Marcel Sieler

Array projection optics: multi-channel design for ultra slim projectors

Common projection optics use a single aperture approach to create a magnified image on a screen. The transmitted flux of such systems always scales with their system dimensions thus preventing the realization of ultra compact devices along with a high lumen output. We introduce a new multi-channel approach that breaks this rule and enables the realization of ultra slim, laterally extended projection devices with high flux and integrated homogenization. Array projection optics consists of a regular two-dimensional arrangement of projective microlenses superposing their images on the screen. First we derive the scaling laws of such a multi-channel projector in contrast to common single aperture optics and analyze the system parameters of a single projection channel by Seidel aberration theory. Based on the application of these results to a variable array size the array projection optics are specified. The technological realization of a sample system with still image projection is shown and characterized with respect to modulation transfer and flux.

Microoptical array projectors for free-form screen applications

The system design of front-projection systems for free-form screens utilizing conventional single-aperture optical layouts always requires a trade-off between system complexity and achievable luminous output. This article presents novel slide pre-processing algorithms based on array projection technology that are able to resolve the design drawbacks for both free-form as well as strongly-inclined planar screen applications by breaking the common contradiction between system simplicity and flux. Starting from describing common design strategies and their drawbacks, the theoretical basics of the novel concept are investigated and applied to raytracing simulations. Experimental results are shown and evaluated regarding their optical performance.

12.4: Interactive See-Through Augmented-Reality Smart Display System

“iSTAR” is dedicated towards components, system and application development of “Interactive See-Through Augmented-Reality Displays”, comprising a VGA OLED microdisplay with embedded image sensor aimed on gaze-control, see-through head-mounted optics, and mobile applications in industry, consumer and security areas. This paper reports on bi-directional microdisplay chip and optics, and intermediate performance results.

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 regarding 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.