Speckle free efficient light engine for high power laser projectors and automobile headlamps

Abstract

Laser speckles and spurious fringes are the major obstacles in the development of emerging technologies relating to laser-based projection imaging and illumination. It becomes more challenging when such systems employ high-power lasers, such as laser-based cinema projectors or laser-based automobile headlamps. Addressing such challenges, we report a compact design and step-by-step development scheme of a laser speckle reduction system in this article. The method comprises a metallic ball-mirror connected with the mechanically dynamic and thermally conductive heat sink. The ball-mirror was highly reflecting and coated with a transparent thick film of ZnO nanoparticle embedded epoxy adhesive that provides volume scattering of a highly directional laser beam. Epoxy layer were further diffused by sandblasting to achieve surface scattering of the laser light. The combined effect of volume and surface scattering were utilized to produce spatial diversity, while the temporal diversity was achieved by the rotation of ball-mirror diffuser system. Spatial and temporal diversities are the fundamental speckle reduction techniques that become more efficient when they are employed with a tiny pyramidal reflective cavity. TracePro simulations demonstrate the efficiency enhancement in the system due to the involvement of a pyramidal reflector for three primary wavelengths (RGB). Qualitative results of the light-scattering for red, green, and blue lasers and the quantitative results of speckle contrast are reported. Speckle contrast reduction was experimentally achieved by 0.0248 for red, 0.0298 for green, and 0.0213 for blue laser diodes.