Doped sillenite crystals applicable for fiber-optic magnetic sensors

Abstract The spectral dependencies of the optical rotatory power (ORP-ϱ) and the Verdet coefficient ( V ) of undoped and Fe- and Cr-doped Bi 12 SiO 20 ( BSO ) crystals are studied in the spectral range of 440–800 nm. The results show that Cr decreases ϱ about 4–5% in the range 600–700 nm, but below 560 nm ϱ strongly increases up to 180–200% compared to the ORP of undoped BSO, which could be related to the earlier observed absorption spectra. Like the ORP, the values of V are lower by about 1–3% at 700-600 nm, whereas below 590 nm V increases about 2%. The influence of Fe on ϱ and V strongly depends on the dopant concentration. For example, at larger concentrations (2.2 mol%) ϱ and V decrease up to 4% and 12%, respectively, whereas at 0.9 mol% Fe ϱ and V increase 3% and 9%, respectively. The influence of the annealung and the illumination on the gyrotropy of undoped BSO are also studied. Some assumption about the nature of the sillenite optical and magneto-optical rotation are made. The possibilities to use these materials for fiber optic magnetic field sensors or to improve their characteristics for photorefractive applications are discussed, too.