JP2003206153A - Optical fiber preform, method for manufacturing the same, and method for manufacturing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber preform capable of sintering a composite preform without deforming and capable of obtaining a larger amount of a portion effective to form a fiber, and to provide the obtained optical fiber preform, and a method for manufacturing an optical fiber from the optical fiber preform by drawing the optical fiber in a simplified step. <P>SOLUTION: The method for manufacturing the optical fiber perform has a first step in which a glass rod including a portion which becomes a core is formed, a second step in which fine glass particles are deposited on the periphery of the glass rod by relatively moving a fine glass particle generator back and forth to form a composite preform 3, and a third step in which the composite preform is dehydrated and sintered in a heating furnace to obtain the objective optical fiber preform 4, wherein, in the second step, fine glass particles are deposited on the periphery of the glass rod in such a way that the inclinations of tapered portions formed at both ends of the composite preform are made different from each other. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber preform useful for producing an optical fiber used for optical communication, a method for producing the optical fiber preform, and a method for producing an optical fiber from the preform.

[0002]

2. Description of the Related Art As a conventional method for producing an optical fiber, glass microparticles are deposited by flame hydrolysis of a raw material gas on the outer periphery of a glass rod including a portion to be a core after the optical fiber is formed, and then a composite base material is formed. It is generally known that an optical fiber preform is manufactured by dehydration sintering (vitrification) of the deposited glass particles, and one end of the optical fiber preform is heated and melted and drawn to form an optical fiber with a constant outer diameter. Has been.

Now, looking at a method for manufacturing an optical fiber preform, for example, Japanese Patent Application Laid-Open No. 10-242242 proposed by the present applicant.
There is a method disclosed in Japanese Patent Laid-Open No. 7430. This method relates to a technique of depositing glass particles on the outer circumference of a glass rod by moving a plurality of glass particle generating devices (burners) in the longitudinal direction of the glass rod while rotating the glass rod. As shown in FIG. 4, a composite preform manufactured by such a technique has a constant outer diameter portion which generally becomes a good quality optical fiber, and a taper at which the outer diameter is gradually reduced toward both ends. The tapered portion has substantially the same inclination at both ends as shown in the figure. Further, in the step of dehydrating and sintering the composite preform thus obtained into the optical fiber preform, the composite preform is suspended vertically in the heating furnace and slowly pulled down while rotating. It is common to process by this. Then, the optical fiber preform obtained by dehydration sintering is introduced into a drawing furnace, the lower portion thereof is heated and melted, and drawn into an optical fiber.

[0004]

By the way, in recent years, there has been a tendency to increase the size of the optical fiber preform for the purpose of manufacturing efficiency and cost reduction due to the expansion of the demand for the optical fiber. As a result, various problems have become clear in the dehydration sintering process and the drawing process. First of all, as a problem in the dehydration sintering (vitrification) process, a very large load is applied to the suspended part of the composite base material, and when the high temperature during sintering is applied to the suspended part, it softens and becomes a base material. Can be deformed. For example, referring to FIG. 5, if the glass particle deposition portion including the tapered portion is entirely vitrified in an attempt to sufficiently obtain a good optical fiber preform, the glass rod 1 extends and as shown in FIG. The base material will fall. Therefore, in order to avoid this, when the composite preform is dehydrated and sintered to obtain the optical fiber preform, the taper on the side of the hanging part is kept so that the high temperature during sintering is not applied to the hanging part. It is necessary to appropriately leave a portion (non-sintered portion) where the glass fine particles are not completely sintered in a part of the portion. that is,
This is because the non-sintered portion functions as a heat insulating material and has an effect of suppressing softening deformation of the suspended portion.

