JP2753426B2 - Method for manufacturing high input optical fiber and preform thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-input optical fiber for long-distance transmission and a method of manufacturing a preform thereof.

[0002]

2. Description of the Related Art In general, in order to realize long-distance optical transmission, it is necessary to, for example, (1) reduce transmission loss of an optical fiber, and (2) increase light incident on the optical fiber. Are known.

With respect to the point (1) of reducing the transmission loss of an optical fiber, research on a practical level has been advanced.
Currently the optical fibers that the GeO ₂ core 0.2 dB /
km or less, and 0.18 dB for an optical fiber having a cladding in which SiO ₂ is a core and F is doped in SiO _2.
/ Km or less.

On the other hand, regarding the point (2) of increasing the intensity of light incident on the optical fiber, the output of the semiconductor laser is improved.
Alternatively, optical amplification technology using an erbium-doped optical fiber amplifier or the like has been remarkably advanced, but it is known that the light intensity that can be incident on an optical fiber is limited. That is, when strong light of about 7 dBm or more is incident, a sound wave is excited in the optical fiber, and an optical nonlinear phenomenon in which the light wave is scattered by the sound wave, that is, stimulated Brillouin scattering occurs. As a result, most of the incident light is reflected toward the light incident end of the optical fiber and does not reach the light receiving end.

[0005] This phenomenon is described in D. Cotter's "Observation of stimula"
ted Brillouin scattering
inlow-loss silica fiber a
t 1.3 μm ”(Electronics lett)
ers, vol. 18, No. 12, 495-49
6, 1982). Therefore, the amount of light that can be effectively incident on the optical fiber is limited. In order to increase the transmission distance, it is necessary to suppress the occurrence of stimulated Brillouin scattering. To do so, the stimulated Brillouin gain width must be increased, that is, the stimulated Brillouin frequency shift (the frequency of the incident light and the frequency of the scattered light) It is necessary to make the difference) non-uniform.

As a conventional technique for suppressing stimulated Brillouin scattering in an optical fiber, there has been reported a method of generating mechanical distortion in an optical fiber. This is based on the fact that the frequency shift of stimulated Brillouin scattering changes when a strain is generated in an optical fiber.

[0007] This phenomenon is described in "Tensile Strain Effect" by Kurashima, Horiguchi and Tateda.
s on Brillouin Frequency
Shift in Single-mode Five
rs Having Pure Silica and
GeO ₂ -doped Cores "(IOOC'8
9, 21C4-2). To increase the threshold of stimulated Brillouin scattering by using this phenomenon, a method of spirally winding an optical fiber in an optical fiber cable and changing the strain in the optical fiber axial direction to increase the stimulated Brillouin gain width. Is N, Yoshizawa,
T. Horiguchi, T .; "Proposal for stimulat" by Kurashima et al.
ed Brillouin scatterings
upby by fibre cabli
ng ", (Electronics Letters,
vol. 27, no. 12, pp. 1100-110
1, 1991).

In the structure of this optical fiber cable, for example, as shown in FIG. 12, the optical fiber 11 has a double helix structure in the axial direction, and the mechanical strain applied to the optical fiber 11 changes from a compressed state to a pulled state. Alternating alternately.
As a result, the amount of stimulated Brillouin frequency shift changes at each location of the cable, and as a result, the Brillouin scattering gain width is increased, and the threshold value of stimulated Brillouin scattering is increased.

As another method, a method of changing the residual stress in the axial direction by changing the tension at the time of drawing an optical fiber is disclosed by Nozawa, Sakai, Wada, and Yamauchi in “Optical Fiber with Stimulated Brillouin Scattering Suppressed” ( 1991, IEICE Autumn Conference, B-546). FIG. 13 shows an FS using SiO ₂ as a core.
4 shows a tension distribution in the optical fiber axial direction of a Brillouin scattering suppression optical fiber having iO ₂ as a cladding.

