Proceedings Volume 5442

Helmet- and Head-Mounted Displays IX: Technologies and Applications

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Proceedings Volume 5442

Helmet- and Head-Mounted Displays IX: Technologies and Applications

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Volume Details

Date Published: 8 September 2004
Contents: 6 Sessions, 31 Papers, 0 Presentations
Conference: Defense and Security 2004
Volume Number: 5442

Table of Contents

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Table of Contents

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  • NVG-I
  • NVG-II
  • HMD Applications
  • HMD Issues: Head Tracking, Symbology, and User Acceptance
  • Test and Evaluation
  • Displays-Optics
NVG-I
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Aircrew visual acuity viewing with different night vision goggle eyepiece diopter settings
The AN/AVS-9 night vision goggle (NVG) has an eyepiece lens that can be adjusted from +2 to -6 diopters (D). We have shown previously1,2,3 that on average NVG users tend to select about -1D, with a range of +0.5D to -4D3. This study was designed to evaluate NVG visual acuity (NVG VA) and subjective ratings for a range of diopter settings including user-selected and three fixed settings of -0.25D, -1D and -2D. Twenty-one experienced USAF Special Operations aircrew members, including 15 pilots, served as subjects. The median user-selected setting was -1.25D and ranged from +0.5D to -3.5D. Only 2 of the 21 subjects had user-selected NVG VA significantly better than a fixed setting of -1D. Of those two, one was not wearing prescribed glasses and the other was 49 years old, presbyopic, and could not focus through the -1D lenses. Subjective ratings and NVG VA indicated that most people could fly with a fixed setting of -1D for each eye, although two individuals needed different diopter settings for the right and left eyes. The new Panoramic NVG (PNVG) has a fixed eyepiece focus of -1D. Results suggest the PNVG should have a limited set of accessory lenses available.
Psychophysical measurement of night vision goggle noise using a binocular display
George A. Reis, Peter L. Marasco, Paul R. Havig, et al.
Users of night vision goggles (NVGs) have reported differences in perceived noise across various NVGs. To understand these differences, we need to measure NVG noise in a psychophysical context. In the precursory study, subjects attempted to characterize NVG noise by examining choices across different parameters of filtered white noise generated on a computer monitor. Subjects adjusted parameters of the filtered noise to match the noise for each combination of two goggles and two luminance levels. Significant differences were found between luminance levels, NVG type, and parameter relationships. Concerns from the previous experiment have yielded this study to better understand if this characterization process has merit. In the previous study, the parameter sequence was constant across trials. We increased the number of trials and subjects, and we included an accounting for parameter sequence. In addition, we used a modified Wheatstone stereoscope to simulate NVG tube independence. We discuss our results in terms of luminance levels, parameter sequence, subject variability, and relationships between parameters.
Validation of synthetic imagery for night vision devices
Night vision devices are important tools that extend the operational capability of military and civilian flight operations. Although these devices enhance some aspects of night vision, they distort or degrade other aspects. Scintillation of the NVG signal at low light levels is one of the parameters that may affect pilot performance. We have developed a parametric model of NVG image scintillation. Measurements were taken of the output of a representative NVG at low light levels to validate the model and refine the values of the embedded parameters. A simple test environment was created using a photomultiplier and an oscilloscope. The model was used to create sequences of simulated NVG imagery that were characterized numerically and compared with measured NVG signals. The sequences of imagery are intended for use in laboratory experiments on depth and motion-in-depth perception.
Detection of motion-defined form under simulated night vision conditions
The influence of Night Vision Goggle-produced noise on the perception of motion-defined form was investigated using synthetic imagery and standard psychophysical procedures. Synthetic image sequences incorporating synthetic noise were generated using a software model developed by our research group. This model is based on the physical properties of the Aviator Night Vision Imaging System (ANVIS-9) image intensification tube. The image sequences either depicted a target that moved at a different speed than the background, or only depicted the background. For each trial, subjects were shown a pair of image sequences and required to indicate which sequence contained the target stimulus. We tested subjects at a series of target speeds at several realistic noise levels resulting from varying simulated illumination. The results showed that subjects had increased difficulty detecting the target with increased noise levels, particularly at slower target speeds. This study suggests that the capacity to detect motion-defined form is degraded at low levels of illumination. Our findings are consistent with anecdotal reports of impaired motion perception in NVGs. Perception of motion-defined form is important in operational tasks such as search and rescue and camouflage breaking. These degradations in performance should be considered in operational planning.