Next, as a problem in the dehydration sintering process and the drawing process, in order to efficiently obtain a good quality optical fiber, as shown in FIG. 6, the outer diameter constant portion of the composite base material is increased and the taper portion is inclined. Even if the taper portion is suddenly shortened to shorten the length, the effect may not be exhibited. For example, in the inclination (FIG. 6) in which the inclination and the length of the tapered portion are substantially the same at both ends of the composite base material, the unsintered portion is appropriately left,
If it is attempted to prevent the deformation of the base material as shown in FIG. 5 (a), the outer diameter of the unsintered portion becomes significantly larger than the outer diameter of the constant outer diameter portion as shown in FIG. 5 (b). If this base material is drawn as it is, it will hit the inlet of the drawn core tube or the inner wall surface of the tube, and it will not be possible to draw efficiently until the end. Therefore, there is a limit to making the taper portion on the side forming the unsintered portion steep so as to shorten its length and increase the outer diameter constant portion. Further, as a problem in the drawing process, another process is required between the dehydration and sintering process and the drawing process in order to steeply incline the taper portion and shorten the length in order to efficiently obtain a good product. It can be mentioned. For example, it is generally performed to process the end portion of the optical fiber preform after the dehydration sintering on the drawing start side into an inclination that is most suitable for drawing. Specifically, the optical fiber preform is stretched. The best shape for drawing is made by cutting or cutting. However, this method requires equipment and a lot of labor and time, and when the optical fiber preform is subjected to this processing,
There is also a lot of loss in the non-defective part, which is very inefficient.

Here, those in which the inclination of the taper portion of the optical fiber preform is defined are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 9-100132 and 2000-264662. However, the tapered portion disclosed in Japanese Patent Application Laid-Open No. 9-100132 is not reduced to the same diameter as the glass rod. Further, even if the taper portion illustrated is reduced to the same diameter as the glass rod, the drawing start portion of the taper portion is longer than the drawing end portion. Further, the tapered portion shown in this publication is assumed to be used as a part of a homogeneous optical fiber to the last, and the purpose is to reduce the longitudinal fluctuation of the glass characteristics, and the problems to be solved by the present invention. Is not relevant. Further, the taper portion disclosed in Japanese Patent Laid-Open No. 2000-264662 is made to have a predetermined inclination by heating the fiber preform, but the inclination of the taper portion before the heat processing is not mentioned because it is not mentioned. is there. Furthermore, it is essentially an essential requirement to perform heat processing, and as described above, the addition of steps causes a decrease in productivity. Therefore, in the present invention, a method for producing an optical fiber preform capable of sintering the composite preform without deformation and obtaining a large number of effective parts for fiberization, the obtained optical fiber preform, and the optical fiber preform. An object of the present invention is to provide a method for drawing and manufacturing an optical fiber from a material by a simplified process.

[0007]

