UV light and is used for applications that require transparency in this region Large natural single crystals of quartz are pure silicon dioxide, and upon crushing are used for high quality specialty glasses Synthetic amorphous silica, an almost 100 pure form of quartz, is the raw material for the most expensive specialty glasses This type of glass can be made so pure that when combined with Germanium Oxide glass hundreds of kilometers of fibre optic cables can be manufactured which are transparent at infrared wavelengths Individual fibres are given an equally transparent core of SiO2/GeO2 glass, which has only slightly different optical properties the germanium contributing to a higher index of refraction Undersea cables have sections doped with erbium, which amplify transmitted signals by laser emission from within the glass itself Amorphous SiO2 is also used as a dielectric material in integrated circuits due to the smooth and electrically neutral interface it forms with silicon Glasses used for making optical devices are categorized using a six digit glass code, or alternatively a letter number code from the Schott Glass catalogue For example, BK7 is a low dispersion bilglass interi-rglass sikkerhetsglass