| 摘要 |
PURPOSE:To obtain an optical fiber composed of a core having desired elliptic shape and a clad having nearly circular circumference, by heating and collapsing a part of a thin-walled glass tube to make a solid rod, and heating the solid rod under definite reduced pressure while shifting the heating spot of the rod to obtain a preform rod. CONSTITUTION:A quartz tube is heated to reduce its radius and ticken its wall thickness. A thin glass layer (e.g. composed of 30mol% of GeO2 and 70mol% of SiO2 and having a thickness of 10mum) which forms a core is deposited to the inner wall of the tube by chemical deposition. The both ends of the glass tube thus prepared are attached to a glass lathe, and a part of the tube 1 is heated with an oxyhydrogen burner 2 and collapsed. One open end of the glass tube is connected to a vacuum tank 4, and the tube is evacuated to a definite pressure by controlling the vacuum control valve 6. A solid preform rod is obtained by shifting the oxyhydrogen burner 2 at a constant speed rotating the quartz tube at a constant rate. An optical fiber obtained by heating and drawing the preform rod thus obtained, has a core having nearly similar elliptic shape to the shape before drawing and an essentially circular circumference having an ellipticity of no more than 1-2% regardless of its original shape. |
