CA1166527A

CA1166527A - Method and apparatus for producing multi-component glass fiber preform

Info

Publication number: CA1166527A
Application number: CA000360496A
Authority: CA
Inventors: Shiro Takahashi; Kazuo Sanada; Koichi Inada; Osamu Fukuda
Original assignee: Fujikura Cable Works Ltd; Nippon Telegraph and Telephone Corp
Current assignee: Fujikura Cable Works Ltd; Nippon Telegraph and Telephone Corp
Priority date: 1979-09-26
Filing date: 1980-09-18
Publication date: 1984-05-01
Also published as: US4336049A; EP0026625B1; DE3066999D1; US4388098A; EP0026625A3; EP0026625A2

Abstract

ABSTRACT OF THE DISCLOSURE

A method for producing a multi-component glass fiber preform which comprises the steps of nebulizing an aqueous solution of at least one metal salt, and reacting the nebulized solution and a gaseous glass raw material with oxygen gas at a high temperature to produce particulate glass material deposited on a substrate. Apparatus for producing such a preform is also disclosed.

Description

~ ~ 66527 S P E C I F I C A T I O N

TITLE OF THE INVENTION
. .

"METHOD AND APP~RATUS FOR PRODUCING MULTI-COMPONENT
GLASS FIBER PREFORM"

BACKGROUND OF THE INVENTION
This invention relates to a method and apparatus for making a multi-component glass fiber preform for fabricating optical fibers for use as transmission lines in communication systems. The term "multi-component preform" denotes a pre-form composed of a plurality of components.
Conventional optical fibers used as transmission linesof optical communication include silica glass fibers, multi-component glass fibers and ionic crystal fibers. It is required that these optical fibers have low loss, are inex-pensive to manufacture and can employ wide band signals.Further, these optical fibers are required to enable easy connection between the fibers and to have a high mechanical strength.
Conventional multi-component glass fibers comprise silica Si02 and a dopant composed of at least one metal salt selected from the group consisting of alkali metal oxide such as Na20, alkaline earth metal oxide such as MgO, oxide oE
lead such as PbO and oxide of lanthanum such as La203. Such multi-component glass fibers can be easily fabricated from a preorm since they have a relatively low melting temperature.

Such multi-component glass fiber~ have another advantage that they have low loss since Rayleigh scattering involved is kept to a low level.
Various methods have been proposed for maXing a multi-5 componen-t glass fiber preform. With these methods, starting materials are irst subjected to extremely high purification and then are mixed together. Thereafter, -the so mixed mate-rials are melted by heat. Thus, these methods have been found not simple. Particularly, where powder materials such as sodium salt, potassium salt, barium salt and lead salt are employed, it is not so easy to mix the starting materials homogeneously. In addition, it is necessary to melt the mixed starting materials, for example, in a crucible for a long period of time. As a result, impurities tend to be introduced into the star-ting materials during this melting operation. The resultant multi-component glass fiber preform has often failed to provide for optical fibers with low loss.

SUM~ARY OF THE INVENTION
It is thereore an object of this invention to provide a method for producing a multi-component glass fiber preform which method is quite simple and ensures that a multi-compo-nent optical fiber with low loss is provided.
Another object is to provide an apparatus for pro-: ducing such a preform which apparatus is simple in construc-tion.
According to a first aspect o the invention, there is provided a method for producing a multi-component glass fiber I ~ ~6527 preform which comprises the steps oF nebulizing an aqueous solution oE at least one metal salt, and reacting the atom-ized solution and a gaseous ylass raw materiaL with oxygen gaq at a high temperature to produce particulate glass mate-rial deposited on a substrate.
The glass raw material is SiC~ , and iE desired, oneor more of GeCe4, POC~3 and BBr3 may be added. The aqueous solution is prepared using at least one metal salt selected from the group consisting of alkali metal nitrate, alkali metal carbonate, al~ali metal sulate, alkali metal acetate, alkaline earth metal nitrate, alkaline earth metal carbonate, alkaline earth me-tal sulfate, alkaline earth metal acetate, lead nitrate, lead carbonate, lead sulfate, lead acetate, lanthanium nitrate, lanthanium carbonate, lanthanium sulfate and lanthanium acetateO The glass raw material and the nebulized solution are mixed together and reacted wi-th oxygen gas at a high temperature to produce particulate glass mate-rial or soot deposited on the substrate to form a multi-component glass fiber preform. The aqueous solution of metal salt or salts is nebulized using a nebulizer u-tilizing super-sonic vibration or a nebulizer utilizing gas under pressure.
The substrate may be in the form of a bar. In this case, the particulate glass material may be deposited on one end or the outer periphery of the substrate bar of circular cross-section. The substrate may take the form of a tube, in whichinstance the particulate glass material is deposited on the inner periphery of the substrate tube. During the deposition operation, the bar is axially rotated and moved, and the tube ..~.