Effects of saturation contrast on color recognition in night vision goggles
Paul R. Havig, Peter L. Marasco, David L. Post, et al.
In the past we have examined the luminance contrast ratios required to maintain color recognition in helmet-mounted displays (HMDs). Using typical daytime viewing conditions as simulated backgrounds we were able to determine 95% correct color recognition thresholds resulting in luminance contrast ratios averaging 1.17:1. Last year we adapted this research to determine the best colors to maintain color recognition of symbology that is on a night vision goggle (NVG) image. We simulated NVG P43 green phosphor and determined 95% correct color recognition thresholds. Results indicated that, on average, a luminance contrast ratio of nearly 1.5:1 was required to maintain color recognition. Review of the studies indicated that our simulated P43 phosphor was a much more saturated background, so saturation contrast may play as important a role as luminance contrast. A P45 white phosphor NVG may therefore be less problematic. Here we investigate the effects of both luminance and saturation contrast by manipulating color mixtures of green, yellow, and red symbology against two different backgrounds, P43 green and P45 white. We discuss our results in terms of both luminance and saturation contrast required for the maintenance of color recognition in NVGs.
NVG-II
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Night vision goggle luminance disparity and the Pulfrich phenomenon
When night vision goggle (NVG) image intensifier tubes (I2Ts) are replaced during maintenance, the output luminances of the two channels must not exceed a ratio of 1.5 (brighter channel luminance divided by the dimmer channel luminance) in order to meet the current allowed binocular luminance disparity specification. Two studies were performed to investigate the validity of this requirement. The first study estimated thresholds of binocular luminance disparity detection for observers looking through NVGs. For eight observers, the 25% corrected-for-chance probability of detecting an ocular luminance difference, yielded an average ratio of 1.43 indicating that the current 1.5 specification is perhaps too loose. The second study investigated the Pulfrich phenomenon, a pseudo-stereo effect that can be induced by presenting luminance imbalances to the eyes. This study created NVG luminance imbalances using neutral density (ND) filters and then investigated whether or not the various imbalance levels were sufficient to cause the Pulfrich phenomenon to be perceived. Results indicated an imbalance ratio of 1.10 was insufficient to cause the effect to be seen, but a ratio of 1.26 was sufficient (p ≤ 0.0003) for the effect to be seen, at least part of the time. Based on these results, it is apparent the allowed binocular luminance disparity ratio should probably be tightened to at least 1.3 with a goal of 1.2.
The impact of changing night vision goggle spectral response on night vision imaging system lighting compatibility
The defining document outlining night-vision imaging system (NVIS) compatible lighting, MIL-L-85762A, was written in the mid 1980's, based on what was then the state of the art in night vision and image intensification. Since that time there have been changes in the photocathode sensitivity and the minus-blue coatings applied to the objective lenses. Specifically, many aviation night-vision goggles (NVGs) in the Air Force are equipped with so-called "leaky green" or Class C type objective lens coatings that provide a small amount of transmission around 545 nanometers so that the displays that use a P-43 phosphor can be seen through the NVGs. However, current NVIS compatibility requirements documents have not been updated to include these changes. Documents that followed and replaced MIL-L-85762A (ASC/ENFC-96-01 and MIL-STD-3009) addressed aspects of then current NVIS technology, but did little to change the actual content or NVIS radiance requirements set forth in the original MIL-L-85762A. This paper examines the impact of spectral response changes, introduced by changes in image tube parameters and objective lens minus-blue filters, on NVIS compatibility and NVIS radiance calculations. Possible impact on NVIS lighting requirements is also discussed. In addition, arguments are presented for revisiting NVIS radiometric unit conventions.
