Tapered and Coated Optical Fiber with Fe₃O₄ Nanoparticlesand Magnetic Fluid for Magnetic Field Detection

Abstract

In this work, an optical fiber sensor was developed for magnetic field detection. Singlemode
and multi-mode fibers were used based on two main processes: chemical etching using
hydrofluoric acid (HF) and coating with Fe3O4 nanoparticles. The nanoparticle layer was deposited using
pulsed laser deposition (PLD) with an Nd:YAG laser operating at a wavelength of 1064 nm and 70
pulses, achieving a thickness of 49.4 nm in the sensing region. This work demonstrates the use of Fe3O4
nanoparticles in the coating process through two different techniques within the optical fiber system. In
the first technique, the nanoparticles were deposited as a solid coating via pulsed laser deposition (PLD),
achieving a thickness in the nanoscale range of 40–60 nm, which provides an effective surface for
interaction. In the second technique, Fe3O4 nanoparticles were used in the preparation of a magnetic fluid
that acts as a liquid coating, forming a stable and magnetically responsive medium. This dual use of
Fe3O4 in both solid and liquid coatings provides more effective interaction than the use of a single
coating technique. The magnetic fluid was prepared by dispersing 5 g of Fe3O4 powder in 13 g of
paraffin oil. The experimental results showed that increasing the etching time during the chemical
etching process using hydrofluoric acid (HF) led to a reduction in the optical fiber diameter,
accompanied by a decrease in the transmitted optical power. These results are consistent with previous
studies, which have shown that the tapering process using hydrofluoric acid (HF) transforms a
conventional optical fiber into a sensitive element capable of responding to external variations.
Therefore, this approach provides a suitable way to improve fiber sensitivity and enables its use in
magnetic field sensing applications.