Laser Nano-Filament Explosion for Enabling Open-Grating Sensing in Optical Fibre

Abstract

Embedding strong photonic stopbands into traditional optical fibre that can directly access and sense the outside environment is challenging, relying on tedious nanoprocessing steps that result in fragile thinned fibre. Ultrashort pulsed laser filaments have recently provided a non contact means of opening high aspect ratio nanoholes inside of bulk transparent glasses. This method has been extended here to optical fibre, resulting in high density arrays of laser filamented holes penetrating transversely through the silica cladding and guiding core to provide high refractive index contrast Bragg gratings in the telecommunication band. The point by point fabrication was combined with post-chemical etching to engineer strong photonic stopbands directly inside of the compact and flexible fibre. Fibre Bragg gratings with sharply resolved pi-shifts are presented for high resolution refractive index sensing from n = 1 to 1.67 as the nano-holes were readily wetted and filled with various solvents and oils through an intact fibre cladding.