JP2006111461A - Method for manufacturing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical fiber capable of manufacturing optical fibers with a small transmission loss and high mechanical strength. <P>SOLUTION: The method for manufacturing an optical fiber comprises feeding a preform 11 with ≤1,000°C crystallization temperature Tx into a fiber drawing furnace 12 to draw the optical fiber 13, wherein, the peak temperature of the fiber drawing furnace 12 is ≤(Tx+55)°C, and the residence time of the preform 11 in a temperature zone in the fiber drawing furnace where the difference of temperature from the peak temperature is within 30°C is ≤15 min. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber manufacturing method.

Propagation loss, mechanical strength, etc. of the optical fiber obtained by drawing the preform while heating and softening are affected by defects such as strain and scratches remaining in the optical fiber. Therefore, conventionally, in order to remove defects remaining in the optical fiber, a method for removing distortion and scratches from the preform by providing an annealing heater above the drawing furnace (see, for example, Patent Document 1) or the like. A method of drawing such that the relationship between the length of the preform heated to the softening temperature or higher and the drawing speed satisfies a predetermined condition (for example, see Patent Document 2), the diameter of the preform and the length of the drawing furnace. There is known a method of drawing so that the relationship between the two satisfies a predetermined condition (see Patent Document 3, for example).
JP-A-4-198036 Japanese Patent Publication No.8-9490 JP 2002-249334 A

  In optical communication, in general, an optical amplifier is required to compensate for propagation loss due to long-distance transmission and loss due to a communication device. As such an optical amplifier, there are a fiber amplifier (EDFA: erbium doped fiber amplifier) doped with erbium in a fiber, a fiber amplifier (TDFA: thulium doped fiber amplifier) doped with thulium, and the like. In addition, an optical switch is necessary at a portion where light is taken in and out. For example, a fiber switch using a nonlinear fiber has been proposed. A silica-based glass optical fiber is generally used for such fiber amplifiers and nonlinear fibers.

  In recent years, wavelength division multiplexing (WDM) optical communication schemes are being put into practical use in order to cope with increasing transmission capacity, and it is possible to widen the communication wavelength band in order to cope with further increase in transmission capacity. Therefore, there is a need for a highly nonlinear fiber having a large nonlinearity so that it can be efficiently switched and a fiber amplifier.

  One of optical fibers that satisfy such a requirement is a bismuth glass optical fiber having a high refractive index of 1.8 or more. However, since the bismuth glass has a low crystallization temperature and a high crystallization speed, a drawing method for a conventional silica glass optical fiber as described in Patent Documents 1 to 3 is applied. In some cases, crystals are precipitated in the preform, and even in an optical fiber drawn from such a preform, the crystals remain in the optical fiber and the propagation loss and mechanical strength of the optical fiber deteriorate. There was a fear.

  Also, when drawing an optical fiber from a preform, generally, a filament that is made as thin as the optical fiber is drawn from the tip of the heat-softened preform, and the filament is wound up. Wind the bobbin and start drawing. None of the above Patent Documents 1 to 3 describe the drawing of this filamentous body, but it is conceivable that a method generally used when the preform is heated and stretched to a predetermined diameter is diverted. . That is, the heat-softened preform tip is held using a jig, and the preform tip held by the jig is placed below the point where the temperature in the drawing furnace reaches the peak temperature. Then, while softening the portion located at the point where the preform reaches the peak temperature, the tip of the preform is mechanically pulled down by a jig, and is positioned above the point where the peak temperature is reached. It is also conceivable to draw out the filament between the upper part of the preform that has not been softened.

  However, when pulling down mechanically using a jig, it is biased to the stress acting on the preform due to non-uniform holding of the tip of the preform by the jig and vibration of the drive device that drives the jig. As a result, the preform may be distorted. Further, even in an optical fiber drawn from such a preform, there is a possibility that distortion remains in the optical fiber and the propagation loss and mechanical strength of the optical fiber are deteriorated.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide an optical fiber manufacturing method capable of manufacturing an optical fiber having a small propagation loss and high mechanical strength.

