A Study of Processing Conditions on the Properties of Diffraction Optical Elements by Injection/Compression Molding Process

Abstract

Abstract The purpose of this work is to develop manufacturing techniques of diffraction optical elements (DOE) and compare the performance of micro injection (/compression) molded products. The DOE mold was fabricated by LIGA-like lithography technique. The optical performance of molded products strongly depends on the replication degree of micro patterns on the surface of DOE. Because of the complex micro patterns on the surface of the DOE, it is very difficult to measure the degree of duplication by traditional microscope measurement like SEM or AFM etc. In this work, a laser computer imaging system was developed to evaluate optical performance of molded parts directly. To achieve better duplication degree and properties of molded DOE, Taguchi's method was employed in the experiments to examine the effects of processing conditions on the performance of molded DOE. Residual stresses of different molded products were measured by a photo-elasticity system. Experimental results reveals that residual stresses of micro injection compression molded elements are much less than those of the micro injection molded ones. This is because compression process provides a higher and more uniform pressure distribution inside the cavity and it can help reduce the unbalanced shrinkage and residual stresses. Compression speed dominates the cavity pressure distribution and becomes the most important factor of final DOE's optical properties.