JPS58208146A - Manufacture of base material for radiation resistant optical fiber - Google Patents

Abstract

PURPOSE:To make the fluorine content uniform and to reduce unevenness in refractive index, by forming a porous preform for a clad on the surface of a vitreous substrate for a core, treating the preform with gaseous fluorine, and converting the substrate and the resulting porous preform contg. fluorine into transparent glass. CONSTITUTION:A porous preform 3 for a clad is formed on the surface of a quartz glass rod 1 for a core by feeding H2, O2, SiCl4 and BF3 to the 1st burner 2 and by moving the rod 1 upward while rotating. H2, O2 and CF4 are then fed to the 2nd burner 4 to treat the preform 3 with reactive gaseous fluorine. The rod 1 and the resulting porous preform 3 contg. fluorine united in a body 5 are converted into transparent glass by heating in a helium atmosphere.

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a base material of a radiation-resistant optical fiber containing fluorine and having a low refractive index cladding. Conventionally, as a radiation-resistant optical fiber having long radiation-resistant characteristics, one using SIO in the core and SIO in the cladding with -BtOsk is known. The optical fiber in this building is B(
Although the refractive index of the cladding is lowered by boron (boron), the reduction in refractive index by B is small, so the relative refractive index! In order to obtain a large optical fiber 1 with (, J), B must be doped multiple times. However, when Bτ multiple doping is used, the thermal expansion coefficient of the cladding is significantly different from that of the core, and this difference in thermal expansion coefficients has the disadvantage that the optical fiber may break. For this reason, original fibers with fluorine-containing cladding in which part or all of the B dopant is replaced with F (fluorine) have come to be manufactured. As a method for manufacturing the original fiber of this fluorine-containing cladding, for example, an F-generating compound and a 6ti-generating product are simultaneously fed into a high-temperature plasma flame,
In a plasma flame, glass particles combined with F and Si are generated.