  The present inventors have paid attention to the fact that the crystallization of the preform proceeds in accordance with the amount of heat energy received by the preform heated to a temperature higher than the crystallization temperature, and as a result of intensive studies to achieve the above-described object , The relationship between the crystallization temperature of the preform and the peak temperature of the drawing furnace, and when the residence time of the preform in a specific temperature range based on the peak temperature in the drawing furnace satisfies a predetermined condition The present inventors have found that it is possible to draw a wire while heating and softening the preform while suppressing crystallization of the preform.

  That is, an optical fiber manufacturing method according to the present invention is a method for manufacturing an optical fiber in which a preform having a crystallization temperature Tx of 1000 ° C. or less is fed into a drawing furnace and is softened to draw the optical fiber. The peak temperature of the preform is Tx + 55 ° C. or less, and the stay time of the preform in the temperature region where the difference from the peak temperature in the drawing furnace is 30 ° C. or less is 15 minutes or less.

  In the optical fiber manufacturing method configured as described above, the peak temperature of the drawing furnace is suppressed to a temperature of Tx + 55 ° C. or less, and the preform in the temperature range where the difference from the peak temperature in the drawing furnace is within 30 ° C. By limiting the stay time to 15 minutes or less, it becomes possible to draw while heating and softening the preform while suppressing the crystallization of the preform, improving the mechanical strength of the drawn optical fiber, and propagation loss. Can be reduced. The staying time is preferably 10 minutes or less.

  In addition, the present inventors have found that the stress acting on the preform is uniform before the optical fiber is drawn in order to further reduce the propagation loss of the optical fiber and further improve the mechanical strength of the optical fiber. The dispersion was achieved and the present invention was achieved.

  That is, an optical fiber manufacturing method according to the present invention is a method of manufacturing an optical fiber in which a preform having a crystallization temperature Tx of 1000 ° C. or less is sent to a drawing furnace and softened to draw the optical fiber. The tip is placed below the point where the temperature in the drawing furnace reaches the peak temperature, the part of the preform located at the point where the peak temperature is reached is softened, and the preform below the softened part A lower end portion is suspended, and a filament formed between the suspended lower end portion of the preform and the upper portion of the preform that is located above the peak temperature and is not softened is wound up. It is characterized by drawing an optical fiber.

  In the optical fiber manufacturing method configured as above, the lower end portion of the preform is positioned below the point where the temperature in the drawing furnace reaches the peak temperature, and the lower end portion of the preform is lower than the softened portion. Is drawn by its own weight, and drawing is started. As a result, the stress acting on the preform can be uniformly distributed without causing unnecessary stress to act on the preform, and the preform can be prevented from being distorted. It is possible to improve mechanical strength and reduce propagation loss.

Incidentally, the preform is typically are composed of a core glass and cladding glass formed from glass material composition, the crystallization temperature Tx of the preform, the core glass crystallization temperature Tx _core or clad glass The lower one of the crystallization temperatures Tx _clad .

  ADVANTAGE OF THE INVENTION According to this invention, the mechanical strength of the drawn optical fiber can be improved and a propagation loss can be reduced.

  Hereinafter, embodiments according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an optical fiber manufacturing apparatus used in the optical fiber manufacturing method of the present invention, FIG. 2 is a cross-sectional view of the heating furnace shown in FIG. 1, and FIGS. It is the schematic for demonstrating the process of the optical fiber manufacturing method which concerns on 2nd Embodiment.

  As shown in FIG. 1, an optical fiber manufacturing apparatus 10 includes a drawing furnace 12 in which a preform 11 is inserted to heat the preform 11, and a preform 11 heated and softened in the drawing furnace 12. A wire diameter measuring device 14 for measuring the outer diameter of the drawn optical fiber 13, a resin coating means 15 for coating the drawn optical fiber 13 with a UV curable resin, and a UV irradiation device for curing the coated UV resin. 16 and a winding bobbin 17 that pulls and winds the optical fiber 13 at a predetermined speed (tension).