[0010]

However, the conventional method of applying strain in the optical fiber axial direction has a problem that the optical fiber is easily broken. For example, when the strain is increased from 0.1% to 0.2% with respect to a normal optical fiber, the breaking rate per km increases by 10 ⁷ times. , "A Method for Guaranteeing Optical Fiber Strength by Screening Test" (Transactions of the Institute of Electronics, Communication, vol. J66-B, N.
o. 7.1983). Therefore, in order to avoid this, it is necessary to use a technique for increasing the strength by coating the optical fiber surface with a carbon film or the like. Further, in the conventional method, since a special strain state must be maintained, there is a problem that the cable structure is restricted, and it is extremely difficult to use the cable for an actual optical fiber line.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a high-input optical fiber for long-distance transmission with high long-term reliability and a method of manufacturing a base material thereof.

[0012]

In order to achieve the above object, the present invention provides an optical fiber comprising a core and a clad surrounding the core, the optical fiber comprising a stimulated Brillouin scattering.
In order to increase the threshold value, the dopant concentration of the core and the cladding continuously changes in the optical fiber axial direction.
The high-input optical fiber is characterized in that the frequency range of stimulated Brillouin scattering is expanded and the relative refractive index distribution standardized by the maximum refractive index of the core is always constant in a cross section at an arbitrary position in the optical fiber axial direction. Further, in the high input optical fiber, the dopant to be doped into the core and the clad is one selected from GeO ₂ , P ₂ O ₅ , Al ₂ O ₃ and F or a combination thereof. in the high input optical fiber, characterized in that the core and cladding are made of GeO ₂ doped quartz, and in the high input optical fiber, an optical fiber core and cladding are made of GeO ₂ doped silica, said core And the dopant doped into the cladding is F
In addition, in the high-input optical fiber, the core is an optical fiber made of GeO ₂ -doped quartz and the clad is made of pure silica, and the dopant doped into the core and the clad is F. Wherein the core and the cladding are made of F-doped quartz, and the dopant doped into the core and the cladding is F. In a high input optical fiber, the core is pure silica and the cladding is F
An optical fiber made of doped quartz, wherein the dopant to be doped into the core and the clad is F, and as a method of manufacturing a high-input optical fiber preform,
Quartz glass particles or Ge synthesized by gas phase reaction
In the method of performing dehydration and / or heat treatment for fluorine addition in a heating furnace on a quartz glass particle doped with O ₂ , and then forming a transparent glass to produce an optical fiber preform, a cross-section in the quartz glass particle is produced. The GeO ₂ dopant distribution is made uniform in the longitudinal direction, and the glass particles are heated in a zone furnace in a heat treatment step for fluorine addition while changing the concentration of fluorine to be added depending on the longitudinal position at which the particles are vitrified. By making it transparent glass ,
A preform for the high input optical fiber is manufactured .

[0013]

According to the present invention, the frequency range of stimulated Brillouin scattering is broadened by changing the dopant concentration of the core and the cladding in the axial direction of the optical fiber, thereby increasing the threshold of the amount of incident light for the generation of stimulated Brillouin scattering. it can. At this time, the refractive index distribution in the optical fiber cross section standardized by the maximum refractive index of the core is kept constant.

That is, taking a step type optical fiber as an example, the relative refractive index difference Δ (= (n ₁ −
By keeping n ₂ ) / n ₁ ) constant, the field distribution of the guided mode is kept constant, and transmission characteristics equivalent to those of ordinary optical fibers can be obtained.

Further, in order to manufacture the optical fiber of the present invention, a manufacturing method for changing the dopant concentration in the longitudinal direction is required. FIG. 8 shows a heating furnace for fluorine addition according to the production method of the present invention, and a method for changing the amount of F dopant in the longitudinal direction will be described with reference to FIG. The heating furnace 1 as shown in the figure is provided with a heater portion 2, and the length Lh of the heater is Lh << L with respect to the length Lb of the base material.
This is a zone furnace in a relation of b. In this zone furnace, fluorine-containing gas SF ₆ and H
e. Other examples of the fluorine-containing gas in place of SF ₆ include CF ₄ , C ₂ F ₆ , SiF ₄ , and F ₂ . The particle body 4 produced by the VAD method or the like is lowered at a constant speed while rotating. The atmosphere of the heating furnace 1 is SF
₆ + He. The final dopant concentration of F is determined by the partial pressure of SF ₆ in this atmosphere. When the particles descend and reach the portion of the heater 2, the temperature of the
The temperature is raised to 00 degrees or more, and the amount of F in the particles is fixed and vitrified. At this time, the amount of F fixed to the particles can be controlled by adjusting the partial pressure of F in the heating furnace 1. In this case, if the portion of the heater is larger than the length of the particle, the amount of F becomes uniform in the longitudinal direction of the particle, so that Lh << Lb shown above is particularly necessary. By doing so, it becomes possible to produce optical fiber preforms having different doping amounts of F in the longitudinal direction. As a result, when the optical fiber preform is converted into an optical fiber by drawing, a high input optical fiber can be realized.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 shows changes in the refractive index of the core and clad of an optical fiber in the axial direction of an optical fiber according to a first embodiment of the present invention. Has a step shape, and uses GeO ₂ as a dopant for both the core and the cladding.

