JPS6126506B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a preform for a fluoride glass optical fiber capable of transmitting infrared rays in the 2-6 μm band.

Conventional optical fiber preforms are mainly composed of silicon oxide (SiO ₂ ) glass, but this glass material has infrared absorption caused by the vibration of Si—O bonds, so Rayleigh scattering loss and infrared absorption The low-loss wavelength range that exists between the loss and the loss is limited to the visible range to the near-infrared range (wavelength 0.6 to 1.7 μm).
It has not been possible to obtain an optical fiber with low loss in a wavelength range longer than that. On the other hand, according to prior art, it is known that Rayleigh scattering is reduced in inverse proportion to the fourth power of the wavelength, and the preform is made of a glass material whose infrared absorption edge is located on the long wavelength side compared to silicon oxide. It has been found that it is possible to further reduce the loss by forming an optical fiber and drawing it to produce an optical fiber, so there is a desire for a method for forming such a preform for an optical fiber.

Optical fibers for communications have a waveguide structure in which a core with a high refractive index is covered with a cladding with a lower refractive index, but currently, optical fibers for infrared transmission that have a waveguide structure are known as ,Ag
(ClBr) core AgCl clad and Tl(BrI) core plastic clad polycrystalline optical fibers.
The production of ultra-low loss optical fibers is essentially impossible due to the effects of grain boundary scattering loss. C ₂ Cl ₄ liquid core SiO ₂ clad optical fibers are also known, but there are major problems in producing long optical fibers and connecting them.

In addition, fluoride glass is attracting attention as a material that eliminates the drawbacks of the various fiber materials mentioned above and has a high possibility of realizing an ultra-low loss optical fiber in the infrared wavelength region of 2 to 6 μm. There is no particular introduction to the manufacturing method of the optical fiber preform, and it is clear that the internal mounting method or shaft mounting method, which is the manufacturing method of the silicon oxide optical fiber preform, cannot be applied as is.

The present invention has been made in view of the above-mentioned current situation, and its purpose is to solve the shortcomings of the prior art and to solve the problems of the prior art.
It is an object of the present invention to provide a method for easily manufacturing an optical fiber preform made of fluoride glass that can transmit μm infrared rays and has extremely low loss.

The method for manufacturing an infrared transmission optical fiber preform of the present invention that achieves the above object heats and vaporizes a raw metal compound, supplies it as a gas stream, and converts this metal compound into fluorine (F ₂ ) gas or hydrogen (H ₂ ) and fluorine (F ₂ ), and the heat generated during the reaction is used to fluorinate and vitrify the resulting fluoride particles or glass particles. The present invention is characterized in that it is deposited to produce a porous matrix for a fluoride optical fiber.

The metals used in the present invention include Li, Na,
Be, Mg, Ca, Sr, Ba, Al, Sn, Pb, Sb, Bi,
Single metals such as Zn, Cd, La, Gd, Lu, Zr, Hf,
or compounds of these metals, such as alcoholate compounds, halides (fluorides, chlorides, bromides, iodides, etc.), or bonds between metals and carbon [e.g., tetraethyl lead: Pb(CH ₂ CH ₃ ) ₄ ]
It is desirable to use a compound such as an organic metal. Furthermore, it is desirable that the reaction system be constructed of a glass container coated with a material that is not easily attacked by fluorine, such as a fluororesin, and that the reaction system be a closed tube system, so that the work can be carried out while preventing the contamination of oxygen.

The method of manufacturing a preform according to the present invention basically involves vertically standing a carbon rod or fluoride glass rod (hereinafter referred to as a seed rod) prepared in advance, and rotating it at a rotational speed of about 30 rpm, around the lower end of the rod. A mixed gas of F ₂ and H ₂ gas is ejected using an installed burner that spouts vaporized raw materials and F ₂ and H _{2 gas, or a burner that spouts vaporized raw materials and F 2 gas} , heated, and ignited. After that, fluorination and vitrification proceed simultaneously by passing the vaporized raw material into the flame, or by blowing out the raw material and F ₂ gas and causing a direct reaction, and this flame is passed through the tip of the seed rod. and deposit the generated fluoride fine particles and glass fine particles to form a porous fluoride matrix.

At this time, the burners that send raw materials for the core and the burners that send raw materials for the cladding are spatially arranged,
Glass fine particles for the core are deposited at the center of the seed rod, and glass fine particles for the cladding are deposited around the seed rod to form a porous base material having a waveguide structure.

EXAMPLES The present invention will be explained in detail below with reference to Examples, but the present invention is not limited thereto in any way.

Example-1 FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus used in the manufacturing method of the present invention.

