| 摘要 |
PURPOSE:To enable the mass production of the title lens of low aberration and a wide aperture angle from a devitrifiable glass by spinning a glass fiber of an coincidal double-layered structure using a specific crucible, subjecting the fiber to ion-exchanging treatment, and removing the sheath glass. CONSTITUTION:The glass fiber-forming unit 10 is composed of the pot zone 11 having the inner chamber 12 and the outer chamber 13 and of the nozzle zone 17 of a desired length where the two zones are arranged in a coincidally double structure. The lens parent glass 20 flows down from the melt pot 14 through the inner chamber 12 into the inner nozzle 17A, while another glass of high devitrification and a similar composition to the core glass for the sheath 21 flows from the outer chamber 13 into the outer nozzle 17B and surrounds the core glass 20 at the meeting point 18. Then, the nozzle 17 is heated up to the temperature of the malted phase of the glass 20 to effect spinning of a glass fiber 22 of a double structure. The glass fibers 22 are cut into a desired length, subjected to ion-exchanging treatment in a molten salt 23 to form a refractive index distribution 24 due to the ion concentration distribution in the cross section of the fibers. Then, the glass fiber is treated with a liquid acid to remove the glass 21 by etching whereby a lens of a refractive index distribution type is obtained. |
