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 an optical fiber having a light transmitting core, the light transmitting core having a core diameter and a coating layer surrounding the light transmitting core, wherein an amount of chlorine in the light transmitting core is homogeneous and at least 3000 ppm by weight and whereby the light transmitting core exhibits a reduction in hydrogen induced attenuation losses when compared with light transmitting cores not comprising chlorine that is homogeneous and at least 3000 ppm by weight, the reduction in the hydrogen induced attenuation losses observed 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 light transmitting 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 an amount of chlorine in the light transmitting core is in a range from 3000 ppm to 8000 ppm by weight.

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

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

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

7. An optical fiber package according to claim 6, wherein the preform includes one or more dopants selected from a range of Al, Ge, F, P present in concentrations in a range from 0 to 10000 ppm by weight.

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

9. An optical fiber package according to claim 8, wherein the diameter of the optical fiber is in a range from 75 m to 130 m.

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

11. An optical fiber package according to claim 10, wherein the core diameter is in a range from 5 m to 50 m.

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

13. An optical fiber package according to claim 1, wherein a refractive index profile of the light transmitting core is one selected from a range of: step profile, graded profile, n graded profile, w graded profile.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) 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;

(3) 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;

(4) 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.

DETAILED DESCRIPTION OF THE INVENTION

(5) 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.

(6) 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.

(7) 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).

(8) 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.

(9) 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.

(10) 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).

(11) 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.

(12) 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.

(13) 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).

(14) 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.

(15) 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.

(16) 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.