US-12623948-B2 - Optical fiber glass preform and method for drawing optical fiber glass preform

US12623948B2US 12623948 B2US12623948 B2US 12623948B2US-12623948-B2

Abstract

Provided is an optical fiber glass preform, in a preliminary step of a final drawing step, in which the optical fiber glass preform is undergone one or more drawing steps to be drawn to a final target diameter, wherein as an outer diameter of an effective portion of the glass preform is continuously measured in a longitudinal direction, and from outer diameter measurement results obtained, a regression line of y=ax+b is obtained using the least squares method with y as the outer diameter and x as a length, an absolute value of a slope a is less than or equal to 0.005 mm/mm; and a maximum value of an obtained absolute value of a curvature of the outer diameter at any given point, in the outer diameter measurement results obtained, is 0.003 or less.

Inventors

Ryo MITTA

Assignees

SHIN-ETSU CHEMICAL CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20210816
Priority Date: 20200819

Claims (5)

1 . An optical fiber glass preform, in a preliminary drawing step of a final drawing step, in which the optical fiber glass preform undergoes one or more further drawing steps to be drawn to a final target diameter, wherein an outer diameter of an effective portion of the optical fiber glass preform continuously measured in a longitudinal direction has an inclined regression line of y=ax+b obtained using a least squares method with y as an outer diameter and x as a length, wherein an absolute value of the slope a of the inclined regression line is between 0.004 mm/mm and 0.005 mm/mm, and a maximum value of an absolute value of a curvature of the outer diameter at any given point over the longitudinal direction is 0.003 mm −1 or less.
2 . The optical fiber glass preform according to claim 1 , wherein the optical fiber glass preform is then further drawn for one or more times to be processed to a final target diameter before being used in a subsequent process.
3 . The optical fiber glass preform according to claim 2 , wherein the outer diameter of the effective portion of the optical fiber glass preform in its original shape before the preliminary drawing step has an inclined regression line of y=cx+d obtained using the least squares method, wherein an obtained absolute value of the slope c is less than or equal to twice the absolute value of the slope a.
4 . The optical fiber glass preform according to claim 3 , wherein the optical fiber glass preform in its original shape is a glass preform obtained by sintering a glass microparticles deposition body produced by a VAD method or an OVD method.
5 . A drawing method of an optical fiber glass preform for drawing processing the optical fiber glass preform, by a plurality of drawing steps, to a final target diameter, wherein the optical fiber glass preform in a preliminary step of a final drawing step is drawn so that when an outer diameter of an effective portion of the optical fiber glass preform is continuously measured in a longitudinal direction, and from outer diameter measurement results obtained, a regression line of y=ax+b is obtained using the least squares method with y as the outer diameter and x as a length, an obtained absolute value of a slope a is less than or equal to 0.005 mm/mm; and a maximum value of an absolute value of a curvature of the outer diameter at any given point, in the outer diameter measurement results obtained, is 0.003 or less.

Description

The contents of the following Japanese patent application are incorporated herein by reference: NO. 2020-138370 filed in JP on Aug. 19, 2020 BACKGROUND 1. Technical Field The present invention relates to an optical fiber glass preform, and a method for drawing the optical fiber glass preform. The optical fiber glass preform is produced by, for example, the VAD method or the OVD method or the like. In this method, silicon tetrachloride and other glass raw materials are supplied to a burner together with oxygen and hydrogen gases to cause a flame hydrolysis reaction, and the resulting glass fine particles are deposited on the starting substrate to form a porous glass preform, which is then dehydrated and converted to transparent glass. The optical fiber glass preform thus obtained has an generally cylindrical shape, and after processing it to the average outer diameter, outer diameter variation, and length corresponding to the wire drawing machine, the optical fiber is obtained by drawing the wire with the wire drawing machine. The glass preform before processing has a generally cylindrical shape, but there is an outer diameter variation in the longitudinal direction. When a preform with a large outer diameter variation is wire-drawn, the clearance at the preform insertion port of the wire drawing machine changes, and the air flow in the furnace of the wire drawing machine is affected by the change, which adversely affects the quality characteristics of the obtained optical fiber. There is also a method of obtaining optical fiber glass preform with an even larger diameter by drawing the optical fiber glass preform produced by the VAD method to a approximately constant outer diameter and providing it as the core material for the OVD method. In this case, the existence of outer diameter variation in the core material causes non-uniform optical properties in the longitudinal direction of the large diameter optical fiber glass preform, which adversely affects the quality characteristics of the optical fiber obtained by wire drawing. For these reasons, it is desirable to perform drawing process on the preform so that the finished outer diameter of the preform is as uniform as possible in the longitudinal direction, and then provide it for the subsequent process. In other words, during the drawing process of the glass preform, the amount of diameter reduction is increased where the outer diameter is large, and the amount of diameter reduction is decreased where the outer diameter is small, resulting in a preform with small outer diameter variation. Glass lathes and electric furnaces are often used for the drawing process of glass preforms as described above. These devices generally consist of a heating source that heats and softens the glass preform, a chuck that grips the glass preform or a dummy rod connected to the glass preform, and a mechanism that reduces the diameter of the softened glass preform by moving the heating source or the chuck. However, there are cases where the glass preform before processing has a large outer diameter variation in the entire longitudinal direction or a local outer diameter variation in a relatively short section, and in these cases, the outer diameter variation of the finished preform after processing are also often large. In particular, glass fine particle deposits produced by the VAD method or OVD method consist of a straight body portion and tapered portions at both ends. It is a common method to obtain optical fiber glass preform by advancing it into a heating furnace with one tapered portion vertically downward, and sintering it sequentially from one end to make it transparent glass. During the process of making transparent glass, the sintered glass gradually rises upward from the bottom, causing a outer diameter variation, especially near the boundary between the lower tapered portion and the straight body portion during sintering, where the absolute value of curvature locally increases. In addition, an inclination is generated where the outer diameter tends to become thicker near the lower tapered portion and thinner near the upper tapered portion. The optical fiber glass preform is used as the original shape of the glass preform before drawing, which is then drawn to a certain outer diameter and used for the subsequent process. In particular, the original shape of the glass preform before drawing has a local outer diameter variation and outer diameter inclination toward the longitudinal direction as described above, and when trying to draw them uniformly to a constant outer diameter, local outer diameter variation and outer diameter inclination toward the longitudinal direction will remain even after drawing. To cope with this issue, it is necessary to perform the drawing step repeatedly until the outer diameter variation becomes small. For example, Patent Document 1 discloses a method for efficiently drawing optical fiber glass preforms that have a large amount of diame