PURPOSE: To make the manufacture of a long-sized fiber economical and the composition uniform by forming a polycrystalline preform of ionic crystals, melting the tip minute part of the preform to grow a single crystal, and manufacturing an optical fiber.
CONSTITUTION: A barrel 11 is filled with powdered ionic crystals 12 of alkali metallic halide or the like, and by pressing the crystals 12 with a ram 14 while heating the barrel 11 with a heater 13, a polycrystalline preform 16 is formed in a cylinder 15. At this time, the ionic crystals are kept at a temp. slightly below the m.p. in the vicinity of the outlet of the barrel 11. The cylinder 15 is then connected to a mouthpiece member 21, the preform 16 is pressed with a ram 23 while heating the member 21 with a heater 22, and a single crystalline optical fiber 24 is drawn from the tip of the member 21. At this time, the ionic crystals are kept at a temp. above the m.p. only in the vicinity of the tip of the member 21.
FUKUDA OSAMU
SANADA KAZUO
