Optical Technology Projects Images Directly Into The Eye

March 19, 1998

A laser and a rapidly rotating reflective polygon are the main components in a new technique to project images directly onto the retina. The so-called Retinal Scanning Display Method (RSD) makes it possible to project the virtual reality simulated by a computer in a very realistic way. The picture quality is much better than that on a computer screen. The laser light used is five thousand times less strong than the critical limit for the eye and is therefore not in any way dangerous. RSD has partly been developed at Delft University of Technology (TUD) with support from the Netherlands Technology Foundation (STW) and from Philips.

The RSD technique produces an image by using a spot of light to draw a series of lines under one another extremely rapidly. The intensity of the light varies according to its position along the line. The process takes place so quickly that the eye perceives the pattern of light as a coherent picture. Existing technology makes use of a screen consisting of tiny luminous elements (pixels) which are switched on and off. The quality of the picture built up in this way is not very good because it is difficult to make the pixels small enough. Existing techniques can therefore not improve the quality of pictures covering a wide field of vision. However, projecting light directly onto the retina with a laser produces an extremely high-quality picture. The laser beam narrows the light down to tiny points which are so close to one another on the retina that the eye is unable to tell them apart.

The RSD technique makes it possible to project realistic pictures covering a wide field of vision. A three-dimensional impression is formed by sending slightly different images to each eye and it is also possible to produce a colour image. Because the laser uses very little light, RSD is economical, in the same way that a set of headphones uses far less energy than a loudspeaker.
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Netherlands Organization for Scientific Research

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