JP2002003235A - Method for producing glass preform, glass preform, and optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a glass preform to be formed into an optical fiber which has a high light-resistance and allows light to have high power density after passing through it. SOLUTION: A glass preform producing method, wherein the glass preform to be an optical fiber is produced, is provided with a core formation step where a core of the glass preform is formed, and a clad formation step where a clad of the glass preform is formed around the core. The core formation step comprises a depositing step where a porous glass preform is formed by depositing fine glass particles on the periphery of a starting rod, and a sintering step where a GI type refractive index distribution, in which a refractive index continuously decreases with increase in a distance from the center of the core, is formed by sintering the porous glass preform in an atmosphere of a mixed gas containing a fluorine compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a glass preform, a glass preform, and an optical fiber.

[0002]

2. Description of the Related Art FIG. 1A and FIG.
(Yttrium-Aluminum-Garnet)
2 shows a refractive index distribution (refractive index profile) of two types of optical fibers used for transmitting laser light. Figure 1
A shows a refractive index distribution of an SI (Step Index) type optical fiber. FIG. 1B shows a GI (GradedIn).
2 shows a refractive index distribution of a (dex) type optical fiber.

As shown in FIG. 1A, the refractive index of an SI optical fiber changes stepwise at the boundary between a core and a clad.
The core has a uniform refractive index. The cladding has a uniform refractive index that is less than the refractive index of the core. Laser light is
The light propagates through the optical fiber while being totally reflected at the interface between the core and the clad.

On the other hand, as shown in FIG. 1B, the refractive index of the core of the GI optical fiber is highest at the center of the core, and continuously increases as the distance from the center of the core increases toward the boundary between the core and the clad. Decrease. Since the refractive index of the GI optical fiber changes continuously, the laser light propagates in the optical fiber while meandering around the central axis of the core.
The difference in the propagation form of the laser light described above is that the beam intensity distribution (power density distribution) of the laser light passing through the optical fiber
Have a great effect on

FIG. 2A shows a power density distribution of a laser beam passing through an SI type optical fiber. FIG.
4 shows a power density distribution of laser light that has passed through an I-type optical fiber. As shown in FIGS. 2A and 2B, the laser light that has passed through the GI optical fiber has a power density distribution approximately twice that of the laser light that has passed through the SI optical fiber at the center of the core. Have. The GI optical fiber relatively well preserves the power density distribution of light at the time of entering the GI optical fiber. Therefore, laser light that has passed through the GI optical fiber has more excellent fusing characteristics than laser light that has passed through the SI optical fiber.

That is, when the light that has passed through the optical fiber is used for welding, the welding penetration depth obtained by the laser light that has passed through the GI optical fiber is obtained by the laser light that has passed through the SI optical fiber. Deeper than the depth of penetration. For example, a laser beam passing through an SI optical fiber cannot weld an aluminum alloy, whereas a laser beam passing through a GI optical fiber is
Aluminum alloy can be welded. Since the laser light that has passed through the GI optical fiber has excellent properties,
Demand for GI optical fibers has increased in recent years.

[0007]

However, when the GI optical fiber is compared with the SI optical fiber, it is difficult to manufacture the GI optical fiber because it is difficult to control the refractive index distribution during manufacturing. Therefore, the GI optical fiber takes longer to manufacture than the SI optical fiber. Therefore, the GI optical fiber has lower productivity than the SI optical fiber.

In a conventional GI optical fiber, germanium is added to a core material, and the refractive index is increased more than that of pure quartz.
Manufactured by forming an I-type refractive index distribution. However, a GI optical fiber doped with germanium has lower light resistance than an SI optical fiber. For this reason, a GI optical fiber doped with germanium is
When used for a high power YAG laser, the strength of the optical fiber may be degraded. Therefore, when the light of the YAG laser is input, there is a possibility that the optical fiber is broken due to the passage of the high power light through the optical fiber.

Accordingly, an object of the present invention is to provide a glass preform manufacturing method, a glass preform, and an optical fiber which can solve the above-mentioned problems. This object is achieved by a combination of features described in the independent claims. The dependent claims define further advantageous embodiments of the present invention.

[0010]

According to a first aspect of the present invention, there is provided a method of manufacturing a glass preform which is a preform of an optical fiber, comprising: a core forming step of forming a core of the glass preform; A cladding forming step of forming a cladding of a glass preform around the core, the core forming step comprising: depositing glass fine particles around the starting rod to form a porous glass preform; Sintering of a porous glass base material in an atmosphere of a mixed gas containing a fluorine compound gas forms a GI-type refractive index distribution in which the refractive index decreases continuously as the distance from the center of the core increases. Sintering step.

The sintering step forms a GI type refractive index distribution by controlling the content of the fluorine compound gas in the atmosphere of the mixed gas containing the fluorine compound gas and the sintering rate for sintering the porous glass base material. Is preferred. Further, the glass base material manufacturing method, the step of recognizing the density of the porous glass base material, and the step of determining the fluorine compound gas content in the mixed gas based on the recognized density of the porous glass base material, Determining a sintering rate based on the recognized density of the porous glass matrix,
Preferably, the sintering step sinters the porous glass base material according to the determined fluorine compound gas content in the mixed gas and the determined sintering rate.

