Low-loss micro-machining of anti-resonant hollow-core fiber with focused ion beam for optofluidic application

Hollow-core fiber (HCF) is a promising candidate for optofluidic applications because it can act as a gas-cell, permitting intense fluid-light interaction over extended lengths with low optical loss and inherent flexibility. Such a platform could pave the way for an all-fiberized, compact, robust and practical system for sensing applications. To facilitate this, we report a high-precision and repeatable micro-machining technique using focused ion beam (FIB) milling on a nodeless anti-resonant hollow-core fiber (ARHCF). Ga+ ions are bombarded on a 43 μm thick outer cladding of ARHCF for 30 minutes, to create a 50 μm deep fluidic channel, that has a negligible influence on the guiding properties of the fiber. The milled channel, followed by the 2.8 μm gap between adjacent 500 nm thin capillary tubes, provides direct access for liquid/gas to diffuse into the hollow-core region. The novel design presented here will allow ARHCFs to be spliced with solid-core fibers while preserving the fluidic channel. Corroborating results from simulation of such a structure are presented to demonstrate that no additional loss is induced by the milled hole.