The design and optimization of lens array for LED backlight in LCD imaging engine of helmet-mounted display

The light-emitting diode has become the mainstream lightsource for backlight in the liquid crystal display imaging engine of helmet-mounted display. The paper proposes a secondary-optics-based design to increase the luminance and obtain a uniform illumination. Based on a point lightsource, a single double-freeform-surface lens is firstly designed. Then an optimization is performed according to the theory of edge-ray to improve the uniformity for planar source. As a result, the uniformity reaches 83.4% in a circular illumination with a diameter of 8 mm. Then the lens is cut and four rectangular lenses are combined to form a lens array. But the combination leads to a non-uniformity. So a method of optimizing the light energy distribution on the target surface is proposed. Finally, the designed lens array is manufactured. The practical measurement results show that the luminance increases by 96.4% compared with the traditional backlight and that the non-uniformity slightly decreases by 0.86%. The lens array designed in this paper presents high practicability for applications in helmet-mounted display.