Comparison of Topas cyclic olefin copolymers to BK7 glass in night vision goggle objectives
The objective of this study was to determine the suitability of Topas cyclic olefin copolymers (COC) as an optical plastic for use in military-grade night vision goggle (NVG) lens objectives. Test objective lenses that could include either a Topas COC window element or BK7 glass window element were manufactured. The test objectives were evaluated for low light resolution, MTF, off-axis veiling glare, and on-axis stray light. Additionally, the spectral transmittance of the individual windows elements was measured. This paper compares the evaluation results of test objectives containing Topas COC with test objectives containing BK7 glass.
AMOLED image source for use in integrated panoramic night vision goggle (IPNVG)
The objective of this paper is to present an overview of the active matrix organic light emitting diode (OLED) microdisplay used in the integrated panoramic night vision goggle (IPNVG). These devices will be used to insert independent and overlaid video imagery into the IPNVG. Interface and operational details of the microdisplay relative to the IPNVG implementation in military aircraft will be discussed.
HMD Applications
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Helmet-mounted displays for unmanned aerial vehicle control
M. Ephimia Morphew, Jay R. Shively, Daniel Casey
An experiment was performed to assess the effect of using a Helmet Mounted Display (HMD) versus a conventional computer monitor and joystick to perform an Unmanned Aerial Vehicle (UAV) sensor operator target search task. Eight subjects were evaluated on objective performance measures including their target detection accuracy and responses, in addition to subjective measures including workload, fatigue, situational awareness, and simulator sickness in both experimental conditions. Subjects were flown through a virtual world and asked to identify objects as targets, non-targets, or distractors. Results for objective measures indicated no difference in the operators' ability to accurately classify targets and non-targets. The subjects' ability to place the cursor on a target of interset (targeting accuracy), was, however, significantly better in the computer monitor condition than the HMD. The distance at which subjects could classify an object's identity was also significantly better in the computer monitor condition. Subjective measures showed no overall differences for sel-reported fatigue, workload, and situational awareness. A significant disadvantage, however, was found for the HMD with respect to self-reported nausea, disorientation, and oculomotor strain. Results are discussed in terms of their implications for the incorporation of HMDs into UAV ground control station operations.
Projection-based head-mounted displays for wearable computers
The projection based head-mounted display (HMD) constitutes a new paradigm in the field of wearable computers. Expanding on our previous projection based HMD, we developed a wearable computer consisting of a pair of miniature projection lenses combined with a beam splitter and miniature displays. Such wearable computer utilizes a novel conceptual design encompassing the integration of phase conjugate material (PCM) packaged inside the HMD. Some of the applications benefiting from this innovative wearable HMD are for government agencies and consumers requiring mobility with a large field-of-view (FOV), and an ultra-light weight headset. The key contribution of this paper is the compact design and mechanical assembly of the mobile HMD.
Helmet-mounted sensor fusion ATR for the dismounted soldier
Pankaj N. Topiwala, David Casasent
Computer vision capabilities have long been available to advanced sensor systems such as those on aircraft, UAVs, helicopters, and ground scout vehicles; but to date, they have not been available to the dismounted soldier. This is understandable since the size/weight/cost metrics of carrying sensors and the image processing, interaction, and display capabilities, not to mention the power supply, have been prohibitive. But recent advances in uncooled IR sensors (up to QVGA), coupled with the steady advances in EO sensors (VGA+) and in microelectronics, are now making the prospect of computer vision for the foot soldier feasible for the first time. In this paper, we develop our initial approaches to all aspects of this problem: (a) sensor system integration, (b) image processing algorithms and initial hardware vision, and (c) display and interaction. As a prototype compute/display platform, we do initial development based on a lightweight commercial wearable computer and helmet-mounted display.