Further, the step of depositing is performed at 0.15 g / cm
It is preferred to form a porous glass preform having a density in the range of ³ to 1.0 g / cm ³ , but more preferably a density in the range of 0.15 g / cm ³ to 0.4 g / cm ³ It is preferable to form a porous glass base material having the following. Further, the sintering step reduces the content of the fluorine compound gas in the mixed gas atmosphere from 0.1 Vol% to 10 Vol%.
Is preferably controlled within the range. In addition, the sintering step is performed when the sintering speed is 5 mm / min to 10 mm / min
Is preferably controlled within the range. Preferably, the deposition step hydrolyzes silicon tetrachloride (SiCl ₄ ) and deposits it on the starting rod. The core forming step may further include forming an inner core in the outer core having a refractive index substantially equal to that of pure quartz.

A second embodiment of the present invention is a glass preform which is a preform of an optical fiber, and has a GI-type refractive index distribution in which the refractive index continuously decreases as the distance from the center increases. And a fluorine-doped cladding having a substantially uniform refractive index distribution. Preferably, an inner core having a refractive index substantially equal to that of pure quartz is further provided inside the outer core. It is preferable that the maximum value of the refractive index of the outer core is smaller than the refractive index of the inner core. Further, it is preferable that the refractive index of the cladding is smaller than the minimum value of the refractive index of the outer core. Further, it is preferable that the absolute value of the difference between the refractive index of the inner core and the refractive index of pure quartz is substantially 0.001 or less.

The optical fiber according to the third embodiment of the present invention has a G whose refractive index decreases continuously as the distance from the center increases.
A fluorine-doped core having an I-type refractive index distribution and a fluorine-doped cladding having a substantially uniform refractive index distribution. Preferably, an inner core having a refractive index substantially equal to that of pure quartz is further provided inside the outer core. It is preferable that the maximum value of the refractive index of the outer core is smaller than the refractive index of the inner core. Further, it is preferable that the refractive index of the cladding is smaller than the minimum value of the refractive index of the outer core. It is preferable that the absolute value of the difference between the refractive index of the inner core and the refractive index of pure quartz is substantially 0.001 or less. Preferably, the optical fiber is for a high-power laser. Further, the high power laser is preferably a YAG laser.

The above summary of the present invention does not list all of the necessary features of the present invention, and a combination of these features can also be an invention.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described through embodiments of the present invention. However, the embodiments do not limit the claimed invention, and all combinations of features described in the embodiments are described. Is not necessarily essential to the solution of the invention.

FIGS. 3 and 4 show an example of an apparatus for manufacturing the glass base material of the present embodiment. The glass preform is the preform of the optical fiber. Optical fibers are manufactured by drawing a glass preform. Just as an optical fiber has a core and a cladding, a glass preform also has a core and a cladding. The core and the clad of the glass base material are manufactured using the apparatus shown in FIGS. FIG. 3 shows a VAD method (Vapor-phase Axial Deposi).
1 shows an apparatus for producing a porous glass preform by using a conventional method. The core is obtained by sintering the porous glass base material. OVD method (Outside
The porous glass base material may be manufactured by using Vapor Deposition method. First, a method of manufacturing a core of a glass base material will be described below.

The VAD apparatus shown in FIG.
And a burner 14. A silicon halide compound is supplied to the burner 14 as a source gas. Examples of silicon halide compounds include SiCl ₄ , HSiCl ₃ , and H
₂ SiCl _{2 and the} like. In particular, silicon tetrachloride SiCl
No. ₄ is most preferable because it is easy to control the density of the porous glass base material within a predetermined range.

The carrier gas is supplied to the burner 14 together with the raw material gas.
Supplied to Ar and N ₂ are examples of carrier gases.
Inert gas like, there is a supporting gas combustible gas, and O ₂ such as H _2. By supplying the source gas and the carrier gas to the burner 14, the source gas is hydrolyzed by the oxyhydrogen flame generated by the combustible gas and the auxiliary gas. Glass particles of silicon oxide are generated by this hydrolysis process.

The burner 14 is used to generate the glass fine particles 12.
Is sprayed onto the starting rod 16 to deposit the glass fine particles 12 on the starting rod 16 to form the porous glass preform 10. The starting rod 16 is pulled up as the deposition process proceeds. The starting rod 16 is pulled upward while rotating, so that the cylindrical porous glass preform 10 is formed on the starting rod 16.

Next, the density of the porous glass base material 10 is measured. In order to measure the density of the porous glass preform 10, the length, weight, and diameter of the porous glass preform are measured. Next, the density of the porous glass base material 10 is calculated by the following equation.

Ρ = W / (π / 4 × D ² × L) where ρ indicates the density of the porous glass base material 10. W
Indicates the weight of the porous glass base material 10. D indicates the diameter of the porous glass preform 10. L indicates the length of the porous glass base material 10.

If the density of the porous glass preform 10 is known in advance because the porous glass preform 10 is manufactured according to a predetermined procedure, the step of measuring the density may be omitted.

