The Development of Data Projectors
The LCDs utilised in projection systems are usually small reflective or transmissive panels lit up by a powerful arc lamp source. A series of lenses expands the reflected or transmitted image and then displays it onto a screen. In front-projection systems the LCD is situated on the same area of the screen as the viewer, but in rear-projection systems the screen is lit up from behind. Projectors of higher cost and performance may use three separated LCD panels, creating separate red, green, and blue images that combine to create a coloured image on the screen.
The growing desire for film displays has had a growth in emphasis on the switching speed of liquid crystals. This has required the creation of items build with smectic liquid crystals, particular kinds of which emit a better electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is at this time the most progressive smectic device. With it the liquid crystal molecules are managed in layers that are perpendicular to the substrate planes, which are separated by one or two micrometres, and throughout the layers the molecules are on a tilt, as displayed in the figure. The host liquid crystal possesses optically active molecules, and a minor turn up of the optical activity and the angle of the molecules is the presence of a permanent charge separation, or ferroelectric dipole, similar to the ferromagnetic dipole of a magnet. The direction of this dipole is perpendicular to the tilt direction of the molecules and in the plane of the layers. Hence, there has to be a permanent charge separation through the liquid crystal layer in the SSFLC, and its sign is directly attracted to the tilt direction of the molecules. An applied voltage of the correct sign can reverse the direction of this dipole in tens of microseconds and hence reverse the tilt direction of the molecules. The respective change in optical properties can cause a change from light to dark if or when one or more polarizers are utilised.
SSFLC devices have been commercialized for big passive-matrix presentations, but their cost and detail has impeded them from having any remarkable progress on the market. Small transmissive and reflective active-matrix SSFLC displays, however, show some probability for use as elements in projection systems or as viewfinders in digital cameras. Their quick reacting allows them to be employed in time-sequential colour systems, in which highly expensive colour filters are emulated with a coloured backlight that flashes red, green, and blue in fast speed (approximately 100 cycles every second). For example, the liquid crystal might be switched to a transmissive state in the red and green periods then to a nontransmissive state during the blue period, with the end result that the eye sees an average of red and green light, or the colour yellow.
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