Application of WGM Resonances to the Measurement of the Temperature Increment of Ho and Ho-Yb Doped Optical Fibers Pumped at 1125 and 975 nm

• Main Authors: Xavier Roselló-Mechó, Martina Delgado-Pinar, Yuri O. Barmenkov, Alexander V. Kir’yanov, Miguel V. Andrés
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Sensors
• Subjects: whispering gallery modes; holmium; ytterbium; doped fibers; fiber characterization; 2 μm fiber lasers
• Online Access: https://www.mdpi.com/1424-8220/21/6/2094

Optical fiber characterization using whispering gallery mode resonances of the fiber itself has been demonstrated to be a powerful technique. In this work, we exploit the thermal sensitivity of whispering gallery mode resonances to characterize the pump-induced temperature increment in holmium doped and holmium-ytterbium codoped optical fibers. The technique relies on the measurement of the resonances’ wavelength shift due to temperature variation as a function of the pump power. Holmium doped fibers were pumped to the second excited level <inline-formula><math display="inline"><semantics><msup><mrow></mrow><mn>5</mn></msup></semantics></math></inline-formula>I<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mn>6</mn></msub></semantics></math></inline-formula> of the Ho<inline-formula><math display="inline"><semantics><msup><mrow></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup></semantics></math></inline-formula> ion using a laser diode at 1125 nm and ytterbium-holmium codoped fibers to the <inline-formula><math display="inline"><semantics><msup><mrow></mrow><mn>2</mn></msup></semantics></math></inline-formula>F<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mrow><mn>5</mn><mo>/</mo><mn>2</mn></mrow></msub></semantics></math></inline-formula> level of the Yb<inline-formula><math display="inline"><semantics><msup><mrow></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup></semantics></math></inline-formula> ion by a laser diode at 975 nm. Our results demonstrate that pumping ytterbium-holmium codoped fibers at 975 nm results in dramatic thermal effects, producing a temperature increment two orders higher than that observed in holmium doped fibers pumped with a 1125 nm laser diode.