Near-to-eye display concepts for air traffic controllers
Tower controllers are responsible for maintaining safe separation between airborne aircraft in the airport traffic control area, and separation between aircraft, equipment, and personnel on the airport surface. The objective of this project was to develop and demonstrate an out-the-window, augmented viewing system concept for Air Force air traffic control tower personnel to reduce look-down time within the tower and to optimize visual airfield operations, particularly during limited visibility conditions. We characterized controller tasks where a near-to-eye display greatly aids performance and identified form factor variables that influence user acceptability of hardware configurations. We developed an "out-the-window concept of operation" and analyzed the hardware requirements and feasibility of three near-to-eye viewing systems: two head-mounted monocular displays (HMMD) and a held-to-head binocular display (HHBD). When fully developed, these display prototypes should enhance tower controller situation awareness, and reduce such distractions as having to frequently attend to and respond to head-down (console) display information. There are potential users of this display concept in all branches of the military services, and in the commercial sector. There is also potential utility for surface surveillance operations in support of homeland security, law enforcement personnel, rescue workers, firefighters, and special operations forces in non-aviation applications.
Safe-to-fly determination for the helmet-mounted little high-end airborne laptop (Lil HAL) system
Fighter aircrews are taking large amounts of paper and other mission essential peripherals into the cockpit for each flight. The aircrews must find places to store these items and be able to access the required information in minimal time. Programs have been initiated to put tablet personal computers (PCs)/digital kneeboards into the cockpit, but due to bulk, ejection risks and sunlight readability issues, these devices have not been transitioned to fighter aircrews. The Air Force Research Laboratory (AFRL) has been tasked to develop a system using a helmet-mounted display, input device, and computer to solve some of the PC tablet issues-and do it quickly. AFRL was directed to conduct an Operational Utility Evaluation (OUE) to determine the usability of the Little High-end Airborne Laptop (Lil HAL) system (Figure 1). Before the OUE could occur, a safety evaluation of the Lil HAL system had to be completed with a receipt of a safe-to-fly clearance. This paper discusses the safety testing that occurred to receive the safety-of-flight clearance.
Lil HAL: digital kneeboard for ejection seat aircraft
In the last few years, airlines, commercial air carriers and the military have begun to introduce electronic tools into the cockpit to replace paper versions of flight publications, flight plans, departure and approach plates, maps, etc. These devices have varied from the common laptop to the smaller pen-tablet type computers. In some instances these devices have been connected to aircraft data buses to collect maintenance data, fault codes and other useful information. None of these devices, however, have been found satisfactory in ejection seat aircraft due to their size, weight, and dynamic characteristics when subjected to the inertial and aerodynamic forces that occur during an ejection. This paper describes an electronic digital kneeboard suitable for use in an ejection seat aircraft. The kneeboard consists of a look at helmet-mounted display, a small streamlined kneeboard input device, a carry-on/carry-off computer and its associated support interfaces.
HMD Issues: Head Tracking, Symbology, and User Acceptance
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Adaptive magnetic tracker: a revolution in electromagnetic tracker technology
Yaron Kranz, Giora Kornblau, Saul Stokar
In this paper we review the problem of measuring position and orientation using AC magnetic fields, outlining the two traditional solutions to the problem: analytical field models and field maps. We analyze the limitations of each of these solutions and present a novel solution to this problem, known as "adaptive magnetic tracking". We present an outline of the theoretical basis of the tracker, a discussion of its advantages and experimental results that demonstrate its unique and revolutionary abilities and flexibility.
Helmet-mounted tracker system accuracy measurements
This paper describes a method for evaluating helmet-mounted tracker accuracy installed in an aircraft sitting stationary on the ground. A test measurement test space is established by surveying numerous targets and ground control points with a laser surveying instrument. An aircraft is inserted arbitrarily into this test space and key points on the aircraft are surveyed along with the same ground control points originally surveyed. Mathematically, the two spaces are made to coincide at the ground control points, and then the entire space is transformed to place the aircraft so that the surveyed aircraft key points are located at their manufacture specified position. The helmet operator then looks at each target while other test operators record tracker output data. Data is subsequently analyzed.
