Optical result for laser technology

Materials World magazine
3 Apr 2011

An optical fibre composed of a zinc selenide core could facilitate more dynamic laser technology.

A research group, led by Professor John Badding at Penn State University, USA, has found that the light-yellow compound enables more effective and liberal light manipulation in a manner that silica glass cannot.

The fibre is composed of a silica glass capillary left hollow for depositing the zinc selenide, a semiconductor. Badding elucidates that previous optical fibre technology has been limited by the use of a glass core that has a ‘haphazard arrangement’ of atoms. ‘In contrast, a crystalline substance like zinc selenide is highly ordered. That order allows light to be transported over longer wavelengths, specifically those in the mid-infrared.’

He says, ‘Exploiting these wavelengths is exciting because it represents a step toward making fibres that can serve as infrared lasers. For example, the military currently uses laser-radar technology that can handle the near-infrared, or 2-2.5 micron range.

A device capable of handling the mid-infrared, or up to five micron range, would be more useful. The fibres we have created can transmit wavelengths of up to 15 micron.’

According to Badding, the long, thin fibres, which are three times as thick as a human hair, can transmit more than a terabyte – the equivalent of 250 DVDs – of information per second.

Essential to the formation was the high-pressure chemical deposition of zinc selenide to ‘paint’ the inside of the capillaries. This is conducted layer-by-layer until the hole is completely filled. Using this technique the team has achieved zinc selenide waveguiding cores for long, thin and smoother fibres in a confined space.

Dr Periklis Petropoulos at the Optoelectronics Research Centre at Southampton University, UK, whose colleagues also contributed to the work, explains, ‘This [class of] fibre benefits from a combination of the optical properties of semiconductor materials and the relatively long lengths facilitated by their incorporation in a fibre geometry’.

On observation, the team discovered that the fibres are also more efficient at converting light from one colour to another.

Badding continues, ‘When traditional optical fibres are used for signs, displays, and art, it is not always possible to get the colours you want. Zinc selenide, using a process called non-linear frequency conversion, is more capable of changing colours’.

The detection of pollutants and environmental toxins could be yet another application for improved laser-radar technology.

‘Different molecules absorb light of different wavelengths – for example, water absorbs, or stops, light at the wavelengths of 2.9 micron. But the molecules of certain pollutants or other toxic substances may absorb light at much longer wavelengths. If we can transport light over longer wavelengths through the atmosphere, we can see what substances are out there much more clearly,’ explains Badding.

The team hopes this work may instigate the development of improved surgical and medical lasers, such as corrective eye surgery.