Manufacturing of multi-element optical lenses requires compliance with design specifications within strict tolerances. Commercially available metrology systems allow verification of surface curvatures, center thicknesses, and overall centration. However, there is no single system that can perform all these measurements, which results in a complex and costly verification process. Additionally, currently available systems do not provide information on relative orientation between different elements within one lens assembly. Additional manufacturing errors may potentially arise when relying on third-party glass suppliers because glass types of individual elements within a compound lens cannot be verified. Here, we describe a method for full characterization of individual elements of compound optical lenses using reflectance confocal microscopy (RCM), low-coherence interferometry (LCI), and computational ray-tracing. RCM provides information about focal plane shifts within an optical elements and LCI is used to measure the corresponding optical thickness at different wavelengths. LCI was also used to measure radius of curvature and center thickness. Computational ray-tracing models were performed to a) estimate individual glass materials, and b) correct for optical distortions for accurate estimation of internal geometry. A database of glass properties of commercially available glass types was built using publicly available information, and glass estimation was performed by exhaustive optimization against the measured parameters for each glass type. We validated our method on commercially available singlet, doublet, and compound lenses. We believe this method may have applications in the lens manufacturing pipeline by providing an integrated-system for verification and quality assurance of compound lenses.
Mohamed T. El-Haddad and Yuankai K. Tao, "Non-contact characterization of compound optical lenses using confocal microscopy and low-coherence interferometry (Conference Presentation)," Proc. SPIE 10925, Photonic Instrumentation Engineering VI, 109250M (Presented at SPIE OPTO: February 06, 2019; Published: 4 March 2019); https://doi.org/10.1117/12.2510811.6009845735001.
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