Helmet-mounted display symbology for enhanced trend and attitude awareness
Joseph C. Jenkins, Donald G Sheesley, Frederick C. Bivetto
A Non-Distributed Flight Reference (NDFR) symbology set intended for fixed-wing aircraft helmet-mounted display (HMD) was evaluated by the U.S. Air Force Test Pilot School (USAF TPS) Have ATTITUDE test team in March and April 2001. Revisions were made to the NDFR symbology based on the Have ATTITUDE test team's recommendations resulting in a new HMD off-boresight symbology design called the Advanced NDFR (ANDFR). The ANDFR symbology was designed to provide continuous ownship status information with more precision and trend information over that of the original NDFR for airspeed, altitude, and attitude by utilizing odometer formats for airspeed and altitude and the arc segment attitude reference (ASAR) in place of the earlier orange peel for attitude. Three off-boresight HMD symbology sets, the ANDFR, baseline (BL) and baseline-plus (BL+) were evaluated using the NF-16D Variable-stability In-flight Simulator Test Aircraft (VISTA). Testing was performed at the USAF Flight Test Center at Edwards AFB, California, by the Have SYCLOPS test team from the USAF TPS in March and April 2003. Two VISTA calibration and twelve VISTA test sorties totaling 19.3 flight hours were accomplished in addition to three target sorties totaling 3.5 hours. The primary objective was to assess pilot awareness of trend concerning airspeed and altitude for the BL and BL+ symbology (i.e., Mil-Std-HUD counter-pointers) compared to the ANDFR (i.e., odometers for airspeed and altitude). Overall, the ANDFR performed equally as well as the BL and BL+ formats for the unusual attitude recoveries and air-to-air and air-to-ground operationally representative tasks. It is recommended that more testing be conducted using the ASAR design with an enhanced horizon reference (e.g., 360° horizon) off-boresight for discerning the location of the nearest horizon during steep climbs as well as an enhanced analog level flight reference for flight path angles less than 20° climb/dive. These results and their implications on the design of future off-boresight HMD symbology sets for trend and attitude awareness are discussed.
AH-64 IHADSS aviator vision experiences in Operation Iraqi Freedom
Keith L Hiatt, Clarence E. Rash, Eric S. Harris, et al.
Forty AH-64 Apache aviators representing a total of 8564 flight hours and 2260 combat hours during Operation Iraqi Freedom and its aftermath were surveyed for their visual experiences with the AH-64's monocular Integrated Helmet and Display Sighting System (IHADSS) helmet-mounted display in a combat environment. A major objective of this study was to determine if the frequencies of reports of visual complaints and illusions reported in the previous studies, addressing mostly benign training environments, differ in the more stressful combat environments. The most frequently reported visual complaints, both while and after flying, were visual discomfort and headache, which is consistent with previous studies. Frequencies of complaints after flying in the current study were numerically lower for all complaint types, but differences from previous studies are statistically significant only for visual discomfort and disorientation (vertigo). With the exception of "brownout/whiteout," reports of degraded visual cues in the current study were numerically lower for all types, but statistically significant only for impaired depth perception, decreased field of view, and inadvertent instrumental meteorological conditions. This study also found statistically lower reports of all static and dynamic illusions (with one exception, disorientation). This important finding is attributed to the generally flat and featureless geography present in a large portion of the Iraqi theater and to the shift in the way that the aviators use the two disparate visual inputs presented by the IHADSS monocular design (i.e., greater use of both eyes as opposed to concentrating primarily on display imagery).
Test and Evaluation
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Quantification of parallax in dual-sensor systems
Sean Moore
Parallax is an issue in any system that contains images from two or more separate, displaced sensors imposed on a single display. The effect can be image quality degradation due to a double image or a blurred image. The impact of this effect can be calculated based on the configuration of the sensors and the position of the object of interest in relation to them and their point of convergence. Parallax quantification is necessary for determining a method to improve the performance of fused-sensor systems. This paper will examine this phenomenon and outline a method that enables calculation of parallax at an arbitrary point of interest.
