Generating Multi-spectral Images And Separating Frequency Components Based On Diffractive Optics Effects

In this dissertation, the design method and the fabrication technology consisted of single step photolithography and single step wet etching for diffractive optical elements are researched carefully. Several diffractive optical elements, which can be used to generate arbitrary multi-spectral images, separate frequency components from incident light, and focus incident Gaussian ray into a very small spot for DVD system, are designed. The technological and optical experiments of several elements fabricated are performanced. The main works are below:(1) The algorithm designing, modeling and simulation for diffractive optical elements are finished. Several common algorithms for diffractive integral and the optimizing algorithms for designing diffractive optical elements, such as IFTA, SA, GA, et al, are analyzed and compared carefully; (2) A new wet-etching method for fabricating diffractive optical elements is proposed. Through modulating the diameter of the hole opened in mask over the wafer, the etching depth can be controlled so as to obtain the diffractive phase-step structure that is the whole technological process for diffractive optical elements can be carried out only through single-step photolithography and single-step wet etching. The simulation of the etching process is performaned, and very good technological results are acquired. (3) Several optical images from target selected by us can be generated by diffractive optical elements. Through comparing algorithms utilized, IFTA is selected to design diffractive optical elements, and several samples are fabricated by KOH etching. The optical reconstruction experiments show that the optical images generated by samples fabricated are very clear; (4) Weighted IFTA is used to design the diffractive optical elements, through which frequency components in incident lasers can be separated. Simulations indicate that the incident lasers with three frequency components can be focused onto the region specified by us. The samples are also fabricated by wet etching method proposed by us; (5) Part of the work of focusing Gaussian Laser into a very small spot using diffractive optical elements is completed. According to the simulation, the incident Gaussian beam can be focused into a structure with sub-micrometer scale. The samples are fabricated by wet etching. Through comparing the focusing results of samples with that of commercial aspherical lenses, the feasibility of the method is proved. Above all, the design method and fabrication technology for diffractive optical elements are explored carefully in this dissertation. A method with single-step photolithography and single-step wet etching is proposed and performanced for fabricating diffractive optical elements with multi-step phase structure. The experiments show that the complexity and the cost in the process of fabricating diffractive optical elements are reduced remarkably compared with traditional methods.