Next Level Rugged Fiber Optic Interconnects: A New Era of High-Speed Data Transmission in Defense

March 1, 2025

State-of-the-art fighter aircraft have a large number of support systems that operate in multiple areas. These systems are continuously optimized to achieve maximum efficiency and performance. Countless sensors monitor the environment and generate important data that helps to understand the areas overflown. But even in life-threatening combat situations, target acquisition systems support pilots and provide additional information that can be decisive with the help of augmented reality (AR) and artificial intelligence (AI). Military aviation is an arena with great potential for the use of technical aids that have transformed the original fighter aircraft into a technological masterpiece.

In addition to the high level of complexity, the upcoming generation change from fifth- to sixth-generation fighter jets poses major challenges for component suppliers and accelerates the pace of technological competition. A military fighter jet is already an extremely demanding environment for technical equipment.

The Harsh Environmental Challenges of Military Aviation

This image shows the light path within a physical contact connection that can be used within a fighter jet, or other aerospace or defense platform. (Image: ODU GmbH & Co. KG)

Compared to civilian applications, there are special requirements for the performance and robustness of subsystems and their connections that are used in aerospace and defense platforms. They must be reliable and withstand high mechanical stresses such as shock and vibration. Eavesdropping security and resistance to jamming signals also play a key role. Environmental influences such as extreme temperature fluctuations or contamination with aerosols and liquids are ever-present and must be considered as a preventive measure.

As the number of subsystems increases, so does the amount of data to be transmitted. Conventional copper-based cabling technology does not provide the required data rates and would be too heavy at sufficient capacity. By using fiber optic systems, these problems can be avoided and more secure data streams can be guaranteed.

The collected data is usually processed by mission computers. These are embedded systems that are customized to meet the specific requirements of the flight platforms and integrated subsystems. Their structure is based on defined standards to ensure uniformity, interoperability and compatibility with subsystems.

Light path crossing through a mated pair of expanded beam performance ferrules. Learn more about the capabilities of ODU’s expanded beam performance ferrules in this video. (Image: ODU GmbH & Co. KG)

The required modules inside are connected via direct backplane interfaces and can be exchanged as needed. Peripheral systems, on the other hand, are connected via I/O interfaces. These are subject to much higher levels of stress in daily use. In order to use the optical signals from the fiber, the cables are connected to the PCBs via optical transceivers.

Current Solutions and Their Problems

Physical Contact (PC) connectors have become well established in the aerospace and defense market. The two fiber ends are polished and precisely brought together using special tools. This physical contact allows the light signal to be transmitted from one fiber to the next. PC connections are characterized by very good transmission properties. Small dust particles or coarser contaminants can quickly scratch the polished surfaces and degrade the transmission properties. Direct physical contact also causes slight wear, limiting connector life to a few hundred mating cycles.

Four Expanded Beam Performance ferrules stacked on top of each other for maximum packing density. (Image: ODU GmbH & Co. KG)

To delay connector failure as long as possible and to ensure reliable, error-free data transmission, the interfaces are manually cleaned after each mating cycle. Modern military aircraft have many of these connections and typically require maintenance before and after each mission. This results in an enormous amount of maintenance and cleaning, as well as a short life span for the contacts.

Despite this, the technology has become the market standard. The filigree standalone contacts are available with an extremely small diameter of 1.25 mm. Special Ferrules like MTs drive this effect even further and provide an extremely high packing density. The standardized MT ferrules allow up to 24 fibers to be bundled together for fast connection and disconnection of data cables. Specific standards exist under VITA 66, VITA 87 and VITA 89 that define the dimensions and quality requirements for those connectors.

Alternatives to the Standard

Expanded beam technology is a possible alternative to PC solutions. A lens expands the light beam at the end of the fiber before it passes through a short air gap. A second lens focuses the light signal and transmits it into the connected fiber.

By dispersing the light signal, the connections are less susceptible to signal interference caused by contamination or mechanical influences. With up to 100,000 mating cycles, Expanded Beam technology offers a robust and durable alternative that requires less maintenance and is significantly more efficient than PC solutions.

This is a backplane connector developed in alignment with the upcoming VITA 96.1 standard. (Image: ODU GmbH & Co. KG)

The downside is that lens-based signal transmission cannot match the outstanding performance of PC connectors. In particular, the higher insertion loss reduces the technology’s potential for military aerospace applications. Another drawback is the physical size of the connector. Due to the larger diameter, it is not possible to achieve such a dense arrangement of multiple contact elements, which means that interconnect solutions for large number of optical fibers would take up a lot of space in the final application.

Best of Both Worlds - Expanded Beam Performance

Expanded Beam Performance technology combines the advantages of PC connectivity with the robustness of lens-based data transmission. The result is connectors that are highly resistant to wear, contamination and mechanical stress, while providing excellent transmission characteristics.

For example, typical insertion loss remains low at <0.15 dB for multimode and <0.35 dB for singlemode, ensuring minimal data degradation. Return loss values are equally impressive, exceeding 45 dB (multimode) and 60 dB (singlemode).

The innovative design of the Expanded Beam Performance Ferrule allows 12 optical fibers to be connected without direct end face contact. This means that up to 50,000 mating cycles can be achieved with no wear and no loss of transmission characteristics. Under normal circumstances, there is no need to clean the joint, as is the case with PC connectors. This makes the technology the perfect basis for data transmission in demanding, harsh environments.

The cassette principle allows multiple ferrules to be stacked in a very small space, making the connection solutions suitable for systems with large amounts of data. The end contact elements are available in different dimensions, depending on the requirements and available space.

VITA 96 Backplane Connection

The Interface of a SHS 17 MIL-DTL-38999, Series III plug with 8 Expanded Beam Performance ferrules, following the upcoming VITA 95 standard. (Image: ODU GmbH & Co. KG)

The backplane connector allows direct connection of modules and mission computers. Its high number of mating cycles and low maintenance requirements make it particularly suitable for applications that require regular module replacement over long periods of time.

The ODU BACKPLANE connection solutions are available in three different versions for the connection of up to 96 optical fibers according to the future standards VITA 96.1, VITA 96.4 and VITA 96.5. Since they fit into the same apertures, they are a low-maintenance alternative to VITA 66 solutions.

Robust and Low-Maintenance I/O Interfaces

I/O interfaces in the form of circular connectors are commonly used to connect peripheral systems. They are characterized by their robust design, intuitive handling and reliable locking mechanisms. Standardized solutions have been available for some time in the form of VITA 87 and VITA 89, which standardize fiber optic connections with a large number of contact elements. However, even these solutions do not offer sufficient durability and require costly maintenance.

The total cost of ownership can be reduced by using low-maintenance alternatives. Applications experience less downtime and are used more efficiently.

Connectors based on the future VITA 95 standard integrate the robust Expanded Beam Performance technology in 38999, Series III housings and are the ideal alternative to conventional solutions. With ODU TACTICS, the first solutions based on this principle are now available on the market. With the AMC Series T, the German manufacturer offers a connection solution in its own design - even smaller, even lighter, but just as robust as the familiar 38999 connections.

Until now, there has been no optimal solution for transmitting large amounts of data in demanding applications such as military aviation. Expanded Beam Performance technology is an important step forward. It provides systems with excellent transmission characteristics and low maintenance requirements. With a long service life, the products are a more cost-effective alternative to current links and reduce application downtime.

This article was written by Thomas Mittermeier, Strategic Business Development Manager, ODU Group (Camarillo, CA). For more information, visit here .