Diode Lasers May Revolutionize Automotive Lighting

High-power diode lasers provide efficient, high-brightness sources for tail lights and signal lamps while offering automotive design engineers new degrees of freedom.

By: Kristin Lewotsky

Just when light-emitting diodes (LEDs) have become commonplace in automotive applications such as after-market brake light indicators, technology is shifting to a higher gear, bringing diode lasers to the forefront. In the lighting technology group of Visteon Automotive Systems (Redford, MI), engineers are designing automobile signal lamps with high-power diode laser sources, developing what may prove to be another killer application for the technology. "The new millennia for high-powered diode lasers is automotive, says Merrill Apter of Coherent Inc. (Santa Clara, CA), and given the size of the market, he could very well be right.

Project engineer Jeff Nold of Vistion is working at the cutting edge of this application. "Package depth and styling flexibility are huge keys for this project," he says. "We can have lamps as thin as a quarter of an inch thick. In the show car we did for the Detroit Automotive Show in January, the lamp is only 0.5 in. wide."

But the styling options go beyond issues of size. In conventional (incandescent) lamps, white light must be filtered to produce red light, whereas diode lasers generate light at the required wavelength. "It's a unique styling opportunity," says Nold. Because there is no need for a parabolic reflector with the diode laser source, designers can use the body color behind the lamp and a clear lens over the lamp. The region appears to be just another part of the car's body until the device is activated, whereupon it generates red light (see Figure 1). Such degrees of freedom allow engineers to think about signal design in completely new ways.

Technology
The group is working primarily on rear signal lighting applications, illuminating an elongated surface area with a single red diode laser providing 200 to 500 mW of output power. "We're able to utilize the advantages of having a single-point light source," says Nold. "We can use one diode laser rather than multiple LEDs. The output is very focused so we can manipulate the light as we'd like to." Currently the group is using divergent lenses to spread the output beam to illuminate the desired area, but they are investigating the use of molded plastic optics.

According to Nold, the devices require 80% less power than conventional technology, a power savings that could translate into improved mileage. He does acknowledge that cooling is an issue, though he declines to elaborate on how the group is attacking that particular problem.

Commercially available components would be sufficiently robust for the application. "We're expecting that source would last as long as the vehicle," says Nold, noting that price would be competitive with other technologies. Don't expect to see the new signals at your local car lot in this year's model, but expect it to appear in the near future—according to Nold, the company is targeting 2003 or 2004 for implementation.