In this work we present the fabrication of silica hollow core photonic crystal fibres (HC-PCF) with guidance at 2.94μm.
As light is confined inside the hollow core with a very small overlap of the guided E-M wave with the fibre material, the
high intrinsic loss of silica at these mid-infrared wavelengths can be overcome. The band gap effect is achieved by a
periodic structure made out of air and fused silica. As silica is bio-inert, chemically stable and mechanically robust, these
fibres have potential advantages over other multi-component, non-silica optical fibres designed to guide in this
wavelength regime. These fibres have a relatively small diameter, low bend sensitivity and single-mode like guidance
which are ideal conditions for delivering laser light down a highly flexible fibre. Consequently they provide a potential
alternative to existing surgical laser delivery methods such as articulated arms and lend themselves to endoscopy and
other minimally invasive surgical procedures. In particular, we present the characterisation and performance of these
fibres at 2.94 μm, the wavelength of an Er:YAG laser. This laser is widely used in surgery since the wavelength overlaps
with an absorption band of water which results in clean, non-cauterised cuts. However, the practical implementation of
these types of fibres for surgical applications is a significant challenge. Therefore we also report on progress made in
developing hermetically sealed end tips for these hollow core fibres to avoid contamination. This work ultimately
prepares the route towards a robust, practical delivery system for this wavelength.