JPH0518768B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transparent precursor of a base material for optical fiber, and in particular to a precursor that can be commonly used in the production of base materials for optical fiber with various design values. The purpose is to provide.

Optical fibers basically consist of a central core layer and a cladding layer surrounding it, and it is necessary that the core diameter and cladding diameter be precisely controlled. In particular, in a single mode fiber, the core cladding diameter is λ _c = 2πa/2.405√ ₁ ² − ₂ ² λ _c : cutoff wavelength a : core diameter n ₁ : refractive index of the core n ₂ : cutoff expressed by the refractive index of the cladding. It is important to match the wavelength to the design value.

The above cutoff wavelength is selected depending on the wavelength used, and in this case, the ratio of the core diameter to the cladding diameter needs to be precisely controlled with different dimensions depending on the respective design values. .

For the above reasons, it is necessary to accurately control the core clad diameter of the optical fiber base material (core clad rod).
In view of these technical issues, research is currently underway into an advantageous manufacturing method for optical fiber base materials.

As a result of extensive research, the present inventors have found that in order to obtain an optical fiber base material in which the core diameter and cladding diameter are precisely controlled, the base material consists of a core center layer and a cladding layer surrounding the core. A transparent precursor for a single-mode optical fiber base material, the layer thickness of which is 10 to 80% of the cladding thickness required for a single-mode optical fiber base material;
Also, it has been found that it is extremely convenient to prepare in advance a transparent precursor for the base material for multimode optical fiber, which has a clad thickness of 3 to 60% of the required cladding thickness for the base material for multimode optical fiber. Completed the invention.

The transparent precursor of the optical fiber base material proposed by the present invention can be obtained by: (1) depositing and vitrifying a required amount of soot for the core cladding in accordance with the core cladding diameter of the intended optical fiber; (2) Can be used in common when manufacturing optical fiber base materials of any design value; (3) Consists of only a core. Since a cladding layer is provided, handling is not required to be as strict as compared to the conventional method, and it has the advantage of being easier to ship as is or to send to the next process.

The transparent precursor of the present invention is produced by depositing silica particles generated by flame hydrolysis of a glass forming material on a substrate to form a core layer and a cladding layer, and then dehydrating, vitrifying and cooling the core cladding soot. manufactured by The method for depositing soot for the core cladding is to flame-hydrolyze the glass raw material that will become the core part, grow the resulting soot in the axial direction, and simultaneously deposit the soot that will become the cladding part continuously around the core part. It is possible to use either a method of depositing soot, or a method of forming a core and then depositing soot to form a cladding around the core.Furthermore, even with a single burner, the peripheral region has a very low density. The method may be such that the dopant is deposited under conditions adjusted so that the dopant in the periphery is volatilized in the next vitrification step to form a cladding layer.

Compounds that can be converted into glass by flame hydrolysis include conventionally known compounds, such as silicon compounds that can be oxidized or hydrolyzed as a main component;
Examples of dopants include germanium compounds and phosphorus compounds, and silicon tetrachloride, germanium tetrachloride, phosphoryl chloride, and the like are generally used.

The core cladding soot produced as described above is then dehydrated, vitrified and cooled. This dehydration and vitrification may be performed by a conventionally known method, that is, a method of exposing to an atmosphere of halogen or halogen compound and vitrification (transparency) by heating to a sintering temperature. A transparent precursor (rod) consisting of a core-part cladding is obtained by vitrification and cooling.

In the present invention, it is necessary that the thickness of the partial cladding layer surrounding this core be adjusted to 3 to 80% of the final cladding thickness required as a base material for optical fiber. If the thickness of the partial cladding layer is thinner than this, and the remaining necessary cladding layer is formed on top of this cladding layer, a considerable amount of light power will propagate to the interface, increasing scattering loss, etc. Furthermore, the remaining required cladding layer must be formed in large quantities, which increases the error in the target final thickness. On the other hand, if it is thicker than 80%, if the distribution shape of the core part, refractive index difference, etc. fail, there will be a disadvantage in terms of manufacturing cost and loss, and the remaining cladding layer will inevitably be removed. This has the disadvantage of reducing control accuracy.

For the reasons stated above, in the transparent precursor of the present invention, the thickness of the partial cladding layer is 3 to 80% of the final cladding thickness required as a base material for optical fiber.
However, this point can be explained individually for multimode fiber and single mode fiber as follows. That is, in a multimode fiber, since the spread of optical power to the cladding portion is small, the partial cladding layer is sufficiently effective even if it is thin. In this case, the thickness is preferably 3 to 60% of the final thickness.
On the other hand, in a single-mode fiber, since the optical power is considerably spread and propagated to the cladding layer, it is preferable that the partial cladding layer is thick, and it is desirable to adjust the partial cladding layer to a range of 10 to 80% of the final cladding thickness.

