In an effort to provide safer and more reliable components for aircraft, researchers have invented an optical on-off switch that can replace electrical wiring on airplanes with fiber optics for controlling elevators, rudders, and other flight-critical elements.


Fiber-optics technology already has transformed life on the ground by replacing copper wire to transmit voice calls, Internet traffic, and other telecommunications. Now, engineers are preparing a new application for liftoff, with their prototype fiber-optics switch thats ready for testing on real-life aircraft.


The technology also has potential applications on the nations highways, as a weigh-in-motion sensor for measuring the weight of fast-moving commercial trucks without requiring them to stop on a scale. The research is described by Zhaoxia Xie and Henry F. Taylor of Texas A&M University in the latest issue of Optics Letters, a journal of the Optical Society of America.


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


The crucial component of the Texas A&M switch is called a fiber Fabry-Perot interferometer (FFPI). It 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 Texas A&M design, a small plank-like object, known as a cantilever, is bonded to the interferometer. The cantilever, in turn, is 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.


That provides a signal to indicate that the switch has been pressed. This information can be transmitted optically to the desired part of the airplane. A network of other interferometers and lasers filters out fluctuations in temperature and other disturbances so that only the pressing of the button registers as a valid signal.


Using fiber optics to transmit signals has specific advantages for aircraft, the researchers say. A fiber-optics system is lightweight and doesnt take up much room, and its immune from lightning and electromagnetic interference. It also has safety advantages for planes because it isnt susceptible to causing fires, the researchers say.


The fiber-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 already uses fiber optics, says lead author Xie. Therefore, integrating other aircraft instrumentation into a single optics package could save weight, space, fuel, and construction costs on future aircraft, she says.


Lockheed Martin has been among the supporters of this research. The next step is to test this system on a real airplane.


Of fiber optics other potential transportation uses, Xie says, Due to the sheer value of car and truck traffic on our highways, current weighing systems using slow and cumbersome static scales arent a viable option. Therefore, theres a strong demand for an economic, effective, and reliable weigh-in-motion system.