First Optical Glasses

Viable glass fibers for optical communication are made from glass of an extremely high purity as well as a precise refractive index stmcture. The first fibers produced for this purpose in the 1960s attempted to improve on the quahty of traditional optical glasses, which at that time exhibited losses on the order of 1000 dB/km. To achieve optical transmission over sufficient distance to be competitive with existing systems, the optical losses had to be reduced to below 20 dB/km. It was realized that impurities such as transition-metal ion contamination in this glass must be reduced to unprecedented levels (see Fig. 

This soft, silver white metal reacts with air and water. The oxide is applied in optical glasses with high refractive indices (special lenses for powerful cameras and telescopes). Used for special effects in optoelectronics and electronics. Lanthanum exhibits catalytic properties. It is a component of flint and battery electrodes. Lanthanum boride (LaB6) is the superior electron-emitter for electron microscopes. Lanthanum is the first of the series of 14 lanthanides, also called the "rare-earth" metals, whose inner N shells are filled with electrons. They do not belong on the "red list" of endangered species they are neither rare nor threatened with depletion. China is particularly rich in lanthanide ores. 

Table 1. Properties of the glasses studied. The manufacturer s data for HK.l for the first three glasses are very different from our results, probably since the former were adjusted for optical resolution limits in accordance with ASTM C 730.

Table 1 has our HK values for 0.98 N (the customary load in the world hardness standards) as well as the manufacturers own data. The BK-7 borosilicate crown hardness at 0.98 N concurs since neither the manufacturer nor we applied a correction factor for optical resolution limits. In contrast, our hardnesses do not agree with the manufacturer s listings for the first three glasses, possibly since the manufacturer... 

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