In order to form a core having a GI type refractive index distribution, the density of the porous glass base material 10 is 0.15 g.
/ Cm ³ to 1.0 g / cm ³ . More preferably, the density of the porous glass base material is preferably formed in the range of 0.15 g / cm ³ to 0.4 g / cm ³ . If the density of the porous glass preform 10 is less than 0.15 g / cm ³ , the porous glass preform 10 cannot be formed integrally because the porous glass preform 10 is soft. Further, the porous glass base material 1
Since the amount of fluorine doped to 0 increases, a uniform refractive index distribution is formed. Therefore, a GI-type refractive index distribution cannot be formed. On the other hand, the porous glass base material 1
When the density of 0 is larger than 1.0 g / cm ^3, it becomes difficult to dope fluorine into the porous glass base material 10, so that a GI-type refractive index distribution cannot be formed.

FIG. 4 shows an apparatus for sintering a porous glass base material to form a core. The sintering apparatus has a heating furnace 20 and a heater 18. The porous glass preform 10 includes a main rod 22.
And is supplied to the inside of the heating furnace 20. S
A gas containing a fluorine compound such as iF ₄ , SF ₆ , or freon is supplied to the heating furnace 20 from the bottom of the heating furnace 20. An inert gas such as He or Cl ₂ may be supplied to the heating furnace 20 together with the fluorine compound gas. Through the above steps, the atmosphere in the heating furnace 20 is filled with the fluorine compound-containing gas. Next, the heater 18 heats the porous glass base material 10 in the heating furnace 20.

Since the main rod 22 is gradually lowered toward the bottom of the heating furnace 20, the heater 18 heats the porous glass base material 10 in an atmosphere containing a fluorine compound. Therefore, the porous glass base material 10 is gradually sintered from the surface of the porous glass base material to the inside, and at the same time, is doped with fluorine. At the same time, the porous glass base material 10 is gradually sintered upward and simultaneously doped with fluorine gradually upward.

The fluorine compound gas content inside the heating furnace 20 and the rate at which the porous glass preform 10 is sintered are determined based on the measured density of the porous glass preform 10. Since the density of the porous glass base material 10 affects the amount of fluorine doped in the porous glass base material 10, the most appropriate fluorine compound content in the mixed gas is determined based on the density of the porous glass base material 10. The amount and sintering rate are determined. At this time, the fluorine compound gas content ranges from 0.1 Vol% to 1%.
It is determined within the range of 0 Vol%. Preferably, the fluorine compound content is determined within the range of 1 Vol% to 10 Vol%. Further, the sintering speed is determined within a range of 5 mm / min to 10 mm / min. For example, the density of the porous glass base material 10 is 0.2 g / cm ³ to 0.3 g / cm ^3.
In the case of g / cm ³ , in order to form a GI type refractive index distribution, the fluorine compound gas content is determined to be 2 Vol%, the sintering speed is determined to be 7 mm / min, and the sintering temperature is determined to be 1330 ° C.

During sintering of the porous glass base material 10, the fluorine compound gas content and the sintering rate in the heating furnace 20 are controlled to predetermined values. The sintering speed is determined by the porous glass base material 1
0 is the speed of passing through the heater 18.

The sintering speed is increased from 5 mm / min to 10 mm / min.
By controlling within the range of min, the amount of fluorine doped into the porous glass preform 10 is large on the surface of the porous glass preform 10 and is reduced in the central region of the porous glass preform 10. Therefore, the central region of the porous glass matrix 10 is vitrified before being doped with a large amount of fluorine. Further, the porous glass base material 10
Is vitrified while being doped with a large amount of fluorine. Therefore, since the refractive index is large in the central region of the porous glass base material 10 and small in the surface region of the porous glass base material 10, the GI after sintering is reduced.
A core having a refractive index distribution of the type is obtained.

Further, the fluorine compound gas content is set to 0.1 V
By controlling the content within the range of 10% by volume to 10% by volume, the central region of the porous glass base material 10 is substantially not doped with fluorine, and the doping amount of fluorine from the center of the porous glass base material 10 is reduced. Gradually increases with the distance of the object. Therefore, after sintering, a core having a GI-type refractive index distribution is more reliably manufactured.

Next, after stretching the obtained core to a predetermined diameter and length as required, a clad is deposited on the core by using the apparatus shown in FIG. That is, by the same manufacturing process as the manufacturing process of the core, the glass fine particles are deposited on the surface of the core to form a porous clad layer. next,
The cladding layer is sintered by the sintering device shown in FIG.

The cladding is formed to have a uniform refractive index. The cladding has an index of refraction less than the minimum value of the index of the core. The clad is sintered at a sintering rate of less than 5 mm / min, for example, 4 mm / min. The fluorine compound gas content is 10 Vo
It is set higher than 1%.

FIG. 5 shows a flow chart of the glass base material manufacturing method. First, the porous glass base material 10 is formed (S14). Next, the density of the porous glass base material 10 is measured (S16). Next, the fluorine compound gas content and the sintering rate for sintering the porous glass base material 10 are determined based on the measured density (S18). Next, the porous glass base material 10 is sintered according to the determined fluorine compound gas content and sintering rate (S20). Next, the sintered porous glass base material 10 is stretched to a predetermined diameter and length (S22). Finally, after forming the clad around the core (S24), the clad is sintered (S26).

