JPS6183642A - Production of parent material of optical fiber - Google Patents

Abstract

PURPOSE:In production of a parent material for optical fiber by vapor phase axial deposition method, to produce optical fiber of multimode graded wide-band in high yield in high reproducibility, by changing periodically a composition of raw material to be fed to a target. CONSTITUTION:Glass fine powder formed by flame hydrolysis method from the quartz burner 8 is sprayed and piled on the target 1 which is pulled up while being rotated, to form the porous parent material 3 for optical fiber. In the above-mentioned device (the winder 5 for measuring reaction temperature of the porous parent material 3), amounts of oxygen and hydrogen to be fed to the outer pipe of the burner 8 is controlled by the electrical signal from the oscillator 11 and the infrared temperature measuring device 6, so that the maximum temperature in the glass powder piled layer is changed periodically in a given range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Background and Objects of the Invention] The present invention relates to a method for manufacturing an optical fiber preform by a vapor deposition (VAD) method.

In general, the VAD method for manufacturing optical fiber preforms is extremely superior in terms of productivity. Then, raw material gas such as silicon chloride (Si Cf14) that becomes the base glass,
Germanium chloride (GeCJa) to control refractive index
), phosphorous chloride oxide (POC) 3), etc. are reacted using heat such as an oxyhydrogen flame. The glass fine powder produced by this reaction is sequentially deposited at the tip of the target, and the radial refractive index distribution of the final glass is controlled by the temperature distribution at the tip. Therefore, controlling the temperature at the leading edge has a large effect on the transmission characteristics of the optical fiber manufactured from the optical fiber base material, particularly on the transmission band characteristics of the multimode graded optical fiber.

Conventionally, methods for adjusting the temperature of the leading edge portion to a constant level have been proposed for each scale, and at present, the technology for adjusting the temperature within the range of ±1 to 2°C has been almost established, and the reproducibility of the characteristics has improved. However, there are still many problems in improving the reproducibility of band characteristics and improving the yield of broadband fibers, and the situation is not necessarily satisfactory.

The present invention was made in view of the above-mentioned situation, and aims to improve the reproducibility of the band characteristics of a multimode graded optical fiber,
The object of the present invention is to provide a method for manufacturing an optical fiber preform that can significantly improve the yield of broadband fiber.

E. Summary of the Invention] The method for producing an optical fiber preform of the present invention involves reacting raw material gases such as silicon chloride and germanium chloride in an oxyhydrogen flame in which oxygen and hydrogen are fed into an oxyhydrogen burner and burned. When producing a powder, depositing the fine glass powder on the tip of a target to form a porous base material, and heating and transparentizing the porous base material to manufacture an optical fiber base material, the flow rate of the oxygen or hydrogen, etc. In this method, the refractive index distribution index α of the optical fiber preform after being made transparent is varied in the longitudinal direction by periodically varying the deposition conditions of the fine glass powder at the tip of the target.

[Example] The method for manufacturing an optical fiber preform of the present invention will be explained below using an example and FIG. 1. FIG. 1 is a longitudinal sectional view of the implementation device. In the figure, 1 is the target, 2 is the chamber, and 3
is a porous matrix (soot) consisting of deposited fine glass powder
, 4 is the end of the porous base material wire of the deposited glass fine powder layer, and is the highest temperature point. 5 is a window for measuring the reaction temperature of the porous base material 3, 6 is an infrared temperature measuring device, and 7 is an oxyhydrogen gas flow direction adjustment 8! It is. 8 is a quartz tube burner, 9 is a chamber stand, 1
0 is an exhaust port, and 11 is an oscillator that changes the target temperature with a constant cycle and amplitude. In addition, the quartz burner 8 discharges raw material gas 3iC1a .Ge C1! from its central burner. a・
It has a composite burner structure in which POCf3, etc. is fed in, and oxygen and hydrogen, or Ar, N2, etc. are fed in from the burner in the outer tube.

The difference between this embodiment and the conventional optical fiber preform manufacturing method is that the oscillator 11, the infrared ray 1! i! The point is that the maximum temperature during the deposition of fine glass powder is intentionally periodically varied within a certain range by adjusting it with an electric signal from the secondary temperature measuring device 6.

Then, the raw material gas, oxygen, hydrogen, and other gases are fed into the quartz tube burner 8, and the high-pressure gas is reacted in an oxyhydrogen flame to sequentially deposit glass fine powder onto the tip of the rotating target 1. While generating, the porous base material 3 is gradually pulled up to form the porous base material 3. On the other hand, oxygen and hydrogen used for combustion, and Ar and N used for reaction control.
The second gas or a part of the generated glass fine powder is exhausted from the exhaust port 10, and the pressure inside the chamber 2 is always maintained at a constant pressure.

Under normal conditions, the M chord is 8.5.1! /min, hydrogen is 4.5I! It is used at a flow rate of about /min. In this case, the flow rate of hydrogen is such that the temperature at the optimum temperature point of the porous base material wire end 4 of the crow fine particles deposited on the target 1 is 102
The flow rate was adjusted to 0℃, and the flow rate was 10cc.
It has been confirmed through experiments by the present inventors that a change in 'min' causes a temperature change of approximately 1° C., and that the refractive index component tri index α changes by approximately 0.03.

