JPS6234701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a glass fiber for optical transmission characterized by a glass material and a method for manufacturing the same.

As this type of raw glass, glass containing silicic acid as a main component has conventionally been widely used. especially
Glass in which GeO ₂ is added to SiO ₂ is suitable because it hardly absorbs light with wavelengths in the visible to near-infrared region. In addition, since raw materials with high vapor pressure near room temperature such as SiCl ₄ and GeCl ₄ are available, vapor phase synthesis is used to produce a transparent glass body by sintering a deposit of fine glass particles synthesized by vapor phase reaction of glass raw materials. According to this method, there is little chance of contamination during the synthesis process, and glass of extremely high purity can be easily obtained, which is advantageous in terms of optical transmission loss. Since SiO ₂ has excellent mechanical strength and weather resistance, fibers with a cladding of SiO ₂ and a core of SiO ₂ glass doped with GeO ₂ are often used.
In reality, there are many problems.

One of the problems is that gas-phase synthesis methods (e.g.
As shown in No. 31291 and No. 56-33327
(vapor phase axis method using H ₂ / O ₂ flame reaction)
When synthesizing SiO ₂ −GeO ₂ glass with an increased GeO ₂ concentration, first a particulate glass deposit (referred to as a soot body) is synthesized, and this is sintered to obtain a transparent glass body. During the synthesis process, there are many opportunities for the formation of GeO ₂ microcrystals, and a glass particulate (referred to as soot) containing the GeO ₂ microcrystals is obtained. These GeO ₂ microcrystals are usually preserved during the sintering process, and when the core material and quartz tube are combined to form a fiber, they are exposed to high temperatures of approximately 2000°C, so the vapor pressure of these microcrystals increases. foaming occurs in the glass, which becomes a low-viscosity substance. Usually, this tendency becomes noticeable when the refractive index of GeO ₂ -doped SiO ₂ glass becomes 1% or more (at this time, the GeO ₂ concentration is about 15% by weight). This trend is also due to other factors other than GeO ₂ concentration.
This is noticeable in areas where the surface temperature of the soot body is low during soot body deposition (the outer periphery of the soot body). For this reason, it is particularly difficult to obtain a good optical fiber in which the difference in refractive index between the core and the cladding is high and the refractive index distribution of the core is close to that of a step type. The above also applies to so-called graded optical fibers, where the refractive index difference is about 1% and the refractive index distribution is a square curve.
Microcrystals of GeO ₂ may be formed, which may create unnecessary microscopic spaces in the fiber or cause fiber diameter variations.

Other problems with SiO ₂ and GeO ₂ glasses include:
As the GeO ₂ concentration increases, the above-mentioned crystallization and GeO ₂ concentration fluctuations increase, and if the core of an optical fiber is made of this, light scattering loss called Ray-Ray scattering increases and optical transmission characteristics deteriorate. There is also.

Another problem with optical fibers with SiO ₂ -GeO ₂ glass as the core and SiO ₂ glass as the cladding is that SiO ₂ glass doped with GeO ₂
As the SiO ₂ concentration increases, the difference in viscosity between the cladding and the SiO ₂ glass increases, which causes a problem in that the core shape changes during drawing. for example
The average GeO ₂ concentration is approximately 20% by weight (if the radial concentration distribution is squared, the central peak concentration is
SiO ₂ core glass (40%) is SiO ₂
In the process of drawing in combination with a tube, the heating section receives an external force that causes the core to be squeezed away from the cladding layer, making it difficult to obtain a predetermined core diameter-to-cladding diameter ratio. In many cases, the core is distorted and deviates from a perfect circle. Therefore, it is difficult to obtain a good optical fiber with an average core-clad refractive index difference of 1.5% or more (if the distribution shape is a square curve, the central peak value is 3.0%). There was a problem.

