Various high temperature phosphor materials, such as glass phosphor, ceramic phosphor, and crystal phosphor have been under stage of development targeting high power white light generation, which are suitable for various high power, small etendue applications. Stationary phosphor plates are getting into commercial projectors for some lower power projectors mostly limited by the power density limits of the phosphor materials. This paper presents a compact rotating, tilted, planar mirror, such that the output focused laser spot can be made to follow an elliptical path on the phosphor plate, increasing the effective area of the focused spot, and resulting in a higher limit of output optical power of the system. The key to such optical design is that the output of the system maintains the same small etendue of a single focused spot, and not the etendue of the circular path, for efficient coupling of the output to the projection optics. The maximum power capacity is very dependent on heat sinking especially the top surface of the phosphor plate. With the current heat sinking methodology, the maximum power is 89 W focused into a spot size in the range of 0.5 mm, which will further be determined accurately. The estimated power density ranges from about 300 to 600 W/sq. mm. along an elliptical path with axes measures 4.23 mm and 6.23 mm at 7,200 RPM. This has an improvement of power density limit many times compared to the phosphor specification of 45W/sq. mm. Further increase of power density limit is expected with further heat sinking developments. It is believed that the heat transmission between the top and the bottom of the phosphor plate would plan an important role in the power capacity. Phosphor plates with smaller thickness are being prepared for further investigation.
Most of smart headlight engines are designed using blue LED or laser light sources for the exciting the phosphor conversion layer producing white light output. The phosphor conversion layers have been fabricated by silicone-based phosphor, glass-based phosphor, ceramic-based phosphor, and single crystal-based phosphor. Among these different phosphor materials, the single crystal phosphor (SCP) exhibits excellent thermal stability, better conversion efficiency, and high transparency to yellow light, but the required high-temperature fabrication process, has been an impediment for widespread commercial production. Recently, the issues of higher fabrication temperature of the SCP have been overcome by using a novel design of single crystal growth to produce SCP with higher yield and better uniformity. In this study, the smart headlight consists of a well-developed, high efficiency, automotive qualified white LED, a TI digit mirror device (DMD), a projection lens, and a LED together with two laser diodes and a SCP plate.
Laser excited phosphor wheel light source has an upper output power limit due to the issues in heat dissipation and the high-power density at the focus on the phosphor. This paper presents a stationary phosphor plate with a compact rotating optical system such that the focused laser spot on the phosphor plate follows a circular path providing a larger effective excitation area while maintain the small etendue of a single stationary focused spot. With an 8 mm diameter circular path, a theoretical total of 1,870 W of laser power focused into a 2 mm spot can produce a total 500,000 lumens of visible light. This will make a 120,000 screen-lumen projector possible.
Besides low cost, automobile design will be another major factor for the mass adoption of the LiDAR in the autonomous vehicles. Extra aperture in the automobile chassis for LiDAR operation will be undesirable for automobile designers. As a result, it will be advantageous to integrate the LiDAR together with the headlight such that the chassis design of the vehicle does not have to deviate from standard practices. This paper presents optical design of integrated LiDAR and smart headlight using a single DMD such that it replaces the current headlight without impact on the overall chassis design of the vehicle. For low cost considerations, the two functions share the same DMD. Preliminary designs of such system and results will be presented.
Lidar, radar, optical imaging and ultrasonic are important environmental sensing technologies in the field of autonomous driving. Among them, the radar can perform long-distance sensing, however it is limited by the resolution and cannot distinguish objects. Optical images have clear object resolving power, but hardly to get distance information. Ultrasonic only detect objects that are in very short distances. Therefore, it is necessary to have a technique that can clearly distinguish the objects and get the object information such as speed and distance at medium-range (100-m) for autonomous driving scheme entering level 4 and level 5.
The existing light technology in the autonomous driving is to place the Lidar module on the roof of a car and perform environment sensing in a rotating manner. Such technology has low sensing capability and is not conform to the development direction of the vehicle industry that not fulfill the demand of autonomous car. In contrast to Lidar module on the roof, placing the Lidar on the front of the car has many advantages, such as easy to collect dust, suffer water corrosion and difficult to set up the electrical system. Integrating the Lidar with headlight system is a feasible direction to solve the aforementioned problems. In this study, we will develop laser headlights system with Lidar module by integrating the optical system of Lidar into headlight a unit, in which the smart laser headlight was achieved by feedback control orders system.
