Development of Total-Internal-Reflection Polarization Interferometry for Refractive Index Measurement

This project aims at developing a "full-field refractive index distribution measurement technique" to solve the inspection problems of the injection molding lenses. Due to the high production efficiency of the injection molding technology and the lightweight of the plastic material, the injection molding lens has gradually replaced the glass lens and is widely used in various fields, such as mobile phone lens, car lens, and optical video lenses, etc. However, variations in manufacturing parameters such as filling, packing, and cooling can seriously affect the optical parameters of the lens, such as refractive index and thickness distribution. Because these two parameters are optically coupled together, the conventional geometric and interferometric measurement techniques can’t measure both them at the same time. This is the biggest challenge facing injection molding manufacturers today. Based on the principle of "maximum phase difference of total reflection", this project will design and develop an innovative "coaxial phase measurement system", which will be applied to the measurement of refractive index distribution to solve the problem of lens curvature and morphology distribution. The innovative highlight of this project is the design of the coaxial polarization interferometry. There is no need to rotate or move any component, just through image rotation with the programming, we can obtain four phase-orthogonal images for phase difference measurement. In other words, this technology has a one-shot function, which can do the instant measurement. On the other hand, the maximum value of phase difference δmax can be measured in real-time, which eliminates the disturbance of the incident angle change or the incident surface rotation caused by the uneven surface shape of the test object, It is suitable for the refractive index measurement of curved or non-planar objects.