Optical system design of seawater refractive index measurement based on ZEMAX

Abstract

The refractive index is an intrinsic optical property of seawater and it is one of the essential parameters in ocean observation. The traditional method of detecting the refractive index of seawater is calculated by measuring the temperature, conductivity, and pressure of seawater using CTD (Conductivity-Temperature-Depth) device. However, CTD can only detect the conductive ions in seawater, but not the non-electrolytic solutes in seawater, which leads to errors in salinity detection, and the accuracy of current seawater refractive index detection methods cannot meet the requirements. In this paper, based on the requirements of seawater refractive index measurement, the Zemax optical simulation analysis of the seawater refractive index measurement system was carried out. The influence of the angle between the two pass lenses in the detection area, the focal length of the focusing lens, and the size of the photo sensitive surface of the detector on the measurement system are analyzed. When the angle between the two pass lenses is 30°, the focal length of the focusing lens is 300 mm and the size of the photosensitive surface of the detector is determined to 4×4 mm2, the optimal refractive index measurement sensitivity of the optical system is obtained. it is calculated that when the detector accuracy is 1μm, the refractive index detection sensitivity of the optical system is 10-6 RIU.