The carbon seed rod No. 2 is held by the rotating collect chuck No. 24, and rotated by the electric motor No. 25 at a speed of 30 rpm. Twelve crud burners and eleven core burners were set around the lower end of this seed rod 2. Ar carrier gas was flowed into this from 18 argon (Ar) gas cylinders through 13 fluororesin tubes with 21 pressure reducing valves, and 1
Zirconium tetrabutoxide [Zr(OC ₄ H ₉ ) ₄ ] in saturator 4, barium nonadecanoate [Ba(OC ₉ H ₁₉ ) ₂ ] in saturator 15, 16
triisobutyl aluminum [Al
(i-C ₄ H ₉ ) ₃ ] was heated and vaporized by the mantle heater 17, and the raw material gases were conveyed to the burners 12 and 11 by the 27 fluororesin tubes. At this time, 19 F ₂ gas cylinders, 20 H _2
F2 from the gas cylinder to burners 11 and 12.
It was heated and ignited by flowing _H2 gas. In order to eliminate the influence of oxygen, a closed tube system was constructed using a glass container coated with fluororesin (3). Due to the HF gas and heat generated at this time, zirconium tetrabutoxide and barium nonadecanoate are fluorinated in the 11th core burner, and triisobutylaluminum is fluorinated in the 12th clad burner. A refractive index distribution was created by changing the distribution continuously. At this time
BaF ₂ ― AlF ₃ ― ZrF ₄ glass fine particles are attached to the tip of the seed rod 2, and the vertical movement 10 is rotated by the column 9 attached to the frame 6 and the rotating gear of the electric motor 22 26. The rotating gear for the base material 8 raises the base material rotation collect chuck support base, and the base material 1 is lifted up.
While rotating at 30 rpm, it maintained a symmetrical shape and grew in the longitudinal direction. Butanol, isobutane, nonadecanol, and hydrogen fluoride produced by the reaction were trapped from the exhaust hole 23 through the vinyl chloride exhaust pipe 4 and the gas washer 5. At this time, suction was carried out through pipe No. 7 to promote exhaust gas. In this way, a porous fluoride matrix of 50 mmφ×300 mm was obtained.

This base material is heated to 360℃ and becomes transparent to approximately 25mm.
A base material for a fluoride optical fiber with a diameter of 150 mm was obtained.
The refractive index distribution of the cross section of this base material 28 is shown in FIG. 2, and since Al ³⁺ ions are more abundant in the peripheral cladding and less distributed toward the central core,
The refractive index distribution is close to a continuously changing refractive index distribution 30 with a shape close to a square law distribution, and the maximum specific refractive index difference is 0.6.
It was %.

Example 2 In Example 1, the distance between the 12 clad burners and the 11 core burners was set apart so that the flames would not mix, and carbon type 2 was used in the same manner as in Example 1. The rod was gripped by a rotating collect chuck No. 24 and rotated at a speed of 30 rpm by an electric motor No. 25, and 12 burners for the cladding and 11 burners for the core were set around the lower end of this seed rod. To this, Ar carrier gas was flowed from a cylinder 18 through 13 fluororesin tubes equipped with 21 pressure reducing valves, zirconium tetrabutoxide [Zr(OC ₄ H ₉ ) ₄ ] was introduced into a saturator 14, and barium was introduced into a saturator 15. Nonadecanoate [Ba
(OC ₉ H ₁₉ ) ₂ ], tributylaluminum [Al(i-C ₄ H ₉ ) ₃ ] is placed in the saturator 16, heated and vaporized by the mantle heater 17, and the respective raw material gases are injected into the fluororesin 27. The tubes carried them to burners 12 and 11. At this time, F 2 _and H ₂ gases were flowed from the F ₂ gas cylinder 19 and the H ₂ gas cylinder 20 to the burners 11 and 12, which were heated and ignited. Using the HF gas and heat generated at this time, the 11 core burners fluorinate zirconium tetrabutoxide and barium nonadecanoate, and the 12 clad burners fluorinate triisobutylaluminum, spatially distributing the aluminum. was concentrated on the cladding to produce a refractive index distribution. At this time, BaF ₂ -AlF ₃ -ZnF ₄ type glass particles adhere to the tip of the seed rod 2, and the column 9 and the 2
By the lifting gear 10 rotated by the electric motor 6, the base material rotating collect chuck support base 8 is raised, the porous base material 1 is rotated at 30 rpm,
It grew longitudinally while maintaining a symmetrical shape. Butanol, isobutane, nonadecanol, and hydrogen fluoride produced by the reaction were trapped from the exhaust hole 23 through the vinyl chloride exhaust pipe 4 and the gas washer 5. At this time, suction was carried out through pipe No. 7 to promote exhaust gas. In this way, 50mmφ
A fluoride porous matrix of ×250 mm was obtained.

This base material is heated to 360℃ and becomes transparent to approximately 25mm.
A base material for a fluoride optical fiber with a diameter of 120 mm was obtained.
The refractive index distribution of the cross section of this base material ³¹ is shown in FIG.
It was found that the refractive index distribution 33 was close to a step-like shape. The relative refractive index difference was 0.6%.

