Irradiation effect on the magneto-optical properties of Bi-doped silica optical fiber based on valence state change

Abstract

Magneto-optical properties of Bi-doped silica optical fibers (BDF) and single mode fiber (SMF) before and after irradiation (0-3.0 kGy) are investigated. BDF is prepared by the atomic layer deposition (ALD) technique combined with the conventional modified chemical vapor deposition (MCVD) process. Before irradiation, the Verdet constant of BDF (1.64 rad/(Tm)) is 27.13% larger than that of SMF (1.29 rad/(Tm)) at 980 nm. Because the Verdet constants of both of them are positive values, this implies diamagnetic behaviors of fiber sample materials. After irradiation, the Verdet constant of SMF keeps increasing with the increase of radiation doses (0-3kGy). However, in the same radiation dose range, the Verdet constant of BDF is decreased first and then increased. It is decreased with the increase of gamma irradiation in the low-dose range (<0.3 kGy). Especially, the Verdet constant of BDF in 0.3 kGy is of a negative value and the Faraday rotation of it is anti-clockwise, which means the fiber sample exhibits paramagnetic material properties. When the radiation dose is from 0.3 to 3 kGy, the Verdet constants of the BDF is increased. Furthermore, in a 3 kGy treatment, the Verdet constant of BDF (1.87 rad/(Tm)) is 23.84% larger than that of SMF (1.51 rad/Tm), and is 44.96% larger than that of SMF without irradiation treatment. The novel change of magneto-optical characteristics of the BDF sample may mainly result from irradiation-induced valence state change of bismuth ions.