JPS62292647A - Production of decentralized-shift single-mode optical fiber - Google Patents

Abstract

PURPOSE:To easily produce the title decentralized-shift single-mode optical fiber by inserting a core base material consisting of an SiO2 central layer contg. GeO2 and an SiO2 outer layer part into an SiO2 cylindrical clad base material contg. F, and integrating the materials on heating. CONSTITUTION:A soot body consisting of the central layer consisting of SiO2 contg. GeO2 and the outer layer part surrounding the central layer and consisting essentially of pure SiO2 is prepared by a VAD process. The soot body is dehydrated, sintered, and clearly vitrified. The obtained transparent glass body is drawn in an atmosphere free of an H atom, and the double-structure core base material consisting of a GeO2-contg. part at the central part and essentially pure SiO2 on the outside is obtained. The essentially pure SiO2 soot body formed by a VAD process is heated at a high temp. in an F-contg. atmosphere to add F to the soot body. The soot body is then sintered and clearly vitrified, a hole is bored at the central part, and a cylindrical clad base material is obtained. The core base material is inserted into the clad base material, both materials are integrated on heating, and the base material for the fiber having a step- formed refractive index is obtained.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method of manufacturing a single mode optical fiber having a zero dispersion wavelength in the 1.5μ band.

[Conventional technology]

1, 5 with minimum transmission loss in silica-based optical fiber
Single-mode fiber (hereinafter referred to as dispersion-shifted fiber), which has all zero dispersion wavelengths in the µm band (t SO ~ 1.60 μm), is being researched and developed as a long-distance, high-capacity optical communication line. There is. Among the refractive index distribution structure designs for dispersion-shifted fibers, a step-like refractive index distribution structure as shown in FIG. 1 has been proposed as a structure that is highly resistant to bending loss. In FIG. 1, 1 is an inner core, 2 is an outer core, 5 is a cladding, and n, . . . are their respective refractive indices.

[Reference 1: Ohashi et al. [Characteristics of dispersion-shifted fiber with stepped refractive index distribution], Proceedings of the 1985 IEICE Semiconductor and Materials Division National Conference, page A15. Reference 2: K., Kwaki et al. “Dispersion-Shifted Convex Index Single Mode Fibers” Electronics Letters, 1985, Vol. 21, 1186-1
187 pages. Reference 3: Kuwagi et al., "Characteristics of α-th power distribution stepped dispersion-shifted fiber," Proceedings of the 1986 Institute of Electronics and Communication Engineers National Conference, p. 1072] As seen in the above-mentioned Reference 5, the refractive index of the inner core is the same as that of the cladding. In comparison, the relative refractive index difference is as high as about 1.0 inches.

Ge is the most common additive for increasing the refractive index in silica-based optical fibers, but if only Ge is used to form the refractive index distribution as shown in Figure 1, The contained GeO,ii becomes extremely high and Go
o! scattering loss increases. On the other hand, the component that lowers the refractive index is 0. and F are often used. In particular, F is B, 0. As it does not have an absorption band near the 1.5 μm band, it is an advantageous material for reducing loss. Therefore, it is effective to reduce the loss by adding F to the cladding part 3 to reduce the amount of Gem2 in the inner core 1 [Reference 4: H, Yokota et al.
Allied Crusting Pie the Paper Phase Axial Deposition Method (VAP)
Dispersion-shifted fibers with F-doped cladding prepared by the method), Funference on Optical Fiber Communications Technical Digest, 1986, Atlanta, Georgia, USA, VIP2).

[Problem that the invention seeks to solve]

The WAD 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,
Another problem is that it is difficult to create a complex refractive index distribution structure such as a base material for a dispersion-shifted fiber in which F is selectively added to the cladding portion and GeO2 is selectively added to the inner core. In view of the current situation, it is an object of the present invention to provide a new and excellent method for easily manufacturing a base material for a dispersion-shifted fiber having a stepped refractive index distribution by effectively utilizing the VAI method. It's a thing.

[Failure to solve the problem]

The present invention uses Gem! a central layer of 5i01 containing substantially pure Si surrounding the central layer;
A soot body consisting of an outer part made of A step of creating a core base material having a double structure consisting of a portion consisting of substantially pure 8102, and creating a soot body consisting of substantially pure SiO1 by WAD method,
That suit? Fluorine is added to the soot body by heat treatment at high temperature in an atmosphere containing fluorine, and this? A hole was made in the center of the transparent glass body obtained by sintering, stretched as necessary, and completely fluorine-contained. Dispersion-shifted single mode light characterized by comprising a step of creating a cylindrical cladding base material, and a step 8 of inserting the core base material into the cladding base material and heating and integrating both parts. This is a method of manufacturing fiber.

