Fiber Optics and Testing in Aerospace
As aerospace engineers look for innovative solutions to reduce component weight while advancing technology, the use of fiber optic systems has recently gained traction. While the lightweight, high bandwidth cable system has been used on various military aircraft since the 1980s, only recently has fiber optic cabling replaced copper wires in domains such as avionics and in-flight entertainment systems. In this blog, we will discuss the history and current usage of fiber optics in aviation and diagnostic testing techniques for such systems.
In fiber optics applications, very thin glass or plastic tubes are bundled together and used to transmit data in the form of light. The technology has long been used in telecommunication and computer networking because of its flexibility, resistance to data loss over long distances, and immunity to electromagnetic interference (EMI). The first use of fiber optics in aviation was in 1981 when the USAF installed a 43ft cable in an aircraft to serve as the primary transmission cable for Communication, Navigation, and Identification (CNI) data. They had originally installed the system with the presumption that it would not survive long and would need a quick replacement, but instead, the opposite was true. The cable worked without failure for over 45,000 hours of flight over five years of service. This demonstration proved that fiber optic cabling was a viable option that could potentially replace traditional metal wiring.
For years after the original experiment, fiber optic technology only found use in high-performance military aircraft, whereas most commercial jets still relied upon copper as the primary medium. Then, in 1995, Boeing introduced an extensive fiber-optic system on their 777 aircraft to wire their avionic and in-flight entertainment systems. Again, the optical system had tremendous success and further served as evidence that such a configuration was equal, if not more optimal, to traditional cable systems.
The current interest in optical aviation technology revolves around three separate domains: eVTOL, glass-cockpit digitization, and communication systems. Advanced eVTOL aircraft use electric propulsion to vertically take off, land, and hover. Currently, several prominent manufacturers, including Boeing, Honda, and Airbus, are working to create eVTOL aircraft which will be used to support air taxi, military, and medical applications. Although the final results are likely to vary, most manufacturers are looking to use fiber optic cable assemblies instead of standard Ethernet cables to save on space and weight. Optical cables are also being implemented to reduce communication latency and EMI between various aircraft systems and the novel glass cockpit architecture, allowing pilots to see a heads-up display (HUD) of pertinent data. Finally, many military communication systems that require operational security are moving wholly to fiber optic cabling, thanks to their high-speed data transfer, network security, and rapid feedback times.
As an ever-growing number of high-performance aircraft move towards implementing fiber optic technology, the demand for an accurate diagnostic system has increased. The most popular class of testing equipment is the optical time-domain reflector (OTDR), which is an instrument that tests the cable's integrity by pulsing light into the system and measuring the reflected signal that returns. More advanced diagnostic systems, such as the optical backscatter reflectometer (OBR), promise higher precision and the ability to identify the locations where a fault may be present.
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