Fiber Optic Technology Used in US Airforce

The optic fiber owed its origin to the development of optical voice transmission system known a photophone by Alexander Graham Bell during the year 1880. The photophone applying free space light could carry the human voice 200 meters. The fiber optical technology has a significant progress during the second half of the twentieth century. The initial success in this regard occurs during the 1950s with the development of fiberscope, an image transmitting device.
This used first practical all-glass fiber and concurrently devised by Brian O’ Brien at the American Optical Company and Narinder Kapany, who first devised the terminology ‘fiber optics’ in 1956 and colleagues at the Imperial College of Science and Technology in London. The fiberscope soon applied in the inspecting welds inside reactor vessels and combustion chambers of jet aircraft engines as well as in the medical field.
The Fiberscope technology has evolved over the period of time to facilitate laparoscopic surgery considered as one of the great medical advance of the twentieth century. The development of laser technology was considered as the next significant application of fiber optics. The laser diode — LD or the light-emitting diode — LED, had the prospective to evolve large amounts of light in a spot tiny enough to be applied for fiber optics. (A brief history of Fiber Optic Technology) Gordon Gould fostered the idea of applying lasers, describing it as an intense light source.

Soon after, Charles Townes and Arthus Schawlow at Bell Laboratories worked on use of the laser in scientific circles. The laser evolved through many generations in terms of ruby laser and the helium-neon laser in 1960 until the realization of semiconductor lasers in 1962. The higher modulation frequency capability of the lasers attracted the scientists to apply this in the filed of communication engineering. Light is realized to have an information carrying capacity of 10,000 times that of the highest radio frequencies being applied.
The US military responded rapidly to apply fiber optics for improved communications and tactical systems. The US navy in the early 1970s established a fiber optic telephone link aboard the USS Little Rock. The Air Force developed its Airborne Light Optical Fiber Technology — ALOFT program in the year 1976. Such initial successes encouraged military R & D funding for development of stronger fiber, tactical cables, ruggedized, high performance components and several demonstrations starting from aircraft to undersea applications.
After the installation of fiber optic telephone system in Chicago and Boston by both AT & T and GTE marked the beginning of commercial application of Fiber optics. (A brief history of Fiber Optic Technology) Presently, the application of fiber optic technology including wave division multiplexing fiber optics is increasingly prevalent in commercial aircraft and satellite systems with the growth of many commercial suppliers. Now the 10 gigabit fiber optic Ethernet in the sphere of many systems and also in aircraft avionic systems is more prevalent.
Moreover, the Fiber Channel and Firewire systems also widely applied in aircraft systems presently. However, such systems are not sufficiently strong and do not quickly respond to deterministic real time necessities like 1553B and ARINC 429 and do not deal with multiple level of security. To cater to such needs, system architectures particularly are a combination of copper and fiber with redundancies for robustness or replication for various security levels/enclaves. (Multi-Level Secure High-Speed Fiber-Optic Data Bus)
A single optical fiber spread through out an aircraft in terms of ring architecture topology is seen have the prospective of meeting all the present and future bandwidth requirements, entailing solutions to different security level requirements, decline redundancies; accommodate all essential legacy and future protocol and timing necessities; being capable of maintenance over the life of the host platform, and significantly decrease weight power, cooling, electromagnetic interference/electromagnetic compatibility shielding and other confinements of prevailing remedies.
This anticipates more efforts in applying the prevailing technology and constructing the integration elements for example, protocol adapters to generate a fiber-optic system backbone appropriate for present and future aircraft systems with low-cost, open and commercially available technology. (Multi-Level Secure High-Speed Fiber-Optic Data Bus)
The next generation digital flight data recording system created by Raytheon Company, the Distributed Flight Data Acquisition Unit — DFDAU system depends primarily on fiber optic technology and remote sensors to gather and record quite considerable amounts of critical flight data on passenger aircraft. The application of technology will permit airliners to cater to the new Federal Aviation Administration regulations that necessitate digital flight data recorders to gather substantially more information than was earlier necessitated.
The new regulations necessitate new aircrafts to have flight data recorders capable to monitoring up to 57 flight testing, Raytheon anticipates the system to be FAA certified and it will start installing the DFDAU in its Beech 1900D, 19 passenger regional airliner. (Fiber optic networks for flight data recorders) The DFDAU has been designed to entail detailed and accurate recording of pilot actions and aircraft responses during a flight by accumulation of information from multiple channel sensing and regulation modules that are integrated by optical fiber instead of traditional shielded, twisted pair wiring.
Since intelligence can be collected from multiple sources distributed across the aircraft and shared through a single fiber optic cable, application of the system minimizes the cumbersome wiring and provides improved signal fidelity that is immune to electromagnetic interferences and failures in transmission. Additionally, the system can more easily safeguard one flight data recorder without the process of redundant wiring. Such advantage will entail considerable savings for airlines when additional flight data recorders are mandated for other destinations on passenger aircraft.
The DFDAU system is expected to apply distributed processing to translate and route data received from over 160 sources and interfaces located across the aircraft. The system is devised to translate the data into an industry standard open protocol -SAE AS-5370- and then thereafter route the data to the 1900D’s digital flight data recorder by applying a fault tolerant fiber optic network. The DFDAU system involves seven identical DFDAUs linked by fiber on the 1900D.
Each DFDAU is able to capture physical parameters up to 32 sources like engine sensors, navigation, traffic collision avoidance system, gyros, position and force sensors along with the warning, deicing and other important systems, cockpit controls, autopilot, flight instruments, altitude and the Global positioning system, flight control surface position sensors. (Fiber optic networks for flight data recorders) Practically, the aerospace platforms universally have the capacity to take advantage of the distributed fiber optic sensors that could be applied in varied range of parameters.