The laser headlight will focus on the development of smart headlights with laser as the light source. With the feedback of the system, it can control the car's light field, avoid high-reflection areas at night. The integrated Lidar module will develop a quasi-static optical scanning system with a wavelength of 1550 nm and embed it in the optical path of the laser headlight. By wavelength differences, the optical path of Lidar does not interfere with headlight and high quality optical data could be obtained. Despite adapting 905 nm as optical wavelength in the current technology, the 1550 nm wavelength selected by this study meets the safety regulations and will not cause damage to the human eye at night or during the day. In this study, we will develop a Lidar module attached to a 10W laser headlight for autonomous driving. The simulation and optical performance of integration of Lidar module with laser headlight will be presented.
The most widely used light sources for projection system and spotlights are discharge lamps. With tremendous advancements over the last decade in blue laser developments, laser excited phosphor systems have been developed for various applications including projectors and spotlights. One major challenge remains in the very high power applications where multi-kilowatt xenon lamps are still being used. In this paper, an advance material, namely, single crystal phosphor has been developed with high optical efficiency, high power handling capability, and a melting point of 1,950°C. To enable such single crystal phosphor to be used to its full capacity, a major effort was placed on the heat sinking of the crystal phosphor pumped at high power, over 70 W of blue laser power from a 4 by 6 array of laser diodes. The nominal dimension of the crystal phosphor of one of the system measures 2 mm by 2 mm by 4 mm and is end-pumped from one end with a set of focusing lenses directing the output from 24 lasers onto the surface of the crystal phosphor. The 4 sides of the crystal phosphor is specially coated and attached to the heat sink for efficient dissipation of heat, keeping the temperature of the crystal low enough for efficient emission. The output from the crystal phosphor is extracted using a CPC reducing the total internal reflection effect inside the crystal phosphor. To accommodate the high power laser at the input face of the crystal phosphor, various methods are used to prevent the local burning of the input face, including the use of diffusers, light pipes, and light tunnels. The computer simulation and experimental results will be presented.
Traditional illumination systems uses various lamps selected based on certain requirements of the applications. One common issue is the trade-off between output brightness and lamp lifetime. LEDs with long lifetimes have been used in many applications. This paper describes a multi-colored LED illumination system with individually controlled red, green, and blue outputs combined together with the etendue of a single LED, having enhanced green and red output brightness with supplementary excitation of the phosphor-based green and red LEDs from additional blue LEDs, increasing the overall output of the system.
Automotive headlight evolved from incandescent, to halogen, to xenon, to LED, and most recently, to laser phosphor lamps with increasing efficiencies and brightness. This paper presents the development of laser phosphor headlights using glass phosphor and single crystal phosphor for efficient and high power operations. Laser diodes are used for pumping the phosphors producing the white light to be projected to the roadway. In addition, various configurations of the laser diodes, which are individual addressable, are to be presented. Together with the used of DLP and LCD imagers, intelligent headlights are developed with the abilities selectively scanning the imagers illuminating the roadway with varying intensities. The design of the systems and the experimental results will be presented.
We report and demonstrate the feasibility of adapting glass as a phosphor-converted layer in laser headlight module, instead of conventional doped silicone that can potentially provide higher reliability and better performance for advanced laser headlight module. A laser headlight module (HLM) consists of blue a high-power laser array, a color phosphor, and an optical micro-lens system. The color phosphor is a key component in the HLM which consists of glass-based yellow phosphor-converted layer. The conversion layer of the yellow Ce:YAG phosphor is bonded on an aluminum substrate. A blue high-power laser array is used to excite the color phosphor and then release yellow light. Then, the combinations of blue and yellow light become white-laser light for use in the HLM. In this study, the fabrication of HLM with the glass-based yellow phosphor-converted layers is presented. The optical performance of the HLM including lumen, lumen efficiency, chromaticity, and transmission is detailed discussion. This study demonstrates the adapting glass as a phosphor-converted color phosphor in the HLMs that provide high-reliability and better performance for use in the new-generation laser headlight module.
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