Design of a freeform illumination structure for digital display projection

The design of a digital light processing (DLP) projection optical system centers on the digital micromirror device chip and consists of two main components: the illumination structure and the projection lens. Traditional illumination structures are often complex, prompting the need for simpler alternatives. This paper proposes the use of freeform surfaces to streamline the illumination structure. A mathematical model for the freeform surface is developed based on Snell's law and the principle of energy conservation. The model is discretized using the finite difference method, and numerical solutions are employed to generate the freeform surface data. Optical simulations of the initial DLP illumination system demonstrate an illuminance uniformity of 92.34% and an optical efficiency of 78.88%. After optimization, these values improve to 98.91% and 84.03%, respectively. The findings confirm that integrating freeform surfaces into DLP lighting systems not only simplifies the optical design but also enhances illumination uniformity and optical efficiency.