1 1 ~6527 is axially rota~ed. The preorm is ~rawn axially to form an op-tical fiber.
The amoun-t of the dopant, i.e., khe metal salt or salts con-tained in the preform can be increased so that the refractive index of the preform can be con-trolled to form an optical fiber either of the core clad type or the graded index type.
The substrate -tube may be made of silica. The parti-culate glass material is deposited on the inner periphery of the tube to produce a multi-component glass fiber preform.
The tube was heat~d to collapse its hollow portion to provide a solid construction. The preform is drawn axially together with the tube to provide a jacketed optical fiber, the tube constituting the jacket for the optical fiber. The jacketed optical fiber has an increased mechanical s-trength.
~ ccording -to a second aspect of the invention, there is provided an apparatus for producing a multi-component glass fiber pre~orm which appara-tus comprises a multi-conduit burner having five concentric conduits, the centrally dis-posed first conduit and the second and third conduits adja-cent thereto being flush with one another at their tip ends, the fourth conduit interposed between the third and outermost conduits extending axially beyond them, the first to fifth conduits serving to feed a gaseous glass raw material, a fuel gas, a nebulized aqueous solution oE at least one metal salt, an inert gas and oxygen gas, respectively, the burner having a nozzle adapted to be directed to an axially rotating and moving substrate to deposit particulate glass raw material on .~ ' ' .

I 1 66r)27 the substrate. With -this apparatus, the dopant content of the glass fiber preform can be increasedO

BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view showing a preform forming apparatus of -this invention;
Fig. 2 is a view similar to Fig. I but showing a modi-fied apparatus;
Fig. 3 is a schematic view of a multi-conduit burner;
Fig. 4 is a view similar to Fig. 1 but showing ano-ther modified apparatus;
Fig. 5 is a view similar to Fig. 1 but showing a fur-ther modified apparatus; and Figs. 6 to 9 are graphs showing the refrac-tive index profile in the direction of diameter of optical fiber pre-forms provided in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION
.
As the gaseous glass raw material, silicon chloride SiC~4 gas is used. One or more of germanium chloride gas GeCe4, phosphoryl chloride gas POC~3 and boron bromide BBr3 may be added to SiC~ to prepare the glass raw material.
SiCe4, GeC~, POC~3 and BBr3 are first purified by precise distillation, and then are gasified. The gasification is carried out by slowly heating a container filled with these materials and bubbling a carrier gas through the materials in the container. High purity argon gas, helium gas or oxygen gas can be used as the carrier gas.

,~

.

