Fiber optic avionics connectors have performance advantages for avionics systems

By John McHale

A steady aerospace and defense market combined with the performance advantages of fiber over copper has designers of optical avionics connectors confident in the short and long-term future.

"Recent economic conditions have affected all industries to varying degrees," says Greg Powers, market development manager for global aerospace, defense & marine at Tyco Electronics in Harrisburg, Pa. "Some segments, such as those funded by civil infrastructure improvement, have fared better than others. The military, while not growing to the extent of previous years, has at least remained stable. Given world events, there has actually been a much higher importance placed on effective and abundant C4ISR (command, control, communications, computing, intelligence, surveillance, and reconnaissance). This segment is highly dependent upon bandwidth, for which fiber optics is ideal, and this trend is not slowing."

Product lines dedicated to avionics connectors are less affected by the economic downturn, says Christophe Masnou, marketing manager RF interconnect at the Aerospace, Defense, Instrumentation Div of Radiall in Chandler, Ariz. These fiber optic avionics connectors "have replaced existing technologies by offering newer capabilities with cost savings, lower weights, and/or higher bandwidth advantages."

"As data rates elevate, copper-based cable assemblies become more sophisticated and expensive, closing the cost differential between fast copper and fiber optic solutions," Powers says. "Fiber optics holds significant advantages over fast copper relative to weight reduction, ground/EMI attributes in composite aircraft and speed over distance. As a result, the primary trend for avionics is the proliferation of proven contact systems into more mainstream applications that were once dominated by copper.

Power says different standards groups – VITA Standards Organization, ARINC/AEEC, SAE, etc. – "are setting the stage for accelerated deployment of standard fiber optics solutions. The key to this is the utilization of fiber optic termini with aerospace pedigree, namely the Expanded Beam, ARINC 801 (1.25mm Ceramic) and the MT ferrule.

"In addition to input/output and production break connectors, these technologies are now being designed into fiber optic based backplane connector modules to facilitate embedded computing applications (such as the VITA 66 standard currently in development)," he continues. "This will allow the network architect true end-to-end fiber optic connectivity via industry standard hardware. Concepts such as location independent architecture, where LRUs [line replaceable units] and LRMs [line replacement modules] are dispersed throughout a vehicle while able to interact as if colocated, are coming closer to realization.

Tyco Electronics produces VITA 66 Fiber Optic Backplane Connector Modules – with three module types presently in development for VITA 66 based on Expanded Beam, ARINC 801, and MT, Powers says. Tyco Electronics's Tactical Expanded Beam Connectors – . M83526/20 & /21 – are rugged fiber optic connectors for multimode and singlemode connectors for adverse environments, he adds.

"Increasing density in connectors is a major concern for avionics," Masnou says. "It equates to developing new high density inserts for existing rack and panel connectors such as EPX (a Radiall product) or ARINC types, suitable for miniature optical contacts such as Radiall's LuxCis," he adds. LuxCis, has been adopted by the ARINC committee and standardized as type ARINC 801, Masnou notes.

"LuxCis is utilizing an industry standard ceramic ferrule size 1.25mm in diameter, which is twice as small as in previous designs," he continues. "To date, the high density MT ferrule technology has not yet been proven successful in avionics applications, but we know that most avionics connector suppliers including Radiall are working towards this direction. The MT ferrule was introduced several years ago for datacom multimode transmissions. MT ferrules can potentially increase the density of as much as ten times. However, there are challenges when using the MT ferrule in avionics because of the difficulty to design a reliable connector solution in this type of environment.

"An additional trend is focusing on the ease of installation and maintenance of fiber optic connectors," Masnou says. "Since fiber optics can be delicate, if the installation is not done properly and taken care of correctly, fibers can easily be damaged. Manufacturers such as Radiall are proposing complete solutions with appropriate training, installation tools, and maintenance kits.

Composite material adoption is "driven by the objective to reduce the weight for interconnects in order to be in compliance with new environmental regulations," he says. "The choice of composite material is not an easy task since extensive tests are required to validate the material and its use."

"The next five years will bring deployment and derivatives of these standard solutions," Powers says. The economy of scale will add to the momentum. Further refinement of active devices and backplane technologies will result, likely opening the door for creative solutions getting off the circuit board. These types of activities are starting to emerge in the commercial world, so it is only a matter of time before the technology is rugged enough for avionic and vetronic applications.

In the future "there is a need for the expansion of the current usage of fiber technology for additional applications where increased temperatures are an environmental issue," Masnou says. Also, new integrated passive and active fiber optic functions at the system level need to be further developed in order to take full advantage of fiber's benefits, he adds.

"The cost of ownership of a fiber optic solution is mostly driven by the transmitters and receivers or transceivers modules converting the electronic signals into optical or vice versa," Masnou says. In this area Radiall offers D-Lightsys, a range of pigtailed transceiver products including multi channel modules, bidirectional modules and 10 gigabit per second modules, dedicated for avionics and harsh environment applications."

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