Light-Focusing Glass Fibers and Rods

Glass fibers and rods with radially parabolic refractive-index distributions were produced by exchanging potassium ions from a salt bath or a lower-index cladding glass for thallium ions in the glass composition. A fiber 1 m long and 0.25 mm in diameter could be bent around a curve of radius 10 cm without deforming the Gaussian mode pattern; the depolarization of a laser beam was < −20 dB. The resolution of a rod 3.14 mm long and 1.0 mm in diameter with a focal length of 1.64 mm was of the order of 450 lines/mm. Attenuation (caused primarily by absorption induced by trace impurities) was 100 to 250 dB/km at 6328 Å; since further improvement with respect to loss is expected, these fiber guides are promising materials for use in long-distance optical communications.