Imaging inside the human body

An Australian world-first in optical fibre technology has opened the way for a major advance in medical imaging inside the human body, as well as personal computers that run on light.

The development of hollow optic fibres made from perspex - only a few times thicker than a human hair - has been achieved by a team from the Australian Photonics CRC and University of Sydney's Optical Fibre Technology Centre.

The fibre promises a new era in medical imaging. Being only a tenth the thickness of a normal endoscope it can penetrate tiny blood vessels and other awkward corners of the body with greater ease, safety and less inconvenience to the patient.

In their first potential medical application they will be used in conjunction with an established Australian medical procedure to cure deafness.

For computers, the fibre promises potentially massive increases in speed and capacity currently unattainable with copper connections, moving the PC closer to becoming a machine that runs on light.

APCRC team leader Dr Martijn van Eijkelenborg says the new fibre was produced by precision-drilling 100 or more holes in an 8 cm thick rod of special perspex, then heating and stretching it until it was up to 400 metres long, and a fraction of a millimetre thick. "This creates a plastic fibre with an array of scores of tiny air channels all along its length. You can send a light signal down each of these channels, or through the perspex islands in between them, which greatly increases the capacity of the fibre - like a coaxial cable with the wires made from air."

In this way, he explains, a fibre with 112 holes drilled in it can create an image with 224 pixels in an area of less than a quarter of a square millimetre. The team has created fibres with up to 300 channels and consider they have not yet reached the limits of the new technology.

The fibres are suitable for coupling with the latest optical-laser micro-arrays and, using these, could become the cables for the future computer.

"As computer speeds build up to around 10 Gigahertz, you start to lose the signal in the copper track which connects the chips. Basically, the faster the computer, the more trouble the chips have communicating with one another. So we thought: why not try an optical solution - use photons (the particles of light) in a plastic cable instead of electrons in a copper wire."

Apart from opening up the scope for ultra-high-speed computing, the plastic cable could improve the interface between computers and video, enhancing both the speed and quality of images.

Dr van Eijkelenborg says that the channels in the fibre can be filled with air, liquid or gas to alter their transmission properties for different applications, and the team is also developing ways of creating 'inverted' structures with the holes filled with a solid, making the fibre completely solid, more rigid and easier to handle.

"Big, thick optic fibres, which are easy to handle, have a lot of dispersion - which causes a smearing out of the optical signals. By having a whole array of channels we can dramatically reduce this effect, which means we can transmit a very high bandwidth - approaching, in fact, that of a singlemode fibre, but far cheaper and easier to handle."

"Polymer materials are suitable for these fibres. They are thicker than glass fibres but more flexible, and the fabrication methods that we use to prepare them allow full control over the positioning and sizing of the cores, he says.

"Any pixel arrangement is possible, both in terms of symmetry (hexagonal, rectangular, etc) and in terms of core dimensions. We have even demonstrated multiple core sizes in one fibre. This makes it straightforward to tailor the fibre to match an array of light emitters with the particular symmetry and dimensions required for a specific application, such as chip-to-chip connectors."

The CEO of the Australian Photonics CRC, Professor Mark Sceats, says, "The mini-endoscope is a great example that neatly illustrates how skills and technologies developed for telecommunications are now finding applications in industries like medicine. "Photonics is becoming a pervasive technology, like electronics 40 years ago. Australia largely lost the plot in developing its microelectronics industry, and our CRC is working hard to ensure that the same fate doesn't befall our fledgling photonics industry."