JPH0558662A - Production of parent material for optical fiber - Google Patents

Abstract

PURPOSE:To rationally produce a large-sized parent material providing a single mode optical fiber capable of securing low-loss properties, in production of the parent material for the single mode optical fiber showing a variance within a range of + or -10ps/km/nm<2> in a wavelength within a range of 1.27mum-1.57mum. CONSTITUTION:In the specified invention method, a quartz-based glass rod (glass for core and glass for part of clad) is produced by MCVD method and glass for the remainder quartz-based clad is produced on the outer peripheral surface of the above-mentioned glass rod by VAD method and/or OVD method. In a related invention method, the glass rod produced by MCVD method is subjected to etching treatment and glass for the remainder quartz-based clad is subsequently produced by VAD method and/or OVD method. The specified invention method enables high yield, scaling up and high productivity of the product and the related invention method enables, in addition to those, production of a parent material capable of forming a single mode low-loss optical fiber.

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 a preform of a single mode optical fiber used in the field of optical communication technology.

[0002]

As is well known, in an optical communication (optical transmission) system, loss characteristics and frequency characteristics of an optical fiber are basic and important factors in system design. Regarding frequency characteristics of optical fiber, in the case of multimode optical fiber,
Multimode dispersion is much larger than chromatic dispersion, and this is the main factor that determines the transmission band, whereas in the case of single mode optical fiber, there is basically no multimode dispersion.
Since the only factor that defines the transmission band is chromatic dispersion, the transmission band is extremely wide. Therefore, when performing large-capacity and high-speed communication, it is desirable to use a silica-based single-mode optical fiber that has a minimum loss in the wavelength range of 1.27 μm to 1.57 μm, for example, the wavelength of 1.55 μm. The dispersion value of such a single mode optical fiber is usually
It is set within a range of ± 10 ps / km / nm ² .

When a quartz-based material is prepared as the base material of such a single mode optical fiber, MCVD method, VAD method are used.
It is common to adopt either one of the laws.

[0004] In the MCVD method, a quartz pipe which is a starting material is heated while supplying a vapor phase glass raw material and a vapor phase dope raw material together with oxygen gas. In these cases,
A thermal oxidation reaction of the raw material gas occurs in the quartz pipe, and the glass produced by the reaction is deposited on the inner surface of the quartz pipe.By repeating this, transparent clad glass and core glass are formed on the inner surface of the quartz pipe. It is formed sequentially.
In the following, a rod-shaped optical fiber preform is obtained by intensely heating and collapsing a quartz pipe.

In the VAD method, a vapor-phase glass raw material, a vapor-phase doping raw material, oxygen gas, hydrogen gas, etc. are supplied to a burner having a multi-tube structure, and a soot-like gas produced by a flame hydrolysis reaction of each of these gases. Glass fine particles are jetted toward the end of a rotating quartz rod (target) and deposited and grown to form a rod-shaped porous glass body. The following is by dehydration and transparent vitrification of the porous glass body,
A rod-shaped optical fiber preform is obtained.

[0006]

When the base material of the above-mentioned single mode optical fiber is produced by the MCVD method, the dispersion value in the wavelength range of 1.27 μm to 1.57 μm is ± 10.
The glass for core and the glass for cladding around it have a complicated refractive index distribution so that it becomes ps / km / nm ² , but each glass in the quartz pipe is subject to size restrictions. It is technically difficult to form a glass for cladding having a complicated refractive index distribution while precisely controlling the deposited thickness of the layer, or to form a glass for core on the inner peripheral surface of the glass for cladding. Therefore, not only the base material cannot be produced at a high production rate, but also the yield rate of the base material having the required characteristics is lowered, and the size of the base material is hindered by the size of the quartz pipe.

On the other hand, VAD without using a quartz pipe
In the case of the method, a large-sized single mode optical fiber preform can be produced, but when depositing glass having a complicated refractive index distribution as described above, one step per layer is unrealistic. As a result, it is necessary to take measures to reduce the loss characteristics even as a base material of a single mode optical fiber.