In the present invention, QeO! A core glass body having an inner core doped with Fl! I: Create a glass body for cladding containing the additive, and After processing the additive cladding glass body into a pipe, inserting and integrating the core glass body into the cladding glass pipe,
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.

(2) Glass body for the core The soot body for the core is manufactured by the VAD method using a configuration as shown in FIG. 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. SiO/4, Gee/4, Hl in the burner 5 for glass particle synthesis for the inner core
+O2 and Ar were supplied, and Si (!/4, B4, 02, A
SiO/4 in flames 5 and 6 of each burner.
, Gee/, to form glass particles (soot)
A soot body 9 consisting of a GeO2-containing soot body 8 corresponding to an inner core and EliQ corresponding to an outer core surrounding the soot body 8 is simultaneously deposited on the rotating starting quartz rod 7. 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 atoms, such as in an electric resistance furnace, a glass body for a core drawn to a predetermined diameter is obtained. In this way, 5 containing Ge
It is possible to obtain a glass body for a core having a double structure consisting of an inner core made of Sing.102 and an outer core made of substantially pure Sing.

Note that when drawing the core glass body, it is not preferable to draw it in an atmosphere containing atoms because the surface of the core glass body will be contaminated with OH groups and cause transmission loss of the optical fiber.

■ Preparation of glass body for cladding A soot body made of pure eio is formed by the WAD method, and the soot body is heated in an atmosphere containing F such as S i F! (approximately 1100 to 1200°C) to dehydrate the soot body and add F to the soot body,
Thereafter, a high temperature (approximately 1,600° C.) treatment is performed to make the material transparent and a glass base material for a cylindrical cladding made of 7-doped Sin can be obtained. A hole is made in the center of the cylindrical cladding glass base material using an ultrasonic drilling machine, etc., and after stretching as necessary, the inside of the pipe is filled with a material such as EIF6 that has a glass etching effect. The inner surface of the pipe is etched and smoothed by heating with an oxyhydrogen flame or the like from the outside while flowing a compound gas. In this way, a pipe-shaped cladding glass body doped with 7 can be obtained.

(5) Integration of core glass body and cladding glass body After inserting the core glass body obtained in step ① into the pipe-shaped cladding glass body obtained in step ②, it is heated with oxyhydrogen flame etc. from the outside. By heating and shrinking the glass body for the cladding and fusing and integrating the glass body for the core and the glass body for the cladding, a refractive index distribution structure as shown in FIG. 1 is obtained.
It is possible to produce a base material for a dispersion-shifted fiber in which GeO2 is added to the core and F is added to the cladding.

In addition, by further depositing a soot body on the outer periphery of the base material produced in steps ① to ① above, adding F to the soot body as described in ②, and performing transparent vitrification treatment,
A base material having the same cross-sectional structure as a dispersion-shifted fiber having a structure in which F is uniformly added to the outermost layer of the fiber can be produced, and a dispersion-shifted fiber can be produced by drawing this base material. Can be done.

Alternatively, a dispersion having a structure in which F is uniformly added to the outermost layer of the fiber can also be obtained by inserting and integrating the base material produced in steps ① to ③ into a glass pipe added with F made in the same process as ②. A base material having the same cross-sectional structure as the shifted fiber can be manufactured.

〔Example〕

Example 1) Preparation 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.
/, 120 squares/min, GθC/.

120cc/min, Ar 2.51/min, Horse 3//min,
02 for 6.017 minutes, S i C/, 550 cc/min, A
r 1017 minutes, horse 121/minute, 0. A core material soot body having an outer diameter of 100 mm and a fin length of 500 mm was synthesized. The soot body for the core material is C1: He snow 1:
5 mice/in a ring-shaped electric furnace at 1100℃ in an atmosphere of
After dehydration treatment, the glass was passed through a ring-shaped electric furnace at 1,600°C in an He atmosphere at a rate of 4 tubes/minute to form transparent glass with an outer diameter of 40 mm and a length of 200 mm. A glass body for a core was obtained. 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 approximately 500× length pieces. The refractive index distribution structure of this core glass material is shown in FIG. This core glass material was washed with 10 g of HF solution for about 3 hours to remove surface stains.

