It may come as a surprise to know that the optimum screen size
for TV viewers is considered to be one with a diagonal measuring
in the region of 50 inches. Most houses in Europe and Asia can only
accommodate such a screen if it is flat, when it could conveniently
hang on a wall, for instance. The race is on, therefore, to produce
such a technological marvel. Researchers in the Sensors and Photonics
group under the leadership of Dr Adrian Travis are very excited
about the prospects of their latest way of achieving this objective,
a simple device known as the Wedge.
The Wedge refers to a wedge-shaped slab of glass which forms the
screen of the display. Images are projected onto this screen using
the same principles as those used for waveguides or optical fibres.
A light ray injected at a shallow angle into the thick end of the
wedge travels inside the glass, bouncing off each air/glass interface
as shown in the diagrams. Each time the ray is reflected off the
angled interface, the ray's direction changes. Its angle at the
glass/air interface becomes progressively less shallow, as shown,
until it becomes so steep that the total internal reflection breaks
down and the ray emerges. By using a series of lenses to firstly
focus the rays from a video projector to a point within the wedge
and then travel along it before leaving the face at the appropriate
points, a magnified image can be formed. This method essentially
provides a method of back projection display which is much thinner
(< 25mm) than those currently available.