  As shown in FIG. 2, the drawing furnace 12 includes a vertical tubular core tube 12a into which the preform 11 is inserted, and a heating element 12b wound around the outer peripheral surface of the axial central portion of the core tube 12a. It has the heat insulating material 12c which covers the outer peripheral surface of the furnace core tube 12a and the heat generating body 12b, and the furnace body 12d which surrounds the outer periphery of the heat insulating material 12c.

  The preform 11 is gradually lowered while its upper end is held by a holding means (not shown), and fed into the core tube 12 a from the upper opening of the core tube 12 a of the drawing furnace 12. The preform 11 supplied to the core tube 12 a is heated and softened and drawn to the optical fiber 13. The drawn optical fiber 13 is coated with UV resin by the resin coating means 15, and the coated UV resin is cured by receiving the UV light from the UV irradiation device 16, and then wound around the winding bobbin 17.

  Next, a first embodiment of an optical fiber manufacturing method according to the present invention will be described.

  In the optical fiber manufacturing method of the present embodiment, the preform 11 having a crystallization temperature Tx of 1000 ° C. or lower is fed into the drawing furnace 12 and softened to draw the optical fiber 13. Is Tx + 55 ° C. or lower, and the residence time of the preform 11 in the temperature range where the difference from the peak temperature in the drawing furnace 12 is within 30 ° C. is 15 minutes or shorter.

  That is, when a preform 11 made of, for example, bismuth-based glass having a Tx of 1000 ° C. or less is drawn using the manufacturing apparatus 10 described above, the drawing is performed so that the peak temperature of the drawing furnace 12 is Tx + 55 ° C. or less. The amount of heat generated by the heating element 12b of the furnace 12 is controlled. The lower limit of the peak temperature of the drawing furnace 12 is typically the glass transition point of the preform 11 + 70 ° C. or higher. For each point of the preform 11, the difference from the peak temperature stays in a temperature range within 30 ° C. from the point (in the vicinity of the heating element 12 b) that becomes the peak temperature in the drawing furnace 12 upward. The lowering speed (feed speed) of the preform 11 is controlled so that the time is 15 minutes or less.

  The preform 11 preferably has a diameter of 12 mm or less. If the diameter is larger than 12 mm, the preform 11 may not be sufficiently softened and strain may remain, and the peak temperature of the drawing furnace 12 must be increased to remove the strain. This is because there is a concern that the propagation loss and mechanical strength of the drawn optical fiber 13 may deteriorate. More preferably, the preform 11 has a diameter of 10 mm or less.

In the optical fiber manufacturing method configured as described above, the preform 11 is heated in the drawing furnace 12 to a temperature at which the viscosity η becomes 10 ⁹ poise or more, and drawn into the optical fiber 13. The outer diameter (clad diameter) of the optical fiber 13 is typically 70 μm to 200 μm.

  Next, a second embodiment of the optical fiber manufacturing method according to the present invention will be described with reference to FIG.

  In the optical fiber manufacturing method of this embodiment, a preform 11 having a crystallization temperature Tx of 1000 ° C. or less is sent into a drawing furnace 12 to be softened and the optical fiber 13 is drawn. The temperature in the drawing furnace 12 is arranged below the point at which the peak temperature is reached, the portion of the preform 11 located at the point at which the peak temperature is reached is softened, and the lower end of the preform below the softened portion A portion is suspended, and a filament formed between the lower end portion of the suspended preform and the upper portion of the preform 11 that is located above the point that becomes the peak temperature and is not softened is wound up. The optical fiber 13 is drawn.

  That is, when the preform 11 made of, for example, bismuth-based glass having a Tx of 1000 ° C. or less is drawn using the manufacturing apparatus 10 described above, first, as shown in FIG. The part 11 a is inserted into the drawing furnace 12. In addition, it is preferable to preheat in the upper part in the drawing furnace 12. Subsequently, as shown in FIG. 3B, the tip portion 11a of the preform 11 is disposed below the point where the temperature in the drawing furnace 12 reaches the peak temperature (near the heating element 12b), The portion located at the point where the peak temperature of 11 is reached is softened by heating. And as shown in FIG.3 (C), the preform lower end part 11b below the said softened part is suspended. At this time, a constricted part (neck down part) 11c is formed between the lower end part 11b of the preform and the upper part 11d of the preform 11 which is located above the point where the peak temperature is not softened, As the preform lower end portion 11 b hangs down, the constricted portion 11 c is gradually reduced in diameter to form a filament having a diameter as small as that of the optical fiber 13. Finally, as shown in FIG. 3D, the filament is wound around the winding bobbin 17, the preform 11 is fed into the drawing furnace 12 at a predetermined speed, and is wound at a predetermined speed (tension). The optical fiber 13 is drawn around the bobbin 17.

