Improvements in UV transmission of all-silica optical fibers with low OH content

Abstract

All-silica fibers with an undoped core are preferred for UV- applications. There are three different types of synthetic silica for core material, differing mainly in OH-content. Up to now, only high-OH fibers seem to be suitable for UV- applications, because fibers with low-OH core material suffer from pre-existing UV-absorbing color centers due to fiber drawing and generation of these defects during UV-irradiation. With the same loading technique used for commercially available high-OH fibers the amount of initial absorption sites and the generation of color centers, especially the E'- centers, has been reduced in low-OH fibers as well. We studied the influence of this processing on the UV-performance of low- OH all-silica fibers. Besides the E'-centers at 214 and 229 nm, the concentrations of further defects at 245 nm, 265 nm and 330 nm became smaller, too. In addition, a further step of reduction takes place during additional UV-irradiation. After these two steps of improvements, the UV-transmission is in the same range compared to high-OH fiber. This UV-VIS-NIR-fiber shows a broadband transmission from 250 nm to 1.7 micrometer wavelengths, using optimized parameters during the whole multiple-step manufacturing process.