1 3 6~527 The dopant is at least one metal ~alt selected from the group consisting of alkali metal nitrate, alkali metal carbonate, al]cali metal sulfate, alkali me-tal acetate, alXa-line earth metal nitrate, alkaline earth me-tal carbonate, alkaline earth metal sulfate, alkaline earth metal ace-tate, lead nitrate, lead carbonate, lead sulfate, lead acetate, lanthanium nitrate, lan-thanium carbonate, lanthanium sulfate and lan-thanium aceta-te. As the alkali metal, lithium, sodi-um, po-tassium and cesium can be used. As the alkaline earth metal, magnesium, calcium and barium can be used. The aqueous solution of metal salt or salts is subjected to ex-tremely high purification, using a solvent ex-traction method or an ion exchange resin. The purified solution is nebulized by a nebulizer utilizing supersonic vibration or a nebulizer utilizing a carrier gas under pressure. Preferably, an inert gas such as argon and helium gases of high puri-ty is used as the carrier gas.
Oxygen gas serving to oxidize the glass raw materials and the nebulized solution should pre~erably have a purity o~
more than 99.99%.
The invention will now be described with reference to the drawings.
Fig. 1 shows a preform forming apparatus 10 which com-prises a multi-conduit burner 11 having a plurality of con-centric conduits. A gaseous glass raw material, H2~ 2 and acarrier gas such as argon or helium are fed simultaneously through their respective conduits. The hydrogen gas is burnt to form a flame 12. As described above, the glass raw mate-5 2 ri~
rial is composed of SiC~ and one or rnore oE GeCC4, BBr3 and POC~3. The glass raw ma-terial is gasified b~ the bubbling operation as described above. An aqueous so:Lution of metal salt or salts, which serve as a dopan-t as described above, is highly puri~ied and charged in-to a nebulizer 13 utilizing supersonic vibration. The aqueous solution is nebulized and injected from a nozzle 14 in-to the flame 12. In the flame 12, the glass raw material and the nebulized material is sub-jected by the oxygen gas to chemical reac-tions such as flame hydrolysis and oxidation to produce a multi-component parti-culate glass material or soot. The particulate material is directed by the flame l2 toward and deposited on the lower end of a substrate bar 15. The particulate material or soot comprises oxides of the glass raw material such as Si02, GeO2, B2O3, and P2O5, oxides of the metal salt such as ~a20, MgO and PbO, and oxides such as those containing Si-O-Na bond, Si-O-Mg bond and Si-O-Pb bond. The substra-te bar 15 is supported on a lathe (not shown) for axial rotation and up-ward movement along the axis. The multi-component particu-late glass material or soot is deposited on the lower end of the thus rotating and moving bar 15 to form a porous multi-component glass fiber preform 16. During the deposition operation, by changing the flow rates of the glass raw mate-rial and the nebulized material, the distance between the nozzle of the burner ll and the lower end of the substrate bar 15, and the angle of the burner 11 with respect to the substrate 15, the glass fiber preform 16 having a desired refractive index profile can be obtained.

1 1 665~7 Fig. 2 shows a modifiecl preform Eorming apparatus 20.
- A gaseous glass raw material, oxygen gas, hydrogen gas and a carrier gas such as argon or helium gas are simultaneously fed through respective conduits of a multi-conduit burner 21, as described above for the burner 11. As described above, the glass raw material is composed of SiC~4 and one or more of GeC~4, POC~3 and BBr3. An aqueous solution of metal salt or salts, purified according to the procedure described above, is contained in a nebulizer 23. Argon gas under pressure is supplied as a carrier gas into the nebulizer 23 through a pipe 2~a so that the purified solution is nebulized and injected from the nozzle 24 into a flame 22 of the burner 21. The glass raw material and the nebulized material are oxidized by the oxygen gas to allow their oxides in the for~ of particular glass material or soot to deposit on the outer periphery of a substrate bar 25 to produce a porous multi-component glass fiber preform 26. The substrate bar 25 is supported on a lathe (not shown) for axially rotation and reciprocal movement along the axis during the deposition operation. By con~rolling the feed rate of one or more components of the glass raw material and nebulized metal salt solution during the reciprocal move~ent of the substrate bar 25, the refractive , index of the preform 26 can be changed either in a continuous or a stepped manner in the radial direction of the substrate bar 25.
Fig. 3 shows a multi-conduit burner 31 having five concentric conduits 31a to 31e. The first to fifth conduits 31a to 31e serve to feed the above-mentioned glass raw ~, .
.

