An Electrically Tunable Focusing Pico-Projector Adopting a Liquid Crystal Lens

An electrically tunable pico-projector adopting a liquid crystal (LC) lens as an active optical element is demonstrated. The focal length of this pico-projector is electrically tunable from 350 to 14 cm and the tunable range is even wider than that of a manually focused pico-projector. The response times of turn-on and turn-off are approximately 313 and 880 ms, respectively. In addition, the location of the projection lens can affect the electrically tunable range of the system. A small shift of the projection lens results in the large tunable focusing range of the pico-projector and a tunable focusing range is determined by the LC lens. The optical analysis is also discussed. This concept can even be applied to design other electrically auto focusing pico-projectors based on other optical elements such as liquid lenses and spatial light modulators. (C) 2010 The Japan Society of Applied Physics