Methods for manufacturing optical fiber preform and methods for manufacturing optical fiber

A method for manufacturing an optical fiber preform, the method comprising:

• a) providing a lining tube as a substrate tube, the lining tube being a pure quartz glass lining tube, the pure quartz glass lining tube having an outer diameter being 45-55 mm, a wall thickness being 2-4 mm, and a hydroxyl content being equal to or smaller than 0.10 ppm;
• b) doping and depositing by a plasma chemical vapor deposition (PCVD) or modified chemical vapor deposition (MCVD) process, comprising transporting a reacting gas comprising silicon tetrachloride and oxygen into the lining tube of a);
• introducing a fluorine-containing gas into the reacting gas for fluorine doping;
• introducing germanium tetrachloride into the reacting gas for germanium doping;
• ionizing the reacting gas, the fluorine-containing gas, and the germanium tetrachloride in the lining tube through microwaves to form plasma, depositing on an inner wall of the lining tube a glass;
• and changing flow rates of the fluorine-containing gas and the germanium tetrachloride introduced into the reacting gas to deposit a depressed cladding layer, an inner cladding layer, and a core layer in sequence to obtain a deposited lining tube;
• c) melting the deposited lining tube of b) into a solid core rod by an electric furnace;
• d) sleeving the solid core rod of c) into a pure quartz glass jacketing tube to produce an optical fiber preform, a difference between a diameter of an inner hole of the pure quartz glass jacketing tube and a diameter of the solid core rod being between 1.5 and 4 mm, wherein an effective diameter of the optical fiber preform is between 95 and 205 mm.
• e) directly drawing the optical fiber preform of d) into fibers through a fiber drawing furnace, and during the fiber drawing process, performing vacuumization between the core rod and the pure quartz glass jacketing tube, and maintaining the internal pressure between 1,000 and 10,000 Pa;
• and
• f) maintaining the fiber drawing speed of the fiber drawing furnace between 1,300 and 1,600 m/min, and during the fiber drawing process, coating a bare optical fiber with two layers of coatings, for a first coating, the modulus of the coating being between 0.8 and 1.5 MPa, and the glass transition temperature being between −55° C. and −35° C.;
• for a second coating, the modulus of the coating being between 900 and 1,100 MPa, and the glass transition temperature being between 60 and 80° C.