At one end (z = 0) of the optical fiber according to the present embodiment, the cladding does not contain a dopant, and has exactly the same structure as a normal optical fiber.

In FIGS. 1, 3, 4, and 5, Le is the effective length of Brillouin scattering generation, and when the optical fiber length is sufficiently long, approximately 4.3 / α (α: loss (dB / k
m)) is shown in the Cotter article cited above. Optical fiber loss is 0.21dB
/ Km, the effective length Le is 20.5 km. Length L
In the section e, Brillouin scattering is likely to occur due to the interaction between sound waves and light waves. Therefore, the threshold value of the occurrence of Brillouin scattering can be increased by changing the dopant concentration in the optical fiber in this section. FIG. 2 shows a refractive index distribution in a cross section at an arbitrary length z of the optical fiber of the present embodiment. Core diameter is 10 regardless of axial position
μm, the cladding diameter is constant at 125 μm, and FIG.
As shown in the figure, the relative refractive index difference Δ (= (n ₁
−n ₂ ) / n ₁ ; n ₁ : the refractive index of the core, and n ₂ : the refractive index of the cladding.

FIG. 4 shows a dopant concentration distribution in the optical fiber axial direction for realizing such an optical fiber structure. When GeO ₂ is used as a dopant, 1 mo
The relative refractive index to SiO ₂ by l% of GeO ₂ is increased by about 0.1%.

In the optical fiber shown in FIG. 3, the amount of dopant in the core is 3 mol% at z = 0 and 4.5 at z = 20.5 km.
mol%, and the amount of dopant in the cladding is 0 mol% when z = 0 and 1.5 mol% when z = 20.5 km. These dopant amounts are continuously changed so that the refractive index difference Δ between the core and the clad at an arbitrary position z is maintained at 0.3%.

In this embodiment, the threshold value of the optical input is set to be ten times higher than that of a normal optical fiber, and is designed as follows. It has been reported that the amount of frequency shift of stimulated Brillouin scattered light changes in proportion to the amount of dopant added to the core. Shibata, Y .; Azuma, T .; Ho
riguchi, M .; “Bri,” by Tateda et al.
llouin-gain spectrum fors
single-moders having v
arious core / claddingmater
ial compositions ”(ECOC'8
8). Cotter reports that the induced Brillouin gain width of quartz material is about 16 MHz at an optical wavelength of 1.55 μm.

Therefore, the input threshold level is set to 10d
To increase B, the induced Brillouin frequency shift amount must be 1
What is necessary is that the frequency is changed by 60 (= 16 × 10) MHz. Ge
The frequency shift amount due to O ₂ is 107 MHz / mol%, It is reported in a paper by Shibata et al.

Therefore, about 1.5 mol% of GeO ₂ may be changed over the effective length Le in the optical fiber axial direction. At this time, since the amount of GeO _{2 to be} doped is small, the increase in loss is about 0.01 dB / km compared to the conventional optical fiber having a loss of 0.20 dB / km, and the loss of the optical fiber is 0.21 dB / km. About. Therefore,
For an incident light increase of 10 dB, 48 (= 10 / 0.2
1) The optical fiber of this embodiment of km can be connected to a conventional optical fiber.

At this time, at the connection point with the conventional optical fiber at a distance of 48 km from the incident end, the light intensity is sufficiently attenuated to the optical input threshold value of the conventional optical fiber, so that stimulated Brillouin scattering does not occur. .

