Thickness measurement of radial GRIN lens based on chromatic confocal technology

Abstract

The chromatic confocal technology (CCT) has ultra-high distance measurement resolution and the characteristics of multi-surface tomography. It is merely widely used to measure the thickness of uniform materials currently. As a typical inhomogeneous material, the iso-refractive index surface of the radial GRIN lens is a cylindrical surface with central axis symmetry. The radial GRIN lens is an important optical element in the field of micro integrated optical instruments, such as optical fiber sensing, optical communication, etc. High precision thickness measurement parameters help to guide the accurate application of the GRIN lens and control the performance of related ultra-precision optical instruments. To measure the thickness of the radial GRIN lens with a single probe by the advantage of the CCT technology in measuring tiny distances. In addition, the placement tilt of the GRIN lens during the measurement would change the incident position of the probe light entering the lens to change the propagation path of the light and inevitably affect the accuracy of thickness measurement. The influence of the GRIN lens placement tilt on thickness measurement is studied theoretically. The thickness measurement error caused by the inclination of the GRIN lens and its axial measurement position is simulated and analyzed. The research results have significance for optimizing the system structure and further improving the system performance for the application of the CCT in measuring non-homogeneous materials or optical thin film.