Characterization of Surface Generation of Optical Microstructures Using a Pattern and Feature Parametric Analysis Method

Optical microstructures have a small scale topography classified as micro-grooves, microlens arrays, pyramids, lenticulations, etc. They are widely applied in optical components such as light guide panels for electronic displays. Most previous research work focuses on either the characterization of individual scale topography, or the optical performance of optical microstructures. There is a lack of surface characterization methods which are capable of characterizing the surface generation in terms of the form errors and the lattice relationships in the small scale topography of optical microstructures with sub-micrometer accuracy. This paper presents a pattern and feature parametric analysis method (PFPAM) for the characterization of the surface generation of optical microstructures. The method includes data acquisition, data processing and pattern analysis, exploration of and analysis of feature parameters, etc. Digital image processing technology has been employed and a series of lattice dislocation parameters have been developed to characterize the features of the distribution and the dislocation of optical microstructures. To verify the PFPAM, a prototype surface characterization system has been built. A series of cutting and measurement experiments have been conducted on microlens arrays and titled flats using a two-axis ultra-precision machining system equipped with Fast Tool Servo (FTS) and examined by a non-contact micro-surface profiler system. The results demonstrate that the PFPAM provides an adequate basis for good form characterization of optical microstructures, with form accuracy down to below sub-micrometer range. The proposed lattice dislocation parameters are shown to be useful for the characterization of the distribution and dislocation features in the small scale topography of the optical microstructures. This is not possible using traditional methods. Potential applications of the PFPAM for quality control and evaluation of optical microstructures are discussed.