Application of photonics technology in automotive LED headlights, night vision safety systems and laser ignition systems

From LED headlights and night vision safety systems to emerging laser ignition systems, photonics technology is showing its strengths in automotive applications with its advantages of compactness, low energy consumption and high performance.

Optical and photonic technologies are providing automakers with an increasingly rich "toolkit" to help them improve the safety of cars, reduce long-term costs, improve efficiency, and add unique design elements to cars. In addition to the common LED taillights, some cars are also trying LED headlights. At the same time, optical fibers are also being used to connect communication and display devices in cars. It is reported that Ford is currently investigating automotive laser ignition systems, and some other high-end cars will also provide night vision systems and driver assistance systems.

LED taillights and headlights

"Although the cost of using LED solutions for taillights and interior lighting is still much higher than that of incandescent lamps, the huge advantages of LED solutions are enough to make automakers accept their higher costs in development and manufacturing." Professor Cornelius Neumann, who specializes in automotive lighting at the University Karlsruhe in Germany, said, "In addition to the ultra-long service life of LEDs (which is usually longer than the life of the car), their fast response time is also an important safety factor for brake lights. Generally, the response time of LEDs is about 75 milliseconds shorter than that of commonly used bulbs. In addition, the low power consumption and novel shape of LEDs are also the main reasons why manufacturers choose LEDs for car signals, etc."

Professor Neumann has conducted in-depth research in the field of automotive lighting for 11 years in collaboration with Hella, a German automotive lighting and electronics supplier. He said that although LED taillights are more common in cars, cars face more challenges when using LED headlights.

“So far, at least three car models on the market have adopted LED headlights: Lexus LS 600, Audi R8 and Cadillac Escalade Platinum.” Professor Neumann said, “But there are still many problems to be solved in the full adoption of LED solutions in headlights.”

Professor Neumann pointed out that dust, moisture, mechanical vibration and harsh environments with ambient temperatures of up to 90°C will pose certain challenges to LEDs, because the performance of LEDs will decrease as the temperature rises, so some high-power LEDs need to be equipped with cooling devices. In addition, LED headlights do not use a single light source (such as halogen lamps or high-intensity discharge (HID) lamps), but rather assemble multiple LEDs together to meet the needs of driving signal lighting. [1] In LED headlights, three different optical systems are usually used to achieve different functions. These three systems need to work together firmly to emit light with a brightness high enough to meet the requirements of driving lighting on the road.

Although LED headlights still face many challenges, Professor Neumann added that LED solutions can save 50% or more energy compared to commonly used bulb solutions (see Table 1). [2] According to some studies, less than 20% of LED light can achieve the same brightness as HID lamps, and LED lighting is safer. [3] With the development of mathematical models and software algorithms, engineers can now design various forms of reflectors and lenses to direct light from light sources to specific areas of the traffic surface (see Figure 1).

Figure 1: The headlights of the Opel Signum are all LED solutions, with different modules for different signal functions: 6 groups of LEDs for low beam; 3 groups of LEDs at the bottom for high beam; 2 groups of small LEDs on the sides for corner lights; 10 groups of LEDs for daytime running lights. The direction indicator lights are composed of 3 groups of LEDs with a reflector system at the top of the headlights. Different LEDs are selected according to the different uses of each signal light.

Table 1: Comparison of power consumption between traditional lighting and LED lighting

High-brightness LED manufacturers have every reason to believe that LED will penetrate the automotive field in the future. Market research company Strategies Unlimited predicts that by 2013, the overall market size of global automotive LED outdoor lighting will grow from US$158 million in 2008 to US$347 million. According to the "2008-2009 Global and China Automotive LED Lighting Industry Research Report" by ResearchInChina, by 2014, LED headlights will be comparable to traditional HID headlights in terms of cost and performance (assuming that LED technology can continue to improve at the current rate of development). By then, the application of LED in the automotive field will be greatly improved, and the market size of automotive headlights alone will reach US$122 million.

