# US 4,392,715 A · Optical fiber

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- Number: US 4,392,715 A
- Document ID: US4392715A
- Status: Granted
- Kind: A
- Application number: 06/122,088
- Filed: 1980-02-19
- Granted: 1983-07-12
- Earliest claimed: 1979-02-27
- Assignees: Heraeus Quarzschmelze GmbH
- Inventors: Hans-Ulrich Bonewitz; Albert Muhlich; Karlheinz Rau
- Web page: https://patentgrep.com/patent/US4392715A

## CPC

- G02B 6/03633: {arranged - -}
- C03C 25/105: Organic claddings
- G02B 6/02: Optical fibres with cladding {with or without a coating}
- G02B 6/02033: {Core or cladding made from organic material, e.g. polymeric material (G02B1/04 takes precedence)}
- G02B 6/0285: {Graded index layer adjacent to the central core segment and ending at the outer cladding index}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- C03C: CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS

## Abstract

In an optical fiber having a core whose material consists essentially of vitreous silica, said core having a jacket of plastic which is optically effective at least on a length of 10 m reckoned from the light input end of the fiber and which has a refractive index n.sub.M which is smaller than that of the core, the improvement wherein the core has an outer layer whose refractive index n.sub.ext is smaller than the refractive index n.sub.K of the remaining inner core portion which is constant and greater than the refractive index n.sub.M of the jacket, and n.sub.ext lies in the range from n.sub.K -(n.sub.K -n.sub.M). (0.25 to 0.8) and whose thickness amounts to between 0.8 .mu.m and 8 .mu.m.

## Claims

### Claim 1

In an optical fiber having a core consisting essentially of vitreous silica, said core having jacket of plastic which is optically effective at least on a length of 10 m reckoned from the light input end of the fiber and which has a refractive index n.sub.M which is smaller than that of the core, the improvement wherein said core consists essentially of an inner portion and an outer portion, which are integral with one another and differ with respect of their refractive indices, said outer portion consisting essentially of vitreous silica having a refractive index n.sub.ext which is smaller than the refractive index n.sub.K of the remaining inner portion but greater than the refractive index n.sub.M of said jacket, said vitreous silica of said core consisting essentially of synthetic vitreous silica made from silicon halides, the OH-content of said synthetic vitreous silica amounting to less than 10 ppm, and wherein n.sub.ext lies in the range from n.sub.K -(n.sub.K -n.sub.M).multidot.(0.25 to 0.8), the thickness of said outer portion amounts between 0.8 .mu.m to 8 .mu.m and the thickness of said inner portion is greater than the thickness of said outer portion.

### Claim 2 (depends on 1)

Fiber of claim 1, wherein the refractive index of the outer layer of the core is constant over the entire layer thickness.

### Claim 3 (depends on 1)

Fiber of claim 1, wherein the refractive index of the outer layer of the core diminishes with increasing distance from the core axis.

### Claim 4 (depends on 1)

Fiber of claim 1, wherein the outer layer of the core consists essentially of fluorine- or boron-doped vitreous silica.

### Claim 5 (depends on 1)

Fiber of claim 1, wherein the inner core portion consists essentially of vitreous silica doped with a substance which increases the refractive index thereof.

### Claim 6 (depends on 1)

Fiber of claim 1, wherein the outer layer of the core consists essentially of vitreous silica and the inner core portion consists essentially of vitreous silica doped with a substance which increases the index of refraction.

### Claim 7 (depends on 1)

Fiber of claim 1, wherein the outer layer has a refractive index n.sub.ext which lies in the range of n.sub.K -(n.sub.K -n.sub.M).multidot.(0.4 to 0.6) and its thickness amounts to 2 to 6 .mu.m.

### Claim 8 (depends on 1)

Fiber of claim 1, characterized in that the plastic jacket consists of silicone resin or polytetrafluoroethylene.

### Claim 9 (depends on 1)

An optical fiber according to claim 1 wherein said inner portions's thickness is between 50 and 500 .mu.m.

### Claim 10 (depends on 9)

An optical fiber according to claim 9 wherein the refractive index of the inner portion is between 1.4439 and 1.4731 and is constant.

### Claim 11 (depends on 10)

An optical fiber according to claim 10 wherein said outer portion's refractive index is between 1.4597 and 1.3592.