The intensity of the light passing through the optical fiber obtained by drawing the glass preform manufactured by the above-described process is the same as that of the light passing through the SI type optical fiber because the core has a GI type refractive index distribution. Greater than strength. Furthermore, since fluorine is doped into the core and the cladding instead of germanium,
The optical fiber of the present embodiment has higher light resistance than the optical fiber doped with germanium.

Hereinafter, the present embodiment will be described in detail with reference to examples and comparative examples, but the present invention is not limited to the scope described in the following examples. The measurement of the refractive index distribution in the examples was performed using a preform analyzer (York).
(Technology Ltd, Model P104). 6, 7, 8, 9, 11, and 12
The refractive index on the vertical axis of the refractive index distribution shown in Fig. 7 shows a difference from the refractive index of the pure quartz measurement cell.

Example 1 FIG. 6 shows a refractive index distribution of a core 36 of a glass base material manufactured by using the method of this embodiment. Core 3 of glass base material having refractive index distribution shown in FIG.
The process of manufacturing No. 6 will be described below.

A glass preform core 36 was manufactured using the apparatus shown in FIGS. First, the porous glass preform 10 was manufactured using a VAD apparatus shown in FIG.
First, an oxy-hydrogen flame from the burner 14 is used to rotate the starting rod 1
6 to the bottom. At the same time, silicon tetrachloride (SiCl ₄ ) used as a source gas was hydrolyzed by an oxyhydrogen flame to produce glass fine particles. While the starting rod 16 was being pulled upward, glass particles were deposited on the starting rod 16 to form the porous glass preform 10. As a result of measuring the density of the manufactured porous glass base material 10, it was 0.22 g / cm ³ .

Next, based on the measured density, the fluorine compound gas content was set to 2 Vol%, and the sintering speed was set to 7.0 mm /
min and the sintering temperature was determined to be 1330 ° C. Next, according to the determined fluorine compound gas content and the sintering rate,
Using the sintering apparatus shown in FIG. 4, the porous glass base material 10 was doped with fluorine while being sintered. First, the heating furnace 20 was supplied with a helium gas at a flow rate of 4.9 L / min and a fluorine compound-containing gas (SiF ₄ ) at a flow rate of 0.1 L / min.
Supplied. The inside of the heating furnace 20 was filled with an atmosphere of a mixed gas obtained by mixing a helium gas and a fluorine compound-containing gas (SiF ₄ ). That is, the fluorine compound gas content in the mixed gas was 2 Vol%. Next, the porous glass preform 10 was sintered at a sintering speed of 7.0 mm / min and a speed of 1 mm.
It was sintered at a sintering temperature of 330 ° C. The porous glass base material 10 was vitrified by the sintering process to obtain a transparent core 36.

As shown in FIG. 6, the core 36 manufactured by the above process has a GI type refractive index distribution.

Next, after stretching the core 36 to a predetermined length and diameter, glass fine particles were deposited on the surface of the core 36 to form a porous cladding layer 38. Next, 2.0 l / m
The flow rate of the SiF ₄ gas was supplied to the heating furnace, and the porous glass base material was sintered at a sintering speed of 4.0 mm / min.
6 around. The refractive index of the resulting cladding 38 was substantially uniform, 0.012 less than pure quartz, and less than the minimum refractive index of the core 36. Through the above steps, a fluorine-doped glass base material having a GI-type refractive index distribution shown in FIG. 7 was manufactured.

(Example 2) The core 3 of the glass base material was produced under the same conditions as in Example 1 except for the condition of the fluorine compound gas content.
6 was produced. That is, 4.7 L / m of helium gas is used.
In and the SiF ₄ gas were supplied to the heating furnace 20 at a flow rate of 0.3 L / min. That is, the content of the fluorine compound-containing gas (SiF ₄ ) was 6 Vol%. The core 36 having a good GI type refractive index distribution was obtained by the above procedure.

(Comparative Example 1) A porous glass base material was subjected to the VAD method.
Manufactured by. Rotating oxyhydrogen flame from the burner
It was fed to the bottom of the starting rod 16. At the same time, as raw material gas
Hydrogenation of the used tetramethoxysilane by oxyhydrogen flame
Decomposed to produce glass microparticles. Departure stick 16 upward
During the lifting, the glass particles are deposited on the starting rod 16
A porous glass preform was formed. Of tetramethoxysilane
Glass particles are deposited on the starting rod due to the large heating value of combustion.
Since the glass particles sintered during stacking, the resulting porous
The density of the base glass material is 0.42 g / cm³And high value
Was.

