High-Resolution Seawater Density Sensor Based on Michelson Interferometer

Abstract

A novel seawater density sensor has been developed, offering high resolution and improved accuracy. The sensor employs a Michelson interferometer as the core sensing element, measuring density by directly incorporating seawater samples into the measurement path. To enhance measurement precision, standard seawater is used in the reference path to mitigate temperature and dispersion effects. The sensor system consists of a superluminescent diode and an interrogator, forming a compact, high-sampling-rate wavelength demodulation system, that is, particularly suitable for measuring seawater density with high spatiotemporal variability. However, the spectrum collected by the interrogator suffers from discontinuity. To address this issue, we designed a high-precision multi wavelength demodulation algorithm. This algorithm not only analyzes the movement of each resonance peak with a resolution of 0.0008 nm within a 70-nm detection range but also enables continuous tracking of specific resonance peaks via a dynamic adjustment mechanism. It overcomes the measurement range constraints typically faced by interference-based sensors, which are limited to a single free spectral range (FSR). The experimental validations demonstrate the sensor’s capability, achieving a density resolution of $1.79 \times 10^{-{5}}$ kg/m3 and an extended measurement range exceeding 35 kg/m3. The sensor’s average relative error in density measurement is 0.0144%, highlighting its effectiveness and potential for advanced oceanographic research.