Dual-channel in-fiber SPR sensor for simultaneous and highly sensitive measurement of salinity and temperature

In this Letter, an in-fiber dual-channel surface plasmon resonance (SPR) sensor is reported that uses polydimethylsiloxane (PDMS)-filled C-type microstructured optical fiber (COF). The COF is made of HF-acid-etched single-sided hole optical fiber (SSHF), and its inner and outer sides are coated with gold film to stimulate SPR. The inner channel is filled with PDMS and acts as the temperature measurement channel, and the outer channel is directly in contact with the salt solution and acts as the salinity measurement channel. Experiments show that the sensor is qualified to detect salinity and temperature simultaneously, and it exhibits a salinity sensitivity of 0.296 nm/‰ in the salinity range of 0-153.32‰ and a high temperature sensitivity of -2.4 nm/°C in the temperature range of 22-44°C. Furthermore, the sensor also enjoys good hysteresis, repeatability, and reversibility in salinity detection. In a word, the high sensitivity, simple preparation, and good integration of the proposed sensor endow it with the potential for deep-sea exploration.