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OSRAM and its partners in the μAFS project have developed a high-resolution headlamp. And that's just the beginning. Stefan Grötsch, an engineer at OSRAM Opto Semiconductors, recounts how a bright idea became a reality.
Every innovation starts with a vision. In our case we wanted to create an LED with lots of individually controllable light points. An LED that would adapt to its environment and be able to respond with precision to users' commands—a completely new concept. We started by designing an LED projector that could be used to project logos and symbols from a mobile phone onto a table. Only the LED light points (pixels) that were required to create the shape of the symbol would light up. But we quickly ran into problems. To get a large number of pixels onto one chip, and thus increase the luminance, we had to work out a way of reducing the distances between the pixels. But this also reduces the amount of space for connectors and wires that supply each pixel with power and information. How could this be achieved in so little space—and we are talking here about four by four millimeters? It was simply impossible using conventional methods. We had to come up with something new.
To drive forward our original idea we opted for a system that required a lower resolution, i.e. fewer pixels over the same area, than an LED pixel display. That would have required us to work with three colors and more pixels, and would be far more complex. In terms of a specific application, an adaptive forward lighting system (AFS) for vehicles appeared to us to be the most suitable. This is exclusively white in color, and we were able to achieve the desired result with just a few thousand pixels. The μAFS project, sponsored by Germany's Ministry of Education and Research, began in 2013. Our partners were Infineon, Hella, Daimler, the Fraunhofer Institute for Applied Solid State Physics, and the Fraunhofer Institute for Reliability and Microintegration. To solve the problem of controllability and space, we combined two chips that are normally separate, mounting them one on top of the other. A silicon chip with integrated drive electronics formed the base. On top of this we mounted a finely structured 4x4 mm multipixel LED chip, which is responsible for generating the light. Usually at least one wire is required for each pixel, i.e. 1024 or more for 1024 pixels. But in the μAFS the power is supplied by a much smaller number of connectors on the silicon chip, which control the pixels digitally. This enabled us to control each light point individually and the distance between the pixels was negligible compared to other systems, thanks to the buried and integrated controller technology. In other systems there is always a small gap between the pixels, whereas in the μAFS these gaps are imperceptible. The whole surface appears to emit light.
The μAFS technology opens up completely new horizons for front headlamps on vehicles. For our headlamp we decided to use three LED chips with 1024 pixels each, i.e. more than 3000 LED pixels in total. As each of them can be controlled individually, the light can adapt to the environment. This makes it possible to drive with high beam on at all times—no more need to dip. The adaptive headlamp masks out other road users detected in the beams' cone of light and prevents the driver of the oncoming vehicle from being dazzled. The closer a vehicle comes, the more pixels switch themselves off, producing a kind of blind spot but without diminishing the illumination of the road ahead. In other words: The light becomes intelligent and thinks for the driver and the other road users.
Cameras and sensors are used to analyze the vehicle’s surroundings. They can distinguish between stationary objects, such as pillars and road signs, and moving objects, such as vehicles ahead or oncoming traffic. The vehicle’s central computer, its brain so to speak, processes the information and determines the beam pattern. A control unit sends this pattern to the silicon chip in the headlamp, which then passes on the information to the multipixel light sources. There are three such light sources in each headlamp and each of them has 1,024 light points. The bitstream that is received by the silicon chip determines how much power is supplied to each light point, and therefore whether it is turned on or off, meaning only those that are needed give off light.
Our μAFS technology is sure to have a wide range of additional applications. We aim to develop it further and use it for the head-up display that projects information about the road ahead and the vehicle speed onto the windshield. The great advantage of this technology is that it uses relatively little energy and takes up relatively little space. Less power is required. That is important for portable devices. It means they don't have to be recharged so often even though their displays are more complex, more intelligent, and more precise. It is likely that μAFS technology will soon become part of our everyday lives - always present whenever we pick up a smartphone or put on a virtual reality headset such as the Oculus Rift or Google Glass.
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