Lab-in-fibers: Single optical fiber with three channels for simultaneous detection of pH value, refractive index and temperature

The refractive index (RI) and temperature variation are two main error factors in the process of pH detection based on optical fiber sensor. In this paper, we reported a three-channel sensor based on double hole optical fiber (DHOF) with the simultaneous detection capability of pH value, RI and temperature. The single-mode core of DHOF is expanded by using the RI modulation of CO2 laser in order to excite surface evanescent wave (SEW) on the two hole surfaces of DHOF. One of the air holes is filled with polydimethylsiloxane (PDMS) as the temperature sensing channel. The open air hole on the other side is exposed to the air as the substrate of bimodal surface plasmon resonance (SPR) sensing channel. One SPR channel coated with Au/TiO2/Polyacrylamide Gel (PAAG) film realizes recognition of pH change, and the other SPR channel coated with Au film is directly used for RI detection. The results show that the temperature sensitivity of the SPR-2 can reach 1.605 nm/℃. The RI sensitivity of the SPR-1 can reach 2940.4 nm/RIU. The pH sensitivity of the SPR-2 can reach 13.34 nm/pH in the range of pH= 1–5 and 5.3 nm/pH in the range of pH= 5–9. This single optical fiber with three channels has high online integration and a good application prospect in the field of Lab-in-fibers.