JPH0558663A - Production of parent material for optical fiber - Google Patents

Abstract

PURPOSE:To provide a method for production of a parent material for an optical fiber, capable of producing an optical fiber excellent in dispersion properties and flexural loss without injury to the intersurface of the core. CONSTITUTION:In production of a parent material of a single mode optical fiber where the core part and the clad part of a soot parent material are synthesized in the same process by VAD method, the ratio (P) of clad diameter/core diameter expressed is controlled to a value within a range of 1.0<P<1.4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber preform in which a core part and a clad part are manufactured in the same process by the VAD method.

[0002]

2. Description of the Related Art Conventionally, there is a method of manufacturing a single mode optical fiber preform by synthesizing a core portion and a cladding portion in the same process by the VAD method. This optical fiber preform is dehydrated and transparentized by heating in the next step. In this case, in order to prevent the deterioration of the transmission loss due to the diffusion of impurities into the core rod and to improve the efficiency of the clad synthesizing process, the clad diameter / core diameter ratio P is synthesized within the range of P ≧ 2.0. It was

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
When dehydrating and transparentizing the porous soot base material synthesized in the method D, GeO ₂ contained in the core diffuses into the clad portion,
In the obtained rod profile, the skirt 3 of the core expands as shown by the broken line in FIG. 1, which causes deterioration of the dispersion characteristics and bending loss of the optical fiber at the time of completion. In addition, cracks are likely to occur in the clad portion. In order to eliminate the spread of the skirt 3, it is conceivable to synthesize only the core (P = 1), make it transparent vitrified, and then synthesize the clad on the outer periphery thereof. At the interface of the core, which influences the characteristics of the optical fiber, is easily scratched, defects near the core increase, and the S wavelength becomes 1.52 μm.
There is a problem that an absorption peak due to the i-H bond occurs. 2 shows that only the core is synthesized using the VAD method,
It is a figure which shows the profile at the time of producing an optical fiber preform by synthesize | combining a clad on the outer periphery after making it transparent glass. An optical fiber obtained by drawing the same optical fiber preform is 1 atm. , 100% H ₂ , 8 at room temperature
When the transmission loss was measured after holding for 48 hours, an absorption peak exceeding 1.0 dB / km appeared at a wavelength of 1.52 μm.

An object of the present invention is to provide a method for producing an optical fiber preform capable of obtaining an optical fiber having good dispersion characteristics and bending loss without damaging the interface of the core.

[0005]

The method for producing an optical fiber preform according to the present invention is a method for producing a single mode optical fiber preform in which a core part and a clad part of a soot preform are synthesized by the VAD method in the same step. The clad diameter / core diameter ratio P is in the range of 1.0 <P <1.4.

[0006]

Since the range of the optical fiber 1.0 cladding portion diameter / core section diameter ratio P in the manufacturing method of the base material <P <1.4 of the effects of the present invention, GeO ₂ is contained in the core during dehydration transparency It is possible to reduce the spread of the skirt 3 of the core portion caused by the diffusion into the clad portion.

[0007]

EXAMPLES In the present invention, when 1.0 <P <1.4, the condition of the burner for core synthesis is changed to increase the core diameter, or the condition of the burner for clad synthesis is changed to reduce the clad diameter. FIG. 1 shows the difference in the profile of the optical fiber preform due to the difference in the clad diameter / core diameter ratio P. In the case of P = 3.2, the spread of the skirt 3 becomes larger than that in the case of P = 1.3. These optical fiber preforms are used to make the preforms that are made into optical fibers, and also the optical fiber preforms with P = 1.4, which are also spun into optical fibers. Table 1 shows the results of comparison of the diameter (MFD) and the like.

[0008]

[Table 1]

From Table 1, P = 3.2 for the same Δ _TOP (maximum relative refractive index difference) and λ c (cutoff wavelength).
Comparing the case of P = 1.3 and the case of P = 1.4, the dispersion characteristics of P = 1.3 and P = 1.4 are
Both FDs are getting smaller. In addition, when P = 1.4, the dispersion characteristics and MFD of P = 3.2 are not so different from the case of P = 1.3, so dispersion due to diffusion of GeO ₂ during dehydration and transparency Influence on characteristics is P ≧ 1.4
It can be seen that the area becomes dull. Incidentally, the reason why the skirt expansion due to the diffusion of GeO ₂ becomes smaller when P <1.4 is considered as follows. The sintering time of the outermost layer of the porous soot base material is considered to be the same if the soot has the same density and diameter. Therefore, the smaller P is, the faster the sintering near the core is completed, and therefore the diffusion of GeO ₂ stops closer to the core. That is, the spread of the hem can be suppressed small. Therefore, the dispersion characteristic can be maintained at a good value by performing the composition with P <1.4. In order to protect the interface of the core part, 1.
Since 0 <P is required, the suitability value of P for maintaining good dispersion characteristics and MFD is considered to be 1.0 <P <1.4.

[0010]

The method of manufacturing the optical fiber preform of the present invention has the following effects. ． The dispersion characteristics of the light propagating in the optical fiber are improved, and Δ
Since the dispersion standard can be satisfied even when the value is larger than the conventional value, an optical fiber with excellent bending loss characteristics can be obtained. ． By reducing the amount of the clad portion, the cracks that occur during dehydration and transparency are reduced.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method of manufacturing an optical fiber preform according to the present invention, wherein P
Explanatory drawing which shows the skirt expansion of a core peripheral part in the case of = 1.3 and in the case of P = 3.2.

FIG. 2 is an explanatory diagram showing an example of a profile of an optical fiber manufactured by a conventional method of manufacturing an optical fiber preform.

[Explanation of symbols]

 3 hem

Claims (1)

[Claims] 1. A method of manufacturing a single mode optical fiber preform in which a core part and a clad part of a soot base material are synthesized in the same step by the VAD method, and a clad part diameter / core part diameter ratio P is 1.0 <P. <1.4 range, optical fiber preform manufacturing method characterized by the above.