Differential Phase Measuring Deflectometry for High-sag Freeform Optics

Abstract

In an effort to produce a more efficient optical system designers have begun to shy away from the traditional `spherical' lens, favoring freeform surfaces which correct for more aberrations, thereby allowing for a more compact system. The challenge now is determining how reliably these components can be manufactured, which requires a tool capable of accurately measuring them. We expand on previous phase measuring deflectometry techniques to enable the measurement of high-sag freeform optics by recording the difference in measured phase values. In this paper we justify the need for these changes by demonstrating where current approximations fall short, and a more generalized solution is derived. A system incorporating these changes was built to measure a high-sag freeform surface, the entire curved portion of a Samsung Galaxy S8 phone in single pass. We demonstrate our method is capable of determining deviations from an expected surface figure which makes it ideal for an industrial setting where quality control and consistency are critical.