DISCLOSURE OF THE INVENTION As a result of earnest studies in view of the above problems, the present inventor has found that it is better to make the inclinations of the taper portions formed at both ends of the optical fiber preform different. The present invention has been completed. That is, the present invention provides (1)
An optical fiber preform obtained by depositing glass fine particles on the outer periphery of a glass rod including a portion to be a core after forming an optical fiber to form a composite preform, and dehydrating and sintering the composite preform, An optical fiber preform characterized in that the taper portions formed at both ends of the optical fiber preform after dehydration sintering have different inclinations, and (2) a glass rod including a portion which becomes a core after being made into an optical fiber. In the first step of forming the glass rod, while rotating the glass rod about its axis, the glass fine particle generator is relatively reciprocated in the longitudinal direction of the glass rod to deposit glass fine particles on the outer periphery of the glass rod. Second to form a composite matrix
A method for producing an optical fiber preform having a third step of rotating the composite preform in a heating furnace while supporting the composite preform in a vertical direction to dehydrate and sinter to obtain the optical fiber preform. A step of depositing glass fine particles on the outer periphery of the glass rod so that the taper portions formed at both ends of the composite base material have different inclinations; The relative movement speed in the longitudinal direction of the glass rod of the glass fine particle generator in the step is gradually increased in the vicinity of one turning point of the reciprocating movement. Production method,
(4) The light according to (2), wherein the supply amount of the glass fine particle raw material supplied to the glass fine particle generating device in the second step is gradually reduced in the vicinity of one turning point of the reciprocating movement. (5) A plurality of glass fine particle generators in the second step are used, the reciprocating movement amplitudes of the plurality of glass fine particle producing apparatuses are made different, and the cycle of the reciprocating movements is substantially the same. (2) The method for manufacturing an optical fiber preform according to (2), characterized in that the inclination is steep among the taper portions formed at both ends of the composite preform. (2) The method for producing an optical fiber preform according to (2), wherein the composite preform is dehydrated and sintered with the taper portion on the side facing downward, and (7) a glass including a portion to be a core after being made into an optical fiber. Forming rod Step: While rotating the glass rod about its axis, the glass fine particle generator is relatively reciprocated in the longitudinal direction of the glass rod to deposit glass fine particles on the outer periphery of the glass rod to form a composite base material. A second step of forming, a third step of rotating the composite preform in a heating furnace while supporting it substantially vertically and performing dehydration sintering to obtain an optical fiber preform, and a dehydration sintering of the optical fiber preform. And a fourth step of introducing the optical fiber preform into a drawing furnace and drawing the optical fiber while substantially maintaining the shape of the end on the downward side. To do.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of each drawing, the same elements will be denoted by the same reference symbols and redundant description will be omitted. First, in the first step, a glass fine particle aggregate including a portion to be a core after being made into an optical fiber is formed by, for example, the well-known VAD method, the aggregate is dehydrated and sintered, and if necessary, a desired outer diameter is obtained. To obtain the desired glass rod. Its outer diameter is 30 mm
-50 mm and length 500-2000 mm are preferable.

Next, in the second step, as shown in FIG. 2A, while rotating the glass rod 1 about its longitudinal axis, a glass fine particle generator (burner) A is provided on the outer periphery of the glass rod 1 in the longitudinal direction of the glass rod 1. Is a step of reciprocating relatively to and depositing the glass fine particles 2 on the outer periphery of the glass rod 1 to obtain the composite base material 3. Here, in the second step, it is desirable to deposit glass particles on the outer circumference of the glass rod so that the tapered portions formed at both ends of the composite base material have different inclinations. FIG. 1 shows an example of the shape of the composite base material 3 of the present invention.
It is shown as a front view in (a). The composite base material of FIG. 1 (a) is
The taper portions at both ends have different inclinations, and the method for producing an optical fiber preform of the present invention is suitable for producing the inclined fiber preform illustrated in FIG. 1 (b). In the tapered portion of the base material of the present invention, the generatrix of the surface is not limited to a straight line, but may be a curved line as shown in FIG. Here, the slope S (%) of the taper portion is S = L × 100 / {, where L is the length of the taper portion, D is the outer diameter of the constant outer diameter portion, and d is the average outer diameter of the glass rod. (D-d)
/ 2}. The inclination S of the taper portion in FIG. 1A is about 150 at the taper portion on the side where the inclination is gentle (upper part).
Is preferably in the range of ~ 350%, more preferably about 20.
0 to 300%, and the taper portion on the steep slope (lower part) is preferably about 50 to 150%, more preferably about 70 to 120%. FIG. 1B is the same as FIG.
FIG. 3 is a front view showing an example of the shape of the optical fiber preform of the present invention when the composite preform of FIG. The slope S of the taper portion in FIG. 1B is preferably about 200 to 600%, more preferably about 350 to 550% in the taper portion on the side where the slope is gentle, and the taper on the side where the slope is steep. A range of about 100-300% by weight is preferred, and more preferably about 130-250%. Further, the outer diameter of the unsintered portion is preferably within a range of about 95 to 120% of the outer diameter of the constant outer diameter portion after sintering.

