Microlens array based LCD projection display with software-only focal distance control

State of the art LED pico-projectors using single-channeled optical layouts are always constricted by a trade-off between achievable flux and minimum system size. Furthermore, their limited depth of focus require additional mechanically moving components for focusing if variable projection distances are essential for their specific application. We present a novel microlens-array based LCD projector breaking these constraints of conventional LED illuminated systems, thus enabling a super compact, robust and bright module while offering new features for electronic focal distance control without additional mechanical components. While the short focal length of each contributing channel maintains a certain system slimness, the superposition of all individual projections on a screen done by image-preprocessing leads to dramatic flux enhancement without blurring effects. Starting with a description of the working principle of array projection we focus on key properties regard ing depth of focus for examining novel image-preprocessing algorithms that enable for only software-controlled focal distance. Further improved program code enables sharp images even onto freeform screen geometries. The realized prototype utilizes a transmissive LCD microdisplay along with a monolithic array of 45 microlenses actively aligned to the top of the display coverglass. While the display is illuminated by a collimated white LED; each channel is assigned to one primary color by applying a color filter array buried below the microlenses to obtain a full color image on the screen. The displayed image content is controlled via PC by a novel software tool, whose correct operation is verified by experimental results.