Misalignment parameters estimation in refractive optical systems

Abstract

High image quality and complex, refractive optical systems, as those used in remote sensing applications, are, in general, very difficult to be manufactured with the required performance. This can be charged to the high sensitivity of such systems to the fabrication tolerances, mainly concerning the relative alignment of the optical components with respect to each other. When the system does not achieve the expected quality, the puzzle is to identify where the problems lies. This is even worsened when the number of optical elements becomes high. Due to these facts, some misalignment characterization and estimation techniques based on Bayesian estimators and wavefront measurements have been proposed in the literature. This paper is the result of a deep study and investigation of these techniques, with emphasis on an application to an intentionally simple system for the sake of illustration that highlights conceptual issues that could be extended to more realistic, complex optical systems. With this purpose, the sensitivity of the wavefront Zernike coefficients to the misalignment parameters, its use in a parameter estimator design that includes nonlinear terms, the study of the system observability, and a statistical analysis of the estimator performance considering the observation noise are addressed in details. Numerical simulation results for the simple system are shown. We also present insights on how to apply the technique to the alignment of a 11-lens optical system used in the Brazilian remote sensing camera MUX, that will fly on-board the upcoming Sino-Brazilian satellites CBERS 3&4.

Modeling Alignment Experiment Errors for Improved Computer-Aided Alignment

“…While environmental, measurement field and micrometer positioning errors play important roles in decreasing the process efficiency of the computer-aided alignment, earlier studies [1][2][3][4][5][6][7] gave less academic attention to these very subjects. On the contrary, this study addresses detailed modeling and analysis of such error sources influencing the alignment estimation performance for actual alignment run.…”

“…These include spatial and temporal variations of environmental conditions in WFE measurement, motion accuracies inherent from the use of alignment tools, etc. In earlier studies, researchers addressed the above effects individually and, to lesser extents, for performance verification of their computer-aided alignment algorithms used in alignment of their target optical system [4][5][6][7]. However, the actual alignment runs were made in inadequate accuracy range so that their algorithm performances were not investigated in detail.…”

Estudo de sensibilidade ao alinhamento e desenvolvimento de uma metodologia para alinhamento de sistemas ópticos por meio da análise de aberrações de frente de onda utilizando redes neurais artificiais

“…Metodologias para alinhamento de sistemas ópticos por meio das informações extraídas da frente de onda desses sistemas já vêm sendo propostas por diversos autores (6,30,32 A etapa 6 consiste no processo de alinhamento propriamente dito.…”