Innovation

Data Projector Evolution

Posted on 01 July 2010

The LCDs put for projection systems are typically small reflective or transmissive panels set off by a strong arc lamp source. A number of lenses magnifies the reflected or transmitted image and then casts it onto a screen.

With front-projection systems the LCD is set on the same side of the screen as the viewer, while in rear-projection systems the screen is set off from behind. Projectors of higher expense and capacity can have three distinct LCD panels, creating separate red, green, and blue images that mesh to reflect a coloured image on the screen.

The increase in requirement for visual displays has granted a special emphasis on the switching speed of liquid crystals. This has demanded the invention of items utilizing smectic liquid crystals, some kinds of which have a quicker electro-optical response than nematic liquid crystals.

The surface-stabilized ferroelectric liquid crystal (SSFLC) display is currently the most complex smectic device. With it the liquid crystal molecules are set out in layers that are perpendicular to the substrate planes, which are separated by one or two micrometres, and inside the layers the molecules are slanted, as displayed in the figure.

The host liquid crystal contains optically active molecules, and a subtle result of the optical activity and the slant of the molecules is the presence of a permanent charge separation, or ferroelectric dipole, comparable to the ferromagnetic dipole of a magnet. The direction of this dipole is perpendicular to the tilt direction of the molecules and throughout the plane of the layers. Thus, there exists a permanent charge separation across 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 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 make a change from light to dark when one or more polarizers are used.

SSFLC devices have been produced for big passive-matrix displays, but their expensiveness and intricacy has prevented them from creating any particular effect on the market. Small transmissive and reflective active-matrix SSFLC displays, however, display some possibility for use as aspects in projection systems or as viewfinders in digital cameras. Their fast reacting allows them to be made use of in time-sequential colour systems, in which dear colour filters are replaced with a coloured backlight that flashes red, green, and blue in rapid speed (around 100 cycles in a second). For example, the liquid crystal might be switched to a transmissive state during the red and green periods then to a nontransmissive state during the blue period, displaying the result that the eye sees an average of red and green light, or the colour yellow.

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