JPH0843663A - Dispersion shift optical fiber and its production - Google Patents

Abstract

PURPOSE:To provide a dispersion shift optical fiber with which easy reduction of a cut-off wavelength (lambdac) is possible and an increase in the bending loss characteristic by an increase in a mode field(MFD) is prevented even if this lambdac is reduced and a process for producing a porous glass base material for this dispersion shift optical fiber. CONSTITUTION:This porous glass base material for the dispersion shift optical fiber has a max. part of referactive index in a first core part and the radius a1 on its outer side and the radius a0 of the bore are 0<a1-a0<a1/100. The base material has a referactive index distribution in which the max. refractive index difference n0 of the max. value is n0>n1. This process for producing such porous glass base material comprises supplying dopants to a burner for the first core part and a burner for the second core part, heating the outer peripheral part of the first core part of the porous glass base material to be formed and providing this part with the max. part of the referactive index.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention provides a cutoff wavelength (λc) when using a 1.55 μm band dispersion-shifted optical fiber, particularly a 1.55 μm band dispersion-shifted optical fiber in the 1.3 μm band which is the existing wavelength used. Even if λc is lowered to set for the 1.3 μm band, the mode field diameter (MF
D) The present invention relates to a dispersion-shifted optical fiber that can prevent an increase in bending loss characteristics due to an increase and can easily perform this, and a method for manufacturing a porous glass preform for the dispersion-shifted optical fiber.

[0002]

2. Description of the Related Art A 1.55 structure having zero chromatic dispersion in the 1.55 μm band, which is the minimum loss wavelength range of a silica optical fiber.
Used wavelength in μm band dispersion-shifted optical fiber
In order to transmit a single mode in the 1.55 μm band, it is necessary to set the cutoff wavelength (λc) to the used wavelength or less. However, in recent years, the need for using such 1.55 μm band dispersion-shifted optical fiber in the 1.3 μm band, which is the existing wavelength used, has increased to 1.3 μm and 1.
In order to transmit a wavelength band different from the 55 μm band with one type of optical fiber, λc must naturally be 1.30 μm or less.

However, this dispersion shift optical fiber is
In order to obtain a structure satisfying the characteristics of reduced glass, a burner for depositing glass particles, a glass source gas, and H ₂
It is necessary to drastically control the refractive index distribution by changing the supply amounts of gas, O ₂ gas and inert gas, but it is very difficult to change such structural conditions, and it is completed. It wastes a lot of time and raw materials. Therefore, as a simple method without making such a large change in the refractive index distribution, simply supply the glass raw material gas for each of the core burner and the clad burner in the glass base material for 1.55 μm band dispersion-shifted optical fiber. There is a method of changing it to lower the core / clad ratio and lower λc. That is, the relationship between the core / clad ratio and λc is illustrated in FIG. 5, but as shown in the figure, for example, λc is
1.50 core / base material of dispersion-shifted optical fiber
The clad ratio is 0.168, and the core / clad ratio is about 0.135 for obtaining the preform for the dispersion-shifted optical fiber having λc of 1.20 μm. Therefore, the core / clad ratio is 0.1
In order to adjust the ratio from 68 to 0.135, either one or both of the means for reducing the supply amount of the glass raw material gas to the core burner and the means for increasing the supply amount of the glass raw material gas to the cladding burner may be used. It is known.

[0004]

However, although the method of reducing λc in the dispersion-shifted optical fiber described above is simple, there is a problem that λc is reduced and at the same time, the mode field diameter (MFD) is increased and bending loss is increased. is there. For example, FIG. 2 shows the relationship between λc and MFD and the change in bending loss, but if the core / cladding ratio is reduced and λc is changed from 1.50 μm to 1.20 μm, the MFD is 7.80 μm.
It becomes 8.57 μm from m, and it is confirmed that the bending loss at this time is larger than the bending loss of λc1.55 μm.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a dispersion-shifted optical fiber and a method for manufacturing the dispersion-shifted optical fiber, which solves the above disadvantages and problems, and the dispersion-shifted optical fiber has a maximum refractive index difference n _{1 at} the center thereof. It has a first core portion having a radius a _{1 and} a second core portion having a lower refractive index than the first core portion and a maximum refractive index difference n ₂ and a radius a ₂ on the outer periphery, and further has a first core portion on the outer periphery. In a dispersion-shifted optical fiber having a cladding with a refractive index lower than that of the two-core portion, the first core portion has a maximum refractive index portion, the outer radius of which is a ₁ , and the inner radius a ₀ is 0 <a which is characterized by having a ₁ -a ₀ <a ₁ /100 Omitashi,kyokudaibunosaidaikussetsuritsusa_n ₀ Gakakinoshiki n _0> n ₁ a is a refractive index distribution, this A method for manufacturing a porous glass preform for dispersion-shifted optical fiber is described in the first core burner, (2) Glass raw material gas, oxygen gas, hydrogen gas and inert gas are supplied to the burner for core and burner for cladding, and the glass fine particles generated by flame hydrolysis of the glass raw material gas in the formed oxyhydrogen flame are rotated up. In a method for producing a porous glass preform for optical fibers, which is deposited on a target member to produce a porous glass preform having a core part and a clad part, a dopant is supplied to a burner for a first core and a burner for a second core. Then, the outer peripheral surface of the first core portion of the formed porous base material is heated to form the refractive index distribution described in claim 1.

