Attenuation measurement in glasses for optical communications: an immersion method

In fiber waveguides for optical communication losses of a few dB/km have been realized. To measure the attenuation in bulk glass rods, which are often used as starting material for fiber production, an accuracy of at least 1 dB/km is desirable. With the method reported, the losses were determined from transmission measurements on 3-cm long samples. To eliminate surface losses the samples were immersed in a liquid of about the same refractive index. For two types of synthetic vitreous silica-Suprasil 1 and Suprasil Wl-the attenuation was measured between 400 nm and 750 nm. These loss-spectra show that for Suprasil 1, with the exception of the region of OH absorption, the limit of the intrinsic losses of pure silica is reached, while Suprasil Wl shows considerably higher attenuation in the whole region. The measuring accuracy achieved so far was estimated to be about +/-1 dB/km.