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Better Switches for Planes

Photonics Spectra
Nov 2006
Fiber-based interferometry may help replace electrical switches in aircraft.

Hank Hogan

Standard electrical wiring in aircraft is bulky, is heavy and can lead to fires. But now, researchers at Texas A&M University in College Station say that switches that once operated electrically may be replaced with those that work optically.

Zhaoxia Xie and the late Henry F. Taylor devised an on/off switch based on a fiber Fabry-Perot interferometer. The interferometer, composed of two internal mirrors that form a Fabry-Perot cavity within the fiber, monitors the intensity of the reflected optical signal, which is determined by the light interference generated between the mirrors. The scientists attached one mirror to a cantilever and, when the lever moved as a result of an applied force — simulating a finger pressing a button — the mirror moved, changing the optical path length between the mirrors and, therefore, the interference pattern.

To measure the absolute optical path difference — necessary to determine the initial state of the switch — they used a superluminescent diode at 1325 nm for a broadband white-light source and a second interferometer, based on a 1540-nm laser, gaining a precision of 0.01 nm.

Tests of the setup indicated that the measured displacement was related linearly with force and so could be used as a switch once the threshold between “on” and “off” was established. Xie noted that the same setup also could function as a multilevel control switch, enabling a single fiber to service hundreds of witches.

The sensor actually responds to any physical change, such as pressure or vibration. According to Xie, pressure changes are not an issue because one can use a reference sensor — one not attached to a switch, but that experiences the same pressure changes as the attached sensor — to compensate. However, the reference sensor technique will not necessarily work for vibration, which is a subject for future research. “The whole system needs to be tested in an airplane for other extreme environmental changes, such as vibration,” she said. 

Optics Letters, Sept. 15, 2006, pp. 2695-2697.


GLOSSARY
fabry-perot interferometer
A multiple-beam interferometer, usually consisting of two flat plates, with high reflective ability. The plates are set parallel to one another by spacers so that lightwaves may bounce back and forth between them several times. The requirements for constructive interference of reflected lightwaves of a given wavelength can be fulfilled only at particular angles, relative to the normal to the plates. Therefore, Fabry-Perot interferometers can be used as spectrometers with high resolution. Used...
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