OPTICAL FIBER AND METHOD OF PRODUCING AN OPTICAL FIBER

Abstract

An optical fiber package is described comprising a light transmitting core having a core diameter, a coating layer surrounding the core, and wherein the amount of chlorine in the light transmitting core region is homogeneous and comprises at least 3000 ppm. The fiber package is such that the optical fiber core exhibits a reduction in the hydrogen induced attenuation losses. A method for fabricating the optical fiber package is also disclosed.

Claims

1. An optical fiber package comprising a light transmitting core having a core diameter, a coating layer surrounding the core, wherein the amount of chlorine in the light transmitting core region is homogeneous and at least 3000 ppm and whereby the optical fiber core exhibits a reduction in the hydrogen induced attenuation losses over operating and transmitting wavelengths in the range from 1000 nm to 1600 nm.

2. An optical fiber package according to claim 1, whereby the optical fiber core exhibits a reduction in the hydrogen induced attenuation losses at a transmission wavelength of substantially 1400 nm.

3. An optical fiber package according to claim 1, wherein the amount of chlorine in the core is in the range from 3000 ppm to 8000 ppm.

4. An optical fiber package according to claim 1, wherein the amount of chlorine in the core is in the range from 4000 ppm to 4500 ppm.

5. An optical fiber package according to claim 4, wherein the uncertainty in the amount of chlorine in the core is in the range from +/120 ppm.

6. An optical fiber package according to claim 1, wherein the chlorine in the core is uniformly distributed with a variation of less than 50% across the core.

7. An optical fiber package according claim 6, wherein the chlorine in the core is uniformly distributed with a variation of less than 20% across the core.

8. An optical fiber package according to claim 1, wherein the fiber package is drawn from a preform having a composition comprising silica SiO.sub.2.

9. An optical fiber package according to claim 8, wherein the preform includes one or more dopants selected from the range of Al, Ge, F, P present in concentrations in the range from 0 to 10000 ppm.

10. An optical fiber package according to claim 1, wherein the fiber diameter is in the range from 50 m to 500 m.

11. An optical fiber package according to claim 10, wherein the fiber diameter is in the range from 75 m to 130 m.

12. An optical fiber package according to claim 1, wherein the core diameter is in the range from 3 m to 100 m.

13. An optical fiber package according to claim 12, wherein the core diameter is in the range from 5 m to 50 m.

14. An optical fiber package according to claim 1, wherein the core comprises SiO.sub.2.

15. An optical fiber package according to claim 1, wherein the refractive index profile of the core is one selected from the range of; step profile, graded profile, n graded profile, w graded profile.

16. A method of manufacturing an optical fiber package by carrying out one or more chemical vapour deposition reactions in a substrate tube, with the optical fiber core exhibiting a low sensitivity to the hydrogen induced attenuation losses over operating and transmitting wavelengths in the range from 1000 nm to 1600 nm, the method comprising the steps of: i) providing an optical fiber substrate preform tube with glass forming precursors; ii) supplying a stoichiometric excess amount of oxygen to the tube; iii) generating a reaction in the substrate tube to form an amorphous glass layer on the interior of the tube; iv) depositing a layer of unsintered soot comprising SiO.sub.2 within the tube; v) supplying a Cl.sub.2 atmosphere; vi) sintering the glass layer in the tube; vii) collapsing the optical preform tube of step (vi) in a Cl.sub.2 atmosphere so as to form a preform; and viii) drawing an optical fiber from the preform formed in step vii) with the application of heat and tension of weight in the range 30 to 70 g and providing an optical fiber coating.

17. A method of manufacturing an optical fiber package according to claim 16, wherein the optical fiber coating comprises a coating material selected from the range; polymer, acrylate, polyimide.

18. A method of manufacturing an optical fiber package according to claim 16, wherein the sintering step vi) is performed at a temperature in the range of 1950 to 2200 C.

19. A method of manufacturing an optical fiber package according to claim 16, wherein the amount of oxygen supplied to the substrate tube in step ii) is in the range of 5 to 10 times the stoichiometric amount.

20. A method of manufacturing an optical fiber package according to claim 16, where the heating step in the draw comprises heating to 1800 to 2200 C.

21. A method according to claim 16, wherein the preform tube has a composition of <30 ppm of water.

22. A method according to claim 16, wherein the preform tube is a natural quartz material having a composition of <30 ppm of water and low chlorine.

23. A method according to claim 16, wherein the preform tube is a synthetic silica material having a composition of <30 ppm of water and low chlorine

24. A method according to claim 16, wherein the amount of chlorine in the core is at least 500 ppm.

25. A method according to claim 16, wherein the amount of chlorine in the core is at least 1500 ppm.

Description

DETAILED DESCRIPTION

[0065] An embodiment of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

[0066] FIG. 1 shows the chlorine doping profile of a chlorine doped core of an optical fiber package wherein the amount of chlorine in the light transmitting core region is not homogeneous, fiber sample here prepared without an excess of chlorine;

[0067] FIG. 2 shows the chlorine doping profile of a chlorine doped core of an optical fiber package of the present invention wherein the amount of chlorine in the light transmitting core region is homogeneous;

[0068] FIG. 3 illustrates a method of manufacturing an optical fiber package, wherein the resulting optical fiber core exhibits a low sensitivity to the hydrogen induced attenuation losses over operating and transmitting wavelengths in the range from 1000 nm to 1600 nm.