Next, the porous glass base material was adjusted to 4.0 mm /
The sintering was performed at a sintering speed of 1300 ° C. and a sintering temperature of 1330 ° C. When the inside of the heating furnace has a fluorine compound gas content of 100
The porous glass base material was doped with fluorine and sintered by being filled with an atmosphere of a Vol.% Fluorine compound gas (SiF ₄ ). The surface of the porous glass base material was vitrified by the sintering process. However, the central region of the porous glass base material was not vitrified. The reason is that the density of the porous glass base material is high, so that the fluorine compound gas (SiF ₄ )
Was not able to enter the central region of the porous glass base material. As a result, the temperature in the central region of the porous glass preform did not reach the sintering temperature (vitrification temperature), so that the central region of the porous glass preform was not sintered.

[0044] That is SiF ₄ has the effect of lowering the sintering temperature of the porous glass preform, the temperature of the outer region of the porous glass preform SiF ₄ gas is impenetrable is 133
The temperature reached 0 ° C. and vitrified. However, the central region where the SiF ₄ gas could not enter could not be vitrified.

Comparative Example 2 FIG. 8 shows a refractive index distribution of a core 40 of a glass base material in another comparative example. The process of manufacturing the glass base material core 40 having the refractive index distribution shown in FIG. 8 will be described below.

A porous glass preform was manufactured by the VAD method. The density of the obtained porous glass base material is 0.20 g.
/ Cm ³ . Next, the porous glass base material was adjusted to 7.0.
Sintering was performed at a sintering speed of mm / min and a sintering temperature of 1330 ° C. Helium gas and a fluorine compound-containing gas were supplied to a heating furnace. The flow rate of the helium gas is 3.25 L / m
in, the flow rate of SiF ₄ was 1.75 L / min. That is, the fluorine compound gas content in the mixed gas atmosphere was 35 Vol%. Under the above conditions, the porous glass base material was doped with fluorine and sintered. But,
As shown in FIG. 8, a large amount of fluorine was doped into the central region of the core 40 due to the large fluorine compound gas content. Therefore, the refractive index distribution was reduced in the entire region of the core 40. Therefore, a core having a GI type refractive index distribution could not be obtained.

Comparative Example 3 FIG. 9 shows a refractive index distribution of a core 42 of a glass base material in still another comparative example. The process of manufacturing the glass base material core 42 having the refractive index distribution shown in FIG. 9 will be described below. 1.0mm / m sintering speed
core 42 under the same conditions as in Example 1 except that the core 42
Was manufactured. However, a large amount of fluorine was doped into the central region of the core 42 due to the low sintering rate. Therefore, as shown in FIG. 9, the refractive index distribution was reduced in the entire region of the core 42. Therefore, a core having a GI type refractive index distribution could not be obtained.

Comparative Example 4 A core of a glass base material was manufactured under the same conditions as in Example 1 except for the content of the fluorine compound gas and the sintering rate. The obtained porous glass base material was sintered at a sintering rate of 1.0 mm / min in an atmosphere of a mixed gas having a fluorine compound gas content of 6 Vol%. However, a core having a GI type refractive index distribution could not be obtained.

Comparative Example 5 A core of a glass base material was manufactured under the same conditions as in Example 1 except for the content of the fluorine compound gas and the sintering rate. That is, the obtained porous glass base material was sintered at a sintering rate of 3.0 mm / min in an atmosphere of a mixed gas having a fluorine compound gas content of 1.6 Vol%. However, a core having a GI type refractive index distribution could not be obtained.

Comparative Example 6 A core of a glass base material was manufactured under the same conditions as in Example 1 except for the content of the fluorine compound gas and the sintering rate. That is, the obtained porous glass base material was sintered at a sintering speed of 3.0 mm / min in an atmosphere of a mixed gas having a fluorine compound gas content of 2 Vol%. However, a core having a GI type refractive index distribution could not be obtained.

Comparative Example 7 A core of a glass base material was manufactured under the same conditions as in Example 1 except for the content of the fluorine compound gas and the sintering rate. That is, the obtained porous glass base material was sintered at a sintering rate of 3.0 mm / min in an atmosphere of a mixed gas having a fluorine compound gas content of 6 Vol%. However, a core having a GI type refractive index distribution could not be obtained.

Table 1 shows the results of Examples 1 and 2 and Comparative Examples 1 to 7. When a desired GI type refractive index distribution is obtained,
When the parameter of the quality of the refractive index distribution is indicated as “good” and a desired GI type refractive index distribution cannot be obtained,
The parameter of the quality of the refractive index distribution is indicated as “poor”.

[Table 1]

As shown in Table 1, in the case of Examples 1 and 2, the fluorine compound gas content was changed from 0.1 Vol% to 1%.
0% by volume and sintering speed 5mm / mi
Since the porous glass base material is sintered while being controlled within the range of n to 10 mm / min, the core 36 of the glass base material has a desired GI type refractive index distribution. On the other hand, in Comparative Examples 1 to 7, the core of the glass base material does not have a GI-type refractive index distribution.
In the case of Comparative Examples 1-2, the fluorine compound gas content was 0.1
It is not within the range of Vol% to 10 Vol%. On the other hand, in the case of Comparative Examples 3 to 7, the sintering speed was 5 mm / min to 10 m.
It is not within the range of m / min. Therefore, in the case of Comparative Examples 1 to 7, a core having a GI-type refractive index distribution could not be obtained.

