Freeform Silica Fibre Optics via Ultrafast Laser Manufacturing
Lead Research Organisation:
Heriot-Watt University
Department Name: Sch of Engineering and Physical Science
Abstract
At a glance: Microstructured optical fibres are transforming science and technology in fields spanning telecommunications through to healthcare. Their unique offering of guiding properties continues to push the limits of established photonics and drive novel innovation and scientific discovery. However, a limit to this potential is approaching because many theoretically transformative fibres cannot be realised in practice due to manufacturing challenges. With this fellowship, I aim to unlock this unmet potential by developing a freeform optical fibre manufacturing process, which is unbound from conventional manufacturing constraints.
The vast majority of optical fibre is produced for the telecommunications sector to satisfy exponentially rising data capacity needs. The type of fibre used in telecoms is typically conventional step-index fibre, comprised of a silica glass core surrounded by a lower-index doped-silica cladding. Solid fibre is inexpensive and guides with reasonably low-loss, but is fundamentally limited in performance by material absorption, scattering and high-dispersion amongst other factors.
Over the past few decades, another type of optical fibre has emerged - microstructured optical fibre (MOF). MOF utilises a structured-material core-cladding in which light is guided through complex waveguiding mechanisms. Depending on the type, MOF can offer several advantages over conventional fibre including broad spectral transmission, low bend-loss, low latency and high-power delivery. Remarkably, certain MOFs guide light within a hollow region of the fibre. These so-called hollow-core fibres overcome problems faced by solid-core fibres such as material absorption, dispersion, optical damage and latency, as well as enabling an innovation-rich field of gas-filled sensors and light sources.
MOF is manufactured by an approach known as stack-and-draw. Stack-and-draw is a two-step process: firstly, circular glass capillaries, rods and tubes are stacked laterally, often with added spacers, to form a scaled-up approximation of the fibre known as a preform. Secondly, the preform is drawn to fibre through a high-temperature furnace. The design of MOF developed so far has been heavily steered by the restrictive stacking process, e.g., hexagonally-packed Kagomé fibre and circle-tubular antiresonant fibre. Unfortunately, several types of MOF that have shown huge potential theoretically cannot be reasonably stacked, and so the vast applicability of MOF is beginning to plateau.
To unlock this potential, we will develop a new preform manufacturing process capable of producing freeform fibre, i.e., fibre with arbitrarily structured cross-section, without compromising on fibre quality. In the proposed approach, short segments of the preform are precisely and arbitrarily machined using tailored laser-manufacturing methods. These segments are then bonded axially to form the preform which is drawn to fibre using traditional methods. Building upon a recent early feasibility demonstration, the fellowship will facilitate an overhaul of the laser-based approach to fabricating preforms and investigation of optimal glass bonding techniques. Amongst a trove of benefits, freeform fibre will bring drastically lower loss, increased stability, faster data transfer speeds and novel spectral guidance.
The later stages of the fellowship will focus on developing fibre with unprecedented guiding performance and exploring applications of fibre with novel geometry. We aim to develop an industry-ready manufacturing method for freeform silica optical fibre, and further improve high-resolution glass macro-fabrication and advanced bonding and assembly capabilities. This work is expected to open up a new field of fibre optics research and nurture a team of dedicated researchers.
The vast majority of optical fibre is produced for the telecommunications sector to satisfy exponentially rising data capacity needs. The type of fibre used in telecoms is typically conventional step-index fibre, comprised of a silica glass core surrounded by a lower-index doped-silica cladding. Solid fibre is inexpensive and guides with reasonably low-loss, but is fundamentally limited in performance by material absorption, scattering and high-dispersion amongst other factors.
Over the past few decades, another type of optical fibre has emerged - microstructured optical fibre (MOF). MOF utilises a structured-material core-cladding in which light is guided through complex waveguiding mechanisms. Depending on the type, MOF can offer several advantages over conventional fibre including broad spectral transmission, low bend-loss, low latency and high-power delivery. Remarkably, certain MOFs guide light within a hollow region of the fibre. These so-called hollow-core fibres overcome problems faced by solid-core fibres such as material absorption, dispersion, optical damage and latency, as well as enabling an innovation-rich field of gas-filled sensors and light sources.
