Double tailoring of freeform surfaces for off-axis aplanatic systems

The optical design of freeform surfaces is particularly demanding due to the inherently large number of degrees of freedom. Therefore the technique of tailoring optical freeform surfaces (mirrors or lenses), which is based on solving the underlying differential equations, is routinely used in non-imaging optics to efficiently achieve predefined light distributions. Tailoring can also be employed in for imaging optics: an optical freeform surface can be tailored such that one condition is exactly fulfilled - i.e. spherical aberration at a specific point is corrected. Recently, we extended this method such that two freeform surfaces can be tailored at the same time (double tailoring). This gives the freedom to impose a second condition and thereby allows for instance to simultaneously correct spherical aberration and satisfy the sine condition. As an example for a tailored off-axis aplanatic system we show a head-up display (HUD) consisting of two simultaneously tailored freeform mirrors.