Left: A double-sided lens array with an embedded slide array. Right: A lens array with embedded color filters. Credit: Fraunhofer IOF
Optics researchers at the Fraunhofer Institute of Applied Optics and Precision IOF (Jena, Germany) have developed novel optical array projectors that can be assembled into a mosaic to project “dazzlingly” sharp images on curved screens. Projection of images on curved and freeform (tilted) screens is typically limited in brightness and sharpness, because the aperture must be reduced to increase sharpness, which then reduces brightness. Peter Schreiber and his colleagues presented an inexpensive and simple solution to this problem at the Vision 2014 trade show in Stuttgart 4-6 November.
The new optical projector uses a camera to close the aperture to only 0.8 mm, which provides a very sharp image, and an array of up to 100 micro-optical projector elements that enable a generous increase in image brightness. Each element, measuring only 1 cm2, has a single light-emitting diode (LED) and approximately 100 micro-projectors that can achieve 60 lm of flux. The array is self-contained on a micro-slide that can measure up to 10 cm2 and 1 cm thick, overlaid with a lenslet array that can be customized for various screen shapes and projection distances. The system’s VGA resolution (640 x 480 pixels) is limited only by the aberrations of the plano-convex lenslets.
The projectors can achieve projection rates of a million images per second, about 10,000 times faster than conventional projectors. Such high frame rates can enable high-definition 3-D projection of dynamic processes, such as real-time quality control in component production. The novel design inspired another Fraunhofer group (Nothni/ Kühmstedt) to replace the slide array with a micro-imager behind the micro-projection lenses to generate different line sequences for stereoscopic 3-D measurement.