~naterial, hydrogen gas, -the above-mentionecl neb~lized metal salt solution, argon yas and oxygen gas, respec-tively. The gaseous glass raw material is ~ed through the centrally dis-posed first conduit 31a by a carrier gas such as argon gas.
The first -to third conduits 31a to 31c are flush with one another at their tip ends. The Eourth conduit 3ld is about 15 to 20 mm longer than -the first to -third conduits and also is about 5 mm longer than -the fifth conduit 31e. With this construction, a mixture area 32 is defined by the Eourth con-duit 31d and the tip ends of the first to -third conduits 31a to 31c. The mixture area 32 serves to sufficiently mix the materials emitted from the first -to fourth conduits 31a to 31d. A flange member 33 is mounted around the outermost or fif-th conduit 31e and extends axially beyond the fourth con-duit 31d. Hydrogen gas is burn-t to form a flame 34.
The glass raw material and the nebulized metal salt solution, ernitted respectively from the conduits 31a and 31c, are ade~uately mixed together and directed into the flame 34 so that the particulate glass raw ma~erial or soot is pro-duced by oxidation and deposited on the lower end of a sub-strate bar 35 to produce a porous multi-componen-t glass fiber preform 36, as shown in Fig. 4 which schematically illus-trates a further modified preform forming apparatus 30. The substrate bar 35 is supported on a lathe (not shown) for axial rotation and movement along the axis during the deposi-tion operation. With this method, the dopant content of the obtained preform can be easily increased to a desired level.
The substrate bar 35 rnay be arranged for horizon-tal recipro-_ g _ .~

~ 1 665~'7 cal movement so that the glas~i fiber preEorm is Eorrned aroundthe outer periphery of the substra~e. E'urther, as described above, by controlling the feed rate of one or more components of the ~aterials supplied through the multi-conduits burner 31, the refractive index of the preform can be con-trolled.
Also, as described above, by changing the flow rates of the glass raw ma-terials and nebulized materials, the distance between the nozzle of the burner 31 and the lower end of the substrate bar 35, and the angle of the burner 31 wi-th respect to the substrate 35, the glass fiber preform having a desired refractive index profile can be obtained.
Fig. 5 shows a further modified pre~orm forming appa-ratus 40 which employs a process commonly known in the trade as "modified chemical vapor deposition process". An elon-gated hollow substrate 41 in the ~orm of silica tube is used.The substrate tube 41 is supported by spaced support portions 42a, 42a of a lathe 42 for axial rotation. A burner ~3 using H and 0 is mounted on the lathe 42 beneath the substrate tube 41 for reciprocal movement therealong to heat the rotat-ing tube 41. The tube 41 has a smooth bore or inner peri-pheral wall which is cleaned. The above-mentioned gaseous glass raw material and nebulized solution, oxygen gas and the carrier gas are introduced into the bore of the rotating tube 41. The glass raw material and nebulized material are heated by the moving burner 43 so that the particulate glass mate-rial or soot is produced through chemical reactions such as flame hydrol~sis and oxidization and is deposited on the inner peripheral surface of -the silica tube 41 -to form a I 1 665~7 porous multi-component prefortn 4~. ~B described above, by controlling the Eeed rate of one or more components of the glass raw ma-terial ancl nebulized metal sal-t solution during the reciprocal movement of -the burner 43, the refractive inde~ of the preEorm 44 can be changed either in a continuous or a stepped manner.
For ~abricating a multi component glass fiber from the multi-component glass fiber preforms produced according to the procedures shown in Figs. 1 and 4, the preform is heated to a temperature above a melting point for vitrification to provide a transparent glass preform. The vitrified preform is then drawn to form an optical fiber. More specifically, where a core preform and a cladding preform are formed on separate substrate bars, the two preforms are introduced respectively into concentrically disposed inner and outer chambers of a crucible, e.g., a platinum crucible and are melted. The preforms thus treated are drawn to provide a multi-component optical glass fiber having a core portion and a cladding portion. Alternatively, a core preform is formed on the lower end of the substrate bar, and thereafter a cladding preform is formed on the core preform to provide an integral preform. This integral preform is heated for vitri-fication to obtain a transparent preform. This -transparent preform is drawn to provide a multi-component optical glass fiber.
For fabricating a glass ~iber from the preform pre-pared according to the procedure shown in Fig. 2, the preform is vitrified to obtain a transparent glass preform in the 1 1 6~527 manner described above. Then, the substrate bar i~ removed from the preform, and this hollow preform i8 heated to col-lapse the hollow portion to provide a solid cons-truction. In the case of -the preform of which refractive index is varied in the radial direction, -the preEorm is simply drawn -to form a multi-component optical glass fiber. In the case of the preform of which refractive index is constant in -the radial direction, the preform is for~ed into a rod of a predeter-mined diameter. Then, a cladding is applied over the pre-form, and the preform with the cla~ding is drawn to provide a multi-component glass fiber.
For fabricating a glass fiber from the preform pre-pared according to the procedure shown in Fig. 4, the sub-strate tube, in which the preform is formed, is heated to collapse the hollow portion to form a solid structure. The preform with the silica tube is drawn axial]y from one end to form a multi-component optical glass fiber. The drawn tube 41 serves as a jacket for the optical Eiber and increases the mechanical streng-th of the fiber.
The invention will now be illustrated by the following examples:

An aqueous solution of 30% by weight NaN03 of extreme-ly high purity was prepared, using an ion exchange resin.
The purified aqueous solution was charged into a nebulizer 13 of a preform forming apparatus lO shown in Fig. 1, the neb-ulizer 13 utilizing supersonic vibration. SiC~4, GeCe4, BBr3 1 1 6~527 and POC-~3 serving as gaseous ylas~ raw material~ were fed throu-3h a first conduit of a multi-conduit burner ll at the :Elow rates of 200 cc per minute, l~O cc per minute, 55 cc per minute and 20 cc per ~inute, respectively, the multiconduit burner 11 having a plurality of concentrically disposed con-duits. Hydrogen gas serving as a fuel gas and oxygen gas were also fed separately through a second and a third conduit at the flow rates of 4000 cc per minute and 6000 cc per min-ute, respectively, the hydrogen gas being burnt to form a flame 12. The purified aqueous solution was subjected to supersonic vibration of 80 kHz by the nebulizer 13, having a power 50W, to be nebulized at the nozzle 14 of the nebulizer 13 and injected into the flame 12 so that the glass raw mate-rials and the nebulized material were oxidized by the oxygen gas to allow their oxides in soot form to deposit on the lower end of an axially rotating and moving substrate bar 15 to produce a porous multi-component glass fiber preform 16 for a core. The aqueous solution to be nebulized was fed at a rate of 50 cc per minute.
Then, according to the procedure described above, a porous multi-component glass fiber preform for a cladding was also prepared, using SiC~4 (flow rate: 200 cc per minute), GeCe4 (50 cc per minute), BBr3 (50 cc per minute), and POC~3 (20 cc per minute) serving as glass raw materials, hydrogen gas (4000 cc per minute), oxygen gas (6000 cc per minute) and an aqueous solution of 30% by weight NaNO3 nebulized at -the rate of 40 cc per minute.
The thus obtained core preform and cladding preform -I ~ ~6~27 were heated in a furnace, respectively, for v:ikrification to obtain -two transparent glass preforms. The vitriEied core preform and cladding preform were introduced respectively into concentrically-disposed inner and outer chalnbers of a platinum crucible. rrhen, the two preforms were drawn at the rate of 20 cm per minute at a temperature oE 800 to fabri-cate a multi-component optical glass Eiber having a core por--tion and a cladding portion. The thus obtained optical fiber exhibited a refractive index profile of the step type as indicated by a graph in Fig. 6.

A multi-component optical glass fiber was obtained ac-cording to the procedure of Example 1, except that an aqueous solution of 32~ by weight KN03 was used instead of the aqueous solution of NaN03. The thus obtained optical fiber, like the optical fiber oE Example 1, exhibited a refractive index profile of the s-tep type.

An aqueo~s solution of 30% by weight MgS0~ of extreme-ly high puri-ty and an aqueous solution of 30~ by weight CsSO4 of extremely high purity were prepared, using an ion exchange resin, The two solutions were mixed in equal amounts, and the resultant mixture solution was charged in-to a nebulizer 23 of a preform forming apparatus 20 shown in Fig. 2. Argon gas under pressure serving as a carrier yas was fed -through a conduit 24a to nebulize the solution.