An example of a method for manufacturing an optical fiber preform having different tapered portions according to the present invention will be described with reference to FIG. First, there is a method by changing the moving speed of the glass particle generator. For example, a glass rod including a portion to be a core after being made into an optical fiber is rotated around its longitudinal axis to deposit glass particles on its outer periphery to manufacture a composite preform. Glass rod 1 and glass fine particle generator (burner) A during the manufacture of the composite base material when reciprocating in the vertical direction (vertical direction)
The positional relationship between and is shown in FIG. The state of the moving speed of the glass particle generator (burner) A arranged in the positional relationship of FIG. 2 (a) is shown in the graph of FIG. 2 (b). Figure 2 (b)
2A, the burner position on the vertical axis corresponds to the burner position in FIG. 2A, the dotted line indicates the turning point, and the horizontal axis indicates the speed of the burner at that position. After moving the glass particle generator at a constant speed under the same supply conditions of the raw material gas and the fuel gas, the moving speed is gradually increased near the turning point (point P) of one of the reciprocating movements (upper in the figure). Then, after turning back, the speed is gradually decreased to the point P, and thereafter, it is moved at a constant speed. The moving speed is appropriately determined according to the gas supply amount, the length of the glass rod, etc., but the constant speed is about 20 to 5
It is preferable to set it within the range of 0 mm / sec, and the maximum velocity after velocity increase is preferably about 100 to 300 mm / sec. Therefore, at the position where the moving speed increases,
Since the adhesion amount of the glass fine particles per unit surface of the base material is reduced, it is possible to easily obtain a composite base material in which the taper portions formed at both ends have different slopes as shown in FIG. The end of the tapered portion is outside the turning point (dotted line position) of the burner as shown in the figure. Here, the movement of the glass particle generator is described, but it goes without saying that the same operation may be performed by fixing the glass particle generator at a fixed position and moving the glass rod. Next, a method by changing the amount of raw material gas supplied to the glass particle generator will be described. FIG. 2C is an example of a graph showing the relationship between the position of the glass fine particle generator and the supply amount of the raw material gas. In FIG. 2 (c), the burner position on the vertical axis corresponds to the burner position in FIG. 2 (a), and the horizontal axis represents the source gas supply amount from the burner at that position. Even if the relative movement speed is kept constant and the raw material gas supply amount is gradually decreased near one turning point (point P) of the reciprocating movement as shown in FIG. Since the adhered amount of glass fine particles per unit surface of the material is reduced, a composite base material as shown in FIG. 1A is also obtained. further,
Even when the method for controlling both the moving speed and the raw material supply amount, which is a combination of FIG. 2B and FIG. 2C, is applied to the glass particle generating apparatus, a composite base material having different taper inclinations is obtained. Needless to say, it can be obtained.

FIG. 3 shows another example of the method for manufacturing the optical fiber preform in which the taper portions formed at both ends of the present invention have different inclinations. FIG. 3A shows a structure in which a plurality of glass particle generators (burners) are vertically reciprocally moved to deposit glass particles on the outer periphery of a glass rod. ) Are arranged so that they do not contact each other, and independently reciprocate. In this method, the reciprocating movement of the glass particle generating device is made to have substantially the same period while varying the amplitude of each glass particle generating device (burner). FIGS. 3B and 3C show the amplitude, that is, the moving range of each glass particle generator (burner) in correspondence with FIG. 3A. If the inclinations of the formed taper portions are made different, the amplitude can be appropriately set in any range.
As shown in (a), it is preferable to shift the burner folding positions by 150 mm at the upper folding position, and preferably shift by 50 mm at the lower folding position. In the case of FIG. 3C, the difference in the moving range of the three burners is small. In either case, the burners are set to different speeds so that one round trip has the same time. By changing the amplitude of each of the plurality of glass fine particle generators in this manner, it is possible to easily obtain a composite base material in which the taper portions at both ends have different inclinations as shown in FIG. The taper inclination can be easily adjusted by appropriately shifting the respective burner folding positions. In this case,
The supply amount of the raw material gas to the glass particle generation device may be appropriately adjusted, and the supply amount may be adjusted by reducing the supply amount in the vicinity of the turning point as shown in FIG.