In view of such technical problems, the present invention has a dispersion value of ± 1 in the wavelength range of 1.27 μm to 1.57 μm.
In producing the base material of single mode optical fiber in the range of 0 ps / km / nm ² , high yield, low loss,
It is intended to provide a method capable of increasing the size of the base material and increasing the productivity.

[0009]

According to a first aspect of the present invention, there is provided a single mode optical fiber having a dispersion value within a range of ± 10 ps / km / nm ² in a wavelength range of 1.27 μm to 1.57 μm. In the method of manufacturing a material, a silica-based glass rod containing glass for core and a part of glass for cladding is manufactured by MCVD method, and then VAD method and / or
Alternatively, the remaining quartz glass for cladding is formed on the outer peripheral surface of the glass rod by the OVD method, and the problem is solved by such means.

The related invention according to claim 2 has a wavelength range of 1.2.
Dispersion value at 7 μm to 1.57 μm is ± 10 ps / k
In a method for producing a base material for a single mode optical fiber within the range of m / nm ² , a silica-based glass rod containing a glass for core and a part of glass for cladding is produced by an MCVD method, and thereafter, The outer peripheral surface of the glass rod is subjected to etching treatment, and thereafter, the remaining quartz glass for cladding is formed on the outer peripheral surface of the glass rod through the VAD method and / or the OVD method. To solve.

[0011]

When a predetermined single-mode optical fiber preform is produced by the method of the specified invention (claim 1), a step by the MCVD method and a step by the VAD method and / or the OVD method are carried out.

As is well known, the MCVD method is a method of repeatedly depositing glass produced by a thermal oxidation reaction of a glass raw material gas and a doping raw material gas in a quartz pipe on the inner surface of the pipe to form a required transparent glass. As a post-treatment, the quartz pipe after glass deposition is collapsed into a rod shape. In the case of the method according to the specific invention, since only a part of the silica-based core glass and the clad glass is formed in the quartz pipe by the MCVD method, these glasses are formed in the quartz pipe having a size limitation. It can be formed large. When forming large glass for cores and glass for clads in this way, it is obvious that the degree of control difficulty in imparting the required refractive index distribution to these is eased, even if the refractive index distribution is complicated. However, it can be formed precisely and easily. Therefore, when the core glass and a part of the cladding glass are formed on the inner surface of the quartz pipe through the MCVD method, both the yield rate and the productivity of non-defective products are increased.

In the VAD method, as is well known, glass source gas, dope source gas, oxygen gas, hydrogen gas and the like are supplied to a burner having a multi-tube structure, and a soot-like gas produced by a flame hydrolysis reaction of each of these gases. This is a method of injecting and depositing glass fine particles toward a deposition surface of a rotating target to grow a required porous glass body. As a post-treatment, the porous glass body is dehydrated and made into transparent vitreous. As is well known, the OVD method is also a method in which a porous glass body is deposited and formed on the outer peripheral surface of a rotating glass rod according to the same principle as the VAD method, and this is made into a transparent glass. The VAD method and the OVD method have different glass deposition types, but they are substantially the same in that porous glass is deposited in layers. In the method of the specific invention, the remaining glass for cladding is formed on the outer periphery of the silica glass rod mainly by the VAD method and / or the OVD method, and the diameter of the glass rod is increased. When using the VAD method and / or the OVD method,
By the glass for the clad formed on the outer periphery of the glass rod,
Theoretically, the outer diameter of the glass rod can be increased without limitation, and in practice, the diameter can be considerably increased. Therefore, the remaining glass for cladding (porous glass body) is formed on the outer periphery of the glass rod through the VAD method and / or the OVD method, and this is dehydrated and made into a transparent glass without any particular difficulty. The glass rod is upsized, and thus a large optical fiber preform can be obtained. Of course, when the size of the glass rod is increased in this way, the complex refractive index distribution (the glass for the core and some of the glass for the clad) at the axis of the glass rod is maintained as it is, and the loss characteristic is not deteriorated.

