JPS59107940A - Optical fiber - Google Patents

Abstract

PURPOSE:To obtain an optical quartz fiber preventing an increase in the optical loss with the passage of time and having stabilized characteristics by restricting the amount of P used as a dopant to a specified range. CONSTITUTION:P is used as a dopant in an optical fiber by 0-0.5%. The optical fiber is practically used because it increases hardly the optical loss and undergoes little change with the passage of time even when used over a long term after cabling, construction or installation. The optical fiber contg. said restricted amount of P increases the loss only by <=about 0.1dB/km at 1.3mum wavelength in 20 years.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stable optical fiber in which optical loss does not increase over a long period of time after being made into a cable or after being laid or strung.

Optical transmission systems using silica-based optical fiber tables are
Since it has better characteristics and is more economical than conventional systems, it is being put into practical use in various communications including public communications. One of the greatest features of optical fibers is their low loss, and as shown in a typical example in Figure 1, 1 clB /
The optical loss is less than km, and it is already 0.8 to 0.5 dg.
Optical fibers with a loss as low as / km are becoming available in mass production. As an optical transmission system, taking advantage of this low loss property, "i (, 1.8 μm or 1.-5 μm
It is advisable to use a light source of around 5 μm, and many practical systems are currently being constructed.

However, recently, when optical fibers have been converted into cables or used for long periods of time after being installed or strung, secondary
As shown in the figure, it has become clear that optical loss increases in the wavelength band of 1.8 μm or more, which can be a major obstacle in practical use. In FIG. 2, the dotted line indicates the initial value of optical loss, and the solid line indicates the optical loss characteristic after two years.

The present invention aims to solve the above-mentioned practical obstacles.

Dopants for silica-based optical fibers include Ge to increase the refractive index, and B and F to decrease the refractive index.
is often used, and At, Ti, etc. are also being studied. Among these dopants, the use of P increases the refractive index at a small rate, but since it significantly lowers the melting point of the glass and facilitates the production of preforms, it has traditionally been used favorably. In particular, it was common to dope Ge and P together.

However, according to the research conducted by the present inventors, it is clear that the optical loss tank in the long wavelength band shown in Figure 2 is caused by changes in chemical bonds contributed by P, both at the initial value and after two years. It was found that if the amount of P doped is reduced, the optical loss tank is rapidly reduced. High-temperature heating tests are useful as a method to accurately predict the increase in optical loss over time. Figure 8 shows, as an example, the optical loss after holding a fiber core at 200°C for 40 minutes. The wavelength characteristics (characteristics shown by the solid line in FIG. 8) were measured and the results were compared with the characteristics before temperature rise (characteristics shown by the dotted line in FIG. 8). Such a temperature increase test was conducted on optical fibers with different P doping amounts, and the loss increase at 200° C. and 1.55 μm was plotted against the doping amount, and the results are shown in FIG.

On the other hand, as a result of investigating the relationship between the aging characteristics of optical cables installed in the field and the P concentration, and the relationship between the optical loss tank and the P concentration at several temperatures between room temperature and 200°C, we found that (LJ P 6 degrees (2) It was discovered that lowering the temperature lengthens the time it takes for loss to increase.

The original cable installed at the site had 0.
It is required that the loss increase is no more than 1 dB/km (wavelength: 1.3 μm), but based on this, the allowable value of the optical loss tank in the high-temperature heating test is calculated to be 1.5 μm.
The loss increase must be less than 10 dB/km. Therefore, it can be seen from FIG. 4 that the P concentration needs to be 0.5 mol % or less.

As explained above, if the optical fiber of the present invention is used,
The optical loss tank of a practical optical cable installed in a field environment can be made smaller.

[Brief explanation of drawings]

Figure 1 shows an example of the typical wavelength characteristics of an optical fiber. Figure 2 shows an example of typical aging deterioration of optical fiber loss. Figure 8 shows an example of optical fiber loss in a high-temperature heating test. FIG. 4 is a diagram showing an example of increase in optical loss. FIG. 4 is a diagram showing an example of the concentration of dopant P in an optical fiber and an optical loss tank in a temperature increase test. Patent applicant: Nippon Telegraph and Telephone Public Corporation Figure 19 Figure 2 Wavelength (μm) Figure 8 Figure 4

Claims (1)

[Claims] In a silica-based optical fiber containing LP as a dopant,
An optical fiber characterized in that the P doped cap is Ff, selected between 0 and 0.6 mol%.