Control of process for fabricating diffractive optical elements by direct laser writing

摘要

In this paper, a new method is developed to precisely control the key parameters for fabricating high quality diffractive optical elements, such as laser intensity and laser writing speed for the case of direct laser writing on photoresists. In order to obtain an accurate profile, the relationship between the final diffractive optical element relief profile and the required laser intensity is first characterized. Secondly, the designed diffractive optical elements' profile is divided into a M-stepped surface-relief profile, where M is decided by the process parameters. The spacing between two adjacent patterns is critical as overlapping of two adjacent traces could lead to over exposure and over development of the patterns. Hence, precise optimization of the fabrication parameters of each step is vital to avoid a rough and inaccurate surface. The computer control system has been programmed to compute the corresponding laser intensity incremental step and the spacing of adjacent patterns and control of process for fabricating diffractive optical elements. The compensation due to the laser variation has also been considered in the program. An example of a fabricated diffractive optical element and their optical performance are also demonstrated. It is proven that the method can control the process well to fabricate arbitrary surface relict profiles.