FIG. 10 shows an embodiment of a glass base material having a pseudo-GI type refractive index distribution. The glass base material shown in FIG. 10 has an inner core 30, an outer core 32, and a clad. The inner core 30 has a refractive index substantially equal to that of pure quartz. The absolute value of the difference in refractive index between the inner core 30 and the pure quartz is 0.001 or less.

The outer core 32 is doped with fluorine.
The outer core 32 has a refractive index that continuously decreases as the distance from the center of the inner core 30 increases. External core 3
The maximum value of the refractive index of 2 is smaller than the refractive index of the inner core 30. The cladding 34 is doped with fluorine. Cladding 34 has a substantially uniform refractive index. Clad 34
Is smaller than the minimum value of the refractive index of the outer core 32. Inner core 30, outer core 32, and clad 3
4 has the above-described refractive index, the glass base material shown in FIG. 10 surely has a pseudo-GI type refractive index distribution. Therefore, the light passing through the optical fiber obtained by drawing the glass base material having the GI-type refractive index distribution shown in FIG. 10 has a higher power density than the light passing through the SI-type optical fiber.

Furthermore, since the inner core 30 is substantially the same as pure quartz, the optical fiber obtained by drawing the glass base material of the present embodiment has a high light resistance to light passing through the optical fiber. Has strength. Also, instead of germanium,
Since the outer core 32 and the cladding 34 are doped with fluorine, the light resistance of the optical fiber of the present embodiment further increases.

Hereinafter, a method of manufacturing the glass base material of the present embodiment will be described. First, as shown in FIG. 3, glass particles are deposited on a starting rod 16 to form a porous glass preform 10. Next, by dehydrating and sintering the obtained porous glass base material, an inner core 30 substantially the same as pure quartz is obtained.
To form Next, the inner core 30 is stretched to a predetermined length and diameter. Next, the glass fine particles 12 are deposited around the surface of the inner core 30 to form a porous glass base material to be the outer core 32.

The density of the porous glass base material is measured by the same method as in the embodiments described in Examples 1 and 2 and Comparative Examples 1 to 7. If the density of the porous glass base material is known in advance in order to manufacture the porous glass base material according to predetermined conditions, the operation of recognizing the density may be omitted. As described in FIG. 3, in order to form the outer core 32 having the GI type refractive index distribution, the density of the porous glass base material is in the range of 0.15 g / cm ³ to 1.0 g / cm ³ . It is preferred that

Next, the sintering conditions of the fluorine compound gas content and the sintering rate are determined based on the measured density. The fluorine compound gas content and the sintering rate are determined within the predetermined ranges described in Examples 1 and 2 and Comparative Examples 1 to 7. That is, the sintering speed is from 5 mm / min to 10 mm / m
It is determined within the range of in. The fluorine compound gas content is determined within the range of 0.1 Vol% to 10 Vol%. Next, the outer core 32 is formed by sintering and vitrifying the porous glass base material in an atmosphere of a mixed gas of an inert gas and a fluorine compound gas. During the sintering process, the fluorine compound gas content and the sintering rate are controlled to the determined values.

By the above sintering process, fluorine is added to the outer core 3.
2 doping, the refractive index of the outer core 32 becomes
It decreases continuously as the distance from the center of the inner core 30 increases. The doping amount of fluorine in the outer core 32 is largest on the surface of the outer core 32, and gradually decreases as approaching the center of the inner core 30. Inner core 30 is substantially not doped with fluorine. Therefore, the refractive index distribution shown in FIG. 10 can be obtained by controlling the fluorine compound gas content and the sintering rate.

Furthermore, the volume of the inner core 30 and the outer core 3
By changing the volume ratio of 2, a desired refractive index distribution can be obtained. For example, by changing the thickness of the outer core 32 formed around the inner core 30, the volume ratio between the inner core 30 and the outer core 32 can be changed.

Next, glass fine particles are deposited on the outer core 32 to form a porous glass base material to be the clad 34. The porous glass base material is vitrified by sintering in an atmosphere of a fluorine compound-containing gas to form a clad 34. Examples of the atmosphere of the fluorine compound-containing gas include an atmosphere containing 100 Vol% of SiF ₄ . In order to stabilize the characteristics of the optical fiber, it is preferable that the refractive index distribution of the cladding 34 is substantially uniform.

Example 3 FIG. 11 shows an example of an inner core 30 and an outer core 32 of a glass base material manufactured by the method of the present embodiment. The process of manufacturing the inner core 30 and the outer core 32 of the glass base material having the refractive index distribution shown in FIG. 11 will be described below.

First, a porous glass preform was manufactured by the VAD method. An inner core made of pure quartz was formed by dehydrating and sintering the porous glass base material.
Next, the inner core was stretched so that the inner core had a diameter of 15 mm. The difference in refractive index between the inner core and pure quartz is +
0.0004.