  In the optical fiber manufacturing method of the present embodiment, the peak temperature of the drawing furnace 12 is set to Tx + 55 ° C. or less, and the difference from the peak temperature in the drawing furnace 12 is within 30 ° C. before the drawing is started. It is preferable that the staying time of the upper portion 11d of the preform 11 in the temperature range is 15 minutes or less. This prevents crystallization of the upper part 11d of the preform 11 inserted into the drawing furnace 12, and further improves the propagation loss and mechanical strength of the optical fiber 13 drawn from the upper part 11d. Can do.

  The optical fiber manufacturing method of the present invention is not limited to the above-described embodiments, and appropriate modifications and improvements can be made.

  For example, in each of the above-described embodiments, the preform 11 is typically composed of a core glass having a high refractive index and a clad glass having a low refractive index laminated in an annular shape on the outer periphery of the core glass. The core glass and / or the clad glass may be composed of a plurality of layers. Further, the core portion may be air, or may have a holey structure having a hole in the preform 11, and is not limited to a specific preform.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example and a comparative example, this invention is not limited to a following example. In the following description, a glass transition point of the glass material forming the preform Tg, T ₉ the temperature at which the viscosity η is 10 ⁹ _poise, temperature T ₇ in which the viscosity η is 10 ⁷ _poise, the viscosity η The temperature at 10 ⁵ poise is represented by T ₅ , the average linear expansion coefficient at 50 to 350 ° C. is represented by α, and the refractive index with respect to a wavelength of 1550 nm is represented by n.

The optical fibers of Examples 1 to 3 and Comparative Examples 1 to 3 are respectively Bi ₂ 0 ₃ —Si 0 ₂ —Al ₂ 0 ₃ —Ga ₂ O ₃ —La ₂ O ₃ —CeO ₂ —Er ₂ O ₃ based cores. Glass (Tx _core = 553 ° C., Tg = 489 ° C., T ₉ = 536 ° C., T ₇ = 571 ° C., T ₅ = 623 ° C., α = 85 × 10 ⁻⁷ ° C.− ¹ , n = 2.03), Bi ₂ O ₃ —SiO ₂ —Al ₂ O ₃ —Ga ₂ O ₃ —La ₂ O ₃ —CeO ₂ clad glass (Tx _clad = 557 ° C., Tg = 491 ° C., T ₉ = 538 ° C., T ₇ = 573 , T ₅ = 625 ° C., α = 85 × 10 ⁻⁷ ° C ⁻¹ , n = 2.02), and a single mode optical fiber having an outer diameter (cladding diameter) of 125 μm. is there.

In addition, the crystallization temperature of said core glass and clad glass is based on a differential thermal analysis (DTA: Differential Thermal Analysis), and is measured on condition of the following.
Apparatus: TG / DTA6300 manufactured by Seiko Instruments Inc.
Sample powder particle system: 105 to 44 μm
Sample amount: 160 mg
Temperature increase rate: 10 ° C / min Standard sample: Alumina

The optical fibers of Examples 1 to 3 and Comparative Examples 1 to 3 have preform crystallization temperatures Tx (Tx _core <Tx _clad in Examples 1 to 3 and Comparative Examples 1 to 3; Tx _core = 553 ° C.) and the peak temperature T of the drawing furnace, and the different residence times of the preform in the temperature range where the difference between the peak temperature in the drawing furnace is within 30 ° C. It has been drawn by changing.