Laboratory system for the evaluation of helmet-mounted displays
Howard H Beasley, Thomas H Harding, John S Martin, et al.
The evaluation of helmet-mounted displays (HMDs) consists of optical, photometric, photographic and system performance tests that involve proper positioning and alignment of measuring tools with respect to the HMD. Evaluations are generally time consuming and involve days of meticulous testing. To shorten the time required to evaluate an HMD, we have developed a laboratory system where the positioning and alignment requirements for each test are accomplished in one step. Further, the system allows for the interchange of measuring instruments so that proper alignment is achieved as soon as the measuring instrument is mounted. In practice, the system has shortened the time required to evaluate an HMD by about 60%. The system allows for ease of position anywhere within the HMD's field-of-view (FOV). A key characteristic of the system is that the entrance pupil of the evaluation system is collocated with the HMD's exit pupil.
Flight simulator evaluation of display media devices for synthetic vision concepts
Jarvis James Arthur III, Steven P. Williams, Lawrence J. Prinzel III, et al.
The Synthetic Vision Systems (SVS) Project of the National Aeronautics and Space Administration's (NASA) Aviation Safety Program (AvSP) is striving to eliminate poor visibility as a causal factor in aircraft accidents as well as enhance operational capabilities of all aircraft. To accomplish these safety and capacity improvements, the SVS concept is designed to provide a clear view of the world around the aircraft through the display of computer-generated imagery derived from an onboard database of terrain, obstacle, and airport information. Display media devices with which to implement SVS technology that have been evaluated so far within the Project include fixed field of view head up displays and head down Primary Flight Displays with pilot-selectable field of view. A simulation experiment was conducted comparing these display devices to a fixed field of view, unlimited field of regard, full color Helmet-Mounted Display system. Subject pilots flew a visual circling maneuver in IMC at a terrain-challenged airport. The data collected for this experiment is compared to past SVS research studies.
Day/night ANVIS/HUD-24 (day HUD) flight test and pilot evaluations
Zvi Yona, Ben Weiser, Oded Hamburger
The Day/Night ANVIS/HUD-24 gives pilots the ultimate head-out flight solution: 24-hour operational capability from a single integrated system. The basic integrated system combines the standard Night Vision Goggle (NVG) image with vital aircraft flight and navigation information, currently operational on over 4500 helicopters worldwide. Introducing the new Day HUD add-on module the same flight information is displayed for day use. The Day Head Up Display (HUD) is an add-on, complimentary to the basic night ANVIS/HUD system (AN/AVS-7). A lightweight optical module enhancing the day flight operation is designed to allow utility and reconnaissance helicopter day-mission operation by providing complete daytime head-out flight information. This add-on unit enhances flight safety, maximizes tactical survivability, and increases situational awareness during critical landing and takeoff phases. The Day HUD offers a unique 25° field-of-view, monocular, see-through flight information display. It mounts directly to the standard NVG mounting, incorporating a state of the art AMLCD flat panel display, high brightness solid-state backlight and compact optics resulting in a high contrast, high visibility display. The Day HUD test and evaluation program included extensive man-machine interface tests and numerous flight test aircraft in more than six separate countries. This paper will also address flight training, customer acceptance and expand on these findings and observations.
Displays-Optics
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Methods for eliminating bright point emissions from liquid crystal microdisplays
Due to limitations in manufacturing technology, current liquid crystal microdisplays cannot be manufactured without pixel defects. Among other defects, pixels can fail in their transmissive state, yielding a bright spot in the image relayed to the display wearer. Experience with military night-vision devices has shown that bright image defects can be extremely objectionable, as they can be distracting or can be incorrectly identified as objects of interest, such as targets. Image intensifier tube manufacturers eliminate bright point emissions by burning the image tube phosphor with a laser, effectively turning the bright spot into a black spot, an image defect considered far less distracting. Unfortunately, formal methods for eliminating bright point defects in liquid crystal microdisplays have not been thoroughly investigated. Methods such as severing circuitry or blasting the liquid crystal display pixel with a laser should be ineffective or even create a larger bright defect, further aggravating the problem. Numerous methods that could be applied are known to have advantages and disadvantages. This paper will examine the use of pixel blocks and fiberoptics as possible methods for eliminating or minimizing the visibility of bright point emissions and their impact on the visibility of the micro liquid crystal display.