1 J ~; 6 5 ~ ~
SiC~4 and POC~3 serving as gaseous gLa~s raw materi~
als, H2 and 2 were fed through respec-tive condui-ts of a multi-conduit burner 21, as described above Eor the burner Il, at the flow rates of 100 cc per minute, 50 cc per minute, 2200 cc per minute and 3000 cc per minu-te. The hydrogen gas was burnt to form a flame 22. The mixture solution was nebulized at the nozzle 24 of the nebuli~er 23 at a rate of 0.3g per minute and injec-ted into the flame 22 so that the glass raw materials and the nebulized material were oxidized by the oxygen gas -to allow their oxides in soot form to deposit on -the outer peripheral surface of a substrate bar 25, rotating about its axis and reciprocally moving along its axis, to produce a porous multi-component glass fiber preform 26. The substrate bar 25 was rotated at a rate of 20 r.p.m.
and reciprocally moved at a speed of 300 mm per minute. Dur-ing the deposition operation, in order to continuously change the refractive index of the preform in its radial direction to obtain an optical fiber of the graded index type, the amount of SiC~4 fed to the burner 21 was increased by 5 cc per minute in the range of between 100 cc per minute and 200 cc per minute every one reciprocal movement of the sub-strate 10.
The thus obtained preform 26 was hea-ted for vitrifica-tion in a carbon resister furnace at a temperature of about 1400C to obtain a transparent glass preform. Then, the sub-strate bar 25 is removed from the preform, and the resulting hollow preform was heated to collapse the hollow portion to provide a solid construction. The solid preform was drawn ~ 1 ~6~27 from one end t~lereof to produce a multi-component optical glass fiber of -the graded inclex type. The re~ractive index profile of the optical fiber was matched substantially to a parabolic curve as plotted in Fig. 7.

EXAMPLE ~
A multi-conduit burner 31 (Fig. 3) ha-~ing five concen-tric conduits 31a to 31e was employed. SiC~4, POCe3 and Ar were fed through the first or central conduit 31a at flow rates of 120 cc per minute, 10 cc per minute and 50 cc per minute, respectively, SiC~4 and POC~3 constituting glass raw materials. H2 was supplied through the second conduit 31b at a flow rate of 3~ per minute. Pb(NO3)2 and H2O mixed in the weight ratio of 3:10 was fed through the third conduit 31c at a rate of 0.28g per minute, the mixture being in nebulized form. Ar was fed through the ~ourth conduit 31d at a rate of 4~ per minute. 2 was fed through the fifth conduit 31e at a rate of 3~ per minute. H2 was burnt to form a ~lame 34 and the glass raw material and the nebulized mixture were oxidized by the oxygen gas to allow their particulate oxides to deposit on the lower end of a substrate bar 35 to produce a multi-component glass fiber preform 36 (Fig. 4). The sub-strate bar 35 was rotated axially at a rate of 20 r.p.m. and moved upwardly at a speed of 40 mm per hour. The thus pro-duced preform was passed through a carbon resister furnace, maintained at a temperature of abou-t 1,300C, for vitrifica-tion to obtain a transparent glass preform. The transparent preform was drawn by a lathe to hava a predetermined diameter ~ 16 -I 1 6652~
or cross-section, and a tube of si.lica was fitted over the thus drawn material. Then, the drawn material with the sil-ica tube was heated at a -temperature of about 2,000C to ob-tain a multi-componen-t optical glass Eiber. The refractive index profile of the optical fiber is shown in F'ig. 8.

A multi-component optical glass fiber of the graded index type was prepared, using a preform forming appara-tus 40 shown in Fig. 5. ~n aqueous solution of 30% by weight Pb(~03)2 of high purity and an aqueous solution of 20% by weight ~a(CH3C00)2 oE high purity were prepared, using either a solvent extraction method or an ion exc'nanye resin. The two solutions were mixed in e~ual amounts, and the resul-tant mixtur~ solution was nebulized by a nebulizer (not shown) using argon as a carrier gas and was introduced into a tube 41 of silica. The amount of argon gas supplied was increased b~ 8 cc per minute in the range of between 0 cc per minute and 400 cc per minute every one reciprocal movement of a burner 43 along the tube ~1, so that the amount of the nPbulized mixture supplied was controlled to the range of between Og per minute and 0.5g per minute.
Simulaneously with the supply of the nebulized mixture into the tube 41, SiC~4 and POC~3, serving as glass raw mate-rials/ and 2 were fed into the tube 41 at flow rates of 150 cc per minute, 30 cc per minute and 200 cc per minute, respectively. The tube 41 was supported by a lathe 42 and axially rotated at a rate of 20 r.p.m. The tube 41 had an - 17 ~