Since the method of the related invention has the method of the specific invention as an essential part, it can be used as a base material for a single-mode optical fiber.
Similar to the above, it is possible to precisely and easily form a large base material having a complicated refractive index distribution in the axis. Moreover, in the method of the related invention, since the step of etching the outer peripheral surface of the glass rod is also interposed between the step of MCVD method and the step of VAD method and / or OVD method,
For the reasons described below, a single-mode optical fiber having a good loss characteristic (transmission characteristic) can be obtained as a base material. Generally, when a glass pipe is made by collapsing a quartz pipe after glass is deposited by the MCVD method, a hardening strain occurs in the outer peripheral portion (surface side) of the rapidly cooled glass rod, and in addition, in the subsequent handling. The outer peripheral surface of the glass rod is slightly scratched or minute impurities are attached. It has been empirically known that when an optical fiber is manufactured by directly drawing an optical fiber preform having such distortion, minute scratches, and impurities, the optical fiber transmission characteristics are deteriorated. In particular, when such a defect occurs in the main part of the optical fiber preform (the glass for core and the glass for cladding around it), it has a great influence on the transmission characteristics of the optical fiber. In the method of the related invention, as described above, since the outer peripheral surface of the glass rod made of the glass for core and the glass for part of the cladding is subjected to the etching treatment, the aforementioned defects concentrated on the outer peripheral surface are removed. .. Therefore, the optical fiber obtained by drawing the optical fiber preform after such a treatment has a high transmission characteristic (low loss property).

[0015]

EXAMPLES First, the structure of an optical fiber preform manufactured by the method of the present invention will be specifically described.

In FIG. 1, 10 is a silica-based optical fiber preform, 11 is glass for the core of the optical fiber preform 10, and 12, 13, 14, and 15 are optical fiber preforms 10.
The glass for clad of is shown respectively. In the above, the refractive index of the core glass 11 is n ₁ , the cladding glass 12
Of the cladding glass 13 is n ₂ .
₃ , the refractive index of the cladding glass 14 is n ₄ , and the refractive index of the cladding glass 15 is n ₅ , these are as shown in FIG.
As shown in the refractive index distribution chart of n ₁ > n ₃ > (n ₄ = n
₅ )> n ₂ is satisfied. As a matter of course, the single mode optical fiber obtained by drawing the optical fiber preform 10 also has the refractive index distribution shown in FIG.

The core glass 11 is made of GeO ₂ , P ₂ O.
₅ , TiO ₂ , Al ₂ O ₃ , and other doped quartz containing one or more dopants for increasing the refractive index, but B ₂ O ₃ for reducing the difference in refractive index and the difference in thermal expansion coefficient.
May also include. As a typical example of the core glass 11, SiO ₂ —GeO ₂ can be cited. The glass for clad 12 is made of F, B ₂ O ₃ ,
It is made of doped quartz containing a dopant for lowering the refractive index. As a typical example of the cladding glass 12, SiO
_2- F can be raised. Glass for clad 13
Has a lower refractive index than the core glass 11, but has a higher refractive index than the other cladding glasses 12, 14, 15 and is made of doped quartz containing the above-described high refractive index dopant. .. As a typical example of the glass 13 for cladding, SiO ₂ —GeO ₂ can be used. The cladding glasses 14 and 15 are both made of pure quartz (SiO 2).
₂ ) consists of. Of these, the glass for cladding 14
Corresponds to a quartz pipe (anhydrous synthetic quartz pipe) used in the MCVD method described later, and the glass for cladding 15
Is a transparent glass formed by forming porous glass (SiO ₂ ) by the VAD method or OVD method described later.

