There is a giant tug-of-war going on in the micro-optical world, in which real and virtual images are battling for supremacy. A real micro-optical display is a heads-up image that appears on screens or glass lenses immediately in front of the viewer. Its origins are in fighter-pilot display technology, where real-time information is displayed transparently on the cockpit screen. Its called “heads-up” because the pilot can continue to look through the window as he views the micro-optical display. The technology has now evolved to wearable devices that attach to eyeglasses or helmets and provide small sharp images. It allows for true mobile computing, with a combination of proprietary optics, low power consumption and lightweight ergonomic design. This makes the devices daylight-readable and hands-free. A recent development interfaces micro-optical viewers with a PC. The possibilities are virtually limitless. From driving a car to typing to full-fledged call center workforce management – the sky’s the limit!
Modern micro-optical viewers weigh about an ounce and accept a wide variety of display protocols, including VGA, NTSC, PAL, RS170 and RS232. To the user, the optical system appears like a free-floating monitor. One important application of the technology is in the medical arena in which patient-monitoring equipment works in tandem with the display system.
In the opposite corner is the challenger: virtual retinal display (VRD). In this technology, a TV-style image (raster) is drawn directly on the retina of the viewer. The display appears to float in front of their eyes, but the image lies on the retina itself. In a full-color VRD, three photon sources are used to create a coherent light beam via a laser diode. The amount of light in the beam is tied directly to the brightness of the image. The light beam is scanned in order to place each pixel precisely within the retina. The scanned beam is then projected into the viewer’s eye, co-planar with the pupil. Once on the pupil, the light beam is focused by the lens and cornea of the viewer’s eye onto his or her retina. The angle of entry of the light beam determines the spot on the retina where the image will appear. The output from the VRD can be coupled to eye-tracking systems to provide real-time control of the image, called augmented visuals.
The advantages of a VRD include small-size wearable devices, a large field of vision, high resolution, full color, contrast and brightness that is sufficient for outdoor use and a true 3-D display. All of this at energy levels that are considered very safe for the eye. Time will tell which of these competing technologies will prevail.