That is, the inventors of the present invention have made various studies as to how to easily change the refractive index distribution of the dispersion-shifted optical fiber. As a result, the first core portion having a high refractive index (maximum refractive index difference n ₁ , radius a ₁ ), a second core portion having a lower refractive index than the first core portion (maximum refractive index difference n ₂ , radius a ₂ ) on the outer periphery thereof, and a clad portion having a lower refractive index than the second core portion on the outer periphery thereof. In the dispersion-shifted optical fiber having the refractive index distribution having the maximum part of the refractive index in the first core part as shown in FIG. 1, the difference in the refractive index of the maximum part is n ₀ , the outer radius is a ₁ , and the inner radius is When a ₀ is set, this a ₁ and a _{0 are} expressed by the formula 0 <a ₁ −
a ₀ <meets a _1/100, maximum refractive index difference n ₀ of the maximum point
It has been found that the refractive index profile can be modified in a simple manner if the equation n ₀ > n ₁ is satisfied.
It is possible to obtain a dispersion-shifted optical fiber that does not increase MFD even if λc is reduced, by preventing an increase in bending loss and deterioration of dispersion characteristics by preventing or reducing MFD from increasing at the same time as decreasing c. The present invention was completed after confirming that it was possible. When n ₀ ≦ n ₁ , the MFD may increase, and the bending loss characteristic and the dispersion characteristic deteriorate. This will be described in more detail below.

[0007]

The present invention relates to a dispersion-shifted optical fiber and a method for manufacturing the dispersion-shifted optical fiber. The dispersion-shifted optical fiber is provided with a maximum portion in the first core portion of the refractive index distribution.
Are those having the effect of concentrating the electrolyte distribution of light energy propagating through the optical fiber in the center portion as shown in FIG. 2, n ₀
If n> ₁ , it is possible to concentrate sufficiently, and as shown by the relationship between λc and MFD, as shown in FIG.
Curve A changes to curve B as it is, so λc is 1.
Even when 50 μm is reduced to 1.20 μm, the MFD hardly increases as compared with the time when the maximum value is set, and may decrease depending on the degree of curve shift. However, n ₀ ≦ n
_In the case of ₁ , the concentration of light energy in the central part of the electrolytic distribution is low and the MFD is increased.

Further, a method of manufacturing a porous glass preform for a dispersion-shifted optical fiber for manufacturing a dispersion-shifted optical fiber includes rotating glass fine particles generated by flame hydrolysis of a known glass raw material gas in an oxyhydrogen flame. In a method of manufacturing a porous glass preform having a clad part by depositing on a rising target member, a dopant is supplied to the first core part and the second core part to form a first core part of the porous glass. The outer peripheral surface is heated to 500 to 1,000 ° C. to form a refractive index distribution having a maximum in the first core portion. According to this, the above porous glass preform for dispersion-shifted optical fiber can be easily formed. The advantage is afforded.

It should be noted that germanium tetrachloride is used as a dopant, and the outer peripheral surface of the first core is locally heated by a burner for the second core or a burner for heating.
The maximum portion is formed in the first core portion of the refractive index distribution that makes the concentration of dissolved GeO _{2 in} the outermost peripheral portion of the core portion extremely high.
Further, since GeO ₂ has a strong volatility, it progresses almost as gas molecules in an oxyhydrogen flame, reaches the deposition surface of the porous glass base material, is cooled, and precipitates in silica fine particles, a part of which Although it is considered that it solidifies, the concentration of solid solution GeO ₂ becomes maximum when the temperature of the deposition surface is about 800 ° C, and when it is lower than 500 ° C, the viscosity of silica fine particles becomes low, so that it is almost precipitated in the silica fine particles. If the temperature is higher than 1,000 ℃, the base material becomes dense and hardly precipitates in the silica fine particles. Therefore, this temperature is 500-1,000 ℃, preferably 700 ℃.
It is good to set it to ~ 900 ℃.

