Carrying capacity

The mission says that the benefits of low volume and signal attenuation seem to be most important to Lockheed-Martin. For example, there are 40 radiofrequency cables, each the thickness of a ringer, running to radar antennae in the nose of the F 16 fighter. The number of these connections will increase as phased array radar becomes more common, so the small cross-section of optical fibres and their ability to carry large amounts of data by wave division multiplexing will become paramount.

The new F-22 fighter contains about 200 in of optical fibre with about half in the central fuselage, and the rest in the wings and forward fuselage. The aircraft will replace the F-15 and the first of 339 aircraft will be delivered to the US Air Force in 2001.

First-generation fibre-optic avinics are based on expensive speialized components, and there is ittle or no standardization between the systems that occur on different aircraft. These systems were designed and developed for reliability and to be compatible with conditions in an aircraft rather than to meet tight budgets.

The result is that these systems contain few commercial off-the shelf components and the results are often over-engineered. When the UK mission returned from the US, it reported that the lessons of the first generation systems are:

Design fibre-optic avionics for the whole Wits life cycle including manufacture, installation and' maintenance. Although there have been few problems with early systems, the fibre-optic cables are often buried deep in the fuselage and there will be a need to splice in replacement cables. e Installers and maintenance crews need to know that optical fibre and copper cables must be handled differently. Reports from Boeing and Lockheed-Martin say that optical systems are easier to work with than coaxial cable. e Common optical launch and test procedures must be used by suppliers, systems integrators and customers.

A single set of standards needs to be written and adopted for all platforms.

Customers remain to be convinced of the merits of fibre optics in avionics.

The large bandwidth, small volume and low weight of fibre optics have yet to be exploited fully.

Second-generation fibre-optic avionics should apply the lessons learned from the first systems. New systems should be based on standard components, topologies and protocols, but they will still represent optical implementations of electrical networks.

The mission says that the development of second generation physical layers will be driven by its ability to compete with copper on the cost per unit bandwidth. Here, component volume and dense parallel interconnects will help optics to compete.

Suppliers want standards

Commercial or modified off-the-shelf parts will have a significant role in second-generation systems. However, such parts will have to prove reliable as well as cost-effective through the whole life cycle of a system because the next fibre-optic avionics will be subject to life cycle cost-benefit analyses. First-generation systems have proved reliable so, if the next generation can be standardized, it is unlikely to need flight trials and more likely to go straight into service.


Suppliers say that two considerations dominate their view of the second generation of optical vehicle management systems: commercial off-the-shelf components to reduce costs and open architecture to allow systems to expand and be upgraded.


The suppliers see a number of problems. First, aircraft systems generally take much longer to develop than the commercial lifetime of many of the optical components needed for avionics.


Commercial off-the-shelf components may reduce the capital cost of the equipment, but they may not reduce running and maintenance costs over the 30 year life of a component.


Second, optics is new in avionics and it faces competition from established manufacturers of electronic components. They will want to improve their cornponents and bring down their costs.


Third, there is currently no standard optical vehicle management system that is capable of meeting the needs of different aircraft, thus delaying the development of hardware and open systems. In other words, if there are too many standard buses, then none of them will exploit the benefits of commercial off-the shelf components.,


Suppliers have suggested alternatives, such as modifying or screening off-the-shelf components. They have also proposed that the aerospace industry should adopt open architecture instead of bus specifications, or performance-based instead of hardware-based specifications.


There are also the problems of packaging and connections. Fibre-optic data systems in aircraft have very short runs between components, and that large numbers of components and connections compared with other multimode area networks. Packaging individual optoelec-tronic parts accounts for about 40 to 50% of the product's cost.


"The development of larger volume, lower-cost optoelectronic manufacturing technologies has to take place to accelerate their installation in lower-speed and shorter-distance networks, such as data communications for onboard defence and commercial platforms," stated the UK mission in its report.


"The problem is the need to align optical parts and optical fibre with submicron precision in typically less than 10 s, with the cost per aligned fibre being significantly less than that of the device to be pigtailed. Tows submicron or nanometre precision is even more critical for the more efficient lensed optical fibre."


Third-generation systems will be designed to exploit the innate benefits of fibre optics, such as wave division multiplexing, the ability to work with smart structures (OLE April 1999 p26) and passive sensors. The mission said: "The full scale and scope of generation three possibilities are not yet apparent."


The mission recommends that Europe co-operates with the US on solving common problems with second-generation systems to develop widely accepted global standards.

"European equipment and component suppliers would benefit especially from this relationship. Airframe manufacturers would also stand to gain from a wider supplier chain, and might also build on the confidence that the US airframes clearly have in this technology. The global standardization of the defence/aerospace photonics market (still relatively small) may also give us some leverage on future commercial developments."


Nigel Aldrige et al. 1999 Report on UK Mission to USA on Photonic Technology for Avionics The Society of British Aerospace Companies and Department of Trade and Industry.