As described above, the optical fiber 48 of the present invention
km to a conventional optical fiber, and a light (17 dB) which is ten times stronger than the input threshold (7 dBm) of a normal optical fiber.
m) is incident from the side of the optical fiber of the present invention, the light intensity at the connection point between the optical fiber of the present invention and the conventional optical fiber becomes just the optical input threshold value of the conventional optical fiber.
The communicable optical fiber length can be extended by 48 km.

It is apparent that FIG. 5 has the same effect as the dopant distribution other than that described in FIG. In addition, according to exactly the same principle, generally, within the effective length Le, the Brillouin scattering frequency shift amount is equal to the Brillouin scattering gain width (16 in the above example) in a normal optical fiber.
MHz), if the amount of the dopant changes in the optical fiber axial direction so as to be G times (10 times in the above example) or more, even if the refractive index distribution shape in the cross section is any shape other than the step shape, It can be seen that the effect of increasing the incident light amount threshold by G times is obtained.

(Embodiment 2) A case where F is used as a waveguide structure controlling dopant will be described as a second embodiment with reference to FIGS. 6 and 7 show the structure of the optical fiber according to the present embodiment (change in dopant concentration in the optical fiber axial direction).

When SiO ₂ is doped with F, the refractive index for SiO ₂ is reduced by 0.4% per 1 wt% of F. Using this, a waveguide structure is realized by adding more F to the cladding than to the core. As in the first embodiment, the core shape is 10 μm, the cladding diameter is 125 μm,
The relative refractive index difference Δ was 0.3%.

On the other hand, when F is added as a dopant to the core of the optical fiber, 356 MH per F wt.
It is known that the amount of frequency shift of z-stimulated Brillouin scattering changes (N. Shibata et al., ECOC'8).
8, 115-118). 13. According to the same design principle as in the first embodiment, the input level is changed by changing the Brillouin frequency shift amount to 30 times the gain width, that is, 480 MHz.
To increase by 8 dB, it is sufficient to change about 1.35 wt% of F in the optical fiber axial direction. At this time, the relative refractive index Δ of the core / cladding is kept at 0.3%, and F
The amount of change in the doping amount is the same for the core and the cladding.

As described above, a pure silica core optical fiber in which only the cladding is doped with F has a loss of 0.18 d.
B / km, but F is further increased up to 1.3 in the length direction.
With 5 wt% doping, the average loss is about 0.21 dB / km due to increased Rayleigh scattering. Therefore, 70
(= 14.8 / 0.21) km of the optical fiber of the present embodiment is connected to a conventional optical fiber, and if light of 21.8 dBm is incident from the end face of the optical fiber of the present embodiment, the optical fiber of the present embodiment is Conventionally, the light intensity at the point of incidence on the optical fiber is
The optical input limit of the conventional optical fiber is just 7 dBm.
As a result, the length of the communicable optical fiber is increased by 70 km.

In each of the first and second embodiments, the refractive index structure at one end of the optical fiber of the present invention can be made to match that of a normal optical fiber. There is no adverse effect such as reflection at the connection point with the fiber. In addition, since the optical fiber does not include mechanical distortion, a highly reliable long-distance optical transmission line can be provided unlike a strain-added optical fiber according to a conventional method.

Next, specific combinations of dopants of the high-power optical fiber according to the present invention, including the cases of the above embodiments, will be described as follows.

(1) When the core and the clad are made of GeO ₂ -doped quartz.

(2) An optical fiber whose core and cladding are made of GeO ₂ -doped quartz, wherein the dopant doped into the core and cladding is F.

(3) When the core is an optical fiber made of GeO ₂ -doped quartz and the clad is made of pure quartz, and the dopant doped into the core and the clad is F.

(4) A case where the core and the clad are optical fibers made of F-doped quartz, and the dopant doped into the core and the clad is F.

(5) An optical fiber in which the core is made of pure quartz and the clad is made of F-doped quartz, and the dopant doped in the core and the clad is F.

As described above, in the embodiment, GeO is used as a dopant.
₂ and F have been described, but Al ₂ O ₃ , P
_The same effect can be obtained by using ₂ O ₅ or the like as a dopant. In addition, the effects described here can be obtained in the same manner for an optical fiber having a special structure such as a dispersion-shifted optical fiber or a polarization-maintaining optical fiber.

