Design and fabrication of a variable-line-space grating surface for a Fresnel-grating lens based miniature spectrometer

摘要

A new type of plane optical lens, the Fresnel-grating lens with variable-line-space grating surface based on dual point-source holographic technique, is demonstrated, optimized and fabricated in this research. The Fresnel-grating lens integrates the function of a diffraction grating and a Fresnel lens, and provides collimation, focusing as well as dispersion effects at the same time, which simplifies the optical structure and fits perfectly for a miniature spectrometer. The variable-line-space grating surface can enhance the modulation ability of the spectrometer system A mathematical model is established based on the least wave-change principle and the system parameters are optimized using optics simulation software ZEMAX. The fabrication procedures for the Fresnel-grating lens with soft lithography are illustrated in detail, and a dual-point holographic exposure optical path to form the grating surface as well as a mold to cast the Fresnel-grating lens are constructed. Samples of Fresnel-grating lens with the size of 16mmx16mmx5mm are fabricated and preliminarily tested. The period on the central part of fabricated grating surface is 926±2nm and the results show great consistency with the simulation. With further testing in the spectrometer system, the Fresnel-grating lens with a variable-line-space grating surface holds considerable potential in the miniature spectrometer area.