Twisting the light fantastic

US researchers develop new, low-cost optical fibres.

It is often the simple things that do the trick and manipulating light is no exception. By twisting optical fibres US researchers have come up with a way to filter light for both wavelength and polarity. Fibre optics revolutionised the communication industry and further advances could be boosted considerably by such low-cost ’in-fibre’ technology.

For information to be moved out of fibres, wavelength selectivity is crucial. A common way to achieve this is to change periodically the refractive index along a fibre by exposing photosensitive areas to ultraviolet light. A research team from the City University of New York, and a US company called Chiral Photonics took a different approach and twisted rectangular-core glass fibre to create a structure with double helix symmetry. The resulting chiral fibre gratings (CFGs) had either right or left-handed symmetry depending on the twist direction and only allowed circularly polarised light of the opposite handedness to the fibre to pass through.

The researchers tested a series of fibres with different amounts of twist. CFGs with a relatively loose twist scattered circularly polarised light with the same handedness out of the core and into the fibre cladding and Chiral Photonics envisages that such structures could be used in temperature and pressure sensors. A tighter twist caused the light to scatter at a wider angle and escape the fibre and the company has already developed such CFGs as broadband, in-fibre polarisers. A still tighter twist created one-dimensional photonic band gap structures which, if doped, could act as lasers.

Daniel Neugroschl from Chiral Photonics believes that ’the whole suite of gratings offer compelling products’. The company’s first standard product is the in-fibre polariser. Neugroschl told Chemistry World that Chiral Photonics is also ’discussing commercialisation of the sensor technology with potential collaborators’ and is developing a chiral fibre laser. This will be pumped by multimode laser diodes to provide a more efficient and higher power laser output than semiconductor lasers, at ’a fraction of the cost’, he said.

Emma Davies