Magnetic Field Fiber Specklegram Sensors Based on Tb3+ Doped Magneto-optical Glasses with High Verdet Constants

• Published in: IEEE sensors journal 2023-04, Vol.23 (7), p.1-1
• Main Authors: Cabral, Thiago D., Franco, Douglas F., Fujiwara, Eric, Nalin, Marcelo, Cordeiro, Cristiano M. B.
• Format: Article
• Language: English
• Subjects: Charge coupled devices; Faraday effect; Faraday rotation; fiber specklegram sensor; magnetic field measurement; Magnetic fields; optical fiber sensors; Optical fibers; Sensors; terbium oxide-doped fiber; Verdet constant
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2023.3244120

Optical fiber specklegram sensors for magnetic field measurements are reported. The probes are compact, with only a fiber length of ~100 mm exposed to a magnetic field and comprised of no-core fibers doped with Terbium oxide (Tb 4 O 7 ), so the Verdet constant is dramatically improved in comparison to regular commercial fibers (~20× increase, 10 mol % fiber), greatly enhancing the modulation of the output specklegram. The response to static magnetic fields was evaluated for different concentrations (6 to 10 mol %) of Tb 4 O 7 , yielding an increase in sensitivity of up to 59× (8.78×10 -2 mT -1 , 10 mol %) and 6× resolution (1.86×10 -2 mT, 6 mol %) in relation to a regular silica multimode fiber. A simple setup with an He-Ne laser and inexpensive webcam CCD camera being was employed, producing results comparable to fiber sensors based on more complicated setups such as fiber interferometers. To the best of our knowledge this comprises the first demonstration of highly multimode magnetic field fiber specklegram sensors based on magneto-optical glass to capitalize on both the Faraday rotation and polarization mode conversion.