Enhancement of laser multiplexing efficiency for solid state lighting through photon recycling

An optical design of a novel structure has been proposed and demonstrated to perform photon recycling in a transmission-type laser-pumping white light. The structure includes a hemisphere reflector and a phosphor plate located at the center of a hemisphere reflector. The hemisphere reflector is not only used for photon recycling to increase the energy efficiency but also to keep the energy efficiency nearly unchanged when the number of the multiplexing laser increases. The experimental measurement shows that the photon recycling with the hemisphere reflector can increase the energy efficiency from 36.2% to 53.3% for on-axis incidence, and 35.2% to 55.7% for off-axis incidence. Besides, the efficiency keeps the same up to three-laser multiplexing in the experiment, and potentially can be extended to more than 10 in the simulation for various hole structures. The result is not only on the efficiency enhancement but also on the enhanced exitance of the laser white light and the unchanged etendue of the light source. This property is an important advantage for lasers rather than LEDs in a solid-state white light source.