Much as mechanics do, medical doctors fix extremely complex machinery—the human body. Surgeons at the Wallace-Kettering Neuroscience Institute, the Baylor College of Medicine, and the Cleveland Clinic Foundation's Minimally Invasive Surgery Center have tested Microvision's see-through, or augmented-vision, laser-based display. As they operate, the surgeons are viewing vital patient data, including blood pressure and heart rate. And in such procedures as the placement of a catheter stent, overlaid images prepared from previously obtained magnetic resonance imaging or computed tomography scans assist in surgical navigation.

Several military units, including the U.S. Army's Stryker Brigade, are using adaptations of the system. The commander of a Stryker, an eight-wheel light-armored vehicle, can view its onboard battlefield computer with a helmet-mounted daylight-readable display. This enhances the commander's ability to observe the surroundings, choose the optimum path, command the vehicle, and use tactical information advantageously. Other military applications include a series of prototype helmet-mounted displays developed with the U.S. Army and Boeing Co. of Chicago. Currently in the initial stages of flight-testing, the system could be a relatively inexpensive way to provide utility- and attack-helicopter pilots with a digital display of the battle space.

The military gave scanned-beam technology its start in the 1980s as part of the U.S. Air Force's Super Cockpit program. Its team, led by Thomas A. Furness III, now at the University of Washington, Seattle, produced helmet-mounted displays with an extremely large field of view that let fighter pilots continuously see vital data such as weapons readiness. The displayed information moved with the pilot's head, giving him an unobstructed view of what was going on in front of him and helping him to distinguish friend from foe.

Now offshoots of that technology may even wind up in such mass-market products as digital cameras, where scanned-beam displays provide better image quality at lower power and cost than liquid-crystal-on-silicon and organic LED displays. Instead of using lasers, which provide the power necessary for bright, see-through, head-up displays, the non-see-through Microvision displays that require full color at low power and low cost—desirable for viewfinders and near-to-eye cellphone displays—rely on LEDs. Microvision is working with Canon Inc., Tokyo, on a near-to-eye microdisplay with several advantages over conventional optical and LCD electronic viewfinders. Linking the microdisplay to the camera's image sensor would give digital cameras the full viewfinder capabilities of a premium single-lens reflex camera. The user could preview a smooth, high-resolution, full-color image, allowing critical focus-control and depth-of-field adjustments to be made [see diagram, What You See Is What You Get].

What You See Is What You Get: The basic technology used in the Nomad head-up display is being adapted to smooth the viewfinder image on a digital camera [top]. The picture captured by a charge-coupled device chip is processed to control the intensities of red, green, and blue light-emitting diodes, as well as the motion of a MEMS scanner. The image is next focused through the viewfinder and onto a user's retina.

Illustration: John MacNeill

A blown-up detail of a test image [left] shows the difference between the hard pixels of a digital display [middle] and the much smoother appearance of a scanned-beam display [right].

There are just four primary components of a scanned-beam display: electronics, light sources, scanners, and optics. Yet with a modular approach, these simple elements can be combined to yield many different products [see diagram, Direct View, again].

Electronics acquire and process signals from an image or data source, such as a Web page or video camera. The processed signals contain information for the intensity and mix of color that best renders the intended image at each location that will be scanned, in sequence. These values are the individual picture elements—pixels—that make up the image. This information is stored in memory until needed, when the data pass through a digital-to-analog converter that controls the light source. Once the image has been rendered into memory, there is no need to recalculate it unless something has changed. The data can simply be replayed from memory, a feature that can be exploited to cut costs or save power.

Depending on the application and cost and size requirements, we can use single color or multiple low-power solid-state lasers, laser diodes, or LEDs as the light source. In the case of a full-color electronic viewfinder display on a camera where low cost and power consumption are critical, modulated red, green, and blue LEDs produce color pixels of varied intensities to generate a complete palette of colors and shades.