Smaller, Lighter, Denser: The Evolution of Fiber Optic Expanded Beam Termini
Presented by TE Connectivity
Aircraft need higher bandwidth systems that are smaller and lighter, which brings us to fiber optic systems. TE Connectivity packed more signals into a smaller space while still meeting aerospace requirements with its PRO BEAM EB connectors.
In aerospace applications, space is always at a premium, and reducing weight is an ever-present goal for designers. Ounces saved here and there can add up to big savings overall, resulting in a lighter aircraft for more fuel efficiency, longer flight times, or bigger payloads.
In addition, as avionics systems have become more sophisticated, computing loads increase, bandwidth requirements grow, and the amount of cabling throughout the aircraft expands.
In short, aircraft need higher-bandwidth systems that are, at the same time, smaller and lighter, which brings us to fiber optic systems. The benefits of fiber are well known. Compared to copper cables, optical fibers are smaller and lighter, can transmit high data rates without the distance limitations of copper, and are immune to electromagnetic interference.
As with copper systems, designers are looking for fiber optic connectors that can pack more signals into a smaller space. At the same time, connectors must meet aerospace requirements to withstand the rugged environments of flight.
In aerospace applications, fiber optic termini using expanded beam (EB) technology offer some advantages over physical-contact ceramic-ferrule-based termini. EB connectors tolerate the vibration of airborne applications extremely well; they are less prone to disruption from tiny dust particles; and they are more easily cleaned and maintained. Because the fibers do not contact, the connectors provide high durability and mating cycles.
The first application of EB connectors was as purpose-built military connectors aimed at aerospace and military tactical ground applications. Over the years, smaller versions emerged. TE Connectivity (TE), for example, offers the Senior, Junior, and Mini versions of its PRO BEAM EB connectors.
Bringing EB to 38999
The popularity of MIL-DTL-38999 Series III connectors in military and aerospace applications led to the porting of EB technology to this form factor. This was done by a special insert for the Mini EB termini, providing low densities of two, four, or eight termini in a size-11 or -15 38999 Series III-style shell.
Higher Density: Size 16 EB Termini
The next step in increasing density was termini that could be used in a size-16 contact cavity. Not only does this allow EB termini to be used in standard 38999 Series III mil-spec connectors, it also allows optical and electrical connectors to be used in the same insert. With standard 38999 inserts, fiber densities range from two fibers in a size-11 shell to 37 fibers in a size-25 shell.
The next step in achieving high density was to combine lens technology with the multi-fiber array technology similar to that found in the MT ferrule. For TE’s High-Density Lensed Termini (HDLT) the multi-fiber ferrule is precision-molded from a material suitable for light transmission at the application wavelength. They are made for 12 or 24 fibers.
The HDLT design allows the termini to fit a size-8 Quadrax cavity. Since 38999 Series III-style connectors are available with up to eight Quadrax cavities, it’s now possible to pack 192 fibers into a size-25 shell.
Higher Densities = Space and Weight Savings
In moving from the densities allowed by PRO BEAM inserts to size-16 termini to HDLT, each step has the potential to reduce the number of connectors required for high-fiber-count applications. As a replacement for copper cable, fiber has inherent size and weight advantages. Fiber connectivity can also make use of the familiar 38999 Series III shell, both in standard mil-spec and 38999-style connectors, gaining weight benefits from the aluminum shell and even more so with composite shells. Adapting tried-and-true EB technology to new termini styles has led to a 24x increase in the number of fibers supported by a single 38999 connector.
About the Author
Earle Olson is business development manager for high-speed/bandwidth solutions for TE Connectivity’s Global Aerospace, Defense, and Marine business unit. Earle has more than 30 years’ experience in the electronics and fiber interconnect industry, specializing in rugged fast protocol solutions, high-speed/high-bandwidth solutions, fiber and copper-based systems, box-to-box, internal-to-the-box, and active optics blended with high-speed copper assemblies.