Authors: Shajila Beegam M.K
Certificate: View Certificate
Virtual Retinal Display (VRD) is an advanced technology for creating visual images. Dr. Thomas A. Furness III created it at the Human Interface Technology Laboratory (HIT Lab). Low power laser light is directly scanned onto the retina by the VRD to produce images. Bright, high-contrast, high-resolution photos are produced with this unique technique. It has been shown that all the technological advancements needed have been made in order for small, laser-scanned, virtual retinal displays to operate effectively. Since several years ago, military and commercial customers have received prototype devices with VGA resolutions (640 x 480 pixels), and Microvision\'s Virtual Retinal DisplayTM (VRDTM) is now ready for accelerated performance expansion. VRD images often use 300 nanowatts or less. Additionally, VRD images can be easily seen when placed on ambient room lighting.
The VRD display technology differs significantly from other, current display technologies. Without the need for displays, the VRD "paints" a high-resolution, full-motion, full-color image directly onto the retina of the viewer's eye using a modulated, low-power beam of light (in a raster scan pattern similar to that of a traditional television set). In some applications, an image is displayed in the viewer's field of vision as if the viewer were standing right next to a high-definition video screen. In other uses, the VRD can overlay an image on the viewer's field of vision (augmented vision), allowing the viewer to see data or other information in the context of his or her natural surroundings. The spectator sees a high-resolution, bright image regardless of how the VRD is used.
In 1991, the Human Interface Technology Lab (HIT) at the University of Washington developed the VRD. In November 1993, construction got underway. A full color, wide field of vision, high resolution, high brightness, and a reasonably priced virtual display was the goal. The sole license for commercializing VRD technology belongs to Microvision Inc. From head-mount displays (HMDs) for military and aerospace applications to the medical community, this technology offers a wide range of possible uses.
The VRD sends an electronically modulated light beam directly onto the retina of the eye, creating a rasterized image. The source image seems to the viewer to be visible from two feet away when seated in front of a 14-inch display. The retina of its eye, not a screen, is where the image is actually located. He or she is viewing an excellent-quality image with stereo vision, full color, a large field of view, and no flickering features.
II. .ARCHITECTURE OF VRD
Through the direct application of modulated light in a raster pattern to the retina of the viewer, the Virtual Retinal Display displays video data. The intensity of the light is varied as it passes over the eye. The VRD is made up of a light source, a modulator, vertical and horizontal scanners, and imaging optics at its most basic level, as depicted in the following picture (to focus the light beam and optically condition the scan).
The retinal image that is created as a result is interpreted as a wide-field of-view image coming from a certain viewing distance in space. The light raster on the retina and the resulting image that is viewed in space are shown in figure2.
A scanner generally scans an angled collimated light beam using magnifying optics. Each collimated beam is targeted upon a specific region of the retina. The location of the matching concentrated area moves across the retina as the scan's angle shifts over time. The raster image as it is seen in Fig:2 is made up of a series of intensity modulated spots.
III. WORKING TECHNOLOGY
A. Three Units Typically Comprise A VRD System
B. Five Major components in typical VRD System
IV. VRD FOR SYNTHETIC VISION INFORMATION SYSTEM
The emergence of cutting-edge image sensor and display technology supports the need to restructure digital synthetic/augmented vision systems. Under Instrument Meteorological Conditions, these systems' operating goal is to deliver range resolution and target recognition performances on par with or better than those attained with unaided human vision. A display for a synthetic vision system must do three tasks.
Firstly, the display must be built to provide the operator with the most information possible. As a result, a head- or helmet-mounted display (HMD) of low mass and great utility must be built to incorporate the picture properties of brightness, contrast (shades of grey), spatial resolution, and color. Color fully engages the human visual system, allowing it to detect and recognize targets, display false-color information from imaging sensors, facilitate color encoding of symbolic information, and improve the intelligibility of information displayed in comparison to ambient luminance.
Second, to align the real and virtual worlds, it is also necessary to track the operator's head's spatial orientation. There are many other technologies available, but because of their high accuracy, rapid update rate, and environmental robustness, a video metric approach is advised whenever it is practical.
Finally, eye-tracking capabilities are needed. Eye tracking enables a virtual world where the user's eye serves as a hands-free "mouse" for "look-to-activate" or "look-to-shoot" operations. The accuracy and update rate necessary are now becoming available using simple, affordable methods. In its visually-coupled HMD systems, Microvision will integrate COTS (commercial off-the-shelf) head- and eye-tracking technology.
V. APPLICATIONS OF VRD
The VRD has a wide range of application sectors, including manufacturing, communications, and classic virtual reality helmet mounted displays (HMDs). The VRD can be set up as inclusive (non-see-through) or see through, head mounted or hand held, and it offers high brightness and high resolution, making it suitable for a variety of applications. The sections that follow provide descriptions of some particular applications in the aforementioned industries.
VI. ADVANTAGES AND DISADVANTAGES
The few milliwatt range of laser diodes is typical. Because of this, laser diode source-based systems will function with low laser output levels or with severe beam attenuation.
6. Power Consumption: The VRD effectively transmits light to the retina. The system's exit pupil can be reduced, allowing the majority of the created light to reach the eye. Additionally, a resonant device that operates with a high figure of merit, or Q, and is also very efficient is used for scanning. As a result, the system requires relatively little electricity to run.
7. Stereoscopic Display: Different images are projected into each viewer's eye via the conventional head-mounted display used to produce three-dimensional views. A stereo pair is produced by producing each image from a slightly different vantage point. This approach results in a conflict but also permits the use of one significant depth cue. For the purpose of detecting depth, humans use a variety of clues. Along with stereo vision, accommodation is crucial for determining depth. The distance at which the eye is focused to see a distinct image is referred to as accommodation. The image is positioned at a convenient and fixed focal distance by the virtual imaging optics utilised in modern head-mounted displays. Since the image is coming from a flat screen, everything in the virtual image is situated at the same focal distance in terms of accommodation. As a result, the accommodation cue suggests that an object is located at a different distance than what is indicated by the stereo cues. It is theoretically feasible to create a more natural three-dimensional image with the VRD (this is still in the development stage). Each pixel in the VRD has a unique wavefront created for it. The curvature of the wavefronts can be changed.
8. Inclusive And See Through: Systems that function both inclusively and transparently have been developed. Most displays are not bright enough to operate in a see-through mode when utilised in an area with medium to high levels of illumination, where the luminance can reach 10,000 candela per metre squared, making the see-through mode a generally more challenging system to create. This is not a problem with the VRD, as was said before. In the VRD, a light source is modulated with image data either directly ('internally') or indirectly ('externally') via a modulator. The MRS and a galvanometer are the current x-y scanning systems that the light passes through. In current VRD systems, light from the scanner pair enters an optical system, creating an aerial image that is subsequently magnified and transmitted to infinity using an eyepiece.
Additionally, there are a number of drawbacks to employing virtual retinal displays:
With so much at risk, many critical agencies have already begun collaborating with the VRD, but it is difficult to get an update on their progress. However, we can state that right now, all of those engineers, fighter pilots, and people who are partially sighted who deal with VRD will be battling various aspects of the same issue. Studying resolution, contrast, and colour perception from scanned laser images, as well as how VRD images interact with images from the real world to improve augmented reality applications of the technology, are among the projects of interest in the field. Other projects include research on how partially sighted people perceive resolution and contrast from VRD images, the development of VRD light scanning paradigms to improve image resolution and contrast in low-vision subjects, and more.
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Copyright © 2023 Shajila Beegam M.K. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.