Enhanced butt coupling efficiency of VCSELs into hollow core fibre using a graded index fibre lens

We present an investigation into direct butt-coupled interconnection of hollow-core fibres to single-mode VCSELs operating at 850 nm. Our results show the coupling efficiency can be significantly improved from 10% to 69% using a graded-index fibre (GIF) based, all-fibre mode field diameter (MFD) converter.