JPS6021930B2 - Optical fiber manufacturing method - Google Patents

Description

[Detailed description of the invention] ‘1} Field of application of the invention The present invention relates to a method of manufacturing an optical transmission fiber.

■Prior Art One method for producing optical fibers is a method called the rod-in-tube method.

As shown in Fig. 1, this method involves inserting a transparent dielectric rod 2 having a higher refractive index into a hollow tube 1 made of a transparent dielectric material such as quartz (Fig. The first step is to sequentially fuse the tube from the end using a heating source 3 such as an oxyhydrogen burner to create an optical fiber bream 4 (a material before being drawn into an optical fiber) (FIG. 2b). Subsequently, as shown in FIG. 2, the preform is drawn using a heating source 5 so that the cross-sectional area of the preform is reduced to obtain an optical fiber. However, the above method has a drawback that minute dust and the like existing on the inner wall surface of the hollow tube or the surface of the rod are trapped inside the preform when the hollow tube and rod are fused together. Further, there is a high possibility that minute air bubbles are left behind at the interface between the hollow tube and the rod for some reason during fusion. Such a defect at the interface between the hollow tube and the rod in the brefohm adversely affects the transmission characteristics of the optical fiber. That is, since the hollow tube constituting the bream serves as the cladding of the optical fiber after being drawn, and the rod serves as the core, defects at these interfaces cause transmitted light to leak out of the optical fiber. therefore,
Defects generated at the interface between the hollow tube and the rod during fusion greatly deteriorate the light transmittance of the optical fiber. Publications related to the Rodin tube method include, for example, Japanese Patent Publication No. 1973-
Publication No. 11071 and Publication No. 45 of Kyokai 50-8 Ball are known.

'3} Purpose of the Invention The purpose of the present invention is to eliminate the above-mentioned defects at the interface between the hollow tube and the rod during fusion.

'4 - General description of the invention The present invention involves attaching a flexible thin film having a softening temperature lower than that of the hollow tube and the rod to the inner wall surface of the hollow tube or the outer circumferential surface of the rod before the above-described fusion bonding between the hollow tube and the rod. be.

By attaching a thin film with a softening temperature lower than that of the hollow tube and rod in this way, a molten material with a low softening temperature is deposited at the interface between the hollow tube 1 and the rod 2 during fusion, as shown in Fig. 3. 8 is formed. When the heating source is moved in the direction of the arrow in the figure, this molten material is pushed out in the direction of the arrow by the surface tension of the heated hollow tube, and after welding the entire longitudinal section of the tube, it forms a blemish. Most of it is discharged outside. At this time, if minute dust or the like is attached to the inner wall surface of the hollow tube or the outer circumferential surface of the rod, it will be incorporated into the melt 8, and after fusion, most of it will be transferred to the outside of the fused material 8. It is discharged along with the Therefore, the light transmittance of the optical fiber obtained by drawing the bleforome produced as described above is greatly improved. By the way, for some reason, all of the molten material 8 formed during fusion bonding may not be discharged to the outside of the preform. At this time, the melt remaining in the preform may adversely affect the transmission characteristics of the optical fiber drawn from the preform. This negative effect is mainly due to the discontinuous change in refractive index from the core to the cladding of the optical fiber due to the residual melt. In order to prevent this, the refractive index of the dielectric thin film to be deposited must be set to n,
If the refractive index of the optical fiber core is n, and the refractive index of the cladding is a ratio, then n may be set to noSn min n'. As a result, even if not all of the melt is discharged out of the bleederm, it will not adversely affect the transmission characteristics of the optical fiber. Incidentally, the adverse effect of residual melt on the transmission characteristics is almost negligible, and when using an optical fiber, there is no need to impose strict restrictions on the refractive index of the attached thin film. Now, as the material for the conductor thin film to be used, when the hollow tube and rod are made of high silicate glass or fused silica, a low softening point glass is most ideal.

As a low softening point glass, soda lime silica glass (N
In addition to general glasses such as a20-Ca○-Si02) and soda borosilicate glass (Na20-B203-Si02), glasses containing cationic oxides as additives to Si02, such as Si02-chord 03, glass Si02
-Sub02-B03 glass, Si02-P205-&03
A material such as glass in which the proportion of Si02 is not relatively large can be considered. In particular, in the Sj02-Ge02-string 02 and Si02-P205-B203 glasses, the serpentine 02 has the effect of making the refractive index higher than that of fused silica, and the &03 has the effect of making the refractive index lower. Therefore, when creating a preform with a hollow tube and rod of high silicate glass, the refractive index n of the two types of glasses mentioned above is set to the above-mentioned noSnSn. can be easily placed within the range of Considering this point, Sj02-
P205-&03 glass and Si02-QQ-&03 glass are considered to be excellent materials since they are less likely to deteriorate the transmission characteristics of the optical fiber. '5} Examples Hereinafter, the present invention will be explained in detail with reference to Examples.

