Seawater refractive index sensor based on a cascaded double grating structure

Seawater salinity is a critical physical parameter in oceanography, affecting ocean circulation, marine ecosystems, and climate. However, current salinity measurement methods have limitations in terms of efficiency, convenience, and integration. Therefore, the development of advanced salinity measurement technology is crucial for ocean exploration and research. In this study, we designed a high-sensitivity ocean refractive index sensor using the guided-mode resonance, which exhibits superior performance in terms of transmission efficiency (approximately 1), full width at half maximum (0.210 nm), and figure of merit (5675.924). Furthermore, we obtained a set of optimized parameters by conducting a systematic study on the relationship between different structural parameters and resonance wavelength, which significantly improves the performance. Additionally, the variation trend of resonance wavelength with the change of refractive index in seawater was studied, which demonstrates that our optimized scheme achieves highly sensitive seawater salinity measurement with good process tolerance, polarization insensitivity, and a wide wavelength working interval. This high-sensitivity ocean refractive index sensor has great potential for a wide range of applications in future ocean exploration studies, such as ocean environment monitoring, marine ecology management, and oceanographic research.