# US 6,298,183 B1 · Optical fiber grating and manufacturing method therefor

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- Number: US 6,298,183 B1
- Document ID: US6298183B1
- Status: Granted
- Kind: B1
- Application number: 09/088,630
- Filed: 1998-06-02
- Granted: 2001-10-02
- Earliest claimed: 1997-09-11
- Assignees: Fujikura Ltd.
- Inventors: Ryozo Yamauchi; Akira Wada; Tetsuya Sakai; Nobuyuki Tanaka; Kensuke Shima; Kenji Nishide; Shigefumi Yamasaki
- Web page: https://patentgrep.com/patent/US6298183B1

## CPC

- G02B 6/02147: {Point by point fabrication, i.e. grating elements induced one step at a time along the fibre, e.g. by scanning a laser beam, arc discharge scanning (G02B6/02133 and G02B6/02142 take precedence)}
- G02B 6/02095: {Long period gratings, i.e. transmission gratings coupling light between core and cladding modes}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

An optical fiber grating is manufactured by heating intermittently an optical fiber, provided with a core having residual stress in the longitudinal direction, softening a peripheral cladding of the core, and forming spatial periodical changes for the relative refractive index-difference between the core and the cladding, in the longitudinal direction of the aforementioned optical fiber by having the index of refraction of the core change, through the releasing of the aforementioned residual stress. As a result, an optical fiber grating and the manufacturing method thereof, which do not require expensive equipment and which exhibit high productivity, and furthermore a grating characteristic which is stable over time can be provided.

## Claims

### Claim 1

A manufacturing method for an optical fiber grating comprising the steps of:
heating intermittently, with a specified spatial period in the longitudinal direction, an optical fiber provided with a core having residual stress;
softening a cladding in the neighborhood of the core; and
forming periodic changes for the relative refractive-index difference between said core and said cladding, in the longitudinal direction of said optical fiber, by releasing said residual stress to change the index of refraction of the core, to form the optical fiber grating.

### Claim 2 (depends on 1)

The manufacturing method for an optical fiber grating according to claim 1, wherein a preform is heated so that the softening temperature of the core is higher than the softening temperature of the cladding, and said optical fiber is manufactured by drawing.

### Claim 3 (depends on 1)

The manufacturing method for an optical fiber grating according to claim 1, wherein said core is composed of pure silica glass, and said cladding is composed of silica glass doped with fluorine.

### Claim 4 (depends on 1)

The manufacturing method for an optical fiber grating according to claim 1, wherein said optical fiber is a single-mode optical fiber.

### Claim 5 (depends on 1)

The manufacturing method for an optical fiber grating according to claim 1, wherein a carbon dioxide laser is used as a heating means for heating the optical fiber.

### Claim 6 (depends on 1)

The manufacturing method for an optical fiber grating according to claim 1, wherein said optical fiber grating has a period of periodic change in said relative refractive index-difference in the range of 200 to 2000 μm.

### Claim 7 (depends on 1)

An optical fiber communication system comprising an optical fiber grating manufactured according to the manufacturing method recited in claim 1.

### Claim 8 (depends on 7)

An optical fiber communication system according to claim 7, wherein said optical fiber communication system comprises a light source; an optical fiber transmission path connected thereto; a light amplifier; the optical fiber grating; and a photodetector for detecting an outgoing light from said optical fiber communication path, wherein the light amplifier and the optical fiber grating are inserted into the optical fiber transmission path.