(Embodiment 3) An embodiment relating to a method of manufacturing a high input optical fiber will be described. Heat treatment and transparent vitrification were performed by using particles of GeO ₂ -doped quartz and clad of quartz synthesized by the VAD method. Transparent vitrification was performed in a F atmosphere using a zone furnace. The particles were gradually moved in a transparent vitrification zone furnace shown in FIG. 8 while keeping the descending speed constant, and SF ₆ and He were used as introduced gases. When the particulate matter comes to the heater portion 2 of the zone furnace, the concentration of F doped into the particulate matter is fixed by the concentration of F in the furnace, and the vitrification is performed. In this case, by changing the amount of gas to be introduced depending on the location of the particle, the concentration of F doped into the particle changes.

FIG. 9 shows an embodiment of the refractive index distribution in the longitudinal direction of the high input optical fiber preform of the present invention. The length of the prototype optical fiber is about 29 km. From the figure, F in the longitudinal direction
Changes in the relative refractive index difference by about 0.2%. Further, the relative refractive index difference between the core and the clad in the longitudinal direction does not change. When SiO ₂ is doped with F, the refractive index for SiO ₂ is reduced by 0.4% per 1 wt% of F. Therefore, in this case, the dopant amount of F changes by about 0.5 wt% between the start and end of the optical fiber. The transmission loss of the optical fiber of this example is 0.43 d at 1.3 and 1.55 μm, respectively.
B / km and 0.23 dB / km, which are almost the same as those of ordinary optical fibers.

On the other hand, when F is added as a dopant to the core of the optical fiber, 356 MHz per 1 wt% of F doping amount is obtained.
z-induced Brillouin scattering frequency shift amount is 1.55μ wavelength
It is shown to vary at m. This corresponds to 424 MHz at a wavelength of 1.3 μm.

FIG. 10 shows the measurement results of the transmitted power and the scattered power with respect to the input power at 1.3 μm in the optical fiber shown in FIG. 9 and the conventional optical fiber. As shown in the figure, the input power level at which the scattered light by the SBS starts to increase rapidly is about 13 dBm. In a conventional optical fiber, it is about 7 dBm. Therefore, the optical fiber of this embodiment has an input level of about 6 dB as compared with the conventional optical fiber.
I could improve.

As described above, the threshold value of the amount of incident light can be improved by changing the amount of the dopant of F in the longitudinal direction of the optical fiber.

(Embodiment 4) FIG. 11 shows an embodiment in which the present invention is applied to a dispersion-shifted optical fiber having a three-layer structure. In manufacturing the optical fiber of this embodiment, first, Ge
A silica glass particle body composed of a center core 5, a side core 6, and a clad 7 containing no dopant using only O ₂ as a dopant is synthesized by a gas phase reaction method. Thereafter, sintering is performed while changing the F concentration in the atmosphere of the heating furnace 1 shown in FIG.
Vitrify. FIG. 11 shows the refractive index distribution of the glass base material thus obtained. The solid line and the dashed line indicate the refractive index distribution at both ends of the base material. The broken line indicates the refractive index distribution at the center of the base material. Assuming that a change in the refractive index due to a change in the doping amount of F in the longitudinal direction is 0.7%, the Brillouin frequency shift is about 300 MHz at 1.3 μm. At this time, the suppression effect of the SBS is about 8 dB because the Brillouin gain width of the optical fiber is usually 50 MHz. As described above, the refractive index distribution of the optical fiber of the present invention is not limited to the step shape, and can be applied to an arbitrary refractive index distribution.

[0046]

As described above, according to the present invention, the property that the amount of induced Brillouin frequency shift changes depending on the dopant concentration added to SiO ₂ glass for forming a waveguide structure is utilized. By changing the dopant concentration in the optical fiber axis direction while keeping the relative refractive index distribution normalized by the maximum refractive index of the core constant in the optical fiber axis direction, the threshold value of stimulated Brillouin scattering generation increases, Light that can enter the optical fiber can be increased. As a result, the transmission distance by the optical fiber can be greatly extended.

Since no distortion is applied to the optical fiber of the present invention, a long-distance transmission line with high long-term reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing an example of a refractive index of a core and a clad in an axial direction z of an optical fiber according to the present invention.

