JPS597651B2 - Manufacturing method for optical transmission materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing an optical transmission material with extremely low optical loss, particularly a single mode material with a large transmission capacity.

In a single mode transmission line, the diameter is 1 as in the case of a multimode transmission line.
00ttm, but the core diameter that becomes the optical path is 10tm.
By keeping it below tm, it is possible to reduce the disturbance of signal light pulses and significantly increase the transmission density of pulse signals compared to a multimode transmission line with a mixture of various modes, so it can be used over long distances such as submarine cables.・It is expected that it will be put into practical use for high-density transmission.

In this way, for the purpose of long-distance transmission, particularly low optical loss is required. The rod-in-tube method, which is a typical manufacturing method for optical transmission materials, involves inserting a quartz glass rod as a core material into a quartz glass tube as a cladding material, heating it, and welding the cladding material and the core material.
This method is spun into fibers for transmission materials. This method allows for easy regulation of the dimensional accuracy of each material and is highly suitable for mass production, but it is prone to bubbles and impurities at the interface between the core material and cladding material. Therefore, the disadvantage was that the optical loss of the fiber was large.

As a method to solve this drawback, the present applicant has already proposed Japanese Patent Application No. 53-143160 (Japanese Unexamined Patent Publication No. 55-171636).
In the specification, before welding the core material and the cladding material, C) at least one member selected from the group consisting of N, O, S, Be and at least a halogen is added to the gap between the core material and the cladding material. Impurities on the inner surface of the cladding material and on the surface of the core material are removed as volatile halides by flowing a compound that is fluid at room temperature and does not contain hydrogen as a vapor phase heat treatment agent. Discloses a method for manufacturing an optical transmission material (hereinafter referred to as the "prior invention") comprising:

When the method of the previous invention is applied to manufacturing a single mode transmission line, the following problems arise.

That is, if a rod with a diameter of 6 mm or more, which is easy to manufacture and handle, is used as the core material, the inner diameter of the clad material suitable for the above-mentioned vapor phase heat treatment and welding of the core material and clad material is 8 to 12 mm. , the wall thickness of the cladding material is 3
0 mm or more is required. In order to heat the inner surface of such thick-walled tubes with low thermal conductivity, external heating methods expose the outer surface of the tube to excessively high temperatures and require a long heating time.
This is unsuitable as it tends to cause thermal deformation of the cladding material. The present invention solves the above-mentioned problems of the previous invention, and makes it possible to manufacture optical transmission materials with extremely low optical loss, especially single-mode materials with large transmission capacity, without causing thermal deformation of the cladding material. This method provides a method for manufacturing an optical transmission material, which comprises welding a core material to the inner wall of a tubular cladding material and spinning the core material, the cladding material and the core material. C. inside the clad material before welding. ．． NlO,S,. A compound that is fluid at room temperature and contains at least one selected from the group consisting of sel and at least one halogen and does not contain hydrogen,
A method for manufacturing a material for optical transmission, characterized by flowing in a gas phase under non-equilibrium plasma generation.

As described above, in the present invention, in order to bring the core material and the cladding material into a heating state for performing the above-mentioned vapor phase treatment before welding,
Instead of the external heating method in the previous invention, non-equilibrium plasma generated inside the cladding material is used.

That is, under a non-equilibrium plasma generated inside the cladding material through a high-frequency induction coil provided surrounding the cladding material, the above-mentioned C, NlO, S, . A gas-phase heat treatment agent made of a compound that is fluid at room temperature and contains at least one selected from the group consisting of Se and at least one halogen and does not contain hydrogen is introduced in the gas phase, and the heat generated by the non-equilibrium plasma or The chemical activation action promotes the purification effect of the gas-phase heat treatment agent on the inner surface of the cladding material or the surface of the core material inserted into the cladding material before welding.
In the present invention, the high frequency power frequency required to generate plasma discharge inside the cladding material tube is 0.2MHz.
~30GHz.

If the frequency is less than 0.2 MHz, the pipe diameter of the cladding material that confines the plasma becomes large, and if the frequency is more than 30 GHz, the cost of the device becomes excessive, so both are inappropriate.
In the present invention, when inserting the core material and the cladding material into the cladding material before welding, they must be mechanically polished, chemically polished, or heat treated in advance, and the core material should not be inserted into the cladding material before welding. Only the inner surface of the cladding material is subjected to the above vapor phase heat treatment, and a core layer is precipitated and adhered to the inner surface of the cladding material purified by this vapor phase treatment in an extremely pure state substantially as if it had been subjected to vapor phase heat treatment. In some cases, the core material is made into a solid core material by stretching, but in this case, it goes without saying that the core material does not need to be subjected to mechanical polishing or the like in advance.

As described above, the present invention generates non-equilibrium plasma within the cladding material, thereby reducing optical loss without causing thermal deformation of the cladding material even in the production of single mode materials with large transmission capacity. This method provides a method for manufacturing optical transmission materials with a small amount of material, and its industrial value is extremely large.

EXAMPLES Next, the present invention will be specifically explained using Examples, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded.

Example 1 A high-purity synthetic quartz glass rod (diameter 6 mm) doped with 1.8% A1203 was mechanically polished, and then superabsorbed in each solution in the following order: perchloroethylene, ethanol, pure water, 10% hydrofluoric acid, and pure water. Sonically cleaned, then heated in an electric dryer for 120
Dry at °C.