BMW's BMW-7 series cars use the second-generation Night Vision 2 night vision system from Swedish Autoliv, which uses a far-infrared sensor to scan pedestrians on the road. Its night vision distance is three times that of low beam headlights. When pedestrians or animals are detected in front of the vehicle, the system automatically analyzes the scene and vehicle dynamics, assesses the risk of the driver colliding with the target, and issues an alert to the driver when necessary (such as through the on-board display screen, see Figure 2). "Autoliv's latest night vision system has taken night driving safety to a whole new level, providing drivers with an 'extra eye' on the road at night," said Stuart Klapper, general manager of Autoliv's night vision system.

Figure 2: When a man was detected crossing the road in front of the car at night, the far-infrared night vision system of the BMW-7 series car issued an alarm to the driver. In urban roads with slow driving speeds and heavy traffic, the system only monitors a small range of roads within close distance to avoid too many alarms; while in rural roads with high driving speeds and sparse traffic, the system monitors a wider range of roads accordingly. In order to make timely and corresponding adjustments to the monitoring range, Autoliv's night vision system continuously collects night vision video images from the surrounding environment, and uses a set of advanced software algorithms to detect more than 50 million "image fragments", and accordingly issues corresponding alarm signals to the driver.

The far-infrared camera used in Autoliv's night vision system uses a 320 x 240 pixel vanadium oxide thermal radiation meter and has a germanium window to protect the camera's lens from the outside world. "We have now succeeded in reducing the cost of the lens by 30 percent compared to the first generation of cameras," Klapper said.

Siemens VDO of Germany has also developed an infrared night vision system with a working distance of 150 meters, which produces an electronically processed video image for real-time display in the car. The system has two working modes: one is a near-infrared system, in which the light generated by two infrared emitters integrated into the headlights is captured by a small camera installed near the rearview mirror; the other is a long-wave infrared system, which requires the installation of a camera and a sensor working in the range of 6 to 12µm to detect thermal radiation from the vehicle's surroundings. Once a person or animal is detected, the system will display the object in a bright form.

Laser ignition

In the summer of 2009, Ford announced that it was working with GSI Group and the University of Liverpool in the UK to develop laser ignition systems for the next generation of automotive engines. In fact, as early as the late 1970s, people had already begun to study laser ignition systems, and many research papers on laser ignition systems had begun to appear in various automotive technology conferences.

Because lasers can be broken up into multiple beams, multiple ignition points will increase the chances of complete combustion of fuel in the engine, thereby reducing emissions and improving fuel combustion efficiency in cold and wet conditions. Even more, some of the laser energy can be emitted back to provide information about how the engine is running, so that the ratio of the air/fuel mixture can be automatically adjusted to achieve better fuel efficiency. Ford also said that it plans to provide laser sparks through a fiber optic cable, which will take up less space than spark plugs, allowing the use of larger and more efficient engine valves for more complete fuel combustion.

In 2007, researchers at the National Energy Technology Laboratory (www.netl.doe.gov) designed a laser ignition system that is combined with an internal combustion engine. The system focuses the 10ns pulse emitted by a 1.06µm laser into the cylinder through the spark plug port to generate an ignition spark. Compared with traditional single-cylinder, four-stroke, spark ignition engines, the use of a laser spark ignition system can not only reduce engine emissions, but also improve fuel combustion efficiency.

Driver Assistance Systems

In addition to lighting and night vision applications, driver assistance systems based on photonics technology have also emerged. Land Rover of the French Valeo Group and BMW's BMW-5 series cars are equipped with driver assistance systems. The entire system includes 5 cameras: a wide-angle camera installed at the rear of the car for parking assistance; two cameras installed on the left and right sides of the front bumper to assist the driver in observing pedestrians or other objects approaching the vehicle when the vehicle enters a street with poor visibility; and two other cameras installed on the two side-view mirrors to directly monitor the environment around the vehicle.

Panomorph technology is a wide-angle lens technology patented by Canadian company ImmerVision. This technology can improve the angular resolution in a specific area of ​​an image field of view, placing the target area of ​​interest in the center or edge of the image (see Figure 3). [4] There are also specific windows for the driver to observe the situation, and other synchronized visual images can be used for road condition analysis. For example, through an intelligent cruise control system, many applications such as collision avoidance, blind spot monitoring, pedestrian and road sign detection, and lane tracking can be integrated.