Optical fiber having a low-dispersion slope in the erbium amplifier region

• US 5,878,182 A
• Filed: 06/05/1997
• Issued: 03/02/1999
• Est. Priority Date: 06/05/1997
• Status: Expired due to Term

• Current Assignee: Furukawa Electric North America Incorporated (Furukawa Electric Company Limited)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Peckham, David W.
• Primary Examiner(s): Ullah, Akm E.
• Application Number:
  US08/869,390
• Time in Patent Office: 635 Days
• Field of Search: 385/122, 385/123, 385/24, 385/127, 385/141, 250/227.28, 307/3
• US Class Current: 385/123
• CPC Class Codes: G02B 6/02233 having at least two dispersion zero wavelengths
• CPC Class Codes: G02B 6/02242 having a dispersion slope <0.06 ps/km/nm2
• CPC Class Codes: G02B 6/03627 arranged - +
• CPC Class Codes: G02B 6/03644 arranged - + -
• CPC Class Codes: H04B 10/2525 using dispersion-compensating fibres

Abstract

An optical fiber is disclosed that is suitable for use in wave-division-multiplex (WDM) systems served by Erbium-doped fiber amplifiers. The fiber has a chromatic dispersion whose absolute magnitude is at least 0.8 ps/(nm-km) over the wavelength region 1530-1565 nm, and has a dispersion slope that is less than 0.05 ps/(nm² -km). This optical fiber exhibits a loss that is less than about 0.20 dB/km and is relatively insensitive to bending; moreover, its effective area exceeds 50 μm². The optical fiber includes a core of transparent material having a maximum refractive index n₁, and a layer of transparent cladding material on the outer surface of said core having a refractive index n₂. The core includes an annular region of transparent material whose minimum refractive index, n₃, is depressed with respect to n₂. These indexes are constrained by the following equations: 0.50<(n₁ -n₂)/n₂ <0.70; and -0.30<(n₃ -n₂)/n₂ <-0.05.

Claims

1. An optical fiber having a chromatic dispersion whose absolute magnitude is greater than about 0.8 ps/(nm-km) for all wavelengths within the region 1530-1565 nm, the optical fiber comprising a core of transparent material having a maximum refractive index n₁, and a layer of transparent cladding material on the outer surface of said core having a minimum refractive index of n₂

CHARACTERIZED IN THAT

the core includes an annular region of transparent material whose refractive index, n₃, wherein n₁ >

n₂ >

n₃ and

0.50<

(n₁ -n₂)/n₂ <

0.70; and

-0.30<

(n₃ -n₂)/n₂ <

-0.05.

2. The optical fiber of claim 1 wherein the optical fiber has a dispersion slope that is less than 0.05 ps/(nm² -km) over the wavelength region 1530-1565 nm.

3. The optical fiber of claim 2 wherein the optical fiber has a dispersion slope that is 0.043±

0.005 ps/(nm² -km) over the wavelength region 1530-1565 nm.

4. The optical fiber of claim 1 wherein the chromatic dispersion is greater than +0.8 ps/(nm-km) in the wavelength region 1530-1565, and wherein

0.50<

(n₁ -n₂)/n₂ <

0.60; and

-0.15<

(n₃ -n₂)/n₂ <

-0.05.

5. The optical fiber of claim 1 wherein the chromatic dispersion is more negative than -0.8 ps/(nm-km) in the wavelength region 1530-1565, and wherein

0.60<

(n₁ -n₂)/n₂ <

0.70; and

-0.30<

(n₃ -n₂)/n₂ <

-0.20.

6. The optical fiber of claim 1 wherein the fiber is encompassed within a sheath system that includes a plastic jacket, thereby defining an optical cable.

7. A silica-based optical waveguide fiber having a material dispersion, and having a refractive-index profile preselected to generate a negative waveguide dispersion such that the overall dispersion of said fiber, equal to the sum of said material dispersion and said waveguide dispersion, has a slope that is less than 0.05 ps/(nm² -km), and has a chromatic dispersion that is greater than about +0.8 ps/(nm-km) at a given wavelength within the region 1530-1565 nm.

8. The fiber of claim 7 comprising a centrally disposed core surrounded by cladding glass, said fiber comprising the following regions named in order of increasing radius:

(i) a central core region of refractive index n₁, (ii) an intermediate region of refractive index n₃, and (iii) a cladding glass of refractive index n₂, wherein n₁ >

n₂ >

n₃.

