling agent-polyvinyl alcohol/graphene oxide (SCA-PVA/GO) hybrid multilayer film to enhance the sensor performance. Two types of sensors are fabricated, one with a plane end face and another with a tapered end surface, which named as sensor 1 and sensor 2, respectively. Their performance are experimentally demonstrated. Within the temperature range of 15°C-35°C and the pH range of 7.55–9.21, the sensitivities of sensor 1 to temperature and pH are 82.94 pm/°C and 1.16 dB/pH, while the corresponding values of sensor 2 are 39.26 pm/°C and 0.4 dB/pH. Experimental results demonstrated that the sensitivities of sensor 1 to temperature and pH are higher than that of sensor 2. But compared with sensor 2, sensor 1 has higher values of crosstalk and random error. By contrast, sensor 2 maintain a good linear relationship with the environmental dual parameters, allowing for the simultaneous measurement of underwater temperature and pH. Moreover, both sensors demonstrate good stability and reversibility when the temperature and pH are varied. Furthermore, the pH response times of the two sensors are less than 0.5 s, with a recovery time of 2 s. Thus, the proposed sensors with outstanding stability, reversibility, repeatability, and rapid response times will have a broad range of applications in the fields of marine environment monitoring, water quality detection, and food and medical device safety testing.