Automated measurement of centering errors and relative surface distances for the optimized assembly of micro-optics

For any kind of optical compound systems the precise geometric alignment of every single element according to the optical design is essential to obtain the desired imaging properties. In this contribution we present a measurement system for the determination of the complete set of geometric alignment parameters in assembled systems. The deviation of each center or curvature with respect to a reference axis is measured with an autocollimator system. These data are further processed in order to provide the shift and tilt of an individual lens or group of lenses with respect to a defined reference axis. Previously it was shown that such an instrument can measure the centering errors of up to 40 surfaces within a system under test with accuracies in the range of an arc second. In addition, the relative distances of the optical surfaces (center thicknesses of lens elements, air gaps in between) are optically determined in the same measurement system by means of low coherent interferometry. Subsequently, the acquired results can be applied for the compensation of the detected geometric alignment errors before the assembly is finally bonded (e.g., glued). The presented applications mainly include measurements of miniaturized lens systems like mobile phone optics. However, any type of objective lens from endoscope imaging systems up to very complex objective lenses used in microlithography can be analyzed with the presented measurement system.