The transparent precursor for optical fiber of the present invention has a partial cladding layer mainly composed of silica formed by a vapor phase method (flame decomposition method), like the core center layer,
It must be selected from silica alone or fluorine, boron, etc. with a lower refractive index than silica, and the main component must be synthetic silica glass containing low OH groups, like the core part. is desirable.

Next, a specific example will be given.

Example 1 In the center of a quartz burner with a concentric quadruple tube structure,
SiCl ₄ 105ml/min, GeCl ₄ 20ml/min, POCl ₃ , 3
ml/min of raw material gas uniformly mixed with 370 ml/min of argon gas for conveyance, and H ₂ 2.8/min on the outside.
An oxyhydrogen flame was formed by flowing Ar into each tube in the order of 0.6/min and O ₂ 5.6/min to form glass particles. The glass particles were deposited on a rotating starting material and grown in the axial direction to obtain a 50 mm diameter cylindrical soot for core cladding.

This suit for core cladding is applied to the peripheral area.
High concentration of Cl ₂ (20% by volume) sufficient to volatilize GeO ₂
After treatment, the material was vitrified in a He atmosphere and cooled to room temperature to obtain a transparent precursor consisting of a 25 mm diameter transparent glass rod core portion cladding. The refractive index distribution of this rod was approximately a square distribution with a maximum refractive index difference of about 1.0%. Also, the diameter of the core part is
The diameter was 17.5 mm, and the cladding thickness was 3.75 mm.

Reference Example 1 From the precursor obtained in Example 1 above, a 50 μm core,
In order to obtain a base material from which a 125 μm clad optical fiber could be made, soot was further deposited by an external CVD method, and the soot was vitrified to a diameter of approximately 8.5 mm to obtain a base material for an optical fiber with a diameter of 43.75 mm. .

The base material thus obtained was heated and melted in an electric furnace at 2100°C and spun to produce an optical fiber with an outer diameter of 125 μm, but the variation range of the core diameter of this fiber was
It was less than ±1 μm with respect to 50 μm.

Example 2 At the center of a quartz burner similar to Example 1,
20 ml/min of SiCl ₄ and 2 ml/min of GeCl ₄ are supplied together with argon gas for transport to deposit core soot, and the side of this soot is continuously heated with a preliminary burner to build up a 20 mmφ core soot rod. I got it. This soot rod is further used as a raw material for glass.
A clad soot was attached externally using a clad burner containing only SiCl ₄ to obtain a soot of 75 mmφ. Next, this soot was vitrified in an atmosphere with a Cl ₂ concentration of 0.5% and cooled to room temperature to obtain a transparent precursor consisting of a core portion cladding of a transparent glass rod having a core portion of 8 mmφ and an outer diameter of 35 mmφ.

Reference Example 2 The optical fiber base material precursor with a core part of 8 mmφ and an outer diameter of 35 mmφ obtained in Example 2 was drawn to an outer diameter of 15 mmφ, and then soot was attached to the outer periphery and vitrified. A base material was obtained. This base material was heated and melted in an electric furnace at 2100℃ and spun to obtain an optical fiber, which had a core diameter of
It had a cutoff wavelength of 8.4 μm and a cutoff wavelength of 1.19 μm, and was considered suitable for single mode transmission in the 1.3 μm band.

Reference Example 3 The optical fiber base material precursor with a core part of 8 mmφ and an outer diameter of 35 mmφ obtained in Example 2 was drawn to an outer diameter of 15 mmφ, and then soot was attached to the outer periphery and vitrified. A base material was obtained. This base material was spun in the same manner as in Reference Example 2 to obtain an optical fiber, which had a core diameter of 5.7μ.
m, the cutoff wavelength was 0.81 μm, and it was considered suitable for single mode transmission at a wavelength of 0.85 μm.

Claims (1)

[Claims] 1. A core layer and a cladding layer are created by depositing fine particles generated by flame hydrolysis of glass forming materials.
This is then dehydrated, vitrified, and cooled to obtain a transparent precursor consisting of a core center layer and a cladding layer surrounding the core, in which the thickness of the cladding layer is 3 times the cladding thickness required as a base material for optical fiber. ~80% transparent precursor of matrix for optical fiber.