JPH0327491B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a single mode optical fiber having a zero dispersion wavelength in the 1.5 μm band.

[Conventional technology]

Single-mode fiber (hereinafter referred to as dispersion-shifted fiber) has a zero dispersion wavelength in the 1.5 μm band (1.50 to 1.60 μm), where the transmission loss is minimum in silica-based optical fiber.
(referred to as fiber) is being researched and developed as a long-distance, high-capacity optical communication line. Among the designs of refractive index distribution structures for dispersion-shifted fibers, a stepped refractive index distribution structure as shown in FIG. 1 has been proposed as a structure that is highly resistant to bending loss. In Figure 1, 1
is the inner core, 2 is the outer core, and 3 is the cladding.
_n1-3 are respective refractive indices.

[Reference 1: Ohashi et al., "Characteristics of dispersion-shifted fibers with stepped refractive index distribution," Proceedings of the 1985 IEICE Semiconductor and Materials Division National Conference, p. 413. Reference 2: K. Kwaki et al., “Dispersion-Shifted Convex-Index Single Mode Fibers,” Electronics Letters, Vol. 21, pp. 1186-1187, 1985. Reference 3: Kuwagi et al., "Characteristics of alpha-power distribution stepwise dispersion-shifted fibers," Proceedings of the 1985 IEICE General Conference National Conference, p. 1072] As seen in the above-mentioned Reference 3, the refractive index of the inner core becomes clad. In comparison, the relative refractive index difference is as high as about 1.0%. GeO ₂ is the most common additive for increasing the refractive index of silica-based optical fibers, but if only GeO ₂ is used to form the refractive index distribution shown in Figure 1, The amount of GeO ₂ contained becomes extremely high, and scattering loss due to GeO ₂ increases. On the other hand, as a component that lowers the refractive index,
B ₂ O ₃ and F are often used. In particular, since F does not have an absorption band near the 1.5 μm band like B ₂ O ₃ , it is an advantageous material for reducing loss. Therefore, it is effective to reduce the amount of GeO ₂ in the inner core 1 by adding F to the cladding part 3 [Reference 4: H. Yokota et al. “Dispersion-Shifted Fibers with Fluorinated Cladding by the Vapor Phase Axial Deposition Method (Dispersion-Shifted Fibers with F-doped Clads Prepared by the VAP Method)” Conference on Optical
fiber communication technical
Digest, 1986 Atonta, Georgia (USA) WF2].

[Problem that the invention seeks to solve]

The VAD method is known as a method for manufacturing optical fiber base materials with excellent mass productivity, but it has a refractive index distribution as shown in Figure 1, and F is selected for the cladding part and GeO ₂ is selected for the inner core. There was a problem in that it was difficult to create a complex refractive index distribution structure such as a base material for a dispersion-shifted fiber doped with carbon. In view of the current situation, it is an object of the present invention to provide a new and excellent method for easily producing a base material for a dispersion-shifted fiber having a stepped refractive index distribution by effectively utilizing the VAD method. It is.

[Means for solving problems]

In the present invention, a soot body consisting of a central layer made of SiO ₂ containing GeO ₂ and an outer layer made of substantially pure SiO ₂ surrounding the central layer is created by the VAD method, and the soot body is dehydrated and sintered. The transparent glass body is stretched in an atmosphere that does not contain H atoms, and the central part
A step of creating a core base material having a double structure consisting of a GeO _2- containing part and an outer part made of substantially pure SiO ₂ , and a step of creating a base material for a core with a double structure consisting of a GeO 2-containing part and an outer part made of substantially pure SiO 2, and
The center of a transparent glass body obtained by creating a soot body made of SiO ₂ , heat-treating the soot body at high temperature in an atmosphere containing fluorine, adding fluorine to the soot body, and sintering the soot body. A step of creating a cylindrical clad base material made of fluorine-containing SiO ₂ by drilling a section and stretching as necessary, and inserting the core base material into the clad base material and stretching the core base material into the clad base material. A method of manufacturing a dispersion-shifted single-mode optical fiber is characterized in that it includes a step of heating and integrating.

In the present invention, a glass body for a core having an inner core doped with GeO ₂ and a glass body for a cladding doped with F are created by the VAD method, and after processing the F-doped glass body for a cladding into a pipe, the above-mentioned core is Insert the glass body into the glass pipe for the cladding,
By integrating them, a stepped refractive index distribution as shown in FIG. 1 can be easily obtained.

Each step of the method of the present invention will be explained in detail below.