Magnifying miniature displays with microlenslet arrays
Current technology trends are focused on miniaturizing displays, although for specific applications such as the use of head-mounted displays (HMD) this limits the advancements for a wider field-of-view (FOV) and a negligible overall weight of the optics. Due to the advancements of electronics that benefit from smaller miniature displays, universities and companies are focused on developing this technology to meet the growing demand of this global market. Higher resolution displays with added brightness are being developed, but these displays are decreasing in their viewable area. HMDs can benefit from these higher resolution and brighter displays but they will undergo an increased optical weight to compensate for the smaller display size. To overcome this hindrance in HMDs, we demonstrate in this paper how to incorporate microlenslet arrays as an optical relay system to magnify miniature displays. Microlenslet arrays provide respectively shorter focal length which yields a smaller overall object to image distance and an incremental overall weight compared to an otherwise increased optical lens assembly. The contribution of this paper is a patented concept of magnifying/demagnifying miniature displays with microlenslet arrays that can be integrated in a spaced limited area.
Optical modeling of a holographic single-element head-mounted display
This paper proposes a new method to design an optically-fabricated holographic element, where the construction optical system and the playback system can be optimized jointly. The method was driven by the use of a new holographic recording material - the photo-thermo-refractive (PTR) glass - that can only be written at 325nm, while its playback takes place in the visible part of the spectrum. Applying the method proposed, a single holographic element head-mounted display (HMD) was modeled. Results show that a single holographic element may be constructed at 325 nm, and inserted in a playback optical system operating at 633nm, with a MTF of over 80% across a 40 degree field of view at 37cycles/mm.
Partial-overlap biocular image misalignment tolerance
Melvyn E. Kalich, Lisa M. Lont, Corina van de Pol, et al.
Partial-overlap biocular helmet-mounted display (HMD) design flexibility and cost are directly related to image misalignment standards. Currently suggested standards are based on highly variable data from a number of studies, most using subjective discomfort or diplopia measures. This study tested the suggested standard for divergent horizontal image misalignment in a partial-overlap biocular optical system by exercising vigilance performance during image misalignment. Also, pre- and post-image misalignment divergence, convergence and heterophoria measurements were taken. The results revealed that clinical visual diagnoses, associated with accommodation and vergence, were clearly related to vigilance task performance, showing a greater number of vigilance errors for subjects viewing misaligned displays. In-device post-image misalignment divergence recovery and convergence break-recovery were significantly decreased. This was not found for the no-offset controls.
Potential see-through performance deficits in U.S. Army developmental helmet-mounted displays
The U.S. Army has several helmet-mounted displays (HMDs) under development, all with unique characteristics and designs. For example, the now cancelled RAH-66 Comanche HIDSS (Helmet Integrated Display Sighting System) uses miniature liquid crystal displays as sources, and Microvision, Inc., of Bothel, Washington, is developing several prototype HMDs for the Army that incorporate a scanning laser or lasers as their source. Gone are new HMD designs that use cathode ray tubes (CRTs) as sources. A potential problem for see-through displays lies in the fact that the MTF (modulation transfer function) of flat panel displays is characterized by a good high-spatial frequency response. Although this seems counterintuitive, this high frequency response may impact the see-through detection and identification of high-spatial frequency targets because of visual masking and/or spatial frequency adaptation. A similar problem exists with the HMDs being developed by Microvision, Inc., where a high-spatial frequency noise pattern is present due to the inclusion of a diffractive exit pupil expander. Simple blurring of the HMD imagery would reduce this potential problem. In an earlier investigation, we found that a little blurring of flat panel displays does not affect small letter acuity even near threshold. Thus, it is possible to reduce the potential for see-through deficits while still maintaining maximum HMD fidelity.
