Simultaneous measurement of salinity and temperature based on ring-shaped microfiber resonator

Abstract

With the increasing intensity of ocean development activities and the impact of global climate change, accurate measurements of seawater salinity and temperature have become essential for understanding ocean dynamics and monitoring the health of marine ecosystems. This study presents an optical sensing platform that employs a microfiber ring resonator (MRR) configuration for the concurrent detection of salinity and temperature. The sensor leverages the inter-mode interference of the ring-shaped microfiber structure and the resonance effect of the resonator ring to facilitate real-time monitoring of both parameters. As salinity and temperature change, the interference and resonance wavelengths shift either redward or blueward due to changes in the refractive index. By establishing a linear correlation between spectral displacement and variations in salinity and temperature, a transmission matrix is created to concurrently obtain the salinity and temperature of marine water samples. Experimental results indicate that the microfiber inter-mode interference exhibits sensitivities of 390 pm/‰ and 810 pm/°C for salinity and temperature, respectively. The resonance ring effect yields sensitivities of 260 pm/‰ and 420 pm/°C for salinity and temperature, respectively. The salinity resolution reaches up to 0.01 ‰, while the temperature resolution achieves up to 0.005 °$C$. Furthermore, the sensor offers advantages such as a simple structure, enhanced electrical safety, and effective protection against electromagnetic interference.