Changes possible for F-35's communication network.

• Author: Jean, Grace V.
• Position: INSIDESCIENCE+TECHNOLOGY

* When the F-35 Joint Strike Fighter becomes operational, it will be the world's most advanced military aircraft with an extensive suite of avionics and weaponry. But the supersonic "network in the sky" does have an Achilles' heel.

Beneath its stealthy skin, the fifth-generation fighter is dependent upon miles of copper wires that snake their way from the electronics bay in the fuselage into compartments found in the wings, nose and tail. Like veins, they connect subsystem components to computer processors to form an intricate communication network.

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The problem is that the copper wires are heavy and susceptible to the extreme environmental conditions of flight operations. Moreover, they do not carry electrical signals efficiently and cannot readily accommodate the introduction of new equipment because of bandwidth limitations.

For those reasons, the Defense Department is slowly making the switch to fiber optics. In fiber, photons, or light energy, transmit the signals.

F-35 program managers at prime contractor Lockheed Martin Corp. are eyeing an emerging technology that would enable them to make the full transition from copper wires to fiber-optic cables.

Some subsystems aboard F-35 communicate via fiber optics already, but the fibers each carry only one digital signal. It would be far more efficient for the fibers to transmit multiple signals.

The Defense Advanced Research Projects Agency and Naval Air Systems Command are jointly funding a program to develop a network of fiber optics that can carry multiple digital and analog signals simultaneously. The development of transmitters and receivers capable of operating in that analog-digital fiber network is key to the effort, which is targeting the multi-billion dollar F-35 and other aircraft programs.

A single fiber can transmit multiple signals via a process called wavelength division multiplexing. By using different wavelengths, or colors, of a laser, any number of signals can travel inside one fiber, said Raj Dutt, chairman and chief executive officer of Culver City, Calif.-based Apic Corp., which is executing the program.

The firm has developed a computer chip that can transmit 32 digital signals simultaneously on a single fiber.

"The chip is what makes it viable for military aircraft," said Dutt.

At Apic's clean-room facility in Honolulu, Hawaii, scientists are fabricating silicon photonic components that integrate electronics on the same computer chip. In order...