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28 Sep 2006
Researchers in Germany have developed a "sugar cube sized" projector, based on a single 2D mirror.
Just a few cubic centimetres in size, such a projector is expected to find numerous applications in displays but also in vehicle proximity monitoring and other specialized systems.
The development team, from the Fraunhofer Institute for Photonic Microsystems IPMS, Dresden, and the Fraunhofer Institute for Applied Optics and Precision Engineering (IOF), Jena, have demonstrated a miniature red-only projector and a slightly larger full-color prototype. The full-color version will be miniaturized when a suitable green source is developed.
The Fraunhofer IOF came up with the design based on the 2D mirror, while the electronic control was developed at the Fraunhofer IPMS.
The partners decided to develop what they call the scanning laser projector (SLP) because they were confident it would generate substantial interest in the market. "The overwhelmingly positive response to our initial publicity confirmed that," said developer Andreas Bräuer of the Fraunhofer IOF. "We are now looking for partners to develop a commercial product."
"What we have so far is the proof-of-principle and some prototypes. There is a version for red light, in which the laser, scanning mirror and micro-optical elements are housed in a box of less than 2 cm³ with the driving electronics in another. The second version is for RGB where the light sources, micro-optics and scanner together measure 7x10x3.5 cm."
The SLP's power consumption is less than 200 mW for the red version. Optical output power is about 100 mW for the red source and several tenths of a milliwatt for the combined RGB source.
The main differences between the SLP and a conventional projector and is that the new type employs laser diodes instead of high pressure lamps and the single 2D mirror instead of a mirror array or liquid crystal display, which allows the size reduction. Also, the new design does not require a front imaging lens and will project sharp images even on to curved surfaces.
Why small projectors?
Cameras, MP3 players and memory chips are growing smaller almost by the day. The next challenge, say the partners, has been to shrink the projector, a device used widely from lecture halls to smaller scale video presentations. Previous attempts at miniaturization have hit certain physical boundaries: the core piece of the classic projector being a micro-mirror array comprising a million mirrors.
These mirrors can be tilted in one plane and are evenly illuminated. By turning towards or away from the light source, they produce light or dark pixels that together form the projected image.
But not only do such arrays preclude miniaturization, their relatively high cost have made it difficult for projectors to join the wider consumer goods market.
The SLP's single mirror, which can be rotated around two axes, makes it significantly smaller, lighter and easier to manipulate than conventional projectors.
The limiting factor on miniaturizing a full color projector is the so far undeveloped "mini" green emitting laser diode; frequency doubling is still necessary.
"Today's technology allows RGB projectors of about 210 cm3," adds Bräuer. "Although this is somewhat larger than a sugar cube, it is just one quarter of the size of a standard projector.
"Researchers worldwide are attempting to scale down the green light source. Such a green laser would permit the full spectrum source. As they evolve, SLPs are expected to be integrated into commonplace mobile devices such as laptops, PDAs and cell phones."
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