Optical salinity sensing based on Michaelson interferometer under water pressure up to 11,500 meters

In oceanographic investigations, the salinity of seawater plays a crucial role as a fundamental parameter. The stringent conditions posed by the high-pressure environments in the deep-sea can be daunting for standard optical apparatus. In this manuscript, a Michaelson interferometer based optical salinity sensor is proposed and demonstrated experimentally with a resolution of 0.0003 PSU in a water chamber with pressure up to 11500 m to simulate the deep-sea environment. The unique design synchronizes the response to variations of both temperature and pressure in the sensing and reference arms, thus mitigating their influence on the optical path difference. This strategy paves the way for seawater salinity measurement with remarkable precision, extensive range, and superior resolution. The theoretical underpinnings and methodology surrounding the sensor's structure, as elucidated in this study, may contribute to the advancement and application of other optical interferometric sensors within deep-sea settings. © 2017 Elsevier Inc. All rights reserved.