The optical fiber preform 10 described above has a dispersion value of ± 10 p in the wavelength range of 1.27 μm to 1.57 μm.
The purpose is to make a single-mode optical fiber in the range of s / km / nm ² , which belongs to the triple clad type based on the refractive index distribution (cladding glass 14, 1
No. 5 has the same refractive index, and thus is regarded as one glass for cladding). However, according to the method of the present invention, a single mode optical fiber preform having less than triple or quadruple or more glass for cladding can be produced according to the production means described below.

Next, a specific example and a comparative example in the case where a predetermined optical fiber preform 10 is produced by the method of the present invention and a predetermined single mode optical fiber is produced from the optical fiber preform 10 will be described. In addition, specific examples 1 and 2 described below
At the time of forming the cladding glass 15,
The D method may be replaced with the OVD method, and the VAD method and the OV method may be used.
You may use method D together.

Concrete Example 1 When a glass rod which is a main part of the optical fiber preform 10 is produced by the MCVD method, a quartz pipe corresponding to the glass 14 for cladding has an outer diameter of 200 mmφ, a thickness of 1 mm and a length of 300 mm, and is anhydrous. A synthetic quartz tube was used, which was rotatably set on a glass lathe.
The exhaust system was connected. Further, as a means for heating the anhydrous synthetic quartz tube from the outside, a glass lathe was equipped with an oxyhydrogen flame burner that reciprocates in the length direction of the quartz tube. In the case of this oxyhydrogen flame burner, the anhydrous synthetic quartz tube is heated strongly at the time of the forward movement, but at the time of the backward movement, the thermal power is low enough to keep the anhydrous synthetic quartz tube warm or less.

In the above, when each glass is formed on the inner surface of the anhydrous synthetic quartz tube by the MCVD method, the cladding glass 13, the cladding glass 12, and the core glass 11 are sequentially formed on the inner surface of the anhydrous synthetic quartz tube. accumulate.
Specifically, while the anhydrous synthetic quartz tube is being heated from the outside by the oxyhydrogen flame burner, first, the glass raw material gas SiCl ₄ and the doping raw material gas GeCl ₄ are supplied into the anhydrous synthetic quartz tube together with the oxygen gas O _2. The SiO ₂ —GeO ₂ glass produced by the thermal oxidation reaction at this time is deposited on the inner surface of the anhydrous synthetic quartz tube to form the glass 13 for cladding, and subsequently, the glass raw material gas SiCl ₄ and the doping raw material gas SF _{6 are formed.} Is supplied into an anhydrous synthetic quartz tube together with oxygen gas O ₂ , and the SiO ₂ —F glass produced by the thermal oxidation reaction at this time is deposited on the inner surface of the glass 13 for cladding to form the glass 12 for cladding. Glass source gas SiCl ₄ and dope source gas GeCl ₄ as oxygen gas O ₂
It was supplied together with the water into an anhydrous synthetic quartz tube, and the SiO ₂ —GeO ₂ glass produced by the thermal oxidation reaction at this time was deposited on the inner surface of the glass for cladding 12 to form the glass for core 11.

After depositing and forming the respective glasses 11, 12, 13 on the inner surface of the anhydrous synthetic quartz tube by the MCVD method, it is well known that the quartz tube is collapsed by an arbitrary collapse means, for example, strong heating by an oxyhydrogen flame. Then, a glass rod which is a main part of the optical fiber preform 10 is thus obtained.

When the cladding glass 15 of the optical fiber preform 10 is formed on the outer peripheral surface of the above-mentioned glass rod by the VAD method, the glass rod is set on a rotary elevating device and vertically suspended so that a plurality of flow paths are formed. Well-known multi-tube burners arranged concentrically were arranged in an inclined shape toward the outer peripheral surface of the glass rod.
After completing this preparation, when performing the first VAD method using a multi-tube burner, glass source gas SiCl ₄ , hydrogen gas H ₂ , oxygen gas O ₂ , and buffer gas Ar are supplied to each burner channel. Then, the multi-tube burner is put into a combustion state, and soot-shaped glass particles generated by the flame hydrolysis reaction in such a combustion state are jetted and deposited on the outer peripheral surface of the glass rod that is moving in the vertical direction while rotating. Let Thus,
A porous glass body was formed on the outer peripheral surface of the glass rod by the deposited glass fine particles.

