Published on March 11, 2014
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A virtual retinal display (VRD) is a display technology that draws a raster display (like a television) directly onto the retina of the eye. The user sees what appears to be a conventional display floating in space in front of them. It is also known as a retinal scan display (RSD) or retinal projector (RP)
The VRD was invented by Kazuo Yoshinaka of Nippon Electric Co. in 1986. Later work at the University of Washington in the Human Interface Technology Lab resulted in a similar system in 1991. Most of the research into VRDs to date has been in combination with various virtual reality systems. In this role VRDs have the potential advantage of being much smaller than existing television-based systems.
Viewing Optics Modulated Light Sources Horizontal and vertical scanners Drive electronics Source image
Pixel Based Display VRD Illumination constant over whole pixel Light scanned across retina Persistent light emission Short transient light emission Non coherent light Coherent light Broadband color Narrow band color Pixels separated by mask Spot can overlap retinals in scans
Size and Weight Small size, as no intermediate screen is present. All components are small and light making it highly portable. Appropriate for Hand held and Head mount displays. Power consumption Light sources consume very less power in order of milli watts. Scanning is done with a resonant device (MRS) with high figure of merit.
Resolution Limited only by diffraction and optical aberration in the optical components, limits in scanning frequency and modulation b/w of photon source. SLD is a coherent source and offer high modulation b/w to give resolutions well over a million pixels. State of the art scanners can scan over a1000 lines per frame which is comparable to HDTV. Brightness Perceived brightness is only limited by power of the light source. SLD sources can provide very good brightness levels even for see through mode in day light.
Field of view • Inclusive systems provide horizontal field of view b/w 60-100 degrees. • See through mode systems have it slightly over 40 degrees. • These figures are far better than existing HMD systems. Stereoscopic display Supports stereoscopic display as both eyes can be separately addressed. Thus provides a good approximation to natural vision. Inclusive & See through See through works very well even at very high illumination conditions of about 10000 candella per meter squared.
Laser sources are introduced into a fiber optic strand which brings light to the Mechanical Resonance Scanner (MRS). The MRS is the heart of the system. It is a lightweight device approximately 2 cm X 1 cm X 1cm in size and consists of a polished mirror on a mount. The mirror oscillates in response to pulsed magnetic fields produced by coils on the system mounting. It oscillates at 15 KHz and rotates through an angle of 12 degrees. The high frequency of scanning allows the fine resolution in the images produced.
As the MRS mirror moves, the light is scanned in the horizontal direction. Because the mirror of the MRS oscillates sinusoidally, the scanning in the horizontal direction has been arranged for both the forward and reverse direction of the oscillation. The scanned light is then passed to a mirror galvanometer or second MRS which then scans the light in the vertical direction. The horizontally and vertically scanned light is then introduced to the eye. The light can be sent through a mirror/combiner to allow the user to view the scanned image superimposed on the real world.
Light must be collected and focused down in a point. This is an inherent property with lasers, but difficult with LED systems. Advances in LED technology are applied to these LASER - LED hybrid displays.
VRDs can reduce the read-time and can act as always-present guides for many tasks. The various fields of application of VRD technology are listed. Radiology Surgery Therapeutics (Scanning Laser Ophthalmoscope) Production Communication Augmented Virtual reality Aerospace Military
Potentially very small and lightweight, glasses mountable Large field and angle of view, greater than 120 degrees High resolution, approaching that of human vision Full color with better potential color resolution than conventional displays Brightness and contrast ratio sufficient for outdoor use True stereo 3D display with depth modulation Bypasses many of the eye's optical and retinal defects scanning light into only one eye allows images to be laid over one's view of real objects. VRD system also can show an image in each eye with an enough angle difference to simulate three-dimensional scenes with high fidelity.
To ensure that VRD device is safe, rigorous safety standards from the American National Standards Institute and the International Electrotechnical Commission were applied to the development. Optical damage caused by lasers comes from its tendency to concentrate its power in a very narrow area. This problem is overcome in VRD systems as they are scanned, constantly shifting from point to point with the beams focus. If the laser stops scanning, permanent damage to the eye will result because the beam stays focused in one spot. This can be prevented by an emergency safety system to detect the situation and shut it off.
When cost of production falls further, we will see VRDs fulfilling many functions and applications, and may perhaps see a time where they become ubiquitous in the more distant future. Future systems will be even more compact with the advent of MEMS(Micro Electro Mechanical System) scanners, miniature laser diodes and application specific IC technology. Another key development to come is the advent of Augmented Reality display systems to assist people in their various tasks.
The VRD is a safe new display technology. VRD provides an unprecedented way to stream photons to the receptors of the eye; affording higher resolution, increased luminance, and potentially a wider field-of view than all previous displays. Virtual retinal display is a breakthrough in imaging technology that will optimally couple human vision to the computer. Cost is currently acting as a blocker of the technology in most industries. If this continues to fall, we will see VRDs fulfill many functions and applications, and may perhaps watch them becoming ubiquitous in near future.
http://www.edutalks.org/downloads/VIRTUAL%20RETINAL%20DISPLAY.pdf http://www.csie.ndhu.edu.tw http://www.hitl.washington.edu/publications/r-98-21/r-98-21.pdf http://en.wikipedia.org/wiki/Virtual_retinal_display https://www.kickstarter.com/projects/jonrodriguez/3d-tv-for-light-field-images-glasses- free http://www.wisegeek.com/what-is-a-virtual-retinal-display.htm#
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