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.
Single crystal phosphor, which is a transparent material, absorbs blue light and emits yellow light. As a result, it is the ideal material for conversion of blue laser light into yellow visible light allowing high efficiency, and high temperature operations. When fabricated into a waveguide, it provides a large volume and surface area for ease of heat sinking. The transparent property of the crystal phosphor material provides features are not available in other phosphor materials such as glass phosphor and ceramic phosphor in which the laser energy is all concentrated in a small spot with small thickness making heat removal very challenging. This paper presents an end-pumped structured crystal phosphor waveguide design such that the volume of laser absorption and heat dissipating surfaces are both larger with a small output cross-section for small etendue operations. Preliminary prototypes have been fabricated and tested with expected results. Several other structures and measurements will be presented.
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.
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