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30 August 2019 Novel active alignment technique for measuring tilt errors in aspheric surfaces during optical assembly using Lens Alignment Station (LAS)
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Abstract
As optical designs require increasingly more aspheric elements to achieve high-resolution, high-quality imaging from smaller, more cost-effective systems, active alignment solutions to center and de-tilt aspheres in-situ during assembly are becoming paramount. Traditional active alignment systems, i.e. autocollimators, determine lens orientation from center of curvature (CC) positions of each surface and are consequently limited when measuring aspheres. Such tools measure the paraxial CC; therefore, measurement is inherently blind to orientation of the aspheric edge, leading to centered yet tilted aspheric surfaces and, thus, degraded image quality from the final optical assembly. Current market solutions to measure aspheric tilt consist of external probes directly measuring the aspheric edge; however, this approach involves addition and alignment of multiple precision stages and secondary sensors, adding to the complexity and cost of alignment systems. This paper demonstrates a novel solution for accurately measuring aspheric tilt during the assembly process utilizing the existing capabilities of the Lens Alignment Station (LAS). The LAS is an active alignment tool whose specialized design extends measurement ability beyond the requirement of confocal reflection. Aspheric measurement begins with standard vertex centration using the LAS at confocal position, but for tilt, we image away from confocal position and flood the surface with a high NA objective sampling the aspheric edge. Beyond confocal reflection, the LAS detects retroreflected concentric fringes that trace an orbit as a tilted asphere rotates. The orbit radius is proportional to tilt magnitude, such that simple software calculations accurately yield aspheric tilt measurements without requiring expensive external hardware.
Conference Presentation
© (2019) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Mark Green and Rognvald Garden "Novel active alignment technique for measuring tilt errors in aspheric surfaces during optical assembly using Lens Alignment Station (LAS)", Proc. SPIE 11103, Optical Modeling and System Alignment, 1110305 (30 August 2019); https://doi.org/10.1117/12.2528822
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