As the module that is most easily perceived by users as the intelligent human-computer interaction module of automotive intelligent cockpit, AR-HUD has ushered in rapid development. Driven by consumer demand and technology upgrade, the AR-HUD field of view Angle is getting larger and larger, the display is becoming clearer and clearer, and the functions are becoming richer and richer, but there are also many small AR-HUD or semi-AR-HUD with castration performance, such as small imaging, fuzzy imaging, poor combination of virtual and real, etc. In addition, stray light has a "veto". Because it directly affects the user's visual experience.

A HUD has a large stray light problem

▎ Stray light, optical "noise" that is difficult to eliminate

In AR-HUD, stray light refers to the light from the outside world and the AR-HUD itself, which is imitated in the AR-HUD display area through a non-imaging path, and is the unexpected light in the system and also the optical "noise". The driver can tolerate tire noise, wind noise, and even play music to reduce the impact of noise, but generally will not tolerate line of sight occlusion and stray light interference. This is because auditory stimuli and visual stimuli compared to visual stimuli, visual processing speed and response speed is faster, but also more sensitive.

When the vehicle is driving, it will face complex situations, the external light is changeable, and the stray light generated by the AR-HUD itself is not as controllable as the laboratory conditions, even if the system is designed to have good imaging quality, unexpected stray light will still affect the imaging quality. Safety is no small matter, in high-speed driving and other dangerous car driving situations, the harm of stray light will be infinitely amplified, even if the smaller stray light can not be ignored. Therefore, stray light has a veto effect on the AR-HUD optical system, and in the design of AR-HUD, stray light is a problem that needs to be paid attention to.

Remote AR-HUD stray light elimination effect

How to eliminate stray light? This tests both the technical strength of the AR-HUD supplier and its project experience, both of which are indispensable.

▎ Different kinds of stray light elimination methods

Stray light generated outside the AR-HUD system includes: stray light on the edge of the mirror, glare on the outside of the dust shield, stray light on the edge of the decorative cover on the car, etc. Stray light generated in the AR-HUD system includes: stray light repeatedly reflected between the LCD screen and the mirror, LCD reflection, mirror edge reflection, dust plate inside stray light, sunlight backflow stray light, structural reflection, etc.

Schematic diagram of glare on the outside of the dustproof plate

Method of eliminating stray light outside system

The edge of the mirror and the outer side of the dust shield are close to the AR-HUD light outlet. External light is reflected through the burrs at the edge of the mirror and the dust shield, forming stray light such as glare or ghost on the windshield.

The edge stray light of the mirror can be treated by edge shielding. Stray light on the outside of the dustproof plate can be avoided by adjusting the arc shape of the dustproof plate, so that the stray light that can be reflected into the eye box is located under the IP, that is, the IP directly blocks the outside light that can enter the eye box, so as to eliminate it.

Stray light caused by repeated reflections between the LCD screen and the mirror

Method of eliminating stray light in system

Because the LCD itself is also a luminous body, the light emitted by the LCD may not reach the human eye through the normal path, then there will be a series of stray light in the system.

The stray light reflected repeatedly between the LCD screen and the mirror and the stray light of sunlight backflow can be eliminated by adjusting the Angle of the LCD design. For stray light inside the dust plate, the relative position and Angle of the mirror can be adjusted to eliminate it.

In optical design, stray light is difficult to form a fixed theoretical analysis of the content, ray tracing results analysis, system design improvement have no unified solution, only through continuous analysis, summary of project experience, to seek more and better ways to eliminate stray light.

Based on this, Jiang Cheng set up an optical design team a long time ago to explore the elimination of stray light under the premise of not increasing the volume, not improving the complexity of the system, and not affecting the quality of imaging, accumulated rich experience in optical design, and successfully mass production landing, and won customer praise. In the future, Jiangcheng will give full play to the advantages of technology development and project experience accumulation, continue to lead the development of intelligent display technology for mobile travel, so that intelligent display can enable safe travel and enrich the mobile third space.