Design of a confocal dispersion objective lens based on the GRIN lens

Abstract

Spectral confocal technology utilizes the principle of dispersion to establish the precise coding relationship between spatial position and wavelength in the axial focal point. The axial dispersion produced by the dispersion lens will affect the measurement range and resolution of the system. Taking into account the above advantages of the GRIN lens, the dispersion objective lens of spectral confocal displacement sensor based on the radial GRIN lens in this paper is proposed. The imaging characteristics of the GRIN lens are analyzed. By deducing the refractive index distribution and optical properties of the radial GRIN lens, the optical focal length and axial dispersion models of the GRIN lens are established. Then, based on the optical focus and dispersion function of the GRIN lens, the calculation of refractive index distribution is completed by MATLAB. The simulation design of the GRIN dispersion objective lens is completed by ZEMAX. Finally, the optimization design of the GRIN dispersion objective lens is completed. The designed results indicate that the dispersion objective lens based on radial GRIN lens can achieve axial dispersion of 1215 µm in the wavelength range of 420 nm ∼ 620 nm as well as the linear correlation coefficient between wavelength and axial dispersion is 99.69%. The resolution of GRIN dispersion objective lens is about 6.075 nm. The focusing effect of the lens at each wavelength is good, and the measurement range and dispersion linearity of the lens are better than those of the same kind of traditional dispersion objective lens. Compared with the same kind of traditional dispersion objective lens, the dispersion objective lens based on GRIN lens has compact structure and small diameter. And the measurement range and resolution of the system are improved. So it is easier to realize precise measurement. The research results of this paper have certain guiding significance and reference value for the application of the GRIN lens in the spectral confocal system.