Method of measuring optical fiber preform

Patent metadata

Field	Value
Publication number	US-11274917-B2
Application number	US-202117213213-A
Country	US
Kind code	B2
Filing date	Mar 25, 2021
Priority date	Sep 28, 2018
Publication date	Mar 15, 2022
Grant date	Mar 15, 2022

Abstract

A method of measuring a diameter of a core portion of an optical fiber preform including the core portion having a relatively high refractive index and a clad portion having a relatively low refractive index. The method includes applying parallel light to the optical fiber preform, and measuring the diameter of the core portion from an image captured by receiving the light having transmitted through the optical fiber preform.

First claim

What is claimed is:

1. A method of measuring a diameter of a core portion of an optical fiber preform including the core portion having a relatively high refractive index and a clad portion having a relatively low refractive index, the method comprising:
preparing an optical fiber preform where when, in a section which extends from the core portion to the clad portion and in which a refractive index changes in a radial direction of the optical fiber preform, a refractive index of the clad portion is set as a reference refractive index ratio of 0.0 and a maximum value of a refractive index of the core portion is set as a refractive index ratio of 1.0, in the radial direction of the optical fiber preform, an absolute value of a ratio of a difference between a refractive index of the optical fiber preform at a first position at which the refractive index ratio is 0.25 and a refractive index of the optical fiber preform at a second position at which the refractive index ratio is 0.75 to a spacing (mm) between the first position and the second position is equal to or greater than 0.0015(/mm) when calculated according to Formula 1; and
applying parallel light to the optical fiber preform, and measuring the diameter of the core portion from an image captured by receiving the light having transmitted through the optical fiber preform;

R
=



n
0.75

-

n
0.25

r
0.75

-

r
0.25



formula
⁢

⁢
1

where:
[R] indicates the absolute value of the ratio of the difference between the refractive indexes to the spacing;
[r 0.25 ] indicates the first position by a distance (mm) from a center of the optical fiber preform;
[n 0.25 ] indicates the refractive index of the optical fiber preform at the first position;
[r 0.75 ] indicates the second position by a distance (mm) from the center of the optical fiber preform; and
[n 0.75 ] indicates the refractive index of the optical fiber preform at the second position.

2. The method according to claim 1 , wherein
the optical fiber preform has a refractive index distribution where a curve indicative of a change in refractive index ratio in the radial direction of the optical fiber preform has an inflection point on an outermore side than the first position.

3. The method according to claim 1 , wherein
a core portion equivalent diameter of a part where the optical fiber preform is substantially cylindrical is 22 mm or greater in diameter.

4. The method according to claim 2 , wherein
a core portion equivalent diameter of a part where the optical fiber preform is substantially cylindrical is 22 mm or greater in diameter.

Assignees

• Shinetsu Chemical Co

Inventors

• Urata Yuhei

Classifications

• C03B2203/22

  Radial profile of refractive index, composition or softening point · CPC title

• C03B37/018 Primary

  by glass deposition on a glass substrate, e.g. by {inside-, modified-, plasma- or plasma modified-} chemical vapour deposition {[ICVD, MCVD, PCVD, PMCVD], i.e. by thin layer coating on the inside or outside of a glass tube or on a glass rod} (C03B37/016 takes precedence; surface treatment of glass by coating with glass C03C17/02) · CPC title

• C03B37/01406

  Deposition reactors therefor · CPC title

• G01B11/08 Primary

  for measuring diameters · CPC title

• C03B2207/70

  Control measures · CPC title