[0069] FIGS. 1 and 2 show the doping profiles of two fiber cores comprising a pure silica core doped with chlorine. The chlorine level in the core was measured using an electron microscope with a wavelength dispersive analysis system. The resolution limit of the system is <50 ppm as determined by a quartz sample, and the accuracy of measurement is 3% with a spatial resolution of 1 m or less according to scan speed (for example FIG. 1 has a spatial resolution of 200 nm and FIG. 2 is 1 um) in the optical core which has a diameter of 5 to 12 m. Concentration of chlorine is plotted against distance (m) to give an indication of the distribution of chlorine across the core region.

[0070] The profile shown in FIG. 1 corresponds to a fiber (SM1500SC(9/125)P 53008 fiber) that was doped using the method of FIG. 3 with a target chlorine doping density of the maximum that can be incorporated by supplying an excess. The excess of chlorine was not maintained in the collapse phase and therefore the chlorine doping was effectively lost from the centre of the core and was reduced from the maximum obtainable value. The plot shows two peak regions in the core where the concentration of chlorine is 3530 ppm with a clear dip in the centre where the concentration of chlorine falls to the background level (200 ppm). For comparison, the inset to FIG. 1 shows the light intensity profile of the single mode light transmitted by the core is plotted against distance (m). It can be seen that most of the light is in the centre of the core where there is very little chlorine, hence why the fiber is sensitive to hydrogen induced darkening in this central region.

[0071] The profile shown in FIG. 2 corresponds to a fiber (SM1500SC(7/125)P 53037 fiber using the method of the present invention (see FIG. 3), in particular the excess of chlorine was maintained throughout the collapse phase. Again, the Gaussian mode profile of the light is shown on the inset figure. In contrast to FIG. 1, a high density of chlorine (4040 ppm120 ppm) with uniform distribution is achieved across the core region (peak with 10 m diameter). The uniformity of the chlorine dopant should be within 30% and preferably within 10% to achieve optimum resistance to hydrogen darkening. This uniformity is achieved by ensuring that there is no oxygen flow and an excess of chlorine in the lathe during the collapse phase of the preform when the fiber is manufactured (see FIG. 3).

[0072] The SM1500SC(7/125)P 53037 fiber (FIG. 2) was tested at 300 C. in the presence of 1 atmosphere (1 atm) of hydrogen. The test results showed only 2 dB/km permanent loss near 1400 nm over 1000 hours and about 4 dB/km temporary loss near 1240 nm. On the other hand, the SM1500SC(9/125)P 53008 fiber (FIG. 1) which has non-uniform chlorine doping showed >30 dB/km permanent loss at around 1400 nm over only a few hours.

[0073] Referring to FIG. 3, there is shown a method 100 of manufacturing an optical fiber package by carrying out one or more chemical vapour deposition reactions in a substrate tube.

[0074] Firstly, an optical fiber substrate preform tube is provided containing glass forming precursors e.g. SiCl.sub.4 (101). The glass forming precursors react with an excess of oxygen supplied to the tube (102), wherein the ratio of O.sub.2 to SiCl.sub.4 is in the range of 10:1 to 5:1 (the stoichiometric amount is 1:1). This reaction forms an amorphous glass layer of pure silica soot on the interior of the tube (103).

[0075] The pure silica soot is deposited (104) using a standard modified chemical vapour deposition (MCVD) technique with a low temperature (1400 C. to 1700 C.) to allow the soot particles to be adhered to the wall, but not sintered in to glass.

[0076] The tube is then filled with a pure chlorine atmosphere (105), and the glass layer is sintered (106) at a temperature between 1950 C. and 2200 C. This incorporates chlorine into the silica structure giving a pure silica core doped with chlorine. There is still a chlorine atmosphere in steps 106 and 107.

[0077] The tube is then collapsed into a rod using standard MCVD techniques (107), but with the internal atmosphere consisting of only chlorine for all stages of said collapse. Maintaining an atmosphere of chlorine is essential to ensure there is a uniform distribution of chlorine across the core with no central dip (as seen in FIG. 1).

[0078] After collapse of the preform, an optical fiber is then drawn from the preform at a high temperature 1950 C. to 2200 C. and low tension (in the range 30-70 g) to give either a 80 m or 125 m optical fiber. The optical fiber can then be coated, for example, with polymer, acrylate or polyimide using known methods.

[0079] The resulting optical fiber package has a core that exhibits a low sensitivity to the hydrogen induced attenuation losses over operating and transmitting wavelengths in the range from 1000 nm to 1600 nm.

[0080] The method 100 is not limited in core size or external fiber diameter and can be applied to single mode and multi-mode fibers, as well as fibers with designed modal profiles.