Fabrication-error analysis of injection-molded aspheric elements using typical aberration terms in transmitted wavefront with Shack–Hartmann wavefront-sensing measurement

Xuemin Cheng,Yu Jen Lin,Qun Hao,Lingcheng Liu,Jie Cao,Lei Yan

doi:10.1117/1.oe.59.12.123102

Abstract

Aspheric lenses help meet the most demanding optical requirements while the precision injection molding technique hits the target for precision and cost. We developed a method of analyzing aberration terms in the transmitted “wavefront measurement,” determined by Shack–Hartmann wavefront sensing to estimate the fabrication errors of injection-molded aspheric elements. Considering aspheric element fabrication using a small training data set and F-measure fuzzy cluster analysis, an unsupervised learning method was applied to extract typical aberration terms from the wavefront polynomial. The experimental results suggest that these aberration terms, which are related to spherical (third-, fifth-, and seventh-order) and coma (third-order) aberration terms in the transmitted wavefront polynomial expansion, can be employed to estimate the surface error and decenter, respectively, of a lens from a specific mold cavity. The sampling lenses evaluated in the proposed measuring process were collected from different mold cavities according to their total working performance in the modulated transfer function measurement for the whole camera module. The performances of the typical aberration terms were discussed by comparing to the ones obtained from an interferometer and a profilometer. The proposed method could provide high detection efficiency and can thus be applied for the quality control of aspheric elements for mobile phones, where the existing errors are mainly spherical, coma, and astigmatism aberrations.

Highlights

Injection-molded aspheric lenses have widespread applications in industrial and consumer electronics,1,2 among other fields
Z7, Z8, Z9, Z16, and Z25 are the terms related to the third-order coma aberrations and third, fifth, and seventh-order spherical aberration (SA), respectively
In addition to the multi-order terms of the SA introduced by the Downloaded From: https://www.spiedigitallibrary.org/journals/Optical-Engineering on 02 Nov 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use injection-molding fabrication error, the system image quality is largely compromised by field-ofview-related aberrations, coma aberrations

Summary

Introduction

Injection-molded aspheric lenses have widespread applications in industrial and consumer electronics, among other fields. During injection molding, surface errors/deformations, surface decentering and asymmetry, element internal stress birefringence, and nonuniform refractive indices are almost inevitable. 3 Measurements are required to identify these errors, optimize the injection-molding characteristics to compensate for them, and modify the prototype molding parameters.. Aspheric element measurements are mainly achieved by either contact or noncontact approaches to estimate the aspheric surface error.. Due to the single-sided physical geometry of the measured injection-molded lens, the imaging quality cannot be determined directly. The transmitted wavefront measurement method, which provides more comprehensive information for error estimation in injection molding, is used to adjust the processes to achieve error compensation

Methods

Results

Conclusion