Applications of microstructured “negative curvature” fibre, for high power and mid-IR transmission

In recent years there has been a considerable amount of interest in the development of novel fibre optic designs to improve the transmission of high power ultra-short pulses. Fibres based on either large mode areas, which exhibit high dispersion and multi-mode behaviour, or hollow core PCF designs, which still exhibit limits in deliverable pulse energy, have only partially addressed the problem. In this presentation we present a novel form of fibre, the negative curvature fibre (NCF) being developed at the University of Bath.
These fibres, under test at Heriot-Watt, allow for the transmission of significantly higher pulse energies than previously demonstrated. This permits truly flexible fibre delivery for a range of laser machining applications. Demonstrations include machining steel, titanium, glass; also potential surgical applications (machining of animal bone and soft tissue). In addition the extremely low overlap between core and fused silica allows the fibre to effectively guide further into the infra-red (3-4μm) without the use of exotic (chalcogenide) glasses.
We have investigated the laser damage threshold, dispersion, bend sensitivity and birefringence properties in the near infrared. The possibilities of transmission of 3-4μm light combined with the hollow core design permits the use of the fibre as a gas sensor. Methane and carbon dioxide, both critical greenhouse gasses, exhibit absorption spectra in this region which can be exploited to form a passive gas sensor.