PURPOSE:To obtain a single-mode optical fiber with a small loss and superior polarized light retentivity by temporarily sintering a porous glass base material, depositing 2 kinds of porous glass with different coeffts. of thermal expansion for applying stress at symmetrical positions, and drawing the base material after sintering. CONSTITUTION:A porous base material for a core and a porous base material for a synthetic clad are formed on a support rod in order and temporarily sintered. Gases such as H2, O2, SiCl4, BBr3 and GeCl4 are fed from torches 14, 15 to the outside of the temporarily sintered porous base material 13 to deposit porous glass 19 composed chiefly of SiO2, B2O3 and Ge parallel to the axis of the material 13. Gases such as H2, O2, SiCl4 and TiCl4 are then fed from torches 16, 17 to deposit porous glass 20 composed chiefly of SiO2 and TiO2 at right angles to the glass 19. The resulting base material is converted into transparent glass by sintering, drawn to the desired diameter, optionally clad with a glass tube for a jacket, and drawn to obtain a single-mode optical fiber.
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