Optofluidic channels in anti-resonant hollow-core fibers using focused ion beam

Silica anti-resonant hollow-core fiber (ARHCF) is a promising platform for optofluidic applications because it can act as fluid-cell, permitting intense fluid-light interaction over extended length with low optical loss from ultra-violet to mid-infrared region. For this kind of applications, an all-fiberized and compact structure is necessary. However, a prerequisite for this purpose is that micro-channels must be created on the side of the fiber, to provide access for the diffusion of fluids (i.e. liquid or gas) into the core. Several attempts based on femtosecond laser micro-machining technology have been made to create micro-channels through the silica cladding, but significant loss could be induced due to the damage of the cladding capillaries of ARHCF. Here, we report a high-precision and repeatable micro-machining technique using focused ion beam (FIB) milling on a nodeless ARHCF. Ga⁺ ion beam is employed to bombard a 43 µm thick outer cladding of ARHCF for 30 minutes, to create a 50 µm deep fluidic channel. The micro-channel in the silica cladding is precisely drilled at the middle position of two adjacent capillaries with a 2.8 µm gap, providing direct access for liquid/gas to diffuse into the hollow-core region, while avoiding the damage of the capillaries. Corroborating results from simulation of such a structure are presented to demonstrate that no additional loss is induced by the milled structure.