FIG. 2 is a characteristic diagram showing an example of a refractive index distribution in a cross section of an optical fiber according to the present invention.

FIG. 3 is a characteristic diagram showing an example of an axial change of a relative refractive index difference Δ between a core and a clad according to the present invention.

FIG. 4 is a characteristic diagram showing an example of an axial change of an amount of a dopant added to a core / cladding according to the present invention.

FIG. 5 is a characteristic diagram showing a dopant distribution of an example different from FIG. 4 according to the present invention.

FIG. 6 is a characteristic diagram showing an example of an axial dopant amount when F is used as a dopant according to the present invention.

FIG. 7 is a characteristic diagram showing an example of an axial dopant amount when F is used as a dopant according to the present invention.

FIG. 8 is a configuration diagram showing an example of a heating furnace for adding fluorine in the method for manufacturing a high-input optical fiber according to the present invention.

FIG. 9 is a characteristic diagram showing an example of a refractive index distribution in the longitudinal direction of the optical fiber preform according to the present invention.

FIG. 10 is a characteristic diagram showing an example of measurement results of transmitted light and backscattered light of the optical fiber according to the present invention and the conventional optical fiber.

FIG. 11 is a characteristic diagram showing a refractive index distribution in a longitudinal direction of a second embodiment in which the present invention is applied to a dispersion-shifted optical fiber.

FIG. 12 is a structural diagram showing a conventional Brillouin scattering suppression optical fiber cable having a double spiral structure.

FIG. 13 is a characteristic diagram showing a change in residual tension in the axial direction of a conventional Brillouin scattering-suppressing optical fiber utilizing residual strain during drawing of an optical fiber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating furnace, 2 ... Heating part, 3 ... Introduction gas supply port, 4
... particles, 5 ... center core, 6 ... side core, 7 ... cladding.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Katsusuke Tajima 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-54-35748 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/10 C03B 37/014 C03B 37/018 C03C 13/04 G02B 6/16

Claims (8)

(57) [Claims] 1. An optical fiber comprising a core and a clad surrounding the core, wherein the optical fiber has stimulated Brillouin scattering.
The dopant concentration of the core and the clad is continuously changed in the optical fiber axial direction so as to increase the light amount threshold, thereby broadening the frequency range of stimulated Brillouin scattering , and relative refraction normalized by the maximum refractive index of the core. A high-input optical fiber, wherein a rate distribution is always constant in a cross section at an arbitrary position in an optical fiber axial direction. 2. The high-input optical fiber according to claim 1, wherein the dopant doped into the core and the cladding is Ge.
A high-input optical fiber comprising one selected from the group consisting of O ₂ , P ₂ O ₅ , Al ₂ O ₃ and F, or a combination thereof. 3. The high input optical fiber according to claim 1, wherein the core and the clad are made of GeO ₂ -doped quartz. 4. The high input optical fiber according to claim 1, wherein the core and the clad are made of GeO ₂ -doped quartz, and the dopant doped into the core and the clad is F. Input optical fiber. 5. The high input optical fiber according to claim 1, wherein the core is an optical fiber made of GeO ₂ -doped quartz and the clad is made of pure quartz, and the dopant doped into the core and the clad is F. And high input optical fiber. 6. The high input optical fiber according to claim 1, wherein the core and the clad are made of F-doped quartz, and the dopant doped into the core and the clad is F. Optical fiber. 7. The high-input optical fiber according to claim 1, wherein the core is made of pure quartz and the clad is made of F-doped quartz, and the dopant doped in the core and the clad is F. High input optical fiber. 8. A quartz glass particle synthesized by a gas phase reaction or a quartz glass particle doped with GeO ₂ is subjected to dehydration and / or heat treatment for fluorine addition in a heating furnace, and then to a transparent vitrification to form an optical fiber. In the method for manufacturing a base material, Ge in the cross section in the quartz glass particle body is used.
O ₂ dopant distribution is uniform in the longitudinal direction, a zone furnace is used as a heating furnace, and in the heat treatment step for adding fluorine, the concentration of added fluorine is changed while changing the concentration of added fluorine depending on the position in the longitudinal direction where the glass particles are vitrified. 2. The high-input optical fiber according to claim 1 by vitrification.
A method for producing a high-input optical fiber preform, characterized by producing a preform.