Measurement of Large Freeform Optics using a Small and High-Precision Sensor

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Using freeform optics, the optical industry can provide compact, efficient, and high performance optical products with many unique features that allow reduction in both the number and size of lenses in an optical system. These products have wide applications including scientific research, solar energy harvest, medical, and military applications. However, manufacturing of freeform optics today relies on the "trial and error" approach due to the lack of efficient metrology to measure freeform optical surfaces during and after they are manufactured. This award supports fundamental research to provide knowledge that is needed to develop a new freeform optics measurement system that can measure freeform optical surfaces efficiently. The new measurement system will provide US companies a competitive edge and can lead to innovations in telecommunication, aerospace, consumer electronics, automotive, and medical industries.The new freeform optical metrology is based on subaperture measurements using a small and high-precision Shack-Hartmann wavefront sensor. These measurements are then combined using novel stitching methods to reconstruct the entire freeform optical surface. The first research objective is to establish the dependence of each stitching method on the system design. Each stitching method will be characterized by its convergence rate and corresponding residual error. The design parameters include aperture size, shape, and selection of Zernike polynomial terms. To achieve this objective, experiments on an Alvarez lens will be performed by changing the subaperture size between 10-100 percent of the full aperture. In addition, a square and a sphere shape subaperture will be tested, and up to 7 Zernike polynomial terms will be used in the experiments. The second research objective is to establish the relationship between the dynamic performance of the system and microlens design and lens array configuration used in the Shack-Hartmann sensor. In experimental investigations, microlens parameters (including f-number and lens geometry) and lens array configuration (including non-uniform lens layout and arbitrary base curve where the microlenses reside) will be varied; dynamic performance of the system will be evaluated in terms of degree of slop change, measurement time, and measurement accuracy.