- Example 1 As shown in FIG. 4, a fused silica tube 16 with an outer diameter of 140 and an inner diameter of 12 is used as a hollow tube made of a transparent dielectric material, and Si02-J02-B203 glass is coated on its inner wall surface. Attached.

The attachment method is as follows: from one side of the fused silica tube 16 to the SIC side 4.
, BBr3, QC24, and ○2 gases are fed into the rotating tube 16 using a moving heating source 3 to locally heat the rotating tube 16, thereby depositing SiQ-J02-B203 glass on the inner wall surface of the tube. It is. Source gases such as SIC and 4 are conveyed by Q carrier gas and fed into tube 16 using bubblers placed in thermostats 10, 12, and 14 whose temperatures are fixed at 2 and 0. In the experiment of this example, SI
C official carrier gas flow rate is 120cc/min, QC
〆4 Gas flow rate is 150cc/min. The gas flow rate for BBr3 was set to 200 cc min. In addition to the carrier gas 02 gas, 130 cc/min of the 02 gas is fed into the pipe 16. The moving heat source 3 was moved twice in the longitudinal direction of the tube at a moving speed V' of 2.5 sails/sec. The reaction temperature at this time is about 900 oo. As a result, it was possible to uniformly deposit Si02-J02-B203 glass on the inner wall surface of the quartz tube in the longitudinal direction with a thickness of about 1 m and having a refractive index almost the same as that of fused silica. Next, as shown in FIG. 3, using fused silica birch doped with Ti02 as the rod 2, the heating source 3 was moved at a speed of about 1 min/min.
While moving the rod 2 and quartz tube 1 at a temperature of 1900
It was fused with oo. The light transmittance of the optical fiber obtained by drawing the preform 2 created in this way is at wavelength 8.
Approximately 5. It was old/boiled. Si02 on the inner wall surface
-02-B203 When an optical fiber is made using a quartz tube without glass deposited, its light transmittance is 20b.
It was better than B/. Therefore, by using the manufacturing method according to the present invention, the light transmittance is improved by more than four times. Example 2 In Example 1, Si02-02-&02 was applied to the inner wall surface of the quartz tube.
Although glass was deposited, in this example, Si02-P2Q-
B03 glass was deposited.

The deposition method was the same as in Example 1, using C as the source gas.
POC part 3 was used instead of part 4. However, P.O.C.
Since POC3 and BBr3 react at room temperature to produce white powder, POC3 was sent into the quartz tube through a different route from the other source gases. The 02 Chiaria gas flow rate for each source is 120cc/min for SIC So4 and 120cc/min for POC.
Part 3 is 400cc/min, BBr3 is 250cc/min
It is min. Also, remove excess 02 gas at 200cc/mi.
n flowed. The moving speed of the moving heating source is 2.5 rails/sec.
, the heating temperature was about 90,000, and the heating source was moved twice in the longitudinal direction of the tube. The resulting Si02
-P205-B203 glass had a film thickness of about 1 m and a refractive index almost the same as that of fused silica. The method of welding with the rod and the material of the rod are the same as in Example 1. The optical fiber thus prepared has a light transmittance of approximately 4.0 at a wavelength of 830. Dish B/Boiled. Therefore, it can be seen that the light transmittance is significantly improved even when Si02-P205-B203 glass is used as the glass material.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating a method of creating an optical fiber beam using the rod-in-tube method. FIG. 2 is a diagram showing a preform drawing process. FIG. 3 is a diagram showing a state in which a film with a low softening temperature is attached and fused to the inner wall surface of a transparent dielectric tube. FIG. 4 is a block diagram showing a method of depositing a glass film with a low softening temperature on the inner wall surface of a transparent dielectric tube (fused silica tube). Ta' Genta Z diagram Ta 5 Europe Ta 4 diagram

Claims (1)

[Claims] 1. A rod made of a transparent dielectric material having a higher refractive index than the core hollow tube is inserted into a hollow tube made of a transparent dielectric material, the two are heated and fused, and then this cut is made. In a method of producing an optical fiber by drawing to reduce its area, a transparent material having a softening temperature or melting point lower than that of the hollow tube and the rod is applied to the inner wall of the hollow tube or the surface of the rod before heat fusing. A light source characterized in that the rod is inserted into the hollow tube after forming an electric thin film, and most of the melted material of the dielectric thin film is discharged to the outside of the hollow tube during heating and fusing. Method of manufacturing fiber. 2 When the refractive index of the hollow tube, the rod, and the dielectric thin film are n_0, n, and n_1, respectively, n_0≦
The method for manufacturing an optical fiber according to claim 1, characterized in that n≧n_1.