9. The fiber of claim 8 wherein

0.50<

(n₁ -n₂)/n₂ <

0.60; and

-0.15<

(n₃ -n₂)/n₂ <

-0.05.

10. A silica-based optical waveguide fiber having a material dispersion, and having a refractive-index profile preselected to generate a negative waveguide dispersion such that the overall dispersion of said fiber, equal to the sum of said material dispersion and said waveguide dispersion, has a slope that is less than 0.05 ps/(nm² -km), and has a chromatic dispersion that is more negative than about -0.8 ps/(nm-km) at a given wavelength within the region 1530-1565 nm, said fiber attenuating light transmitted along its length, the attenuation of said fiber at 1550 nm being no greater than 0.20 dB/km.

11. The fiber of claim 10 comprising a centrally disposed core surrounded by cladding glass, said fiber comprising the following regions named in order of increasing radius:

(i) a central core region of refractive index n₁, (ii) a first intermediate region of refractive index n₃, (iii) a second intermediate region of refractive index n₄, and (iv) a cladding glass of refractive index n₂, wherein n₁ >

n₄ >

n₂ >

n₃.

12. The fiber of claim 11 wherein

0.60<

(n₁ -n₂)/n₂ <

0.70; and

-0.30<

(n₃ -n₂)/n₂ <

-0.20.

13. The fiber of claim 12 wherein

0.05<

(n₄ -n₂)/n₂ <

0.25.

14. A communications cable comprising a plurality of optical fibers enclosed within a sheath system that includes a plastic jacket, each of said fibers having an overall chromatic dispersion whose magnitude exceeds +0.8 ps/(nm-km) over the entire wavelength region 1530-1565 nm

CHARACTERIZED IN THAT

each of the plurality of fibers has a refractive-index profile preselected to generate a negative waveguide dispersion component such that the overall dispersion of said fiber, equal to the sum of a material dispersion component and the waveguide dispersion component, has a slope that is less than 0.05 ps/(nm² -km), and a loss that is no greater than 0.20 dB/km at 1550 nm.

15. A communications cable comprising a plurality of optical fibers enclosed within a sheath system that includes a plastic jacket, each of said fibers having an overall chromatic dispersion whose absolute magnitude exceeds 0.8 ps/(nm-km) in the wavelength region 1530-1565 nm

CHARACTERIZED IN THAT

each of the plurality of fibers includes a core of transparent material having a maximum refractive index n₁, and a layer of transparent cladding material on the outer surface of said core having a refractive index of n₂ ;

and

each of said cores includes an annular region of transparent material whose minimum refractive index is n₃, wherein n₁ >

n₂ >

n₃ and

16. 50<

(n₁ -n₂)/n₂ <

0.70; and

-0.30<

(n₃ -n₂)/n₂ <

-0.05.

18. The WDM system of claim 16 wherein the transmission path further includes an optical amplifier.

20. The WDM system of claim 16 wherein the transmission path further includes a second optical fiber, connected in series with the first optical fiber, the second optical fiber having a chromatic-dispersion characteristic whose slope is approximately equal to the slope of the first optical fiber, but whose magnitude is opposite in sign to the magnitude of the first optical fiber within the wavelength region 1530-1565 nm.

17. A wave-division-multiplex (WDM) system comprising:

plural sources of optical signals modulated at different wavelengths within the region 1530-1565 nanometers;

apparatus for multiplexing the optical signals at the input of the WDM system;

apparatus for demultiplexing the optical signals at the output of the WDM system;

a transmission path extending between the multiplexing apparatus and the demultiplexing apparatus, said path including a first optical fiber having a chromatic dispersion whose absolute magnitude is greater than about 0.8 ps/(nm-km) for all wavelengths within the region 1530-1565 nm, the optical fiber comprising a core of transparent material having a maximum refractive index n₁, and a layer of transparent cladding material on the outer surface of said core having a refractive index of n₂, said core including an annular region of transparent material whose minimum refractive index is n₃, wherein n₁ >

n₂ >

n₃ and

0.50<

(n₁ -n₂)/n₂ <

0.70; and

-0.30<

(n₃ -n₂)/n₂ <

-0.05.

19. The WDM system of claim 17 wherein the optical amplifier comprises an Erbium-doped fiber amplifier.