Looking on the bright side for defence
Published 15 October 2024 in ANFF’s 2024 Casebook ‘ANFF NEXT‘. Posted on on 5 May 2025
Advances in optical fibre technology will enable high-power fibre lasers, positioning Australia as a leader in light-based defence systems.
Currently, 31 countries possess ballistic missiles, and counter-missile systems were developed as the primary means of defence. These systems are highly advanced, designed to detect, track, intercept and destroy incoming missiles. However, their cost remains a significant challenge. Each counter-missile costs millions, and even a single test of such a system can be a hundred times more expensive than the projectile it is designed to stop.
Beyond their traditional use against ballistic missiles, counter-missile systems are increasingly deployed to defend against a wider range of projectiles and weapons, such as rockets, mortars and drone swarms. These lower-cost, easily deployable threats are becoming mainstream and have the potential to overwhelm expensive missile defence systems. In particular, drone swarms can exhaust valuable counter-missiles, limiting the availability of these expensive assets for other, more critical engagements.
As a response to this emerging threat, directed energy weapons like high-powered lasers are being developed as a more cost-effective solution to neutralise drones and other small-scale aerial threats. Lasers work by generating photons using an energy source, typically electricity, and creating a focused beam output. The power of the beam can vary significantly – from low-energy lasers like pointers to high-powered military lasers capable of cutting through steel.
However, older generations of such lasers for military use required high power levels, extensive power generation and cooling infrastructure, necessitating large platforms like naval ships or permanent ground installations.
An alternative approach involves using optical fibres to channel light and generate a highly focused beam. The resulting laser is more precise because it produces a cleaner, more uniform circular beam that can be focused over long distances. Additionally, fibre laser systems offer a range of benefits such as a smaller physical footprint, higher electrical efficiency and lower overall operating costs. Despite these advantages, scaling up the power output of fibre lasers for military use has proven challenging due to technical limitations.
Optical fibres are great for interacting with light over long distances, but they can experience nonlinear effects like stimulated Brillouin scattering (SBS), which scatters light and limits power delivery.
SBS occurs when light interacts with sound waves (acoustic phonons) in a medium, such as an optical fibre. A high-intensity light beam travelling through a fibre generates ultrasound waves, creating periodic density variations. The light interacts with these variations, causing some of it to scatter. If the scattered light travels in the opposite direction to the original beam, it can be amplified by the sound waves.
SBS becomes significant only above a certain threshold power. Below this threshold, the effect is minimal, but above it, SBS can reflect a substantial portion of the light back towards the source, limiting the laser’s power output.
Minimising the impact of SBS is crucial in fibre optics and telecommunications because it can limit the performance of high-power fibre optic systems. Understanding and controlling SBS is crucial for improving the efficiency and reliability of these systems
Dr Linh Nguyen and Dr Ori Henderson-Sapir, along with colleagues from the University of South Australia, University of Ã×À¼µç×Ó and Yale University – with support from ANFF-OptoFab Ã×À¼µç×Ó â€“ have scaled up fibre laser power by an order of magnitude without degrading beam quality. By shaping the input light’s wavefront in a multimode fibre, they significantly mitigated the SBS power further. This method also allowed control over the output beam’s shape, enhancing efficiency and robustness for applications like directed energy to neutralise drones.
Australia is now positioned to lead in developing next-generation, high-power fibre lasers, benefiting both defence and scientific research. The continued improvements in fibre optic laser technology will offer new possibilities in applications from defence to remote sensing.