[There is a method in which transparent glass is deposited on a quartz rod that serves as the core. However, with this method,
Requiring complex and peripheral equipment such as plasma equipment;
Since the reaction between Si and F is reduced in the hot flame of the pot, there are drawbacks such as the fact that the amount of fluorine contained in the glass that becomes the cladding is not constant. There is also a rod-in-tube method in which a soot shield, which is a fluorine-containing cladding, is formed on the inner surface of a glass tube by a filling method, and a quartz rod serving as a core is inserted into this glass tube and heated. However, in this method, it is difficult to obtain a large Δ sound with F alone, so Bi is doped at the same time, but as mentioned above, doping with B increases the coefficient of thermal expansion with the core, so inserting the rod There is a risk of cracking due to thermal distortion when heating and igniting. This invention was made in view of the above circumstances, and it is possible to stably contain a sufficient amount of F without requiring any special packaging, and moreover, it will not crack due to thermal distortion during manufacturing. The object of the present invention is to provide a method for manufacturing a radiation-resistant optical fiber base material having a F-containing cladding. Hereinafter, the present invention will be described in detail with reference to the drawings. The drawings schematically show an example of the manufacturing method of the present invention, and reference numeral 1 in the drawings indicates a round rod made of quartz glass that serves as a core. This rod 1 is rotated by a rotary moving device (not shown) with its axis as a rotation axis, and is gradually raised upwards. A porous preform 3 is formed. That is, the first burner 2 is a well-known multi-tube burner, and this burner 2 is supplied with glass chamber gas SIC/H2 gas, 0 gas, and gas from vibrators 2a, 2a, . . . , respectively. are supplied at the same time. At this time, depending on the scenery, BBr3, BP
, etc. are used as dopants at the same time in burner 2.
Although it is possible to lower the refractive index of the preform that becomes the cladding in advance by supplying it to the cladding material, it is preferable that the amount of the added hair be as small as possible. The above glass raw cedar gas etc. supplied to the first burner 2 undergoes a hydrolysis reaction and a thermal oxidation reaction in the flame, and contains particulate sio, +B20. The glass is deposited on the surface of the iron 110 to form a porous preform 3 which becomes a cladding. After the porous preform 3 is formed on the rod 1 by the first burner 2 in this way, the second burner 4 provided above the first burner 2 performs treatment with reactive fluorine gas. It will be done. The second burner 4 is also a multi-tube burner, and this burner 4 contains F, OF4, SF6, and CCl2F, which decompose in gas and flame to generate Ft.
, form an oxyhydrogen flame with gaseous fluorine compounds such as ■
2 gas, 0! Gas is supplied through the supply pipes 42.4a and 4a, respectively.
can be sent at the same time. F is heated in the flame of the second burner 4, and the F gas is in an active state with high direct reactivity.
Furthermore, the fluorine compound is once decomposed into F, which is then turned into F in a highly reactive active state, and is sprayed onto the preform 3, which will become the cladding, deposited on the rod l. As a result, active F penetrates deeply into the porous preform 3 in a gaseous state, reacts with a portion of 5io2, and generates a 5i-F bond such as SiF4. Due to the presence of the porous preform 3id, F which has been treated with such a reactive fluorine gas, the refractive index when vitrified is lowered. Next, the integrated body 5 of the rod 1 and the porous preform 3 that has been treated with the reactive fluorine gas is heated in an electric furnace or the like, and the porous preform 3 is made into a transparent glass to form an optical fiber base material. Become. This optical fiber base material is made into a step-index type radiation-resistant optical fiber having a 1t rod core and a treated porous preform as a cladding by a conventional bath melt spinning method. The thus obtained optical fiber contains F in its cladding, and will be described in detail by way of examples. [Example] On the quartz glass rod 1 that serves as the core of the 12 mm direct mounting,
8i0. by the first burner 2. -B203 porous preform 3 was formed. The first burner 2 has H
2 gas 4000cc/min, 0. Gas 8000cc/min,
5iCA 4600 cc/min, BF, 300 cc/min were supplied respectively, and the rods were rotated by i30 R, P, M and raised at a moving speed of 100 m/hour. As a result, a porous preform 3 serving as a cladding having a diameter of 48 mm was formed. Then, to the second burner 4,
Gas 5000cc/min, 0. Gas 8000cc/min, 0
F4300 cc/min tp was supplied, and the porous preform 3 was treated with reactive fluorine gas. Next, the integrated body 5 of the core 1 and the porous preform 3 was heated at 1800°C in a helium atmosphere to turn the porous preform 3 into transparent glass, thereby obtaining a rod-shaped optical fiber preform with a diameter of 19 m11. . This original fiber base material is spun to form a core with ε;0
An optical fiber with a μ shoulder and a length of 125 μm was obtained. The relative refractive index difference Δ of this optical fiber was 1 chi. 1. The ratio of B to the refractive index of the cladding was about 6% when the B-containing lid was about 300 ml, so there was little possibility of it breaking due to thermal strain. As explained above, in the method for manufacturing a radiation-resistant optical fiber base material of the present invention, a porous preform that is bonded to a cladding is formed on the surface of a glassy base material serving as a core, and then this porous preform is The process involves treating the film with reactive fluorine gas to form a fluorine-containing porous preform, and then converting this preform into transparent glass. Therefore, fluorine easily penetrates and reacts into the porous preform that becomes the cladding. However, a sufficient amount of fluorine can be contained, and the refractive index of the resulting optical fiber cladding is sufficiently reduced.
The optical fiber has a large relative refraction of 4M.Furthermore, in the case of processing with reactive fluorine gas using fluorine gas contained in an oxyhydrogen flame, the fluorine content can be easily adjusted, and the fluorine content can be easily adjusted. It is possible to keep the refractive index constant and reduce variations in the refractive index.Furthermore, since it contains a sufficient amount of fluorine, there is no need to worry about cooling B so much in order to lower the refractive index. There is no grain loss due to heat # can coefficient, and there is no risk of cracking due to thermal strain caused by heating during the manufacturing process.Furthermore, the manufacturing equipment can use the multi-tube burner normally used for original fiber manufacturing, so Equipment costs are much lower than the plasma method, and manufacturing costs are also low.
- Because the papule-porous preform is formed and then treated with reactive fluorine gas, the fluorine Due to the etching action of the glass by the gas, there are fewer preforms to be produced, which has the advantage of reducing the density of the preform and eliminating problems such as breakage during the preform stage.

[Brief explanation of drawings]

The drawings are explanatory drawings showing an example of the method for manufacturing the radiation-resistant optical fiber base material of the present invention. DESCRIPTION OF SYMBOLS 1... Rod, 2... First burner, 3... Porous preform, 4... Second burner. Applicant: Kneeneck Kamigantai Company Representative Patent Attorney: Masatake Shiga

Claims (1)

[Claims] +lj A porous preform to be a cladding is formed on the surface of a glass base material to be a core, and then this porous preform is treated with a reactive fluorine gas to form a fluorine-containing porous preform. By forming and then vitrifying the fluorine-containing porous preform, it has a radiation resistance of 11%. A method for manufacturing optical fiber base material for use. (2) The method for producing a radiation-resistant optical fiber base material according to claim 1, wherein the treatment with reactive fluorine gas is performed with fluorine gas contained in an oxyhydrogen flame.