Refractive index measurement for plane parallel plate using fiber point diffraction lateral interference and numerical modeling

A plane-parallel-plate (PPP) refractive index (RI) measurement method based on fiber point diffraction lateral interferometry and numerical modeling is proposed. Two fiber point light sources (PLSs) generate lateral interference through PPP, and the interferograms are collected by a linear array camera (LAC). Employing ray tracing of an ideal PLS and numerical simulation, the theoretical model of RI measurement is established by polynomial fitting with the RI of PPP as the output, the PPP thickness and the phase change at specific positions of the LAC detector as the inputs. To enhance measurement accuracy, the theoretical model is further corrected using PPP samples with known RI, measured thicknesses and phase changes. The experimental results indicate that the RI measurement accuracy can reach 10⁻⁴. Remarkably, this method features a simple structure and eliminates the intermediate optical components, except for the fiber PLSs, PPP samples, and LAC. We demonstrate how to simulate an ideal PLS with fiber PLSs and correct the numerical simulation model to improve the accuracy of RI measurement. Furthermore, this approach can be extended to other optical measurements.