Next, glass particles were deposited on the surface of the inner core using the OVD method. Next, the deposited glass particles were sintered in an atmosphere of a mixed gas containing a fluorine compound gas. Helium gas and a fluorine compound-containing gas were supplied to a heating furnace of a sintering apparatus in order to generate an atmosphere of a mixed gas. At this time, the flow rate of the helium gas was 4.9 L / mi.
n, the flow rate of the SiF ₄ gas was 0.1 L / min. That is, the fluorine compound gas content in the mixed gas atmosphere was 2 Vol%. The sintering speed is 7.0m
m / min. Next, the porous glass base material was sintered according to the sintering conditions described above.

As shown in FIG. 11, the core of the glass base material manufactured in the above process had a pseudo GI type refractive index distribution. Next, glass particles were deposited on the outer core using the OVD method. Next, the glass fine particles deposited on the outer core were converted to SiF ₄ having a fluorine compound gas content of 100 Vol%.
By sintering and vitrifying under the atmosphere described above, a clad was formed to obtain a glass base material.

The produced glass preform was drawn into an optical fiber to obtain a guide fiber for a high power laser. Since the core of this optical fiber had a pseudo GI type refractive index distribution as shown in FIG. 11, the power density of the light passing through the optical fiber was high. Furthermore, since the inner core has a refractive index substantially equal to that of pure quartz, the light resistance was also high. In particular, since the area occupied by the inner core in the optical fiber is large, the optical fiber has high light resistance.

Example 4 FIG. 12 shows another example of the refractive index distribution of the inner core and the outer core of the glass base material. FIG.
The steps of manufacturing the inner core and the outer core of the glass base material having the refractive index shown in FIG.

The inner core and the outer core of the porous glass base material were manufactured under the same conditions as in Example 3 except for the conditions of the diameter of the inner core and the thickness of the outer core. The diameter of the inner core of Example 4 was smaller than the diameter of the inner core of Example 3. Further, the thickness of the outer core of Example 4 was formed larger than the thickness of the outer core of Example 3. As shown in FIG. 12, the obtained core had a pseudo-GI type refractive index distribution. As shown in FIG. 12, the area occupied by the internal core of the fourth embodiment is smaller than the area occupied by the internal core of the third embodiment.

The produced glass preform was drawn into an optical fiber to obtain a laser guide fiber for a high power laser. Since the core of this optical fiber had a pseudo-GI type refractive index distribution as shown in FIG. 12, the power density of light passing through the optical fiber was high. Furthermore, since the inner core has a refractive index substantially equal to that of pure quartz, the light resistance was also high. In particular, since the optical fiber obtained by drawing the glass base material of Example 4 had a refractive index similar to that of the GI type, the power density of light passing through this optical fiber was high.

FIG. 13 is a flowchart for manufacturing the glass base material of the present embodiment shown in Examples 3 and 4. First, an internal core is formed without doping with fluorine (S5
0). Thus, the inner core is substantially the same as pure quartz. Next, an outer core doped with fluorine is formed around the inner core (S52). The outer core is doped with fluorine such that the amount of fluorine doping increases with increasing distance from the center of the inner core. Therefore, the outer core has a GI-type refractive index distribution. Finally, a cladding doped with fluorine is formed around the outer core (S5).
4). Since the cladding is uniformly doped with fluorine, the cladding has a substantially uniform refractive index distribution over the entire area of the cladding.

As described above, the present invention has been described using the embodiments. However, the technical scope of the present invention is not limited to the scope described in the above embodiments. Various changes or improvements can be added to the above embodiment. It should be noted that embodiments with such changes or improvements may be included in the technical scope of the present invention.
It is clear from the description of the claims.

[0073]

As is apparent from the above description, according to the present invention, it is possible to obtain an optical fiber having a high light resistance and a high power density of transmitted light.

[Brief description of the drawings]

FIG. 1 shows the refractive index distribution of two types of optical fibers used for transmitting light of a YAG laser.

FIG. 2 shows a power density distribution of laser light passing through an SI type optical fiber and a GI type optical fiber.

FIG. 3 shows an apparatus for producing a porous glass base material using a VAD method.

FIG. 4 shows an apparatus for sintering a porous glass base material to form a core.

FIG. 5 shows a flowchart of the glass base material manufacturing method of the present embodiment shown in Example 1 and Example 2.

FIG. 6 shows a refractive index distribution of the core manufactured in Example 1.

FIG. 7 shows a refractive index distribution of the glass base material manufactured in Example 1.

FIG. 8 shows a refractive index distribution of a core manufactured in Comparative Example 2.

FIG. 9 shows a refractive index distribution of a core manufactured in Comparative Example 3.

FIG. 10 shows an embodiment of a glass preform having a pseudo-GI type refractive index distribution.

FIG. 11 shows a refractive index distribution of a core manufactured in Example 3.

FIG. 12 shows a refractive index distribution of a core manufactured in Example 4.

FIG. 13 shows a flowchart for manufacturing the glass base material of the present embodiment shown in Example 3 and Example 4.