The present invention has been made in view of the above problems.
The purpose is to provide glass for optical fibers that has no bubbles in the cross section of the optical fiber, has a perfectly circular core diameter, has excellent dimensional accuracy, weather resistance, mechanical strength, and has excellent transmission characteristics. be.

Another object of the present invention is to provide a glass that can be easily formed into a so-called high-NA fiber with excellent characteristics, especially a fiber having a large core-cladding refractive index difference.

The present invention provides an optical fiber consisting of a core and a cladding, in which the average composition (weight %) is 65≦SiO ₂ ≦85 5≦GeO ₂ ≦20 5≦Al ₂ O ₃ ≦15 0≦F≦3; The present invention relates to an optical fiber characterized by having a cladding made of SiO ₂ or F-containing SiO ₂ .

In the above core glass composition, if the GeO ₂ content is greater than 20% and the Al ₂ O ₃ content is less than 5%, the glass tends to crystallize, resulting in bubbles on the cross section of the optical fiber and wires. When pulled, the dimensional accuracy of the core diameter is poor and it is difficult to form a perfect circle.

If Al ₂ O ₃ is greater than 15%, sufficient solid solution of Al ₂ O ₃ will not occur in the glass, and transparent glass will not be obtained by normal sintering.

If the GeO ₂ content is less than 5%, a sufficient difference in refractive index between the core and the cladding cannot be obtained, and a stable optical fiber cannot be constructed.

Although it is possible to construct an optical fiber having the above-mentioned advantages without the content of F, an optical fiber with good optical transmission characteristics can be obtained by containing F.
In particular, when producing a focusing type (referred to as GRIN) optical fiber according to the present invention, good band characteristics can be achieved by incorporating fluorine so that the refractive index value at the outer periphery of the core region matches the refractive index value of the cladding. Optical fibers can be obtained in which the core or cladding can contain fluorine.

In the case of the present invention, by containing fluorine as described above, an optical fiber with good band characteristics can be obtained, and transmission loss in a long wavelength band can also be reduced. However, the content in the core is 3%
If the amount is larger than this, in the case of the present glass composition, it is not preferable because it adversely affects the refractive index value and the hardness of the glass. For the outer layer of the cladding, SiO ₂ glass that does not contain fluorine is advantageous in terms of mechanical strength, weather resistance, etc.

FIGS. 1A and 1B show examples of the refractive index distribution and dopant concentration (wt%) distribution of the focusing optical fiber according to the present invention.

FIG. 1A relates to a fiber structure in which F-containing SiO ₂ is arranged around the core of the cladding region, and the outside thereof is made of SiO ₂ . As mentioned above, this fiber has extremely good band characteristics and transmission loss characteristics, and is also excellent in terms of mechanical strength, weather resistance, etc. In the case of the present invention, the fluorine content concentration in the cladding region is desirably 3% by weight or less in view of physical property matching between the core glass and the outermost SiO ₂ cladding glass. In Figure 1B, the cladding is SiO ₂ and the core is SiO ₂ −GeO ₂ −
The present invention relates to a fiber structure made of glass made of Al ₂ O ₃ -F.

In the above description, the effects of the present invention can basically be achieved even if a part of Al ₂ O ₃ is replaced with Ga ₂ O ₃ . This is because Al and Ga have similar effects on the physical properties of glass and can be substituted. If the content of Ga ₂ O ₃ is increased relative to Al ₂ O ₃ , the difference in refractive index can be increased, but crystallization becomes easier. The Ga ₂ O ₃ concentration condition is preferably in a range of 10% by weight or less.

All of the oxide components of the present invention can be produced in a gas phase reaction to obtain the high purity raw materials necessary to obtain the products. It is possible to obtain glass with extremely low light absorption in the visible to near-infrared region.

