Fabrication and measurement of freeform mirror for head-up display system

Abstract

Recently, freeform surfaces have been widely used in various optical systems because of their high flexibility and ability to correct aberrations when off-axis optical components are considered. Among freeform optics there are the head-up displays (HUDs) for vehicles, HUDs are increasingly used in new vehicles as they keep the driver’s head up and eyes focused on the road for the sake of improved safety. Fora compact size in the limited space of the vehicle, an HUD is typically an off-axis mirror system (including the windshield). The freeform mirror is not only employed to correct the off-axis aberrations caused by the windshield but also is used to provide an optical power for system magnification. This paper focuses on the design, fabrication, and measurement of a freeform mirror developed for a vehicle HUD system. We herewith report the design of the freeform surface including extended its polynomials description and its optimization. Using an ultra-high precision manufacturing and metrology strategy that is based on the use of a multi-axis machining center and advanced nano-metric profiler, the form error of the freeform mirror was precisely controlled according to system requirement. The fabricating method was realized on a machine equipped with a servo tool servo (STS) a and the combination of CXZ coordinates was programmed,. Finally, the freeform surface is fabricated and measured experimentally by ultrahigh accurate 3D profilometer.