Illumination uniformity of an edge-lit backlight with emission angle control

Viewing range of a liquid crystal display can be controlled by a liquid crystal device inserted between a light source and a light-guide of an edge-lit backlight unit. Here, we propose an output coupler with a vertical optical window through which light is extracted from a light-guide. Rays with large propagation angles and those with small angles have a comparable probability of hitting this window. As a result, a single set of these output couplers can provide uniform light extraction for both settings of a wide viewing range and a narrow one. Ray tracing simulations confirm these findings.