The military and commercial aircrafts presents bewildering maintenance costs presently soaring to tens of billions dollars in annual terms. The diagnostic system necessitates the system that can make way for the performance and the maintenance to be performed when required. This would permit improved levels of safety by insuring that essential tasks are being performed while reducing the amount of costs by eliminating the expensive and unnecessary amounts of procedures.
Additional enhancement in safety and performance can be generated by integrating such systems into control systems to improve over that of flight control and assessment of in-flight damage. The applications of test beds to demonstrate the usage of distributed fiber sensor systems are seen in terms of reusable launch vehicle development programs which are advanced. (Fiber Optic Distributed Sensing Systems for Harsh Aerospace Environments) Delta Clipper is one such application that had a system of fiber gathering based strain sensors integrated into its hydrogen fuel tank.
This system at the beginning operated as backup to a set of electrical strain gages to represent new technology. Practically, some of the program managers were very doubtful regarding its usage. By the end of the program the intention had varied from the ‘why to apply optic grating based strain sensors while we are having electrical ones on board’ to the ‘lets scrap the electrical strain gages that perform poorly and only use the fiber optic grating strain gages’. (Fiber Optic Distributed Sensing Systems for Harsh Aerospace Environments)
The advantages of this is seen in the possibility that the Fiber optic grating strain sensors can conveniently be grouped directly into a composite hydrogen tank becoming an important aspect of the structure, they do not fall when vibration and shock attacks; the fiber optic grating strain gages do not perform as an electrical hazard, they are light weight, superior in terms of environmental aspects, easy to install and can be multiplied in numbers through a single fiber line.
Since fiber sensors persistently applied and proven in such advanced systems, the persistent decline in cost as a result of advances in the telecommunication and optoelectronic industries will continue to provide more cost effective types of applications for the purpose of military transports, military fighters, and commercial aviation. (Fiber Optic Distributed Sensing Systems for Harsh Aerospace Environments) The in-Flight Entertainment has attained a high level of sophistication with the inception of a high bandwidth system by Rockwell Collins, Cedar Rapids, IA known as Passport.
The system facilitates varied passenger amenities and also the Internet access. The system involves a fiber optic structure, associated with expanded-beam fiber-optic interconnects, an ATM switch and a downstream copper distribution system. The system servers originate optical digital signals and travel on the fiber structure. In its path downstream it converts to a Fire Wire distribution network that provides the signals to electronics boxes at individual passenger seats. The system incorporates the fiber-optic expanded beam interconnection technology from Tyco Electronics, Harrisburg, PA.
Such connectors provide high dependability in extreme circumstances entailing thermal, vibration and mechanical stability for reliable transition of the light beams from one fiber to another. Other developments over a copper based system incorporate freedom from electromagnetic interference and crosstalk. (Fiber Optics Lift Aircraft Video-on-Demand Systems) The fiber system also declines considerably the weight and provides non-sparking contacts. The expanded beam technology safeguards and seals each fiber faces and ferrule behind a spherical lens instead of butting two fiber ends together.
Such interconnection entails a precision coupling of fiber-optic signals without having physical contact at the fiber-to-fiber interfaces. The connectors modular format simplifies manufacturing, making it to be competitive in economic terms with traditional interconnect technologies. The blind-mating is facilitated by the precision alignment pins; those which are quite integral to the connector. The Passport has already functioned successfully without flaws for a year in commercial aircraft and the technology has surpassed to military aircraft for in-flight networks.
Tyco also works towards the expansion of beam fiber optic connector technology to discover its wide application in the rugged industrial usages. Such new fiber optic connectors also cater to the avionics standard ARINC 628 for IFE systems. (Fiber Optics Lift Aircraft Video-on-Demand Systems) The fiber optic technology being developed by NASA Dryden Flight Research Center — DFRC, Edwards, California appears to be an integral element of future aircraft system in the development programs for fighter aircraft, and new large transport aircraft, and have considered fiber optic technology as an important part of future aircraft systems.
The traditional fly-by-wire system configurations sometimes necessitate unique interfaces for each fight control surface actuator that results in a large amount of wiring. The Fiber optics has been regarded as aerospace vehicle application due to its high bandwidth capability, immunity to electromagnetic interference — EMI, and considerable weight savings. This technology has been applied in a new smart actuator as the primary communication interface. The application of fiber optics makes easier system integration and considerably decreased the wire count.
The flight test outcomes revealed that fiber optics could be conveniently being applied in aircraft systems and identified critical areas of development of fly-by-light technology. The smart actuator flight test program has demonstrated the possibility of fault monitoring, in-flight local control and redundancy management of surface actuator. (Zavala, Eddie. Fiber Optic Experience with the Smart Actuation System on the F-18 Systems Research Aircraft Eddie Zavala Dryden Flight Research Center Edwards, California)
As the flight test reveals the presentation of the smart actuator was exceptional and compared very well to that of the standard F-18 aileron actuator. Irrespective of the fact that the serial interface of the smart actuator could have been traditional forms of electrical interface, valuable fiber optic experience was being attained via the means of application of 1773 communication links. The system integration becomes more effective and simple in terms of bringing about a reduction of both installation time and cable harness weight considerably.
The fiber optic interface, however, complicated the system of integration tests. The smart actuator program brought out the significant areas of development for the general application of fiber optics in aerospace vehicle systems. Such critical areas apply to a broad range of fiber optic applications and will thereby influence the system of operation and reliability unless specific attention and considerable progress is being made. (Zavala, Eddie. Fiber Optic Experience with the Smart Actuation System on the F-18 Systems Research Aircraft Eddie Zavala Dryden Flight Research Center Edwards, California)

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