Femtosecond Laser Ablated FBG Multitrenches for Magnetic Field Sensor Application

Abstract

Three-dimensional multitrench microstructures, femtosecond laser ablated in fiber Bragg grating (FBG) cladding, TbDyFe sputtered is proposed and demonstrated for magnetic field sensing probe. Parameters such as the number of straight microtrenches, translation speed (feed rate), and laser pulse power of laser beam have been systematically varied and optimized. A 5- $\mu \text{m}$ -thick giant Terfenol-D magnetostrictive film is sputtered on to FBG microtrenches, and acts as magnetic sensing transducer. Eight microtrench samples produced the highest central wavelength shift of 120 pm, nearly fivefold more sensitive compared with nonmicrostructured standard FBG. An increase in laser pulse power to 20 mW generated the magnetic sensitivity of 0.58 pm/mT. Interestingly, reduction in translational speed contributed dramatically to the rise in the magnetic sensitivity of the samples. These sensor samples show magnetic response reversibility and have great potential in the magnetic field sensing domain.