A highly efficient method for using lasers to transport particles along hollow optical fibres has been developed in the UK. The technique could eventually lead to minute biomedical devices that could diagnose disease and engineer individual cells.
A team at Bath University used a laser to transport five micrometre polystyrene beads along a type of optical fibre called a photonic crystal fibre (PCF). Lasers have already been used to transport particles along ordinary glass capillary tubes but this process is hampered by light leakage.
“People have guided particles in narrow bore capillary tubes,” says Bath researcher Philip Russell. “The trouble is it doesn’t work well at all.”
However, PCFs are more efficient than conventional optical fibres at carrying light. Light travels through a central hole and smaller surrounding holes generate a “photonic band gap” effect that maintains much more light energy travelling through the core.
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The researchers say this enabled them to push the particles much more efficiently. Russell says: “You can maintain a high intensity over a long distance in a tube because it doesn’t leak out. So the diametric forces you can achieve on particles are maintained.”
Long range
Particles can only be moved a few millimetres through capillary tubes. The new technique makes it possible to transport particles 15 centimetres. Russell believes better fabrication techniques will improve this performance even further.
PCFs are constructed from many thin glass tubes. These are bound together around a hollow core. In this case the overall PCF diameter measured 125 microns and the core 20 microns across.
Kirhan Dholakia, at St Andrews University in Scotland, says advances in this field could eventually result in a range of new biomechanical technologies. He told New Scientist: “Certainly optical guiding is very interesting for things like cell sorting and bioengineering, basically manipulating biological matter in a controlled way.”
But Russell concedes that the research is at a very early stage. “It’s the very first results of what could be very large project. At the moment it’s very much driven by scientific curiosity.”
Russell and colleagues Fetah Benabid and Jonathan Knight presented the research at the Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference 2002, held in California between 21 and 23 May.
