Influence of Geometric Length Perturbation of Optical Path on Measurement Error of Seawater Refractive Index

As the demand for high-precision measurements of refractive index variations in marine environments increases, eliminating potential sources of measurement errors has become an urgent issue. One of these error sources is the impact of optical path length perturbations. This study investigates the effect of optical path perturbations on the accuracy of the measurements using the interference method. By establishing an error analysis model, this study analyzes the systematic errors induced by optical path perturbations and verifies the error patterns under different refractive index variations through simulations and experiments. The results show that the errors introduced by optical path perturbations are linearly related to the magnitude of the perturbations, and the error increases as the magnitude of the perturbation grows. The error becomes negligible when the magnitude of the optical path perturbations relative to the measurement zone length is one order of magnitude smaller than the refractive index measurement accuracy. The experimental and simulation results are consistent, validating the accuracy of the model. This indicates that in high-precision seawater refractive index measurements using the interference method, perturbations in the measurement region cannot be ignored, and it is difficult to achieve higher measurement precision through physical vibration isolation alone, highlighting the urgent need for new solutions.