THE LASER USER
ISSUE 115 MARCH 2025 LASER ETCHING
Figure 3: The Axi-Stack process for manufacturing freeform optical fibre.
transmitted in air rather than glass) has caught the attention of technology giants for applications in data centres and AI [3]. This type of fibre is currently manufactured by a process known as “stack-and-draw”, whereby glass rods and capillaries are stacked by hand to form a preform, a scaled-up precursor from which the fibre is then drawn from. Using this method, incredibly fine glass structures can be fabricated along km-lengths of optical fibre which outperform conventional solid glass fibre with record low-loss guiding. However, scaling this method is challenging, and certain fibre geometries simply cannot be stacked.
We are developing a radical approach to manufacturing optical fibre preforms called “Axi-Stack” [4]. The approach utilises SLE to fabricate precise cross-sectional preform discs that are stacked axially and bonded via ultrafast laser welding (see Figure 3). Each disc can be structured arbitrarily by the laser, allowing freeform fibres to be manufactured.
In a recent feasibility demonstration (see Figure 4), we stacked a 30 cm long, 50-disc preform featuring a square-lattice photonic crystal fibre structure. The preform was drawn to fibre in a conventional fibre drawing tower and the fibre performed well. We are currently optimising the disc alignment and bonding processes.
Figure 4: A square lattice photonic crystal fibre fabricated by Axi-Stack. (A) A single fabricated silica disc. (B) A stacked preform. (C) The drawn fibre.
Freeform optical fibre is expected to have immediate application in telecoms and networking where low latency and fast data transfer speeds are essential. Beyond these fields, the transportation of quantum states within ultra-low-loss fibre (Figure 5), the study of pulse dynamics in an axially varying fibre, and broad spectrum fibres for photodynamic therapy are just some of the exciting application areas to explore in the future.
References
[1] M. Ochoa et al. Lab Chip 23, 1752–1757 (2023).
[2] S. R. McArthur et al. Opt Express 30, 18903–18918 (2022).
[3] "How hollow core fiber is accelerating AI | Microsoft Azure Blog,"
https://azure.microsoft. com/en-us/blog/how-hollow-core-fiber-is- accelerating-ai/.
[4] C. A. Ross et al. Opt Express 32, 922–931 (2024).
Figure 5: A freeform fibre structure, with potential low-loss applications, inscribed in a silica substrate. A faint plasma is visible at the laser focus.
Axi-Stack
One area where we are utilising SLE and beam shaping is for the fabrication of microstructured silica optical fibre preforms. Optical fibres are the backbone of modern telecommunications, and recently, hollow-core optical fibre (in which light is
Calum Ross is a UKRI Future Leaders Fellow at Heriot- Watt University with an interest in ultrafast laser processing of glass for applications in photonics.
SEE EE OBSERVATIONS P30 29 25
Contact: Calum Ross
Calum.Ross@
hw.ac.uk www.hw.ac.uk
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