Research on the filter system of making diffractive micro-lens

With the development of optical micro-machining technology, micro optical elements, especially diffractive micro lens are widely applied more and more in the fields of fiber communication, airborne, optical storage, optic information processing, micro optical sensor and so on. In the ways of fabricating micro optical elements, gray-scale mask method is much studied and promising. On the basis of digital gray-scale mask technique, a new method, namely digital rotating mask method used to fabricate diffractive optical elements, is presented in this paper. Applying reduction projecting system based on digital micro-mirror device (DMD), digital gray-scale mask technique and filter system, using the output image of DMD to be equivalent to the gray-scale mask, and through the system the equivalent gray-scale will be projected and imaged on the substrate coated with photo-resist. Finally, the DOEs such as Fresnel zone plate and large-numerical-aperture diffractive micro lens can be obtained after reduction exposure, development, fixation, and etc. In the paper, the design theory and method of Fresnel diffractive micro is simply introduced. The main party is the construction and the function of low-pass filter in the projecting system. Through comparing the relevant micro optical elements, the importance of the filter is tested.