MOF is manufactured by an approach known as stack-and-draw. Stack-and-draw is a two-step process: firstly, circular glass capillaries, rods and tubes are stacked laterally, often with added spacers, to form a scaled-up approximation of the fibre known as a preform. Secondly, the preform is drawn to fibre through a high-temperature furnace. The design of MOF developed so far has been heavily steered by the restrictive stacking process, e.g., hexagonally-packed Kagomé fibre and circle-tubular antiresonant fibre. Unfortunately, several types of MOF that have shown huge potential theoretically cannot be reasonably stacked, and so the vast applicability of MOF is beginning to plateau.
To unlock this potential, we will develop a new preform manufacturing process capable of producing freeform fibre, i.e., fibre with arbitrarily structured cross-section, without compromising on fibre quality. In the proposed approach, short segments of the preform are precisely and arbitrarily machined using tailored laser-manufacturing methods. These segments are then bonded axially to form the preform which is drawn to fibre using traditional methods. Building upon a recent early feasibility demonstration, the fellowship will facilitate an overhaul of the laser-based approach to fabricating preforms and investigation of optimal glass bonding techniques. Amongst a trove of benefits, freeform fibre will bring drastically lower loss, increased stability, faster data transfer speeds and novel spectral guidance.
The later stages of the fellowship will focus on developing fibre with unprecedented guiding performance and exploring applications of fibre with novel geometry. We aim to develop an industry-ready manufacturing method for freeform silica optical fibre, and further improve high-resolution glass macro-fabrication and advanced bonding and assembly capabilities. This work is expected to open up a new field of fibre optics research and nurture a team of dedicated researchers.
Publications

Ross CA
(2024)
Axi-Stack: a method for manufacturing freeform air-silica optical fibre.
in Optics express
Description | Energy Transfer Technologies Doctoral Training Hub: Ultrafast Laser Inscription for Novel High-Power Fibre Laser Components |
Amount | £124,000 (GBP) |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 08/2025 |
End | 10/2029 |
Description | Methods of drawing novel optical fibre preforms |
Organisation | University of Bath |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | We design and manufacture optical fibre preforms using a novel preform stacking process which enables novel preforms to be constructed. |
Collaborator Contribution | Our partners inform on the design of novel fibre preforms, offer guidance related to the fibre drawing process, and facilitate the fibre drawing process. |
Impact | Journal paper: Optics Express 32 (1), 922-931 Conference talks: Cleo 2022 (inc proceedings), LPM 2023) Photon 2024 |
Start Year | 2022 |
Title | METHOD OF FABRICATING AN OPTICAL FIBRE PREFORM |
Description | A method of fabricating an optical fibre preform is disclosed comprising using a subtractive process on an optical monolith to define therein at least a transverse section of the optical fibre preform, wherein the transverse section comprises at least two regions with different refractive indexes. An optical fibre preform fabricated in accordance with the method is also disclosed along with a method of assembling optical components using a subtractive process to define a first interconnecting feature in or for use with a first optical component; using a subtractive process to define a second interconnecting feature in or for use with a second optical component; and coupling the first and second components together using the first and second interconnecting features such that the coupling dictates a passive alignment of the first and second components. |
IP Reference | WO2021180763 |
Protection | Patent / Patent application |
Year Protection Granted | 2021 |
Licensed | No |
Description | Featured in magazine article in "Optics and Photonics News" (Optica) titled "The light at the end of the tunnel" |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | Featured in an article written by Susan Curtis which discussed recent innovation in hollow-core optical fibre technology. |
Year(s) Of Engagement Activity | 2025 |
URL | https://www.optica-opn.org/home/articles/volume_36/march_2025/features/the_light_at_the_end_of_the_t... |
Description | Magazine Article in The Laser User (published by AILU) |
Form Of Engagement Activity | A magazine, newsletter or online publication |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Industry/Business |
Results and Impact | I published an article in "The Laser User" titled "Selective Laser Etching: Towards Industrial Application". The article was edited by Catherine Rose and published in Issue 115, pages 24-25. The magazine is popular amongst both researchers in laser physics and key industries. It has so far led to engagement with companies interested in collaborating. |
Year(s) Of Engagement Activity | 2025 |