This doped quartz glass rod was inserted into the axial center of a quartz glass tube (inner diameter 12u1 outer diameter 72 mm) that had undergone a similar cleaning process, and was rotated on a glass lathe to connect the quartz glass tubes from one end of the quartz glass tube. While evacuating the space between the quartz glass rod and the quartz glass rod using an oil rotary pump, 20 m1/min of He gas and gaseous CCl4O were supplied from the other end of the quartz glass tube.
, 5 ml/min, and the nonequilibrium plasma zone generated by a high-frequency induction coil surrounding the quartz glass tube was traversed 20 times along the gas flow at a moving speed of 90 cTn/min. A water-cooled copper pipe (outer diameter 4 m 1 fL) wound 6 turns within a width of 30 u was used as a high-sonic induction coil, and high-frequency power at a frequency of 13.56 MH2 was applied. The input was 300 W, of which it is estimated that about 70% was consumed in the cavity within the high-frequency induction coil. On the other hand, the degree of vacuum inside the quartz glass tube was about 5T0rr at the inlet of the oil rotary pump. After traversing the plasma zone 20 times, gaseous CCl4
The flow of 02 gas was stopped, and 0.5 m1/min of 02 gas was flowed instead, and the plasma zone was transferred and heated 20 times to oxidize and remove the carbon deposited by thermal decomposition of CCl4. The inflow of both the gas and the 02 gas was stopped, and the quartz glass tube was externally heated with an oxyhydrogen burner while maintaining a vacuum, thereby welding the quartz glass tube and the quartz glass rod.

Next, this rod-shaped molded body was drawn to a diameter of 2011 mm using a drawing machine, and then made into a fiber with an outer diameter of 120 ttm and a core diameter of 10 μm using a drawing device.The optical transmission loss of this fiber was measured, and it was found that at a wavelength of 0.8 μm. 3.7dB
/K7l was obtained. As a comparative example, the light transmission loss of the fiber without the above gas phase heat treatment using CCl4 was 18.3 dB/Km at a wavelength of 0.8 μm. Example 2 An undoped high-purity synthetic quartz glass rod (diameter 7m7!L) was mechanically polished and wet-cleaned in the same manner as in Example 1. A 0.5% fluorine-doped quartz glass tube was wet-cleaned in the same manner. (inner diameter 14 m7! L1 outer diameter 75.5 mm), and rotated it with a glass lathe, and then inserted the CF2Cl2O. 2ml/min, Ar gas 5
m1/min, 02 gas at 0.2 m1/min, and a plasma band generated at a frequency of 0.44 MHz by the same high-frequency induction coil as in Example 1 was transferred at a moving speed of 30 m1/min. Thirty traverses were made along the flow.

The input power of the high frequency oscillator was 150 W, and it is estimated that 80% of it was consumed in the cavity within the high frequency induction coil. On the other hand, the degree of vacuum inside the quartz gas tube was about 1T0rr at the inlet of the oil rotary pump. Next, the inflow of all the above gases is stopped, and the quartz glass tube is externally heated with an oxyhydrogen burner while being evacuated to weld the quartz glass tube and the quartz glass rod. After reducing the diameter of the rod to 20 mm using a drawing machine, spinning is carried out. The obtained fiber (outer diameter 125 μm, core diameter 1
0ttm) optical transmission loss is 2.9 dB at a wavelength of 0.8 μm.
/Km. As a comparative example, the optical transmission loss of the fiber was 14.2 dB/Km at a wavelength of 0.8 μm when the gas phase heat treatment using CF2Cl2 was not performed.

Example 3 Fluorine 0.0% was subjected to wet cleaning in the same manner as in Example 1.
5% doped quartz glass tube (inner diameter 10mwL1 outer diameter 1
5.5 mm) on a glass lathe, and while drawing a vacuum from one end of the tube with an oil rotary pump, add 2 lml of SOBr from the other end.
A mixed gas of 2 ml/min of Ar gas and 2 ml/min of Ar gas was introduced, and a plasma zone similar to that in Example 1 was formed along the flow of the mixed gas for 30 ml/min. / minute.

The output of the high frequency oscillator was 80 W, of which it is estimated that 90% was consumed in the cavity within the high frequency induction coil. The degree of vacuum inside the quartz glass tube was about 0.5T0rr at the inlet of the four oil rotary pumps. After repeating the movement of the plasma zone 20 times, the above mixed gas is converted into gaseous SiCl.
42ml/min, 02 gas 3ml/min, He gas 10ml
Switch to a mixed gas of / min and increase the high frequency oscillator output to 400
W and the plasma zone was traversed 80 times at 60 CTrL/min to deposit a quartz glass layer on the inner wall of the quartz glass tube. Next, while the inside of the mixed glass tube is evacuated, it is ignited with an oxyhydrogen burner to soften and close the quartz glass tube to form a solid rod-shaped molded product.
It was spun into a fiber with a core diameter of 8 μm. The optical transmission loss of this fiber is 2.8 dB at a wavelength of 0.8 μm.
/Kml was 1.2 dB/Km at a wavelength of 1.0 μm. As a comparative example, the light transmission loss of the fiber without the above-mentioned SOBr2 vapor phase heat treatment is 0.8 at wavelength.
19.7dB/K7 in μm! l, and at a wavelength of 1.0ttm, it was 3.4dB/Km.

Claims (1)

[Claims] 1. In a method for manufacturing an optical transmission material, which comprises welding a core material to the inner wall of a tubular cladding material and spinning the core material, C, N, A compound that contains at least one selected from the group consisting of O, S, and Se and at least one halogen and does not contain hydrogen and is fluid at room temperature is caused to flow in a gas phase under non-equilibrium plasma generation. Features: A manufacturing method for optical transmission materials.