Any two-dimensional interpolation scheme which has continuous derivatives may be used to represent an optical surface for ray-tracing purposes. We present bicubic splines in their application to the design of asymmetric surfaces. An as example of a problem requiring an asymmetric system, we analyze the design problems of a color TV lighthouse lens.
T. P. Vogl, A. K. Rigler, and B. R. Canty, "Asymmetric Lens Design Using Bicubic Splines: Application to the Color TV Lighthouse," Appl. Opt. 10, 2513-2516 (1971)