~i inner diame-ter of 18 mm, and the length of the tube between opposed support portions 42_, 42a was 1 m. The tube 41 was heated by the hurner 43 using ~12 and 2 which burner ~/as reciprocally moved along the tube 41 at a speed oE 30 cm per S minute. The glass raw material and the nebulized material in the tube 41 were oxidized by the oxy~en gaæ in the tube -to allow their particulate oxides to deposite on the inner peri-phery of the tube 41 to produce a ~ulti-component glass fiber preform 44. After the burner 43 reciprocally moved along the tube 41 fifty times, the introduction of the materials into the tube 51 was stopped. Then, the -tube 41 was heated to 1,900C -to collapse the hollow portion of the tube to provide a solid struc-ture, The solid preform with the tube was drawn at 2,100C at a speed of 30 m per minute to produce a jacketed multi-component optical glass fiber. Thus, t'ne tube 41 is simultaneously drawn to form jacket for the optical fiber. The refractive index profile of the optical fiber was matched æubstantially to a parabolic curve as plotted in Fig.
9.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for producing a multi-component glass fiber preform which comprises the steps of nebulizing an aqueous solution of at least one metal salt by supersonic vibration, and reacting the nebulized solution and a gaseous glass raw material with oxygen gas at a high temperature to produce particulate glass material deposited on a substrate.

2. A method according to claim 1, in which said glass raw material is silicon chloride SiC?4.

3. A method according to claim 2, in which said glass raw material further comprises at least one material selected from the group consisting of germanium chloride GeC?4, phosphoryl chloride POC?3 and boron bromide BBr3.

4. A method according to claim 1, in which said metal salt is selected from the group consisting of alkali metal nitrate, alkali metal carbonate, alkali metal sulfate, alkali metal acetate, alkaline earth metal nitrate, alkaline earth metal carbonate, alkaline earth metal sulfate, alkaline earth metal acetate, lead nitrate, lead carbonate, lead sulfate, lead acetate, lanthanium nitrate, lanthanium carbonate, lanthanium sulfate and lanthanium acetate.

5. A method according to claim 1, in which said aqueous solution of metal salt is nebulized by a gas under pressure.

6. A method according to claim 1, in which said glass raw material, said nebulized solution and said oxygen gas are applied into a flame produced by a burner to deposit said particulate glass material on said substrate, said substrate being in the form of a bar and being axially rotating and moving along the axis.

7. A method according to claim 6, in which said glass raw material and said oxygen gas are fed through individual concentric conduits of said burner respectively.

8. A method according to claim 6, in which said glass raw material, said nebulized solution and said oxygen gas are fed through individual concentric conduits of said burner, respectively.

9. A method according to claim 6, in which said particulate glass material is deposited on one end of said substrate bar.

10. A method according to claim 6, in which said particulate glass material is deposited on the outer periphery of said substrate bar.

11. A method according to claim 1, in which said substrate is in the form of a tube, said glass raw material, said nebulized solution and said oxygen gas being introduced into said tube, said tube being heated by a heating means from the outside there-of to deposit said particulate glass material on the inner peripheral surface thereof, and said heating means moving along said tube during the deposition operation.

12. Apparatus for producing a multi-component glass fiber preform which comprises a multi-conduit burner having five concentric conduits, the centrally disposed first conduit and the second and third conduits adjacent thereto being flush with one another at their tip ends, the fourth conduit interposed between the third and outermost conduits extending axially beyond them, the first to fifth conduits serving to feed a gaseous glass raw material by supersonic vibration, a fuel gas, a nebulized aqueous solution of at least one metal salt, an inert gas and oxygen gas, respectively, and said burner having a nozzle adapted to be directed to a substrate.