Design and development of speckle-free high-power laser-driven phosphor converted compact automotive headlamp module

Abstract

Applicability of diode-lasers in an automobile headlight is an advanced innovation for the automobile illumination industries. It is because of the extraordinary properties of the laser light over the conventional light sources, such as laser’s high brightness, wide color gamut, high directionality, low energy consumptions and long lifetime. Lasers are highly coherent in nature, so they encounter a problem of unwanted speckles and spurious fringes and always require a high level opto-thermal engineering along with speckle reduction mechanism for applying them in high lumen laser applications. Targeting such challenges, in this paper, we report an innovative design and development scheme of a high lumen laser-based automotive headlamp module. The headlamp prototype comprises a set of four cylindrical diffusers which distributes the high energy of laser radiation via scattering along the length of the diffusers within a metallic mirror based pyramidal cavity reflector. The scattered laser light from cylindrical diffusers interacts with a remote phosphor layer that prevent phosphor resin burning. The pyramidal cavity reflector plays an important role to make the laser light uniform and speckle free, via spatial and angular diversity, as light exits from the cavity after multiple internal reflections. This reflector redirects the highly concentrated white light to a long range without using any projection lens. The design and performance of the headlight system was studied on TracePro simulation software and tested experimentally in photometric laboratory. CIE coordinates of the light generated by the headlamp was (0.3947, 0.4908) and CCT was 4240 K which represent warm white light illumination.