Gas Flow Modelling of Hollow-Core Optical Fibre Evacuation Through Laser-Machined Channels in the Cladding

Hollow-core optical fibres (HCF), where light is guided in air-filled holes inside a silica fibre structure, have exceptional guidance properties such as low loss, low optical nonlinearity, and low noise-induced phase fluctuations. HCF nonlinearity and thermoconductive noise [1] could be significantly reduced further, if the fibres could be evacuated and guidance achieved in vacuum. However, because of the small core size, evacuating a HCF from the fibre ends is a very slow process, e.g. it takes over 60 h to reduce the average pressure in a 100 m long fibre with 20 μm core diameter from 1 bar to 0.1 bar (250 days for 1 km length). One way to accelerate fibre evacuation is by machining small holes through the cladding along the fibre length, e.g. through laser ablation [2]. Here we use fluid dynamics simulations to establish the required shape and size of the machined holes and their spacing to achieve given evacuation times.