Digital light processing (DLP) is currently a cutting-edge technology for desktop projection optical engines. Due to the passive luminescence characteristics, the DLP projection engine needs a few specific illumination optical components for light collimation, homogenization, and color combination, together with a projection lens matching the DLP chip and magnifying the image. In this paper, we propose a design approach that first splits the DLP projection optical engine into individual components for separate design, and then integrates them into a whole system for further verification. For the first step, the collimating lens group is designed for light collection, and the dichroic mirrors are used to fold the light path based on tri-color LED light sources. For the second step, a fly-eye lens and the corresponding relay lens group are designed to achieve uniform illumination on the DMD chip. The third step is to optimize the projection lens group for high-resolution projection display. Based on the design and simulation, the optical efficiency is 63.4% and the uniformity reaches 94.9% on the projection screen. The modulation transfer function (MTF) of the projection lens is higher than 0.4 at 66 lines for the distance of 500 ∼ 1500 m m , and the distortion is lower than 1%. Simulation results show that the total luminous flux is estimated to reach 224.15 lm when the powers of tri-color LEDs are 21 W, 15.5 W, and 25 W, respectively. A projector prototype is built and tested for further verification, which provides a luminous flux of 220.43 lm and uniformity of 90.22%, respectively. The proposed design, demonstrated by both simulation and experiment, exhibits high feasibility and application potential in state-of-the-art commercial projector design.

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Pico-projection displays are the main developing direction for future projection displays, but the balance between the optical efficiency and the system size is still a big concern. This paper presents a pico-projector design based on micro-LED (μLED) light sources. Firstly, based on the analysis of the characteristics of μLED, a highly integrated microlens array is designed to improve the system efficiency by reshaping the spatial light distribution. In addition, the matching relationship between the aperture angle of projection lens and the divergence angle of μLED is studied, and on this basis, a set of four-piece spherical lens group is proposed to achieve compact size. Simulation results show that the μLED equipped with the microlens array can concentrate about 86% of the light energy within a dispersion angle of ±20 , thus increasing the light energy utilization by about 3.5 times and reducing the size of the pico-projector to 30.18 mm 3 . The designed pico-projector has high performance and compact size with great potential for future applications.