Active matrix OLED for rugged HMD and viewfinder applications
Kia Low, Susan K. Jones, Olivier Prache, et al.
We present characterization of a full-color 852x3x600-pixel, active matrix organic light emitting diode (AMOLED) color microdisplay (eMagin Corporation's SVGA+ display) for environmentally demanding applications. The results show that the AMOLED microdisplay can provide cold-start turn-on and operate at extreme temperature conditions, far in excess of non-emissive displays. Correction factors for gamma response of the AMOLED microdisplay as a function of temperature have been determined to permit consistent luminance and contrast from -40°C to over +80°C. Gamma adjustments are made by a simple temperature compensation adjustment of the reference voltages of the AMOLED. The typical room temperature full-on luminance half-life of the SVGA+ full color display organic light emitting diode (OLED) display at over 3,000 hr at a starting luminance at approx. 100 cd/m2, translates to more than 15,000 hr of continuous full-motion video usage, based on a 25% duty cycle at a typical 50-60 cd/m2 commercial luminance level, or over 60,000 hr half-life in monochrome white usage, or over 100,000 hr luminance half-life in monochrome yellow usage at similar operating conditions. Half life at typical night vision luminance levels would be much longer.
CRTs: electrostatic focusing systems for performing Laminar electron gun
Current CRT technology suffers from a reduced bright image response, and a reduced image resolution due to the distribution of beam current densities following a Gaussian rather than a uniform distribution. A uniform distribution of beam current necessary achieved by proper manipulation of CRT's electro-static focusing system. Functional connection has been found between three electrodes of CRT's electro-static focusing systems, which provide "Laminar" electron flow in system. This technology provides unique characteristics that is providing uniformly distributed output current density. Theoretical analysis is given for some current Electro-optical systems through the calculation of trajectories of electrons in the system without taking into account the different starting velocities. This analysis proves the importance of producing the Electro-optical systems with uniform distribution of current density. As the result it has been achieved ideal explicitness of the image and picture compression from 1 (transfer 1:1, for night vision devices) to 50 times (transfer 1:0.02, for electron-optics transmission) and more accompanied by uniform distribution of current density. Usage of this technology allows 10 time's reduction of time resolution and 2500 times increasing of light intensity for a compression of 50x. There is no need in corrective electrode in order to achieve high power brightness. With this technology no gain correction is required.
A new normally black high-contrast wide symmetrical viewing angle AMLCD for military head-mounted displays (HMDs) and other viewer applications
Hiap L. Ong, Ollie C. Woodard, Ngwe Cheong, et al.
Kopin's miniature Active Matrix Liquid Crystal Displays (AMLCD's) are used in military head mounted and sensor viewer applications. These low power, ruggedized displays operate from -37°C to +65°C with excellent imaging characteristics and reliability. Kopin and the US Army Night Vision and Electronic Sensors Directorate (NVESD) are developing high resolution, full-color displays for day/night operations and image fusion applications. Kopin has begun the development of a miniature, spatial color SXGA display using a new Kopin design and process to fabricate multi-domain vertical alignment (MVA displays. The MVA display offers a normally black screen, very high contrast ratio and wide, symmetrical viewing-angle. MVA monochrome SXGA, monochrome VGA (640x480 pixels) and color filter VGA displays have been demonstrated. A 0.97" diagonal, color filter SXGA MVA display is the goal for this program. The patented MVA process uses a simple fabrication process that makes use of the intrinsic fringe field in each pixel to control the LC alignment. Contrast ratios greater than 1000:1 and 120-degree symmetrical viewing angles are routinely achieved. The power-off state or failed state on MVA displays is black, which reduces the visibility of defective pixels. The normally black AMLCD is the preferred mode for night military operations / applications, and see-though Head Mounted Display (HMD) optical designs. Performance data and specifications for Kopin's monochrome and color filter MVA displays will be presented with reference to military (HMD and weapon sight), industrial, and commercial applications. Application extensions that utilize the new MVA color filter technologies developed will be highlighted.