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 line of lenses expands the reflected or transmitted image and sends it on 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 lit from behind. Projectors of greater cost and performance may be found with three separate LCD panels, forming separate red, green, and blue images that blend to reflect a coloured display on the screen.

The increase in desire for film presentations has put a growth in emphasis on the switching speed of liquid crystals. This has necessitated the manufacture of devices employing smectic liquid crystals, certain types of which have a quicker electro-optical response than nematic liquid crystals. The surface-stabilized ferroelectric liquid crystal (SSFLC) display is at this point the most developed smectic device. With it the liquid crystal molecules are cast in perpendicular layers to the substrate planes, which are differentiated by one or two micrometres, and within the layers the molecules are tilted, as demonstrated in the figure. The host liquid crystal holds optically active molecules, and a subtle result of the optical activity and the tilt of the molecules is the appearance of a permanent charge separation, or ferroelectric dipole, likeable 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. So, there is a permanent charge separation across 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 by doing so reverse the tilt direction of the molecules. The consequential change in optical properties can effect a change from light to dark if one or more polarizers are used.

SSFLC devices have been produced for larger passive-matrix displays, but their expensiveness and detail has stopped them from creating any remarkable movement on the market. Small transmissive and reflective active-matrix SSFLC displays, however, have shown some possibility for use as elements in projection systems or as viewfinders in digital cameras. Their quick response allows them to be used in time-sequential colour systems, in which highly expensive colour filters are removed for a coloured backlight that flashes red, green, and blue in quick pulsing (approx 100 cycles a 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, having the result that the eye sees an average of red and green light, or the colour yellow.

For help with choosing and purchasing your data projector, contact projectors brisbane and projectors gold coast.