The Development of Data Projectors
The LCDs put for projection systems are most often small reflective or transmissive panels set off by a forceful arc lamp source. A number of lenses magnifies the reflected or transmitted image then sends it onto a screen. In front-projection systems the LCD is situated on the side of the screen as the viewer, but in rear-projection systems the screen is set off from behind. Projectors of higher expense and performance may use three discrete LCD panels, casting separate red, green, and blue images that combine to form a coloured picture on the screen.
The increasing requirement for film displays has put a growth in emphasis on the switching speed of liquid crystals. This has demanded the creation of devices employing smectic liquid crystals, particular types of which give a faster electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is at this point the most sophisticated smectic device. Inside it the liquid crystal molecules are managed in layers that are perpendicular to the substrate planes, which are differentiated by one or two micrometres, and throughout the layers the molecules are tilted, as shown in the figure. The host liquid crystal holds optically active molecules, and a slight outcome of the optical activity and the tilt of the molecules is the presence of a permanent charge separation, or ferroelectric dipole, analogous 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. So, there exists a permanent charge separation over the liquid crystal layer in the SSFLC, and its sign is directly coupled to the tilt direction of the molecules. An applied voltage of the corresponding sign can reverse the direction of this dipole in tens of microseconds and hence reverse the tilt direction of the molecules. The corresponding change in optical properties can make a change from light to dark if or when one or more polarizers are employed.
SSFLC devices have been commercialized for big passive-matrix presentations, but their expensiveness and complexity has hindered them from enjoying any great progress on the market. Small transmissive and reflective active-matrix SSFLC displays, however, show some possibility for use as parts in projection systems or as viewfinders in digital cameras. Their immediate response allows them to be employed in time-sequential colour systems, in which dear colour filters are replaced by a coloured backlight that flashes red, green, and blue in rapid speed (approx 100 cycles per second). For example, the liquid crystal may be switched to a transmissive state between the red and green periods but to a nontransmissive state in the blue period, displaying the outcome that the eye sees an average of red and green light, or the colour yellow.
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