[Explanation of symbols]

10 ... porous glass base material, 12 ... glass fine particles, 14 ... burner, 16 ... departure rod, 18 ...
Heater, 20: heating furnace, 22: main rod 30: inner core, 32: outer core, 36, 4
0, 42 ... core, 34, 38 ... clad, S1
4: forming the porous glass preform 10, S16: measuring the density of the porous glass preform 10, S18: determining the fluorine compound gas content and the sintering rate based on the measured density, S20: sintering the porous glass base material 10 according to the determined fluorine compound gas content and sintering speed, S
22: The sintered porous glass base material 10 (core) is stretched to a predetermined diameter and length, S24: a clad is formed around the core, S26: a clad is sintered, S50.
..Formation of the inner core without doping with fluorine, S52 ..
Forming an outer core doped with fluorine around the inner core, S54 ... Forming a clad doped with fluorine around the outer core

Continued on the front page (72) Inventor Shinji Makikawa 2-13-1, Isobe, Annaka-shi, Gunma Shin-Etsu Kagaku Kogyo Co., Ltd.Precision Functional Materials Research Laboratories (72) Inventor Masatake Ejima 1873 Higami Miki-cho, Kida-gun, Kagawa Prefecture No. 9 F term (reference) 2H050 AA04 AB04X AB10Z AC25 AC73 AD11 4G021 CA12 CA13 EA01 EA03 EB04

Claims (21)

[Claims] 1. A method for manufacturing a glass preform which is a preform of an optical fiber, comprising: a core forming step of forming a core of the glass preform; and forming a clad of the glass preform around the core. A core forming step of depositing glass microparticles around a starting rod to form a porous glass base material, and forming the porous glass base material with a fluorine compound gas. Sintering in an atmosphere of a mixed gas containing the sintering step to form a GI-type refractive index distribution in which the refractive index decreases continuously as the distance from the center of the core increases. Characteristic glass base material manufacturing method. 2. The GI type refractive index distribution by controlling the content of a fluorine compound gas in the atmosphere of the mixed gas and a sintering rate for sintering the porous glass base material in the sintering step. The method for producing a glass base material according to claim 1, wherein 3. A step of recognizing a density of the porous glass base material, and a step of determining a content of the fluorine compound gas in the mixed gas based on the recognized density of the porous glass base material. Determining the sintering rate based on the recognized density of the porous glass base material, wherein the sintering step includes determining the content of the fluorine compound gas and the determined sintering rate. The method according to claim 2, wherein the porous glass base material is sintered according to a setting speed. 4. The method according to claim 1, wherein said depositing step is performed at 0.15 g / cm.
Glass base material manufacturing method according to claim 1, characterized in that to form the porous glass preform ³ having a density in the range of 1.0 g / cm ^3. 5. The method according to claim 1, wherein said depositing step is performed at 0.15 g / cm.
Glass base material manufacturing method according to claim 4, characterized in that to form the porous glass preform ³ having a density in the range of 0.4 g / cm ^3. 6. The method according to claim 2, wherein the sintering step controls the content of the fluorine compound gas in a range of 0.1% to 10% by volume. 7. The method according to claim 7, wherein the sintering step comprises:
The method for producing a glass base material according to claim 2, wherein the control is performed within a range of 10 mm / min to 10 mm / min. 8. The method according to claim 1, wherein the depositing step comprises: Add water
Claims: disassembled and deposited on the starting rod
Item 4. The method for producing a glass base material according to Item 1. 9. The glass of claim 1, wherein the step of forming a core further comprises forming an inner core in the core having a refractive index substantially equal to that of pure quartz. Base material manufacturing method. 10. A glass base material as a base material of an optical fiber, wherein the glass base material has a GI-type refractive index distribution in which the refractive index decreases continuously as the distance from the center increases, and is doped with fluorine. A glass preform comprising: a core; and a fluorine-doped cladding having a substantially uniform refractive index distribution. 11. The glass preform according to claim 10, further comprising an inner core having a refractive index substantially equal to that of pure quartz inside the core. 12. The core according to claim 11, wherein a maximum value of the refractive index of the core is smaller than a refractive index of the inner core.
The glass base material described in the above. 13. The method according to claim 12, wherein a refractive index of the cladding is smaller than a minimum value of a refractive index of the core.
The glass base material described in the above. 14. The glass preform according to claim 11, wherein an absolute value of a difference between a refractive index of the inner core and a refractive index of the pure quartz is 0.001 or less. 15. A fluorine-doped core having a GI-type refractive index profile in which the refractive index decreases continuously with increasing distance from the center of the core, and a substantially uniform refractive index profile. An optical fiber, comprising: a cladding doped with fluorine. 16. The optical fiber according to claim 15, further comprising an inner core having a refractive index substantially equal to that of pure quartz inside the core. 17. The method according to claim 16, wherein a maximum value of the refractive index of the core is smaller than a refractive index of the inner core.
An optical fiber according to claim 1. 18. The method according to claim 17, wherein a refractive index of the cladding is smaller than a minimum value of a refractive index of the core.
An optical fiber according to claim 1. 19. The optical fiber according to claim 16, wherein an absolute value of a difference between a refractive index of the inner core and a refractive index of the pure quartz is 0.001 or less. 20. The optical fiber according to claim 15, which is used for a high power laser. 21. The optical fiber according to claim 20, wherein said high power laser is a YAG laser.