In this case, if the heating range of the outer peripheral surface of the first core portion is increased or decreased, the maximum refractive index difference n ₀ of the first core portion can be increased or decreased. However, this significantly changes the manufacturing conditions. Even if it is not necessary, it is possible to manufacture the porous glass preform for dispersion-shifted optical fibers without spending a lot of time and wasting raw materials as compared with the conventional change of the refractive index distribution.

[0011]

EXAMPLES Examples of the present invention and comparative examples will now be described.
The porous glass base material manufacturing apparatus used for manufacturing the porous glass base material for dispersion-shifted optical fiber is shown in FIG. The porous glass preform manufacturing apparatus according to FIG. 4 is provided with a burner 2 for the first core, a burner 3 for the second core, a burner 4 for the clad, and a smoke exhaust device 5 in a reaction vessel 1, and each of these burners is made of SiCl as a glass raw material. ₄ , O ₂ and H ₂ as flame forming gases and Ar gas as an inert gas are supplied, and silica fine particles are deposited on the target 6 that rotates and rises to form the porous glass base material 7.

Example 1 A porous glass preform was manufactured using the apparatus shown in FIG. 4, but in order to manufacture a porous glass preform for 1.55 μm band dispersion-shifted optical fibers with λc of 1.30 μm or less. , The position of the burner for the second core part is changed so as to locally heat the outer peripheral part of the first core part so that the local heating temperature of the outer peripheral surface of the first core part becomes 830 ° C, and λc1.30 μm. In order to achieve the following core / clad ratio, the glass raw material gas amount for the cladding burner 4 is deposited, and the glass fine particles formed in the flame of each burner are deposited on the target member 6 that rotates and rises, and the porous glass matrix is obtained. Material 7 was manufactured.

The porous glass base material produced in this manner is dehydrated in a sintering furnace to make the glass transparent and used as a glass base material for dispersion-shifted optical fibers, and then the glass base material is melted and drawn. A dispersion-shifted optical fiber was created by measuring the refractive index distribution of this optical fiber.
As shown in Fig. 5, the maximum part is formed in the core part.
c decreased from 1.48 μm to 1.17 μm, but MFD was 7.85
It was confirmed that there was almost no change from μm to 7.90 μm, and that the bending loss also hardly changed.

Example 2 A porous glass preform for a λc1.30 to 1.55 μm band dispersion shifted optical fiber was manufactured by using the same apparatus as in Example 1.
In order to locally heat the outer peripheral portion of the first core portion, the H ₂ gas flow rate of the second core portion burner 3 is increased to change the flame condition to change the temperature of the locally heated portion of the outer peripheral surface of the first core portion. 780
The glass raw material gas supplied to the cladding burner was increased to obtain a core / cladding ratio of λc of 1.30 μm or less, and a porous glass preform was manufactured.

Then, a glass base material for dispersion-shifted optical fiber was prepared in the same manner as in Example 1, and the glass base material was melted and drawn to prepare an optical fiber, and its refractive index distribution was examined. It was confirmed that the maximum part was formed in the core part as shown in Fig. 1, but when examining the fiber characteristics, it was found that it decreased from λc1.52μm to 1.21μm, but the MFD was 7.75μm. It was confirmed that there was almost no change to 7.78 μm, and the bending loss characteristics also changed.

Comparative Example 1 Using the same apparatus as in Example 1, λc 1.30 to 1.55 μm of 1.
We produced a porous glass preform for 55-band dispersion-shifted optical fiber, and increased the amount of glass raw material gas supplied to the cladding burner to obtain a core / cladding ratio of λc 1.30 μm or less. Produced a porous glass base material without locally heating the outer peripheral portion of the first core portion.

Then, a glass base material for dispersion-shifted optical fiber was prepared in the same manner as in Example 1, and the glass base material was melted and drawn to prepare an optical fiber. The refractive index distribution was examined. Almost no change was observed other than the ratio, and when the characteristics of this fiber were examined, it was found that
Was decreased from 1.50 μm to 1.2 μm, but the MFD was 7.
It was confirmed that the diameter significantly increased from 79 μm to 8.60 μm, and the bending loss in one turn of 25φ was significantly deteriorated from 0.002 dB / km to 1.505 dB / km.

