Influence of light-sources on UV fiber damage measured with DIN standard 58145

Abstract

The DIN standard 58145 “Measuring method for determination of solarization effect of fused silica optical fibers” was introduced over 5 years ago to standardize the quality control for UV fibers. A deuterium lamp with a lens-based imaging system, coupling a light power density of approx. 200 µW/(cm2 nm) at 214 nm into the fiber under test, was specified as light-source. With time, the availability of new powerful broadband light-sources stimulated new applications. Further, improvements in deuterium lamps and imaging coupling systems resulted in higher light power densities. It was quickly determined that these new conditions induced different spectral and temporal UV losses, which needed to be studied. As a result, the cw-power coupled into the fibers under test, referenced at 214 nm in the original set-up, increased. We observed that two measurement systems, both assembled by the DIN standards recommendations, showed significant deviations in solarization effects at 215 nm (E’ center) and 265 nm (NBOH center). Therefore, we investigated ideal lens coupling conditions, influence of lens aging (solarization) and the influence of N2 purging of light-source and detector on permanent and transient solarization effects in fibers. A closer analysis and selective change of the spectral power between 190 nm and 260 nm wavelength coupled into silica-based fibers with undoped high-OH silica core is presented and an improved system for solarization measurements on UV fibers is recommended.