Figure 2 shows the relationship between the refractive index distribution index α at each wavelength on the horizontal axis and the band on the vertical axis. Nippon Telegraph and Telephone Public Corporation Research and Application Report No. 29 @ No. 2 (1980)
11.3am? This is a graph derived from a theoretical calculation formula published in JLLFT Grated Optical Fiber Manufacturing Technology. In Figure 2, the solid curve is o, 82
μm wavelength, the dotted curve is the wavelength of 1.27 μm. As can be seen from the figure, the range of the refractive index distribution index α that provides a wide band at each wavelength is extremely narrow, and furthermore, the obtemum values for short and long wavelengths are slightly different, so it is difficult to widen each wavelength band. Of course, it can be inferred how difficult it is to improve the reproducibility of so-called double-window type manufacturing, which aims to achieve a wide band for both waves.

In this embodiment, the electric signal from the oscillator 11 is oscillated at a period of approximately 2 minutes, and this is fed back to the flow direction of the hydrogen gas, thereby controlling the temperature at the extreme temperature point of the tip 4 of the opposing material base material during deposition. , and the flow rate of hydrogen gas is changed within a range of about 3°C, and the change in the flow rate of hydrogen gas is about ±3Qcc/min.

The optical fiber manufactured from the porous base material 3 manufactured as described above should have a refractive index distribution index α changing in the longitudinal direction with a period of about 200 to 300I11, and this is about 500 m. When the band characteristics were examined in the longitudinal direction, it was found that the fluctuation range was small and the proportion of broadband characteristics was significantly improved. In particular, the yield of double-wind type fiber, which can be used for both long and short distances, has been significantly improved, and the band degradation index (γ
:0.5≦T≦1) was also smaller than the conventional product, and was found to be suitable for long-distance transmission. It has also been confirmed that there is almost no difference in characteristics other than band characteristics, such as connection loss characteristics, FRF stress characteristics, temperature characteristics, and loss characteristics at room temperature, from conventional products.

In addition, in multimode graded optical fibers in which the refractive index distribution index α varies in the longitudinal direction, the optical fibers that propagate each mode easily cause coupling, reducing the total delay time difference between modes. It is well known that it is possible to increase the bandwidth by increasing the bandwidth. However, if the temperature at the tip of the target is precisely controlled to a constant value, due to subtle differences in other manufacturing conditions, the refractive index distribution index α may end up being controlled to a constant value at a point that deviates from the target value. In many cases, it was a narrowband fiber. In addition, there were also large variations in band characteristics in the longitudinal direction.

According to the method of this embodiment, the refractive index distribution index α does not deviate from a constant, and even when it deviates slightly, the refractive index distribution index α fluctuates periodically, so an extremely narrow band will not occur. It disappears.

In this way, in the method for manufacturing the optical fiber preform of this example, the refractive index distribution after transparentization is controlled by periodically changing the deposition temperature of the fine glass powder at the tip of the target and the flow rate of oxygen or hydrogen. The index α can be changed in the longitudinal direction, and the yield of fibers with broadband characteristics can be greatly improved, and changes in the band characteristics in the longitudinal direction can be reduced. In particular, the yield of both long and short-purpose fibers is greatly improved, and the index γ of band characteristics, which deteriorates as the length of transmission increases, is smaller than that of conventional products, making it suitable for long-distance transmission.

[Effects of the Invention] As described above, the method for manufacturing an optical fiber preform of the present invention has the effect of significantly improving the reproducibility of band characteristics of multimode graded optical fibers and the yield of broadband fibers. It is.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an apparatus for carrying out the optical fiber preform manufacturing method of the present invention, and Figure 2 shows the refractive index distribution index α and band at each wavelength published in the research and practical application report of Nippon Telegraph and Telephone Public Corporation. It is a graph of a theoretical calculation formula expressing the relationship. 1: Target, 3: Porous base material, 4: Tip of porous base material, 7: Oxygen hydrogen gas flow rate adjustment device, 8: Quartz tube burner, No. 2 Figure 1.7 +, 8 1. q 2. o2.
1. Representation of the incident 2. Name of the invention Method for manufacturing optical fiber base material

Claims (3)

[Claims] (1) Oxygen and hydrogen are fed into an oxy-hydrogen burner and reacted with raw material gases such as silicon chloride and germanium chloride in an oxy-hydrogen flame, which burns, to generate fine glass powder, and the fine glass powder is deposited on the tip of the target. In the method of manufacturing an optical fiber preform by forming a porous preform by heating and making the porous preform transparent, the flow rate of the oxygen or hydrogen is periodically varied to remove the fine glass powder at the tip of the target. A method for manufacturing an optical fiber preform, characterized in that the refractive index distribution index α of the optical fiber preform after being made transparent is changed in the longitudinal direction by changing the deposition conditions. (2) The method for manufacturing an optical fiber preform according to claim 1, wherein the period of varying the flow rate of oxygen, hydrogen, etc. is 500 m or less in terms of finished fiber length, etc. (3) The range in which the refractive index distribution index α is changed is ±0.
．． 01 to ±0.1. The method for manufacturing an optical fiber preform according to claim 1.