Scalable, fast and low optical loss fs-laser-based machining of holes in hollow core fibers

Hollow-core fibers (HCFs) represent a promising platform for distributed gas sensing as they offer an extended gas-light interaction length in a compact, lightweight and robust format. However, slow gas exchange into and within the fiber core, particularly with passive end-filling methods, limits the sensor response times and effectively restricts sensing to single-point measurements. In this work, we present a side-wall microchannel fabrication method based on femtosecond-laser machining, combining a galvo-scanner and a 4F-relay system. The presence of microchannels not only facilitates faster gas diffusion but also opens opportunities for distributed sensing schemes. A single microchannel can be produced in under 110 seconds, a processing time achieved by integrating a galvo scanner with an optimized channel geometry. The dedicated machining protocol minimizes the introduction of debris into the fiber core, yielding an average loss of 3.0 mdB per microchannel. Together, these results demonstrate a scalable, rapid fabrication technique capable of producing precise, extremely low-loss mi crochannels for distributed gas sensing.