Fibre optics poised to reach new heights

In an effort to provide safer and more reliable components for aircraft, researchers have invented a fibre-optic on/off switch that can replace electrical wiring for controlling elevators, rudders and other flight systems on aircraft.

Fibre optics have already transformed life on the ground by replacing copper wire to transmit voice calls, internet traffic and other telecommunications. Now, engineers are preparing a fibre-optic switch for practical testing.

The research is described by Zhaoxia Xie and Henry F Taylor of Texas A&M University in the current issue of Optics Letters, a journal of the Optical Society of America.

Xie and Taylor's device senses the press of a button from a pilot. Such switches are usually electrically based and require electrical wiring which could get complex and bulky with the many buttons in cockpits and throughout an aircraft. But a system based on a single optical fibre could potentially sense presses from hundreds of buttons simultaneously by detecting light signals coming from different buttons.

The crucial component of the switch is called a fibre Fabry-Perot interferometer (FFPI) that consists of two parallel mirrors. When white light passes through the mirrors, some of it bounces between the mirrors and some passes through. These light waves combine or "interfere' to produce a pattern. The interference pattern changes if the distance between the mirrors changes.

In the design, a small plank-like object, known as a cantilever, is bonded to the interferometer and attached to a switch. Pressing the switch creates a force on the cantilever, which causes it to bend, changing the spacing between the mirrors and altering the interference pattern.

The pattern provides a signal to indicate that the switch has been pressed. This information can then be transmitted to the flight system. A network of other interferometers and lasers filters out fluctuations in temperature and other disturbances.

Using fibre optics to transmit signals has specific advantages for aircraft. It is light and compact and immune from lightning and electromagnetic interference. It also is a safer alternative for planes as it is fireproof. At least 26 accidents or serious incidents in aircraft since 1983 were caused by fires or other failures related to electrical wiring systems, according to the Federal Aviation Administration.

The fibre-optic approach is intended for both military and commercial aircraft. It could either be incorporated into new designs or retrofitted into existing aircraft. Voice communications equipment in newer aircraft is already fibre-based, according to Xie.

03/10/2006