JPS6227014B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a glass fiber for optical transmission with low transmission loss in a long wavelength region and a method for manufacturing the same. Recently, the development of fibers used in optical communications has progressed rapidly, and some have already been put into practical use. One of them is quartz fiber made by the M-CVD method. Until now, the core has mainly been GeO ₂ −SiO ₂ or
GeO ₂ −P ₂ O ₅ −SiO ₂ cladding is SiO ₂ , P ₂ O ₅ −SiO ₂
Or, silica-based fibers of P ₂ O ₅ -B ₂ O ₃ -SiO ₂ have been mainly studied. Regarding the transmission loss of these fibers in the long wavelength range, analysis of Rayleigh scattering loss and absorption loss due to the Suso field of infrared absorption is progressing, and these are, for example, presented by S. Sentsui et al. (Optical Communication Conference 17-
19, 1979 5.3). The present invention provides a fiber with lower transmission losses at longer wavelengths than those described above. It also provides a fiber that is resistant to radiation environments. Absorption loss in the long wavelength region (1.1 to 1.6 μm) is
First, OH
The number of groups must be reduced as much as possible, and light elements such as B and P are also not preferred as dopants.
_Dopants such _{as GeO2 , SnO2} , PbO, _As2O3 , _Sb2O3 , _Bi2O3 are preferred. In particular, to reduce the number of OH groups, M
- CVD is preferred. However, in M-CVD, the oxidative decomposition reaction and the melting and vitrification are performed simultaneously.
The dopant added to SiO ₂ is preferably a dopant that lowers the melting temperature even in a small amount. Here, the melting temperatures of the simple oxides corresponding to the above dopants are different as shown in the table below, so using the melting temperatures of the simple oxides as a guide, GeO ₂ ,
SnO ₂ and PbO are undesirable because their melting temperatures are high, and As ₂ O ₃ is difficult to dope because it is too low.

