A Southampton University researcher has succeeded in building electronic devices inside an optical fibre, opening up the possibility of integrating optoelectronic components in the transport medium.

Dr Pier Sazio developed a high pressure version of the chemical vapour deposition (CVD) process commonly used to deposit layers of semiconductors on planar substrates.

Applying CVD in very restricted geometries - such as microstructured optical fibre – is difficult because any deviation from perfect filling leads to a blocking of the pore at the centre of the fibre, which ends deposition.

By cranking up the system pressure to 10-100MPa, Sazio managed to deposit polycrystalline and single crystal layers of silicon and germanium inside fibres with pores as small as 10nm in diameter. Sequential deposition yielded a silicon germanium heterojunction, and a Fet with complete pinch-off at 100V.

“The reason we actually built the Fet inside the fibre was that doing electrical characterisation measurements is a very, very sensitive way of understanding the material properties of a semiconductor,” said Sazio.

“An electro-optic function is something you could immediately think of if you wanted to make a real device.”

An example of a real device that could be moved into the fibre is the 980nm pump laser needed for the erbium-doped fibre amplifiers (EDFAs) used in long-haul networks, which at the moment is pigtailed onto the fibre.

There is also significant potential in exploiting optical non-linearities to perform useful functions.

“If you were trying to exploit a non-linearity in a semiconductor, for example on a chip, you’ve got a very small length in which to do that,” exaplined Sazio.

“Here we have an opportunity to have the semiconductor interacting with the light over enormous electromagnetic interaction lengths. You really can exploit non-linearities that wouldn’t be evident in a normal device geometry.”

With the CVD process demonstrated, Sazio and his colleague John Badding at Penn State University in the US will develop techniques to enable the creation of functional structures such as p-n junctions inside the fibre.

www.soton.ac.uk