Comparative Example 2 Using the same apparatus as in Example 1, 1.55 of λc 1.30 to 1.55 μm
A porous glass preform for a μm band dispersion-shifted optical fiber was manufactured. In this case, it was decided to significantly change the refractive index distribution. In this case, the desired change in the refractive index distribution could be completed. Instead, it consumes a great deal of time, raw materials, and so on.

[0019]

According to the present invention, when the porous glass preform for dispersion-shifted optical fiber is manufactured, the refractive index can be changed by simply moving the position of the second core burner or changing the gas condition. It is possible to form a maximum in the first core portion of the distribution, thereby preventing an increase in MFD even when the core / cladding ratio of the porous glass preform is decreased and the λc of the dispersion shifted optical fiber is decreased. It is possible to prevent the deterioration of bending loss characteristics. Therefore, the wavelength used is 1.
Since the 55 μm band dispersion-shifted optical fiber is used even in the 1.3 μm band, the bending loss characteristics are good even if the λc is lowered. This makes it possible to reduce the λc without degrading the bending loss characteristics by a simple method. The yield of the core member can be significantly improved without consuming a large amount of time, raw materials and labor, and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a radius r and a refractive index difference (%) of a dispersion shifted optical fiber of the present invention.

FIG. 2 is a diagram showing the relationship between the radius r and the electrolytic distribution of the dispersion-shifted optical fiber of the present invention.

FIG. 3 is a diagram showing the relationship between the cutoff wavelength (λc) and the mode field diameter (MFD) of the dispersion shifted optical fiber of the present invention.

FIG. 4 is a vertical cross-sectional view of an apparatus for producing a porous glass preform for dispersion shifted optical fibers according to the method of the present invention.

FIG. 5 is a diagram showing a relationship between a core / clad ratio and a cutoff wavelength (λc) in a conventionally known dispersion shifted optical fiber.

FIG. 6 is a diagram showing a relationship between a cutoff wavelength (λc) and a mode field diameter (MFD) in a conventionally known dispersion shifted optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Reaction container 2 ... 1st core burner 3 ... 2nd core burner 4 ... Clad burner 5 ... Smoke exhausting device 6 ... Target 7 ... Porous glass base material

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Hirasawa 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory

Claims (3)

[Claims] 1. A maximum refractive index difference n ₁ and a radius a _{1 at the} center
Of the first core portion, and a second core portion having a lower refractive index than the first core portion and a maximum refractive index difference n ₂ and a radius a ₂ on the outer periphery thereof, and further on the outer periphery thereof. In a dispersion-shifted optical fiber having a cladding with a lower refractive index, the first
Has a maximum portion of the refractive index in the core part, at its outer radius a _1, the inner radius a ₀ satisfies the equation _{0 <a 1 -a 0 <a} 1/100 below, the maximum refraction of maximum portion A dispersion-shifted optical fiber having a refractive index profile in which the index difference n ₀ is the following formula n ₀ > n ₁ . 2. A glass raw material gas, an oxygen gas, a hydrogen gas and an inert gas are supplied to the burner for the first core, the burner for the second core and the burner for the clad, and the glass raw material gas is supplied in the oxyhydrogen flame formed. A method for producing a porous glass preform for an optical fiber, wherein glass particles generated by flame hydrolysis are deposited on a target member that rotates and rises to produce a porous glass preform having a core portion and a clad portion. The refractive index profile according to claim 1 is formed by supplying a dopant to the burner for the second core and the burner for the second core and heating the outer peripheral surface of the first core portion of the porous base material to be formed. And a method for producing a porous glass preform for dispersion-shifted optical fiber. 3. A glass raw material gas, an oxygen gas, a hydrogen gas and an inert gas are supplied to the burner for the first core, the burner for the second core and the burner for the clad, and the glass raw material gas is supplied in the oxyhydrogen flame formed. A method for producing a porous glass preform for an optical fiber, wherein glass particles generated by flame hydrolysis are deposited on a target member that rotates and rises to produce a porous glass preform having a core portion and a clad portion. Of the porous glass preform formed by supplying the dopant to the burner for the second core and the burner for the second core
A method for producing a porous glass preform for dispersion-shifted optical fibers, characterized in that the outer peripheral surface of the core part is heated to a temperature in the range of 500 to 1,000 ° C. to form the refractive index profile described in claim 1. .