Thus, the composite base material as shown in FIG. 1 (a) can be efficiently obtained. Then, in the third step, the composite base material is rotated with the taper portion on the steep slope side facing downward in the heating furnace while being supported substantially vertically, and while feeding helium gas, chlorine gas, etc., about 1100 ° C. or higher. Then, it is dehydrated and further sintered at a high temperature of 1400 ° C. to 1600 ° C. to manufacture an optical fiber preform 4 with a small amount of unsintered portion 5 left on the upper portion as shown in FIG. Since the upper support portion side of the composite base material has a long taper, the glass rod in the vicinity of the support portion is not exposed to high temperature and there is no fear of softening deformation, and the sintering process operation is easy. Then, as a fourth step, the obtained optical fiber preform may be appropriately treated if desired.
Furthermore, the wire can be introduced into the wire drawing furnace as it is without any special treatment or processing that changes the shape, and wire drawing can be performed. Then, it is possible to obtain a good and uniform optical fiber with little transmission loss. As a result, compared with the conventional optical fiber manufacturing method, the process of heating the optical fiber preform before the drawing of the optical fiber preform is not required, so the process is shortened by several hours, and the obtained optical fiber is a good product. The rate increased by about 10 to 20%. The embodiments of the present invention are not limited to those described above, and various modifications can be made within the scope of the invention described in the claims.

[0013]

EXAMPLE A quartz glass rod having an outer diameter of 36 mm and a length of 1800 mm including a core portion was manufactured by the well-known VAD method. As shown in FIG. 2 (a), this glass rod is arranged vertically and the rotation speed is 200 to 25 rp with time.
The composite base material was manufactured by moving the burner in the vertical direction while changing the value to m and rotating the burner to deposit glass particles. 200 liters / min of hydrogen from each gas supply device for the burner,
90 l / min of oxygen, 100 g / min of silicon tetrachloride, and 1.5 l / min of argon gas for sealing were supplied, and glass fine particles were produced by a flame decomposition reaction. Figure 2
As shown in (b), the speed change point P was set about 200 mm below the upper turning point. The burner moved at a constant speed of 50 mm / sec from the lower turning point to the P point, gradually increased its speed from the P point to the upper turning point, and had a maximum speed of 150 mm / sec immediately before turning. This burner movement was repeated to deposit glass particles.

In the obtained composite base material, the outer diameter of the constant outer diameter portion is about 250 mm, and the length of the upper tapered portion is about 300 mm.
The shape was as shown in FIG. 1 (a) having a size of 100 mm and a lower part of about 100 mm, and the inclination was 280% in the upper part and 93% in the lower part. The composite base material was subjected to dehydration sintering treatment for about 15 hours while vertically supporting and rotating the composite base material in the heating furnace with the taper portion on the steep inclination side facing downward. In the obtained optical fiber preform, the outer diameter of the constant outer diameter portion was 150 mm, and the maximum outer diameter of the taper portion including the unvitrified upper portion was about 160 mm. The length of the upper taper portion was about 300 mm, and the length of the lower taper portion was 100 mm. Therefore, the slope is about 530% at the top and about 180% at the bottom.
Is. Thus, optical fiber preforms having different inclinations of the taper portions formed at both ends were obtained. The optical fiber preform was put into the drawing furnace as it was, and the drawing could be performed satisfactorily.

[0015]

As described above, according to the present invention, since the optical fiber preform after sintering can be manufactured without any special treatment, the manufacturing process of the optical fiber can be simplified. And the manufacturing cost thereof can be reduced. Further, even if a large number of portions effective for fiberizing are taken during the sintering of the composite base material, the deformation due to the softening of the base material can be suppressed, and the sintering operation is easy.

