Theoretical and experimental evaluation of surface quality for optical freeform surfaces

Optical freeform surfaces have become indispensable in the products of photonics and telecommunication. Due to the geometrical complexity and optical particularity, it is difficult to test and evaluate the surface quality of optical free form surfaces in terms of the form accuracy and surface finish. This paper presents a surface metrology model for the evaluation of surface quality of the optical freeform surfaces. The model is built based on a freeform surface-matching algorithm using the five-points-position-fixed, layered-step, and multilevel method with the match precision higher than 1 nm. Some parameters are also proposed for evaluating the surface quality of the freeform surfaces. The model is validated through a series of simulation and actual measurement experiments. The theoretical results agree well with the experimental results.