Optoelectronic Analog Signal Transmission Takes Center Stage Amidst Aerospace and Defense Innovation

September 1, 2023

It is hard to imagine an industry more reliant on seamless, resilient, and secure communication than aerospace and defense (A&D). Communication and electromagnetic signal processing are at the core of advanced systems, which is why the trend towards higher frequencies (and millimeter waves) makes optoelectronic signal transmission a critical topic in this sector as technology advances at a rapid pace and demands better performance.

A&D communication networks use a mix of digital and analog transmission, with emphasis on the former, but given the industry’s proclivity towards lower latency and higher bandwidth applications, analog transmission will play an even larger role in the future. Passive and active electromagnetic sensing (e.g., radar, radio telescopes, and other listening devices) requires high fidelity signal transport for “remote” processing. It brings transport of radio frequency signals over fiber (RFoF) to the forefront, which is an analog technique of converting radio frequency (RF) into light waves for secure, resilient, long-distance data/signal transmission.

Data Intensive and Autonomous Future for Aerospace and Defense

A&D domains rely increasingly on communications such as control signals for unmanned vessels, surveillance drones, and tactical data from battlefield sensors. In 2021, the Pentagon received $7.5 billion to fund unmanned systems across the U.S. Air Force, Army and Navy. The Department of Defense (DoD) has also recently expressed interest in ramping up its use of AI in defense technologies.

All these applications are data-intensive, always requiring low latency and high bandwidth communication to operate successfully. Most of the signals are transported over-the-air but there is a need for transport between the processing equipment (e.g., at a bunker) and the outside antenna. The challenge with high frequency technologies required to meet current and emerging needs is the high attenuation over cable or waveguide medium, which makes long distance transport impractical. As does its heightened sensitivity to natural and man-made obstructions.

Presently, the Ku-band (12.5-18 GHz) is one of the most common RF bands used by A&D for satellite communication, remote sensing, military communication (i.e., common data link), radar systems and broadcast services. But the Ka-band (26.5-40 GHz) is emerging as a popular choice in military communication systems due to its higher data transfer rates and increased capacity. RFoF technology offers a distinct advantage here by converting RF into optical signals traveling long distances over fiber optic cable, without attenuation and signal degradation. This is preferable to transmitting over coaxial cable, which is illustrated in figure 1.

Furthermore, RFoF systems can support higher bandwidths, accommodating the ever-increasing data demands of modern military operations. With the proliferation of high-resolution sensors, sophisticated radars, and advanced communication equipment, the need for bandwidth scalability has become paramount. RFoF links ability to support higher data rates ensures that the A&D industries can keep up with evolving technological demands. The fiber media is not bandwidth limited so future upgrades do not necessitate infrastructure rebuild.

Another benefit of RFoF is it bypasses the encoding and decoding process associated with digital communications, which introduces latency and creates more security vulnerabilities. Consider all the important communication that begins over the air including military radar, avionics, cellular and satellite communications, GPS and GNSS, etc. RFoF converts those RF signals to light waves without introducing other processors that allow “listening” at both endpoints. Fiber is nearly impossible to intercept without physically locating and tapping it. The importance of security in A&D needs no explanation, but the stakes grow even higher when discussing sabotaging autonomous weapons, drones, and vehicles. RFoF is also used today in SCIFs (sensitive compartmentalized information facilities) to establish completely secure Wi-Fi for similar reasons.

RFoF: Ideal to Support Communication in Harsh Environments

RFoF technology exhibits high resilience in the face of physical damage or environmental hazards, which is a standard expectation for the majority of A&D communication. Traditional RF systems may suffer from signal degradation or complete loss when subjected to harsh conditions like extreme temperatures, moisture, lightning, or radiation. Conversely, fiber used in RFoF is inherently durable and can withstand adverse environments, ensuring continued communication even in the most challenging circumstances.

For example, many of the Navy’s unmanned surface vessels (USV) use waveguides to transport Ku-Band CDL communications payloads between radome mounted high above deck of a ship and equipment rooms situated within the hulls of ships. However, rough ocean environments and corrosion from saltwater causes significant waveguide interference because they are fragile and must be kept extremely clean and dry. Using optical fiber cables as a replacement to transmit these payloads is more suitable for these conditions. The negative impact of communication downtime on unmanned vessels only becomes greater as the fleet grows in scale.

Beyond physical damage or the environment, conventional RF systems are also susceptible to interference from electromagnetic pulses (EMPs), which can disrupt communication and compromise mission-critical data. RFoF technology’s transmission of optical signals through fiber provides inherent immunity to electromagnetic interference, safeguarding vital communication links from electronic warfare threats and enabling uninterrupted information exchange.

RFoF has emerged as a game-changing technology for A&D communication. Its ability to extend communication ranges, immunity to electromagnetic interference, enhanced security, low latency and high bandwidth make it indispensable for modern A&D operations. However, successful implementation of RFoF solutions in this sector will depend on suppliers with a flexible technical platform that can be cost-effectively tailored by a specific mission/application. As technology continues to advance, RFoF is poised to play an even more significant role in ensuring seamless, secure, and reliable communication for the military and aerospace industries.

This article was written by Meir Bartur, President and CEO of Optical Zonu Corporation. For more information, visit here  .

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