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A Team from MIT Creates Optical Fibre From Low Cost Materials

The discovery opens up the possibility of integrating electronic devices (semiconductors) directly inside the fibre.
  • The discovery opens up the possibility of integrating electronic devices (semiconductors) directly inside the fibre.
Chong Hou holds a bag containing fibres
Graduate student and member of the research team Chong Hou holds a bag containing fibres with a diameter of 100 microns and a coating which further improves their resistance. Image author: Jose Luis Olivares/MIT.

Optical fibres are optical conductors with a capacity to transmit large amounts of data over long distances. To put it another way, they are long glass filaments with a diameter of just 125 microns (twice the breadth of a human hair), through which data is transmitted via pulses of light. The core is very pure, 8-micron silica. Explained crudely, the fibres are made using large glass tubes which create the fibre structure at a macroscopic scale. The tubes, known as preforms, are heated and stretched to obtain filaments that are subsequently coated in plastic to protect them.

Various types of low-cost silicon dioxide tubes
Various types of low-cost silicon dioxide tubes and rods in the MIT laboratory. When filling these tubes with different kinds of metals to create a preform, the researchers noted unexpected results in their experiments with aluminium. Image author: Jose Luis Olivares/MIT.

For decades, and to date, the fibre materials and geometry have been identical to those in the preform, but with a much smaller diameter. However, a group of researchers at MIT has discovered a surprising method for making fibres with a different composition from the original materials. While experimenting with how to incorporate metal threads inside the fibres, they noticed that when they tested with aluminium, the core of the fibre had transformed into very pure crystalline silicon, a substance which had not been in the preform.

The equipment used to draw the fibre.
The equipment used to draw the fibre. The furnace heats the tubes to around 2,200 degrees Celsius. Image author: Jose Luis Olivares/MIT.

The team, whose lead researcher is Yoel Fink, has referred to the process as a type of “alchemy”. Using a preform which contains base materials of aluminium and silica glass, they have produced a fibre with an extremely pure crystalline silicon core. One of the advantages of this discovery is that both aluminium and silica glass are abundant, low-cost materials, which are frequently used in the fabrication of windows and window frames, for instance. But the implications go much further: with this technique of transforming aluminium into crystalline silicon cores, which are used to make solar cells and microchips, it may be possible to integrate electronic devices (semiconductors) directly inside the fibre, which opens up a range of applications, such as smart clothing or devices with even greater integration than existing ones. The results of the project have already been published in Nature Communications.

Sources:

MIT, Massachusetts Institute of Technology

Nature Communications

http://www.madehow.com/Volume-1/Optical-Fiber.html

http://nemesis.tel.uva.es/images/tCO/contenidos/tema2/tema2_1_1.htm