Hollow antiresonant fibres for visible and ultraviolet beam delivery

空心光纤在空心（通常是充气的）芯中引导光，而不是像所有传统光纤那样在固体玻璃芯中引导光。空心芯的使用意味着由于芯材料的特性而对光纤性能的许多限制被解除（通常是许多数量级），并且光纤的性能远远优于更熟悉的传统对应物。然而，有一个问题：如何在空心核中捕获光？在过去的20年里，人们投入了大量的精力来开发所谓的光子带隙光纤。这些光纤依靠复杂的包层结构以低损耗将光捕获在空心核心中。它们已经发展到很高的程度，但仍受到一些显然无法克服的实际问题的阻碍。这些因素特别限制了它们在短波长的性能，而短波长在高精度激光加工和材料改性等许多应用中非常重要。最先进的激光系统现在可以为这些应用提供必要的辐射，但是，目前还不存在真正灵活的传输系统。这种将脉冲激光从激光系统灵活地传送到应用点的能力是开发实际和商业上可行的应用所需的关键进步。在过去的18个月里，这项合作以及欧洲其他几个实验室的研究人员已经证明，一种更简单的光纤设计实际上比带隙光纤更有效。这在长波（中红外）和短波（如1微米及以下波长）中尤其如此。现在的数值模拟表明，这些设计可以扩展到提供它们在几乎任何波长下超越任何现有光纤的可能性。这项提议是在短波长范围内展示这些纤维，并与四家英国公司合作，使它们在制造和临床环境中发挥作用。这包括制造几种设计的纤维，验证它们的性能，确定使用它们的障碍并克服它们，然后在我们合作者的实验室里工作，使它们在工厂车间以及医学和工程测量中发挥作用。在此过程中，我们的目标是展示有史以来最低损耗的光纤（在更长的波长下），并研究这些设计是否可以扩展到传输低光束质量的激光束。

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.