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Fibre laser points to woven 3D displays

12 March 2012

Most light emitters look the same from any angle. But in a paper published on the Nature Photonics website, Massachusetts Institute of Technology (MIT) researchers report the development of a new light source, a fibre only a little thicker than a human hair, whose brightness can be controllably varied for different viewers. This opens the possibility of 3D displays woven from flexible fibres that project different information to viewers’ left and right eyes say the researchers.

A new fibre developed by a MIT research team emits blue laser light only at a precisely controlled location
A new fibre developed by a MIT research team emits blue laser light only at a precisely controlled location

The fibre could enable medical devices that can be threaded into narrow openings to irradiate diseased tissue, selectively activating therapeutic compounds while leaving healthy tissue untouched.

The newly developed fibre has a hollow core; surrounding this core are alternating layers of materials with different optical properties, which together act as a mirror. In the core is a droplet of fluid that can be moved up and down the fiber. When the droplet receives energy, or is “pumped” — in experiments, the researchers used another laser to pump the droplet — it emits light. The light bounces back and forth between the mirrors, emerging from the core as a 360-degree laser beam.

Surrounding the core are four channels filled with liquid crystals, which vary the brightness of the emitted light; each liquid-crystal channel is controlled by two electrode channels running parallel to it. Yet despite the complexity of its structure, the fiber is only 400 micrometers across. (A human hair is usually somewhere around 100 micrometers in diameter).

In experiments, the researchers simultaneously activated liquid crystals on opposite sides of the fiber to investigate a hypothetical application in which a transparent, woven display would present the same image to viewers on both sides — not mirror images, as a display that emitted light uniformly would. The researchers believe that, in principle, there is no reason a fibre couldn’t have many liquid-crystal channels that vary the light intensity in several different directions. As many of these liquid-crystal channels can be built as required around the laser, making the process very scalable.

As a display technology, the fibres have the obvious drawback that each of them provides only one image pixel. To make the fibres more useful, the researchers are investigating the possibility that the single pixel — the droplet of water — could oscillate back and forth fast enough to fool the viewer into perceiving a line rather than a coloured point.

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