3D Laser Engineering of Molten Core Optical Fibers: Toward a New Generation of Harsh Environment Sensing Devices

Abstract Aluminosilicate glasses offer wide‐ranging potential as enabling materials for a new generation of optical devices operating in harsh environments. In this work, a nonconventional manufacturing process, the molten core method, is employed to fabricate and study sapphire (Al₂O₃) and YAG (yttrium aluminum garnet) derived all‐glass silicate optical fibers in which a femtosecond (fs) laser is used to imprint oriented nanostructures inside the fiber cores. Both writing kinetics and thermal stability of the laser‐modified regions are investigated over a wide temperature range (20–1200 °C). The laser‐imprinted modifications in these high alumina‐content fibers exhibit improved thermal stability with respect to commercial pure silica and GeO₂‐doped silica analogs. Furthermore, optical devices in the form of Rayleigh backscattering and fiber Bragg grating sensors are fabricated to demonstrate the high‐temperature sensitivity and stability of these nonconventional fibers. This functionalization of aluminosilicate fibers by fs‐laser direct writing opens the door to a new generation of optical devices suitable for high‐temperature operation.