The porous glass body formed on the outer peripheral surface of the glass rod is dehydrated in a high-temperature Cl ₂ -containing atmosphere, and is transparentized in a high-temperature He-containing atmosphere to obtain a glass 15 for cladding. Partial.

At this stage, the optical fiber preform 10 is stretched while being heated and stretched to a length of about 900 mm, and then the second VAD method is carried out according to the above-mentioned contents to form a porous glass body. After being formed, this was dehydrated in the same manner as described above to be transparent vitrified, and the remainder of the glass 15 for cladding was formed.

Clad glass 15 thus formed
Of the total thickness of the cladding glass 13 is 7.2
And the dimensions of the optical fiber preform 10 have an outer diameter of 60 mm.
φ, length 900 mm.

When the optical fiber preform 10 of Example 1 is drawn by a heating and drawing means, a single mode optical fiber having an outer diameter of 125 μmφ can be obtained with a length of about 200 km. On the other hand, an outer diameter of 20 mmφ obtained by the standard MCVD method,
Even if the optical fiber preform with a length of 300 mm is drawn, an optical fiber with an outer diameter of 125 μmφ can be obtained only for about 8 km.

The characteristics of the single-mode optical fiber obtained from the optical fiber preform 10 of Example 1 are as follows:
The loss characteristic in μm is 0.39 dB / km, and the wavelength is 1.
The loss characteristic at 39 μm is 3.0 dB / km and the loss characteristic at a wavelength of 1.55 μm is 0.20 dB / km, and these values are above the standard level.
The dispersion characteristic of this single mode optical fiber is 1.27 μm.
± 10 ps / km / in the wavelength range of ~ 1.57 μm
It was in the range of nm ² .

Specific Example 2 When the optical fiber preform 10 was manufactured by the same MCVD method and VAD method as in Specific Example 1, the glass rod obtained by the MCVD method was etched and then the VAD method was performed.

The etching treatment is carried out by immersing the glass rod in a solution having a glass corrosive action. The corrosive solution used here is hydrofluoric acid, a mixed aqueous solution of an aqueous solution of hydrofluoric acid and a strong acid (eg, sulfuric acid, hydrochloric acid, nitric acid, etc.), an ammonium fluoride aqueous solution, an aqueous solution of an ammonium fluoride aqueous solution and hydrofluoric acid. Examples thereof include a mixed aqueous solution of an ammonium fluoride aqueous solution and a strong acid, an aqueous mixed solution of an ammonium fluoride aqueous solution, hydrofluoric acid and a strong acid, and the like. As a specific example of the etching treatment, a glass rod obtained by the MCVD method was dipped in hydrofluoric acid to remove a portion from the surface to a depth of 0.5 mm.

After the etching treatment, the glass rod is washed by any washing means such as washing with water, washing with a neutral solution, washing with an alkaline solution to completely wash off the corrosive solution, and then 6
Clean air flow above 0 ° C, preferably above 100 ° C (eg:
Dry in contact with air and inert gas. As a specific example, the glass rod is washed with water and then the glass rod is washed with 120
It was dried by exposing it to a He stream maintained at 0 ° C.

In the following, the VAD method was mainly used to form the cladding glass 15 on the outer periphery of the glass rod in the same manner as in Example 1. The optical fiber preform 10 in the specific example 2 is the specific example 1
Similarly, the outer diameter is 60 mmφ and the length is 900 mm.

The characteristics of the single mode optical fiber obtained from the optical fiber preform 10 of Example 2 are as follows:
The loss characteristic in μm is 0.36 dB / km, and the wavelength is 1.
The loss characteristic at 39 μm is 0.60 dB / km and the loss characteristic at a wavelength of 1.55 μm is 0.19 dB / km, and these values are considerably higher than the characteristics in the first specific example. The dispersion characteristics of this single mode optical fiber are
As shown in FIG. 3, 1.27 μm to 1.57 μm
The predetermined dispersion value in the wavelength range of is secured.

