Physical and geometrical hybrid design of two-layer and depth-chirped holographic image guide for see-through glass type head mounted display

We designed the image guide with discretely depth-chirped holographic grating for head mounted display to equalize luminance over the Field of View (FOV) and increase throughput. To reduce the time required to optimize depth-chirped pattern, the mathematical optical efficiency prediction method was devised. The design approach enables, rapid turnaround in design process and precise prediction of optical performance of image guide incorporated depth-chirped grating. Display performance of the depth-chirped image guide identified by the mathematical optimization was verified by the geometrical and physical hybrid optical simulation that the RCWA code is integrated to geometrical ray trace code via DLL to incorporate effects of the diffraction. As a results, the design exhibited 315 cd/m ² /lm for the FOV (35° (H) x 20° (V)) and eye box size (±8.5 mm (H), ±6.5 mm (V)). The value of luminance was increased by 37% than unchirped image guide. Uniformity of luminance was further improved, from 33% to 47%. In conclusion, we made clear the effect of depth-chirped image guide to increasing the performance of the image guide.