Hollow antiresonant fibres for visible and ultraviolet beam delivery

Hollow core optical fibres guide light in a hollow (usually, gas-filled) core rather than in a solid glass core as in all conventional fibres. The use of a hollow core means that many of the constraints on optical fibre performance which are due to the properties of the core material are lifted (often by many orders of magnitude) and the fibres can by far outperform their more familiar conventional counterparts. There is a problem, however: how can you trap light in a hollow core? Substantial effort has been put into developing so-called photonic bandgap fibres over the last 20 years. These fibres rely on a complex cladding structure to trap light in the hollow core with low losses. They have been developed to a high degree but have been held back by some apparently insurmountable practical problems. These have especially constrained their performance at the short wavelengths which are important in many applications such as high precision laser machining and materials modification. The state-of-the-art laser systems can now deliver the necessary radiation for these applications: however, a truly flexible delivery system does not currently exist. This ability to deliver the pulsed laser light flexibly from the laser system to the point of application is a key advance required to develop practical and commercially viable applications.

Over the last eighteen months, researchers in this collaboration and at a couple of other laboratories across Europe have demonstrated that a much simpler fibre design can actually be far more effective than the bandgap fibres. This is especially true at long wavelengths (in the mid-infrared) and at short wavelengths (eg 1 micron wavelength and below.) Numerical simulations now suggest that these designs can be extended to offer the possibility of their outperforming any existing optical fibres at almost any optical wavelength.

This proposal is to demonstrate these fibres at a range of short wavelengths and to work with four UK-based companies to establish them as useful in manufacturing and clinical environments. This involves making fibres with several designs, verifying their performance, identifying the barriers to their use and overcoming them, and then working in the laboratories of our collaborators to establish them as useful on the factory floor and also in medical and engineering measurements.

Along the way, we aim to demonstrate the lowest-loss optical fibre ever (at a longer wavelength) and to investigate whether these designs can be extended to deliver laser beams with low beam quality.

This project is designed around impact. That has been possible because work done over the last 12-18 months has reduced some of the key scientific risks in the project to the point where we and our collaborators have high confidence in the relevant fibre performance targets being met. This confidence has enabled us to take the following steps:

1. We have pulled our project partners right inside the research programme, rather than seeing them as eventual beneficiaries of the research. A significant part of the work programme (WP3 and WP4) consists of working directly with our partners, often in their laboratories, to integrate our fibres into their systems. This will enable improved technology transfer compared to other project models, and will focus attention on the "real issues" during the later parts of the work programme.

2. We have requested funding for fabrication and supply of stock fibres by a technician. Our intention is to develop specifications for 4-6 fibres during the first 12-18 months of the programme, and then fabricate long (minimum 1km) lengths of these fibres to be used in the subsequent stages. As well as ensuring that the applications development is not inhibited by a limited fibre supply, this will also enable us to investigate production/tolerance issues in our fabrication processes for these fibre types.

3. These stock fibres will also be made available through our more general industrial outreach programme, in which we will engage with a wider range of (UK-based) companies and businesses.

The impact which we expect this work to have is that we anticipate our fibres being incorporated into product lines, or made available as an option, by UK-based companies who require fibre delivery of intense or high-energy laser light at 1064nm, 532nm and into the ultraviolet. This will make those companies more competitive, enabling them to grow their business and employ more people in the UK.

In order to ensure that our impact plan is delivered effectively we have requested support for dedicated staff (Veronica Ferguson) at Heriot-Watt to coordinate the process. This will be further boosted by links with the EPSRC Centre for Innovative Manufacturing in Laser Based Production Processes (based at Heriot-Watt and led by the Heriot-Watt PI) that acts a national hub for activity and research into technologies well aligned with this programme. This will therefore provide a conduit for knowledge exchange and a natural pathway to impact.