In this example, the supply of H ₂ gas from the 20 H ₂ gas cylinders was stopped, and the same fluoride fiber base material as in this example was obtained by reacting F ₂ with the raw material.

Application Example The preforms obtained in Example-1 and Example-2 were drawn by the method shown in FIG. That is, 34 transparent fluoride optical fiber matrix materials are
The fluoride optical fiber was inserted into the fluororesin tube No. 5, and the small electric furnace No. 36 placed on the electric furnace stand No. 39 was raised at a rate of 0.1 cm/min, and the fluoride optical fiber No. 38 was wound onto the winding bobbin No. 37. The base material of Example 1 produced a fluororesin coated grade index type optical fiber, and the base material of Example 2 produced a fluororesin coated step index type optical fiber (outer diameter 500 μm, cladding diameter 200 μm). Obtained. All of these optical fibers were capable of transmitting infrared rays and had a low loss window of 0.3 dB/m or less in the 2.5 μm and 3.5 μm bands.

As explained above, according to the present invention, a preform having a core clad waveguide structure inside can be easily manufactured, and the refractive index distribution can be set to any shape such as step index type or graded type, and these can be drawn. The obtained optical fiber has the advantage that it can be used as an optical fiber for infrared transmission having a low-loss window of 2.5 μm or 3.5 μm. In addition, by growing the base material in the axial direction,
Since the glass is deposited in a fluorine or hydrogen fluoride atmosphere, it has the advantage of being able to produce a base material for large-sized fluoride optical fibers with extremely few OH groups.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of the configuration of an apparatus used in the manufacturing method of the present invention, and FIG. 2 is an embodiment of the present invention.
FIG. 3 is a diagram showing the refractive index distribution of the base material obtained in Example-2 of the present invention, and FIG. 4 is a diagram showing the refractive index distribution of the base material obtained in Example-1 and Example-2 of the present invention. FIG. 2 is a schematic diagram of the drawing of the base material obtained in Example-2. DESCRIPTION OF SYMBOLS 1... Base material (porous base material), 2... Seed rod, 3... Fluorine resin coated glass container (reaction tube), 4... Exhaust pipe, 11... Burner for core, 12... Burner for cladding, 14, 15, 16...Saturator, 17...
Mantle heater, 18...Ar gas cylinder, 19...
F ₂ gas cylinder, 20...H ₂ gas cylinder, 28,3
1... Fluoride optical fiber base material, 29, 32... Position on the base material corresponding to refractive index distribution, 30, 33... Refractive index distribution, 34... Transparent fluoride optical fiber base material,
35... Fluorine resin tube, 36... Electric furnace, 38
...Fluoride optical fiber.

Claims (1)

[Claims] 1. A raw material gas formed by heating and vaporizing a metal or metal compound as a raw material in a gas phase reaction system;
and fluorine (F ₂ ) gas, or fluorine (F ₂ ) that produces hydrogen fluoride (HF) gas by reaction.
A mixed gas of gas and hydrogen (H ₂ ) gas is introduced to cause an exothermic reaction, and the fluoride particles or glass particles generated by the reaction with the raw material gas are
1. A method for producing a fluoride optical fiber preform, which comprises depositing it on a seed rod of a predetermined shape to form a porous preform for an optical fiber made of fluoride glass. 2 The metal or metal compound that is the raw material is
Li, Na, Be, Mg, Ca, Sr, Ba, Al, Sn, Pb,
Selected from the group of metals Sb, Bi, Zn, Cd, La, Gd, Lu, Zr, Hf, alcoholate compounds of the above metals, halogen group element compounds, and organometallic compounds having bonds between the above metals and carbon. at least 1
The method for producing a base material for a fluoride optical fiber according to claim 1, which comprises a seed. 3 The gas phase reaction system is a burner that ejects and ignites and burns raw material gas and fluorine (F ₂ ) gas, or a burner that ejects and ignites and burns raw material gas, fluorine (F ₂ ) gas, and hydrogen (H ₂ ) gas. 3. A method for producing a preform for a fluoride optical fiber according to claim 1 or 2, characterized in that the method comprises a burner for causing a fluoride optical fiber. 4. The gas phase reaction system ejects fluorine (F ₂ ) gas and hydrogen (H ₂ ) gas by a burner, ignites and burns them to form a flame, and introduces the raw material gas into the flame. A method for producing a base material for a fluoride optical fiber according to claim 1 or 2. 5. Claim No. 5, characterized in that the gas phase reaction system is constituted by a burner that ejects and ignites and burns the raw material gas for the core, and a burner that ejects and ignites and burns the raw material gas for the cladding. A method for producing a fluoride optical fiber according to any one of Items 1 to 4.