Glass body for the core The soot body for the core is manufactured using the VAD method using the configuration shown in Figure 2. In FIG. 2, 3 is a burner for synthesizing glass particles for the inner core, and 4 is a burner for synthesizing glass particles for the outer core. SiCl ₄ in the burner 3 for glass particle synthesis for the inner core,
GeCl ₄ , H ₂ , O ₂ , Ar are supplied, and SiCl ₄ , H ₂ , O ₂ , Ar are supplied to the burner 4 for synthesizing glass particles for the outer core.
SiCl ₄ ,
GeCl ₄ is reacted to generate glass particles (soot), which corresponds to the rotating soot body 8 containing GeO ₂ and the outer core surrounding the soot body 8.
A soot body 9 made of SiO ₂ is simultaneously deposited.
The core soot body is grown in the axial direction by gradually pulling the starting quartz rod 7 upward in accordance with the growth of the soot bodies 8 and 9 using a rotating/pulling device. A transparent glass body for a core is obtained by heat-dehydrating and sintering this soot body for a core. By heating and softening the transparent glass body for a core in an atmosphere not containing H atoms, such as in an electric resistance furnace, a glass body for a core stretched to a predetermined diameter is obtained. In _this way, _{a two}
A core gas body having a heavy structure can be obtained.

Note that when stretching the core gas body, stretching in an atmosphere containing H atoms may cause the surface of the core glass body to
This is undesirable because it is contaminated by OH groups and causes transmission loss in the optical fiber.

Preparation of glass body for cladding A soot body made of pure _SiO2 is formed by the VAD method, and the soot body is dehydrated by treating it at high temperature (approximately 1100 to 1200℃) in an atmosphere containing F such as _SiF4 . At the same time as treatment, F is added to the soot body, and then heated to an even higher temperature (approximately 1600℃)
SiO ₂ treated to become transparent vitrified and added with F
A glass base material for cylindrical cladding can be obtained. A hole is made in the center of the cylindrical glass base material for the cladding using an ultrasonic drilling machine, etc., and after stretching it as necessary, it is heated from the outside while flowing an F compound gas such as SF ₆ that has a glass etching effect inside the pipe. By heating with an oxyhydrogen flame, etc., the inner surface of the pipe is etched and smoothed. In this way, a pipe-shaped glass body for a cladding doped with F can be obtained.

After inserting the core glass body obtained by integrating the core glass body and the cladding glass body into the obtained pipe-shaped cladding glass body,
By heating from the outside with an oxyhydrogen flame, etc., the glass body for the cladding is contracted, and the glass body for the core and the glass body for the cladding are fused and integrated, resulting in a refractive index distribution structure as shown in Figure 1. , to the inner core
A base material for a dispersion-shifted fiber can be produced in which GeO ₂ and F are added to the cladding portion.

In addition, by further depositing a soot body on the outer periphery of the base material produced in the above steps, adding F to the soot body as described in , and performing transparent vitrification treatment, F is applied to the outermost layer of the fiber. A base material having the same cross-sectional structure as a dispersion-shifted fiber having a structure in which the dispersion-shifted fiber is uniformly added can be produced, and a dispersion-shifted fiber can be produced by drawing this base material.

Alternatively, a dispersion shift having a structure in which F is uniformly added to the outermost layer of the fiber can be obtained by inserting and integrating the base material produced in the above process into a glass pipe containing F added in the same process as above. A base material having the same cross-sectional structure as the fiber can be produced.

〔Example〕

Example 1 Production of glass body for core In the configuration shown in FIG. 2, a multi-tube burner was used as the burner 3 for synthesizing glass particles for the inner core, and SiCl ₄ was fed at 120 c.c./min and GeCl ₄ was fed at 20 c.c./min. minutes, Ar
2.5/min, H ₂ at 3/min, and O ₂ at 6.0/min to burner 4 for glass particle synthesis for the outer core.
SiCl ₄ at 350 c.c./min, Ar at 3.0/min, H ₂ at 12/min
min, supply _O2 6.0/min, outer diameter 100mm length 500
A soot body for core material of mm was synthesized. The core material soot body was dehydrated by being passed through a ring-shaped electric furnace at 1100°C in an atmosphere of Cl ₂ :He = 1:40 at a speed of 5 mm/min, and then passed through a ring-shaped electric furnace at 1600°C in an atmosphere containing only He. This was passed through an electric furnace at a speed of 4 mm/min to obtain a transparent vitrified core glass body having an outer diameter of 40 mm and a length of 200 mm. This core glass body was heated to 1850° C. in a ring-shaped electric resistance furnace, stretched to an outer diameter of 4 mm, and divided into lengths of approximately 300 mm. The refractive index distribution structure of this core glass material is shown in FIG. This core glass material has a 10%
It was washed with HF solution for about 3 hours.

