Development of Magnetooptical Plastic Fiber

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This report describes a current sensor using Bi-YIG nanoparticle-dispersed optical prastic fiber with magnetooptical activity. Bi-YIG nanoparticles were prepared by coprecipitation followed by heat treatment. MMA was used for the matrix and PMMA was used for a dispersion agent in the matrix. Both optical absorption coefficient and magnetooptical properties such as saturation Faraday rotation and Veldet constant increased with increasing the volume fraction of the Bi-YIG particle in the fiber. Under the optimized conditions of the fiber length and the volume fraction the Veldet constant, which is the most important parameter for the current sensor, was 10 times as high as rare-earth doped glass. The most preferable wavelength of the optical source was 520 nm.Dispersability of the Bi-YIG particles improves the magnetooptical properties. Two additives for the coprecipitation were tried to improve the dispersibility, in other words, to improve grindability during the milling process. One was NaOH solution, and the other was ammonium sulfate. Adding NaOH solution decreased the crystallization temperature, leading to smaller particles after the milling process. TEM observation revealed that the Bi-YIG particles with the size of 20-40 nm were well dispersed in the case of the coprecipitation using NaOH and ammonium sulfate while coagulations exist in the case of the conventional process. The difference in the dispersibility led to the reduction in the absorption coefficient and the increase in the Faraday rotation. The maximum value of figure of merit reached 4.8, which is twice or higher than the conventional one.