2) Preparation of glass body for cladding A pure 810 glass body with an outer diameter of 120 mm and a length of 600 mm was prepared using the WAD method.
Create a suit body consisting of 1, and convert this suit body to SiF,
: C31t: He-(LO8: CLl 5:15
2. The inside of a ring-shaped electric resistance furnace heated to 1150°C in an atmosphere of 2. /min, the soot body was subjected to dehydration and P treatment, and further 5ilF4:He -(LO8: 1
The cod was passed through a ring-shaped electric resistance furnace heated to 1,600°C in an atmosphere of
A glass body for cladding containing 5% by weight was obtained.

The dimensions of the cladding glass body at this time were an outer diameter of 50 days and a length of 280+wa. A hole with a diameter of 8 mm was made in the center of this glass body for cladding using an ultrasonic drilling machine, and then heated and stretched using an oxyhydrogen flame to form an outer diameter of 25 m, an inner diameter of 41 m,
A pipe-shaped cladding glass with a length of 1120 cm was used. This was divided into 280m+ length sections. Furthermore, SF was applied inside the cladding pipe at 200 cc/min, 0° to 60°.
While flowing at 0 cr for 7 minutes, the inner surface was heated with an oxyhydrogen burner and smoothed while etching the inner surface, reducing the inner diameter to 6.
It was set to 1111.

S) Integration of core glass body and cladding glass body After inserting the core glass body obtained in 1) into the cladding pipe obtained in 2), it is heated from the outside with an oxyhydrogen flame to form a core glass body. After cleaning the surface of the glass body and the surface of the glass body for cladding, the glass pipe for cladding was heated and shrunk to weld and integrate the glass body for core and the glass body for cladding. FIG. 4 shows the refractive index distribution of the base material thus obtained.

4) The base material obtained in subsequent steps 1) to 3) is stretched to an outer diameter of 15fi, and a soot body made of pure EIi02 is deposited on the outer periphery of the base material in a configuration as shown in FIG. Thereafter, F was added to the soot body under the conditions shown in 2) and the soot body was made into transparent glass to obtain a preform having a structure as shown in FIG. 6. In FIG. 5, 10 is a burner for glass particle synthesis, 11 is the base material obtained in 1) to 5) stretched to an outer diameter of 1511s, 12 is a soot body, and 15 is a supporting dummy rod. The preform was drawn to have an outer diameter of 125 μm to obtain a dispersion-shifted fiber. The zero dispersion wavelength of this fiber is 1.552μ
The transmission loss at 1.55 μm is α2 s aB/km
Therefore, characteristics with no problems in practical use were obtained.

〔Effect of the invention〕

In the present invention, GeO! A dispersion-shifted fiber with a stepped refractive index distribution in which 7 is selectively added to the cladding can be realized by separately fabricating the core and cladding glass bodies and integrating them. The dispersion-shifted fiber according to the present invention has zero dispersion in the 1.5 μ inertia band and has excellent transmission loss characteristics.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the stepped 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. FIG. 4 is a schematic diagram showing the refractive index distribution structure of the core glass body manufactured in the example of the present invention, and FIG. 4 shows the refractive index distribution structure when the cladding glass body and the core glass body are integrated in the example of the present invention. FIG. 5 is a conceptual diagram illustrating the structure when a soot body is further synthesized on the outer peripheral part of the cladding glass body in an example of the present invention, and FIG. 6 is a schematic diagram showing the structure obtained in an example of the present invention. FIG. 3 is a schematic diagram showing a refractive index distribution structure of a preform.

Claims (1)

[Claims] A central layer made of SiO_2 containing GeO_2 and a substantially pure SiO_2 surrounding the central layer are formed by the VAD method.
A soot body consisting of an outer layer portion consisting of 2 is prepared, and a transparent glass body obtained by dehydrating and sintering the soot body is stretched in an atmosphere containing no H atoms to form a central GeO_2-containing portion and a substantially outer layer thereof. A process of creating a base material for a core having a double structure consisting of a portion consisting of pure SiO_2, and a step of creating a soot body made of substantially pure SiO_2 by the VAD method, and placing the soot body in an atmosphere containing fluorine. Fluorine is added to the soot body by heat treatment at a high temperature, and the resulting transparent glass body is sintered. The central part of the transparent glass body is perforated and stretched as necessary to form a cylindrical shape made of SiO_2 containing fluorine. 1. A method for manufacturing a dispersion-shifted single mode optical fiber, comprising the steps of: creating a cladding base material; and inserting the core base material into the cladding base material and heating and integrating the two.