Comparative Example First, a porous glass body corresponding to the core glass 11 and a porous glass body corresponding to the clad glass 12 were simultaneously synthesized via the VAD method, and this was made into a transparent glass to prepare a glass rod. did.

Then, a porous glass body corresponding to the cladding glass 13 is externally attached by the first OVD method,
After this was made into a transparent vitreous material, a porous glass body corresponding to the cladding glass 14 and the cladding glass 15 was externally attached by the second OVD method to make them transparent vitrified materials.

The optical fiber preform produced in the comparative example has an outer diameter of 25 mmφ and a length of 340 mm.

The characteristics of the single mode optical fiber obtained from the optical fiber preform of the comparative example are as follows: loss characteristic at wavelength 1.30 μm is 0.58 dB / km and loss characteristic at wavelength 1.39 μm is 4. The loss characteristics at 20 dB / km and a wavelength of 1.55 μm are 0.43 dB / km, and these values are considerably lower than the characteristics of not only the specific example 2 but also the specific example 1.

[0038]

According to the method for producing an optical fiber preform according to the specified invention, a quartz glass rod containing a glass for core and a part of glass for cladding is produced by the MCVD method, and thereafter,
Since the remaining silica-based cladding glass is formed on the outer peripheral surface of the glass rod through the VAD method and / or OVD method, the dispersion value in the wavelength range of 1.27 μm to 1.57 μm is ± 10 ps / km / nm ² . When producing the base material of single mode optical fiber within the range, high yield of products,
Larger size and higher productivity can be achieved.

In the method for producing an optical fiber preform according to the related invention, a silica-based glass rod containing glass for core and a part of glass for cladding is produced by MCVD method, and then the outer peripheral surface of the glass rod is formed. Etching, then VAD
The remaining glass for silica-based cladding is formed on the outer peripheral surface of the glass rod through the method and / or the OVD method. Therefore, when the base material of the above-mentioned predetermined single-mode optical fiber is manufactured, the high yield of the product, In addition to achieving large size and high productivity, it is possible to obtain a base material capable of producing a low loss single mode optical fiber.

[Brief description of drawings]

FIG. 1 is a sectional view of an optical fiber preform manufactured by the method of the present invention.

FIG. 2 is a refractive index distribution diagram of an optical fiber preform manufactured by the method of the present invention.

FIG. 3 is a dispersion characteristic diagram of an optical fiber preform manufactured by the method of the present invention.

[Explanation of symbols]

 10 Optical Fiber Base Material 11 Glass for Core 12 Glass for Clad 13 Glass for Clad 14 Glass for Clad 15 Glass for Clad

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location // G02B 6/00 356 A 7036-2K

Claims (2)

[Claims] 1. A method for producing a base material for a single-mode optical fiber having a dispersion value in a wavelength range of 1.27 μm to 1.57 μm within a range of ± 10 ps / km / nm ² .
A silica-based glass rod containing a core glass and a part of the cladding glass was produced by the MCVD method, and then VAD
A method for producing an optical fiber preform, characterized in that the rest of the silica-based cladding glass is formed on the outer peripheral surface of the glass rod by an OVD method and / or an OVD method. 2. A method for producing a base material for a single-mode optical fiber having a dispersion value in the wavelength range of 1.27 μm to 1.57 μm within a range of ± 10 ps / km / nm ² .
A silica-based glass rod including a core glass and a part of the cladding glass is produced by an MCVD method, and then an outer peripheral surface of the glass rod is etched, and then a VAD method and / or an OVD method is used. A method for producing an optical fiber preform, characterized in that the remaining glass for silica-based cladding is formed on the outer peripheral surface of the glass rod.