Example 1 Using SiCl ₄ , GeCl ₄ , Al(CH ₃ ) ₃ , and SiF ₄ as raw materials for glass synthesis, these raw materials were introduced into a flame in a vapor phase to synthesize a deposit of fine glass particles, By sintering this, that is, using the vapor phase axial method, the average composition of the cylindrical glass base material is
SiO ₂ = 84% GeO ₂ = 7.5% Al ₂ O ₃ = 6.8% F =
1.7% (however, for GeO ₂ , the concentration distribution in the radial direction of the base material has a square curve) was synthesized. This was enlarged into a glass rod with an outer diameter of 10 mm. On the other hand, the outer diameter is 25.5mm and the inner diameter is 11mm.
A core glass rod was inserted into the quartz tube and drawn in a furnace with a heater temperature of approximately 2000°C to produce a fiber with an outer diameter of 125 μm. The outer diameter variation of this fiber was 125 μm ± The wire diameter remained at 0.5 μm, and no local variations in wire diameter were observed over the entire length of approximately 20 km. Moreover, the core shape of the fiber cross section was a perfect circle. Also, as a wavelength characteristic of optical transmission loss,
It has a characteristic of 0.5dB/Km or less at wavelengths of 1.50 to 1.65μm, and a 6dB reduction band characteristic of 1.3
A product with a wavelength of 500MHz/Km or more in the μm wavelength band was obtained.

Example 2 Using the same vapor phase axial method as in Example 1, the average composition of the cylindrical glass base material was SiO ₂ = 66%, GeO ₂
A core glass having Al ₂ O ₃ = 20% (however, the GeO ₂ concentration distribution in the cross section was shaped almost like a fourth power curve) was synthesized. This was enlarged into a rod-shaped glass with an outer diameter of 10 mm, and the outer diameter was 15 mm and the inner diameter was 11.5 mm.
A quartz tube was prepared, and a fiber with an outer diameter of 140 μm was made using the same method as in Example 1. The refractive index difference between the core and cladding is approximately 3.0% at the center of the fiber cross section.
I got something. The outer diameter variation of this fiber is
There were two locations over a total length of 5 km where the wire diameter varied by ±3 μm or more compared to 140 μm. Moreover, the core was perfectly round.

Comparative Example 1 Using the same method as in Example 2, the average composition of the core was SiO ₂ = 70%, GeO ₂ = 30% (however, the refractive index distribution in the cross section was shaped to have almost the same distribution as in Example 2). A fiber with an outer diameter of 140 μm was fabricated. As for the variation in the outer diameter of this fiber,
Local wire diameter fluctuations of ±3μm or more are 5Km in total length.
There were 15 cases total. When the cross section of the fiber at the point where the wire diameter fluctuated was observed under a microscope, a space with an outer diameter of approximately 10 μm was observed at the interface between the core and the cladding.
Also, regarding the shape of the core, the long axis to short axis is 1:0.8
It had an elliptical shape.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of the refractive index distribution and dopant concentration distribution of a focusing optical fiber according to the present invention. FIG. It is a fiber with a cladding of ₂ .

Claims (1)

[Claims] 1. In an optical fiber glass consisting of a core and a cladding, the average composition of the core region is
65-85% by weight of silica calculated as SiO ₂ and GeO ₂
5 to 20% by weight of germanium oxide in terms of
It is a glass containing 5 to 15% by weight of Al ₂ O ₃ and 0 to 3% by weight of F, and the cladding contains SiO ₂ or F.
Glass for optical fibers characterized by being SiO ₂ glass. 2. The average of the core area, which is characterized in that the core glass is synthesized using a vapor phase synthesis method in which a deposited body of particulate glass synthesized by subjecting glass raw materials to a vapor phase reaction is sintered to form a transparent glass body. The composition is
65-85% by weight of silica calculated as SiO ₂ and GeO ₂
5 to 20% by weight of germanium oxide in terms of
It is a glass containing 5 to 15% by weight of Al ₂ O ₃ and 0 to 3% by weight of F, and the cladding contains SiO ₂ or F.
A method for manufacturing optical fiber glass consisting of a core and a cladding, which is SiO ₂ glass.