See the Light
Keep your eyes on fiber optics
By Fred Workley
The fiber optics industry has developed rapidly with many new innovations. Those of us that are involved in aircraft maintenance now have to add knowledge of basic photonics to our list of skills. We are aware of fly-by-wire and now we are finding more and more applications of fly-by-light.
Optical fibers are a key component in photonics. They are long, thin strands of treated glass — about the diameter of a human hair and are arranged in bundles that form cables. The light bounces off the cladded surface of the cable similar to that of a flashlight on multiple mirrors.
When we transmit signals over a wire using electricity, electrons move over the wire. Photonics sends light through glass and is cheaper and faster than wire. Optical cable costs far less than copper wire. Furthermore, optical fibers are thinner and more flexible than copper. This permits more lines or channels in a smaller space thus weighing far less than copper. Photonics use less energy while carrying a higher volume of information over a longer distance without any loss. Also, unlike electricity in copper wires, light signals do not generate heat or cause a fire hazard. There is no interference with other wires, which eliminates shielding costs and improves quality of signals. Light signals do not degrade as much as electrical signals and thus require less power to be added to maintain the original signal strength.
The more bandwidth, the more capacity is available to pass higher volumes of data, audio and video. Recent innovations are primarily directed to increasing bandwidth. The new ways to increase volume and speed thus reduce costs are the so-called "next generation" of equipment for fiber optics.
Two approaches: WDM and DWDM
With Wave Division Multiplexing (WDM), multiple wavelengths can be sent down a single fiber at the same time, multiplying the amount of data that can be sent by using different wavelengths of light. Dense Wavelength Division Multiplexing (DWDM) refers to spacing between the various wavelengths. The most advanced systems can stream up to 160 waves of light down a single fiber.
Replacement of every electronic function in data collection systems can be done with all-optical networks. The latest technology creates optical switches and systems that keep the signals traveling as photons at every part of the system rather than ever converting them back to electrons passed around wires. The industry offers an extensive line of optical fibers and accessories, including patch cords, bifurcated assemblies and splitters, for a variety of UV-VIS and VIS-NIR applications. All optical fibers couple easily via SMA terminations.
A fly-by-light aircraft system is a closed–loop system. It can reduce take-off weight by eliminating pneumatic, hydraulic, and mechanical systems. Ground equipment is also reduced. Along with weight savings is EMI (Electro Magnetic Field) immunity. Some of the challenges that have already been met are fiber optic position sensor development, decoding of electronics into optics, optical power management, and cable design and manufacturing for aircraft applications meeting vibration standards.
The wireless flight control system (WFCS) is a reality using a Jam Resistant Composite Actuator (JRCA). This is done through Feed Forward Remote Units with an Interface Converter through Dual Redundant Actuators. The major components are the Flight Control Computer, an interface box, aircraft 400Hz power source, Power Control Monitor Electronics and an actuator. There are essentially three types of actuators: EHA (Electro-Hydraulic Actuator), EPAD (Electrically Powered Actuator) and EMA (Electro-Mechanical Actuator).
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