By Chris Chinnock
Head-mounted or helmet-mounted display (HMD) systems in military platforms have typically been big and bulky. The reason for this is HMD designers most often must use miniature cathode ray tubes (CRTs) instead of their smaller, lighter cousins — miniature flat-panel displays (FPDs). Even though scientists have long touted the promise of miniature FPDs replacing miniature CRTs to reduce bulk and weight, the newer technology has yet to materialize. Today, in fact, there are no HMDs for military platforms in production that use miniature FPDs.
This situation may be changing, however, as activity in the HMD arena begins to pick up. One big change in the last two years has been the funding allocated for FPD-based headsets, says Darrel Hopper, chief of the U.S. Air Force Wright Laboratory at Wright Patterson Air Force Base in Dayton, Ohio. "Much of the money has come from congressional plus-ups that have added money to programs," Hopper says. "Funding is fine now, so we are concentrating on technical challenges."
Hopper, whose group is developing display technology for next-generation HMDs and projection systems, is overseeing several development programs. One technology that he says is starting to pay-off is the emissive active-matrix electroluminescent (AMEL) display from Planar Systems in Beaverton, Ore. Systems designers have chosen a VGA monochrome-green version to show symbology in a soldier`s HMD display under the U.S. Army`s Land Warrior program. Originally, 70,000 units were set for production, but system-level problems forced managers to shelve the program for at least a year. But recently, there have surfaced industry rumblings that the program may soon get back on track.
The VGA displays are often used to overlay symbology on top of imagery, such as monochrome video or FLIR (Forward Looking Infrared) data. Under the U.S. Panoramic Night Vision Goggle program, designers are expanding device`s field of view (FOV) from 40 to 100 degrees. Symbology, such as target data, will overlay in the central portion of the wide-FOV headset, driven by an AMEL display.
Designers also are developing high-resolution SXGA (1,280 by 1,024 pixels) display systems for primary navigation or targeting headsets that require gray scale. The U.S. Army`s RAH-66 Comanche scout-attack helicopter program office has emerged as a leader in the use of flat-panel displays in headsets.
Earlier this year, Comanche developers decided to become the first to commit to using microdisplays instead of mini-CRTs in a major headset program. They plan production to begin in 2003 and the current first choice is an SXGA display from Kopin Corp. of Taunton, Mass. Kopin`s monochrome transmissive LCD microdisplay has just begun to sample, but the company`s quarter-VGA product has reached full production, and is part of a JVC camcorder viewfinder.
Mini-CRTs, however, still have their proponents. Program managers with the U.S. Joint Helmet-Mounted Cueing System (JHMCS) have opted not to use flat-panel displays as the baseline technology. Instead, they will use 12-millimeter mini-CRTs.
The JHMCS enables jet fighter pilots to target enemy aircraft and is scheduled for deployment on the Lockheed Martin F-16 and F-22 fighters, as well as on the Boeing F-15 and F/A-18 fighters. Currently, JHMCS has successfully passed critical safety of flight qualification tests and has entered the flight test phase for these aircraft. Production could begin by 2001. Recently, Lockheed Martin designers chose the same headset for their version of the future Joint Strike Fighter, which is scheduled to begin evaluation in 2000, with production expected in 2008.
The Visually Coupled Acquisition Targeting Systems (VCATS) is one program where designers are looking at next-generation technology for upgrades in HMDs. Under a contract with the U.S. Air Force`s Armstrong Lab at Brooks Air Force Base, Texas, engineers from the Boeing Phantom Works in St. Louis are looking at adding a video capability to the JHMCS headset and expanding the role of the headset to encompass air-to-ground operations. The idea is to integrate the functionality of a current air-to-ground HUD into the helmet.
Meanwhile, many other flat-panel display technologies are vying to earn a spot in these headset programs. For example, Planar officials say they have demonstrated AMEL brightness of 1,000 foot lamberts in the lab, which when coupled to a 60 percent efficient optical system, would provide the needed luminance at the eye for the Comanche program. The current VCATS design, from Kaiser Electronics of San Jose, Calif., uses a Kopin display, but is thought to only be about 25 percent optically efficient.
Virtual Retinal Display (VRD) systems from Microvision in Bothell, Wash., are also considered a major contender for future headset programs. Microvision leaders have received almost $10 million from the Army`s Aircrew Integrated Systems office to support development of their HMD technology for the Aircrew Integrated Helmet System Program.
Support for similar programs is in the pipeline as well. The Army`s Aviation Applied Technology Directorate at Fort Eustis, Va., is supporting a virtual cockpit concept, the Defense Advanced Research Projects Agency (DARPA) in Arlington, Va., is helping Microvision designers look at an armored vehicle "glass turret" concept, and the Air Force and Navy have provided research contracts for HMD development. Microvision executives have raised close to $45 million in the last six months to support military and commercial development projects for it VRD technology.
Raising the light output for daytime operation remains a major goal of head-mounted displays. Toward that end, Microvision experts have recently joined with Cree Research in Durham, N.C., to develop high-power LED and laser sources.
Producing a high-luminance display for daytime operations is also the goal at FED Corp. in Hopewell Junction, N.Y. FED engineers are working on active-matrix organic light emitting diode (AM-OLED) technology, and recently, reported the highest efficiency devices yet. The company has set up a production line and expects to have monochrome SXGA devices ready by this fall.
Reflective LCD microdisplays using a silicon backplane are also under evaluation for HMDs. So far, Hopper says, the optical systems have proved to be too large for helmet-based systems that must survive the air blast during pilot emergency ejection from the aircraft. Work continues on alternative approaches, however, since these displays will offer acceptable color outputs if perfected.
For ground-based applications, experts from MicroOptical Corp. of Westwood, Mass., are working on one of the most elegant headset designs yet put forward.
They have two eyeglasses concepts. One uses a tiny display module that clips on to an ordinary set of eyeglasses. The other embeds the image routing and magnification optics inside a modified pair of eyeglasses.
Company engineers are evaluating AMEL, transmissive LCDs, and reflective microdisplays for commercial and military versions of the eyeglasses. A DARPA program, for example, will add a tiny camera to the headset to aid military police using wearable computers in recognizing faces.
Microdisplay-based headsets are already moving into ground-based simulation and training applications too. For example, experts from Kaiser Electro-Optics in Carlsbad, Calif., are offering the SimEye XL100 that replaces the 1-inch CRTs with three poly-silicon LCD panels. The result is a reduction in cost from $165,000 per helmet system to $75,000. Fixed FOV versions of the XGA resolution headset can be obtained for $15,000.