[Table] Next, from the point of view of raw materials, gases or compounds that can be easily gasified at room temperature are important in order to avoid impurity contamination of iron and copper. For example, Sicl ₄ ,
Gecl ₄ , Sncl ₄ , Pbcl ₄ , Ascl ₃ , Sbcl ₃ , and Sbcl ₅ are preferred, but Bicl ₂ and Bicl ₃ have high melting points of 163°C and 230°C, so they are not preferred. Therefore, Sb ₂ O ₃ is preferred as the dopant. However, in order to increase the refractive index difference between the core and _the cladding, it is necessary to use SiO 2 glass doped with a large amount of Sb ₂ O ₅ for the core, and use SiO ₂ glass doped with a small amount of Sb ₂ O ₅ for the cladding. . In such a case, since the core is doped with a large amount of Sb ₂ O ₅ , Rayleigh scattering loss becomes large, and it becomes difficult to match the difference in expansion coefficient between the core and the cladding. Therefore, in the present invention, we focused on the fact that F has the effect of lowering the refractive index, and by doping F in combination with Sb ₂ O ₃ , we can reduce the refractive index difference while taking advantage of Sb ₂ O ₃ 's advantage of lowering the melting temperature. and also match the melting temperature. _In this case, _Sb2O3
Since it lowers the melting temperature of synthetic glass, doping with Sb ₂ O ₃ also has the advantage of making it easier to dope with F. Such co-doping has the advantage that the amount of Sb ₂ O ₃ doped into both the core and the cladding can be reduced, resulting in lower costs. Moreover, it is further advantageous that this co-doping has almost no effect on transmission loss. Further F or Sb ₂ O ₃
Doped glasses are relatively resistant to radiation damage, and can be said to be radiation-resistant fibers, especially when the glasses are synthesized at low temperatures and thus have few structural defects. Considering the above conditions and pursuing the optimal doping amount of Sb ₂ O ₃ or F in the core and cladding, it was found that 50% of Sb ₂ O ₃ or F was doped in the core.
When mixed with ~35% by weight, the melting temperature is 1300~1100℃
The refractive index is about 1.470 to 1.530. On the other hand, when Sb ₂ O ₃ and F are mixed in the cladding in an amount of 2 to 25% by weight and more than 0 but not more than 5% by weight, the melting temperature becomes about 1350 to 1150℃, and the thermal expansion coefficient with the core increases. The difference can be suppressed to about 50%, and the difference in refractive index can be increased by about 0.3 to 3.5%. As described above, in the optical transmission glass fiber of the present invention, the high refractive index portion is made of SiO ₂ glass doped with Sb ₂ O ₃ , and the low refractive index portion is made of SiO 2 glass doped with Sb ₂ O ₃ and F.
It is characterized by being made of SiO ₂ glass. Next, a method of manufacturing the above optical transmission glass fiber will be explained. The manufacturing method utilizes the M-CVD method. First, a quartz glass tube is rotated in a glass lathe, and the outside of the tube is heated with a flame such as an oxyhydrogen flame that moves slowly on the way there and quickly on the way back. Next, a gas consisting of oxygen and the following combination is fed into the glass tube as a raw material gas. Of course, in this case, an inert gas such as He or N ₂ may be used as the carrier gas. a Sicl ₄ , Sbcl ₅ , F-containing gas (SoF ₂ or CF ₄ ,
CCl ₅ F ₂ etc.) b SiF ₄ , SbF ₅ , c Sicl ₄ , SbF ₅ d SiF ₄ , Sbcl ₅ The above gases undergo oxidative decomposition to become SiO ₂ glass co-doped with F and Sb ₂ O ₃ inside the above glass tube. It is deposited on the surface and becomes clad glass. Next, oxygen gas and Sicl ₄ and Sbcl ₅ are supplied to the inside of the glass tube as raw material gas for core glass, and oxidized and decomposed.
A SiO ₂ glass doped with Sb ₂ O ₃ is produced and deposited on top of the clad glass layer. Of course, in this case as well, an inert gas or the like may be used as the carrier gas, if necessary. The above optical transmission glass fiber can be obtained by heating a glass tube in which the core glass and clad glass are laminated to a high temperature, collapsing it, and melt-spinning it. In addition, in the above manufacturing method, Sicl ₄ , Sbcl ₅ , SiF ₄ ,
SbF ₅ , SoF ₂ , CF ₄ , CCl ₂ F ₂ etc. are easy to handle. Furthermore, although the M-CVD method was used as the manufacturing method, these raw material gases and the basic principles of the manufacturing method are not necessarily limited to those described above and can be implemented. Next, one embodiment of the present invention will be described. A quartz glass tube with an inner diameter of 16 mmφ and an outer diameter of 20 mmφ was placed in a glass lathe and heated with a moving H ₂ /O ₂ flame.
He gas is fed into Sicl ₄ at 30℃ and SbF ₅ at 90℃ at 300c.c./min and 200c.c./min, respectively, and these saturated vapors are combined with O ₂ at 1000c.c./min. Sb ₂ O ₃ −F−SiO ₂ was then fed into the above glass tube for 3 hours.
Glass was deposited on the inner surface, then Sicl ₄ at 30°C,
200% He gas in Sbcl ₅ solution at 70℃
cc/min, 200c.c./min. These saturated vapors were combined with O ₂ 1000c.c./min and fed into the above glass tube for 1 hour to layer Sb ₂ O ₃ -SiO ₂ glass on the inner surface. I let it happen. After this, the tube was crushed by heating it to a higher temperature (the movement of the H ₂ /O ₂ flame was slow).
I made a preform of 16mmφ. This was heated to 2200°C in an energized heating furnace, spun to a diameter of 150 μφ, and a primary coat was applied to form a fiber. Furthermore, it was covered with nylon to make it 0.9mmφ. The loss of this fiber was less than 1.0 dB/Km at λ = 1.55 μm, and was strong even under radiation ( ⁶⁰ Co). The optical transmission glass fiber and the manufacturing method thereof of the present invention described above have the following advantages. (i) A fiber with low loss at long wavelengths can be obtained. (ii) Easy to manufacture and low cost fibers are obtained. (iii) Fibers that are resistant to radiation can be obtained. (iv) Raw materials are cheap and easy to handle.

Claims (1)

[Claims] 1. A light characterized in that the high refractive index portion is made of SiO ₂ glass doped with Sb ₂ O ₃ and the low refractive index portion is made of SiO ₂ glass doped with Sb ₂ O ₃ and F. Glass fiber for transmission. 2 The content of Sb ₂ O ₃ in the high refractive index part is 5 to 35% by weight, and the content of Sb ₂ O ₃ and F in the low refractive index part does not exceed 2 to 25% by weight and 5% by weight, respectively. A glass fiber for optical transmission according to claim 1, characterized in that: 3 A rotating high silicate glass tube is heated from the outside by a reciprocating flame, and Si and Si are heated inside the glass tube.
SiO 2 glass containing Sb _{2 O 3} and F is laminated inside the glass tube by supplying raw material gas containing Sb and F, respectively, and O ₂ gas, and then SiCl is layered inside the glass tube. ₄ , SbCl ₅ and O ₂ gas are supplied, SiO ₂ glass containing Sb ₂ O ₃ is laminated on the glass layer, and the glass body is then melt-spun. Method of manufacturing fiber. 4 The above raw material gas is SiF ₄ or SbF ₅ , or in addition to these, the Si-containing gas is SiCl ₄ or Sb-containing gas.
SbCl ₅ , F-containing gas is SOF ₂ , CF ₄ or CCl ₂ F ₂
A method of manufacturing a glass fiber for optical transmission according to claim 3, characterized in that: