Optical structure design of automotive head-up display with long-distance imaging

Aiming at the demand of automobile augmented reality-head up display (AR-HUD) with farther visual distance and bigger field of view(FOV) angle for virtual images, a virtual image display optical path was designed by using the free-form surface off-axis reflection optical path structure with a focal length of -309 mm, a visual range of 7.5 mand a virtual image FOV angle of 9.8°×5.5° for the virtual image. According to the typical human eye resolution angle of 1′, the source image display module adopted the backprojection digital light processing (DLP) micro-projection system with resolution of 854 ×480 pixel to ensure the virtual image clarity observed by the driver.The optical path of human eye and virtual image display was designed as a whole. The Eyebox(aperture stopmigration range)was used to simulate the driver's eye movement range. Results show that, for different aperture stop positions, the modulation transfer function (MTF) of the virtual image plane of the optical system is more than 0.6 at Nyquist spatial frequency of 0.33 lp/mm, and the MTF of the whole field of view is more than 0.3. In addition, Monte Carlo method was used to analyze the tolerance of the system. The MTF value of 90% of the system is greater than 0.49, which shows that the system has better tolerance ability.