[Brief description of drawings]

FIG. 1A is a front view of a composite preform obtained in a manufacturing process of an optical fiber preform of the present invention, and FIG. 1B is an optical fiber when the composite preform of FIG. 1A is dehydrated and sintered. It is a front view of a base material.

FIG. 2 is an explanatory view showing an example of a second step of the method for producing an optical fiber preform according to the present invention, FIG. 2 (a) is a front view showing a state of a positional relationship between a glass rod and a glass fine particle generator (burner). It is a figure, (b) is a graph which shows the position of a burner, and the relationship of moving speed, (c) is a graph which shows a burner position and the relationship of source gas supply amount.

FIG. 3 is an explanatory view showing another example of the second step of the method for producing an optical fiber preform according to the present invention, in which (a) shows the state of the positional relationship between the glass rod and the glass particle generator (burner). It is a front view shown, and (b) and (c) show the moving range of a burner, respectively.

FIG. 4 is a schematic view illustrating a conventional method for manufacturing a composite base material and the shape of the obtained composite base material.

5A is an explanatory view of a state in which a base material hanging portion is deformed during sintering, and FIG. 5B is an explanatory view showing an example of a shape of a conventional optical fiber base material.

FIG. 6 is a schematic view of a conventional composite base material in which the taper portion has a steep inclination.

[Explanation of symbols]

1 glass rod 2 glass particles 3 Composite base material 4 Optical fiber base material 5 Unsintered part A, B, C Glass particle generator (burner)

Claims (7)

[Claims] 1. An optical fiber preform obtained by depositing glass fine particles on the outer periphery of a glass rod including a portion to be a core after forming an optical fiber to form a composite preform, and dehydrating and sintering the composite preform. In the optical fiber preform, the taper portions formed at both ends of the dehydrated and sintered optical fiber preform have different inclinations. 2. A first step of forming a glass rod including a portion to be a core after forming an optical fiber, wherein the glass particle generating device is relatively arranged in a longitudinal direction of the glass rod while rotating the glass rod about its axis. The second step of depositing glass fine particles on the outer periphery of the glass rod by reciprocating the glass rod to form a composite base material, rotating the composite base material in a heating furnace while supporting the composite base material almost vertically, and performing dehydration sintering. A method for manufacturing an optical fiber preform having a third step of obtaining an optical fiber preform, wherein the second step is performed so that the taper portions formed at both ends of the composite preform have different inclinations. A method for manufacturing an optical fiber preform, characterized in that glass particles are deposited on the outer periphery. 3. The relative movement speed in the longitudinal direction of the glass rod of the glass fine particle generator in the second step is gradually increased near one turning point of the reciprocating movement. The method for producing an optical fiber preform according to 1. 4. The glass fine particle raw material supplied to the glass fine particle generator in the second step is gradually reduced in supply amount near one turnaround point of the reciprocating movement. Manufacturing method of optical fiber preform. 5. A plurality of glass fine particle generators in the second step are used, the reciprocating movement amplitudes of the plurality of glass fine particle generating apparatuses are made different, and the reciprocating movement periods are made substantially equal to each other. The method for manufacturing an optical fiber preform according to claim 2. 6. The third step is to dehydrate and sinter the composite base material with the taper portion having a steep slope, of the taper portions formed at both ends of the composite base material, facing downward. The method for producing an optical fiber preform according to claim 2. 7. A first step of forming a glass rod including a core portion after being made into an optical fiber, wherein a glass particle generating device is relatively arranged in a longitudinal direction of the glass rod while rotating the glass rod about its axis. The second step of depositing glass fine particles on the outer periphery of the glass rod by reciprocating the glass rod to form a composite base material, rotating the composite base material in a heating furnace while supporting the composite base material almost vertically, and performing dehydration sintering. In the third step of obtaining the optical fiber preform and the dehydration sintering of the optical fiber preform, the optical fiber preform is introduced into the drawing furnace while substantially maintaining the shape of the end on the side facing downward. And a fourth step of drawing.