Shaping the future of high-power lasers for defense with the French Aerospace Lab

High-power lasers are becoming crucial for defense applications, with numerous current projects advancing from cutting-edge research to real-world demonstrations. Exail, leveraging its deep expertise in optical components, plays a key role in supporting these efforts, particularly through a long-standing partnership with ONERA, the French Aerospace Lab, which advises the French Defense Procurement Agency (DGA) on critical laser innovations.

Fiber laser technologies for high-power lasers

The energy of a laser can be concentrated on a very tiny spot, resulting in extremely high-power density, making it a powerful technology. In defense, high-power lasers are developed for Directed Energy Laser (DEL) systems or for laser dazzling applications like Directional Infrared Counter Measures (DIRCM).

For over 20 years, Exail has been integrating optical fibers and electro-optic modulators for applications in the most demanding environments like deep ocean and space. Some Exail’s fiber-optic-gyroscopes have clocked more than 6 million hours in orbit until today, on more than 30 satellites without incident. In the last decade, fiber lasers have become the dominant technology for generating high-power within compact, efficient systems that are less sensitive to temperature variations. The company has leveraged its industrial expertise and R&D partnerships to develop cutting-edge optical solutions for high-power laser applications.

Advising French Defense procurement agency on high-power laser technologies

Pierre Bourdon is a Special Advisor on high-power lasers at ONERA’s Optics and Associated Techniques Department (DOTA), working on optics for aerospace and defense applications.

“Our goal at ONERA is to advance high-power laser research to Technology Readiness Level (TRL) 4-5. We develop proof-of-concept prototypes for field testing. And we transfer our knowledge to the industry for further development, when power requirements exceed our experimental capabilities.” says Pierre Bourdon

ONERA’s team is recognized as scientific expert on high-power lasers for defense by the DGA, together with the French-German research institute of Saint-Louis (ISL – another partner of Exail – read about it). DGA faces key technological decisions and ambitious investments ahead. In the last decades, Pierre Bourdon’s team has made extensive investigations, supporting the advantages of fiber-based laser technologies for continuous wave (CW) DEL applications.

“We combine a wide range of scientific and technological expertise – from literature reviews and theorical studies to simulations and experimental validation – to effectively advise the DGA. Our mission includes objectively evaluating the field readiness of various technologies by considering their scientific and operational limitations.” Bourdon explains

The two main challenges for broad field adoption of laser technologies are footprint (size/weight) and “wall plug efficiency”, the ratio of electrical power consumed to optical power output – considering the power needed to cooldown the system for example. 500 kW of electricity can be required to generate a 100 kW CW laser, highlighting the need for improved efficiency.

Leveraging Exail’s industrial expertise to build a national sovereignty in high-power lasers

Pierre Bourdon’s team experiments have focused on a main technological approach: the coherent beam combining (CBC) of multiple CW laser sources using active phase control.

“We are not yet certain which beam combining technique is best. Hybridizing several techniques may be the key. For instance, we have worked with Exail on two approaches that could be integrated in future systems: fiber laser architecture in the 2 µm range, using Exail’s holmium-doped and thulium-doped fibers, and CBC using Exail’s phase electro-optic modulators” explains Bourdon

Fiber amplifiers (at 1 or 2 µm) offer powerful emission, while electro-optic modulators enable fast phase control of laser beams. One of the latest projects involving Exail, ONERA, and ISL—supported by the DGA and funded by French Defense Innovation Agency (AID)—is the AMFITRIHIUM project. This project aims to develop a new fiber laser architecture using holmium fibers pumped by thulium fibers as laser sources. The architecture has achieved a remarkable 180W laser emission at 2120 nm, with 60% efficiency (from 300W input). More significantly, heat generation remained low, indicating that the system could handle even higher outputs, such as 250W or more.

“This is a global state-of-the-art achievement in terms of efficiency for this architecture. While holmium-doped fibers are not widely used in this field yet, I believe they will be the long-term solution for operational fiber laser technology.” says Pierre

Bourdon notes the importance of addressing the long-term aging of optical fibers for field operations, where maintenance is critical. Temperature is another challenge for high-power lasers in embedded applications. While standard optical fibers have acrylate coatings that tolerate up to 100°C, Exail has developed fibers with high-temperature acrylate (HT acrylate) coatings that can withstand up to 150°C and polyimide coatings for even more extreme conditions, as well as special triple clad fibers for high power generation around 2 µm.

“Optical fibers, like those developed by Exail for fiber amplifiers, are strategic components in building high-power laser systems. Having a national manufacturer of such a key component is vital for our technological sovereignty. We emphasize this in our advice to the DGA. Additionally, optical fibers cannot easily or even possibly be reverse-engineered, making their manufacturing process even more valuable than the product itself.” Bourdon highlights.

From single fiber lasers to coherent beam combining architectures

A single fiber laser with narrow bandwidth can deliver several kilowatts of continuous wave power. However, for defense applications requiring hundreds of kilowatts, optical combination of multiple laser sources is necessary.

During last Exail’s Photonics Users Conference in (2024), Pierre Bourdon showcased one of his team’s most advanced field demonstration: power scaling of seven laser beams using “Target-In-the-Loop CBC” (TIL-CBC). Exail’s phase modulators were used to actively control the phase of six laser beams, adjusting them to the phase of a seventh central beam. This allowed maximum power density to be focused on the central lobe and precisely targeted. With this method, 42% of the total laser power was concentrated on a 2 cm² target placed 1 km away

ONERA also developed a tip-tilt control system – allowing two additional degrees of freedom per laser – to further refine laser targeting. A unique aspect of the experiment was the active monitoring of backscattered laser phases, which enabled dynamic control of the emitted laser phase to counteract atmospheric turbulence detrimental effects and maximize power density deposited on a remote target.

This combination of active phase control, backscatter monitoring, and tip-tilt adjustment has proven effective in various demonstrations. ONERA is now tackling more complex cases (specific weather conditions and different target types) to further enhance the system and is exploring how AI could assist in analyzing large amounts of data rapidly.

“The more beams we combine, the faster we need to analyze each beam’s phase, in the highest speed feedback-loop possible. There will be more complex phase fluctuations to compensate for, and AI could help. That’s also why we need faster electro-optic phase modulators with broader bandwidth, to quickly identify and correct beam phase differences.“ says Bourdon

Another challenge is deciding whether to combine only a few but very powerful lasers or a large number of lower power ones. “There’s significant complexity in efficiently combining numerous small lasers. But very powerful lasers require more maintenance, which can be problematic for defense applications where robustness is key. We regularly discuss these operational considerations with the DGA to ensure practical feedback informs our technology development,” Bourdon explains. “A multi-kilowatt laser experiment is expensive, so it’s essential to make well-informed choices upfront.”

High-energy lasers find applications for defense but also for Earth-to-space optical communications. In both cases, a large quantity of photons must be directed on a tiny target (or tiny sensor), with the main difference being power levels. Beam combining techniques and adaptive optics are often used in both cases to compensate for atmospheric turbulence. ONERA is currently exploring how these two techniques could eventually work together.