2 Preparation of glass body for cladding Pure SiO ₂ with outer diameter 120 mm and length 600 mm by VAD method
Create a suit field consisting of
1150 in an atmosphere of SiF ₄ :Cl ₂ :He=0.08:0.15:15
The soot body was passed through a ring-shaped electric resistance furnace heated to ℃ at 2 mm/min, dehydrated and subjected to F treatment, and further heated at 1600 °C in an atmosphere of SiF ₄ :He = 0.08:15.
The glass was passed through a ring-shaped electric resistance furnace heated to 0.degree. C. at a rate of 6 mm/min to obtain a transparent glass body containing about 0.65% by weight of F. The dimensions of the glass body for the cladding at this time are outer diameter 50mm and length 280mm.
It was hot. A hole with a diameter of 8 mm was drilled in the center of this glass body for the cladding using an ultrasonic drilling machine, and then heated and stretched with an oxyhydrogen flame to form a hole with an outer diameter of 25 mm, an inner diameter of 4 mm,
This is glass for a pipe-shaped cladding with a length of 1120 mm.
This was divided into 280mm length pieces. Furthermore, while flowing SF ₆ at 200c.c./min and O ₂ at 600c.c./min inside the clad pipe, it was heated from the outside with an oxyhydrogen burner, and the inner surface was etched and smoothed to reduce the inner diameter to 600c.c./min.
mm.

3 Integration of core glass body and cladding glass body The core glass body obtained in 1) was inserted into the cladding pipe obtained in 2), and then heated from the outside with an oxyhydrogen flame to form the core glass body. After cleaning the body surface and the inner surface of the cladding glass body, the cladding glass pipe was heated and shrunk, and the core glass body and the cladding glass body were welded and integrated. FIG. 4 shows the refractive index distribution of the base material thus obtained.

4 Subsequent steps The base material obtained in steps 1) to 3) was stretched to an outer diameter of 15 mm, and a soot body made of pure SiO ₂ was deposited on the outer periphery of the base material in the configuration shown in Figure 5. Thereafter, F was added to the soot body portion under the conditions shown in 2) and the soot body portion was made into transparent glass to obtain a preform having the structure shown in FIG. 6. In Fig. 5, 10 is a burner for synthesizing glass particles, 11 is the base material obtained in 1) to 3) stretched to an outer diameter of 15 mm, and 12 is a burner for synthesizing glass particles.
13 is a soot body, and 13 is a supporting dummy rod. The preform was drawn to an outer diameter of 125 μm to obtain a dispersion-shifted fiber. The zero dispersion wavelength of this fiber is
The transmission loss at 1.552 μm and 1.55 μm was 0.25 dB/Km, and characteristics with no problems in practical use were obtained.

〔Effect of the invention〕

The present invention creates a dispersion-shifted fiber with a step-like refractive index distribution in which GeO ₂ is selectively added to the cladding in the center of the core, which was difficult to fabricate using a simple VAD method, and the core and cladding glass bodies are separated. The dispersion shifted fiber according to the present invention has zero dispersion in the 1.5 μm band and has excellent transmission loss characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the stepwise refractive index distribution structure of the dispersion-shifted fiber of the present invention, FIG. 2 is a conceptual diagram schematically explaining an embodiment of the production of a core soot body in the present invention, and FIG. 3 is a schematic diagram showing the stepwise refractive index distribution structure of the dispersion-shifted fiber of the present invention A schematic diagram showing the refractive index distribution structure of the core glass body manufactured in the example of
FIG. 4 is a schematic diagram showing the refractive index distribution structure when the cladding glass body and the core glass body are integrated in an embodiment of the present invention, and FIG. FIG. 6 is a conceptual diagram illustrating a configuration for further synthesizing a soot body on the outer peripheral portion, and FIG. 6 is a schematic diagram showing a refractive index distribution structure of a preform obtained in an example of the present invention.

Claims (1)

[Claims] 1 The VAD method creates a central layer of SiO ₂ containing GeO ₂ and a substantially pure layer surrounding the central layer.
Create a soot body consisting of an outer layer made of SiO ₂ ,
The transparent glass body obtained by dehydrating and sintering the soot body is
Stretched in an atom-free atmosphere, the central part
A step of creating a core base material having a double structure consisting of a GeO _2- containing part and an outer part made of substantially pure SiO ₂ , and a step of creating a base material for a core with a double structure consisting of a GeO 2-containing part and an outer part made of substantially pure SiO 2, and
The center of a transparent glass body obtained by creating a soot body made of SiO ₂ , heat-treating the soot body at high temperature in an atmosphere containing fluorine, adding fluorine to the soot body, and sintering the soot body. A step of forming a cylindrical cladding base material made of fluorine-containing SiO ₂ by drilling a hole in the cladding base material and stretching as necessary; A method for manufacturing a dispersion-shifted single mode optical fiber, the method comprising the step of heating and integrating.