A process of manufacturing an optical fiber will be described by taking Example 2 as an example.
The preform had a diameter of 10 mm and was drawn using a drawing furnace having a core tube inner diameter of 24 mm. The draw furnace peak temperature T was 606 ° C. (<608 ° C. (553 ° C. + 55 ° C.)). Further, the distance L from the point at which the peak temperature T in the drawing furnace reaches the upper point where the difference from the peak temperature T reaches 30 ° C. is 12 mm, and the preform is drawn at a feed rate of 1.5 mm / min. Inserted into the furnace. Accordingly, the residence time of the preform in the temperature region where the difference from the peak temperature T in the drawing furnace is within 30 ° C. is 8.0 minutes. Then, the drawing was performed at a drawing speed of 9.6 m / min so that the outer diameter of the optical fiber was 125 μm. As described in the second embodiment, the lower end portion of the preform is suspended and the drawing of the optical fiber is started.

  The diameters of the preforms of Examples 1 to 3 and Comparative Examples 1 to 3, the peak temperature T of the drawing furnace, the distance L until the difference from the peak temperature T reaches 30 ° C., the feeding speed, the staying time, and the drawing speed. Table 1 shows.

  The optical fibers of Examples 1 to 3 and Comparative Examples 1 to 3 obtained by drawing as described above were cut into appropriate lengths, and tensile strength (breaking strength) was obtained using the strength test apparatus 30 shown in FIG. Was measured. That is, both ends of the optical fiber were held at a holding interval W = 17 cm, and when one end was pulled at a speed V = 60 mm / min, the strength when the optical fiber was cut was defined as tensile strength. Moreover, the propagation loss of the optical fiber of Examples 1-3 and Comparative Examples 1-3 was calculated | required by the cutback method. The results are shown in Table 1.

As shown in Table 1, each of the optical fibers of Examples 1 to 3 has higher breaking strength, that is, mechanical strength, and smaller propagation loss than the optical fibers of Comparative Examples 1 to 3. Was confirmed.
In Comparative Example 1, the residence time of the preform in the temperature range where the difference from the peak temperature T in the drawing furnace is within 30 ° C. is 16.7 minutes (> 15 minutes), and the crystallization of the preform is Since the crystal substance is advanced and remains in the optical fiber, the breaking strength of the optical fiber is lowered.
In Comparative Example 2, the peak temperature T in the drawing furnace is 617 ° C. (> 608 ° C. (553 ° C. + 55 ° C.)), and the crystallization of the preform progresses so that the crystalline substance remains in the optical fiber. Therefore, the breaking strength of the optical fiber is reduced and the propagation loss is increased.
In Comparative Example 3, the peak temperature T in the drawing furnace is 611 ° C. (> 608 ° C. (553 ° C. + 55 ° C.)), and the difference from the peak temperature T in the drawing furnace is within 30 ° C. The stay time of the preform in the temperature region is 20.8 minutes (> 15 minutes), and the crystallization of the preform progresses so that crystals remain in the optical fiber. This is a decrease and an increase in propagation loss.

  As described above, the optical fiber manufacturing method according to the present invention has an effect of increasing the mechanical strength of an optical fiber drawn from a preform having a low crystallization temperature and reducing propagation loss. This is useful as an optical fiber manufacturing method for manufacturing an optical fiber having a high refractive index of 1.8 or more.

It is a schematic block diagram which shows the optical fiber manufacturing apparatus used for the optical fiber manufacturing method of this invention. It is sectional drawing of the heating furnace shown by FIG. (A)-(D) are schematic for demonstrating the process of the optical fiber manufacturing method which concerns on 2nd Embodiment of this invention. It is a schematic block diagram of the test apparatus for measuring the breaking strength of an optical fiber.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Preform 12 Drawing furnace 12a Core tube 12b Heat generating body 12c Heat insulating material 12d Furnace body 13 Optical fiber 17 Winding bobbin

Claims (2)

An optical fiber manufacturing method for drawing an optical fiber by feeding a preform having a crystallization temperature Tx of 1000 ° C. or lower into a drawing furnace and softening the preform.
The peak temperature of the drawing furnace is Tx + 55 ° C or less,
A method for producing an optical fiber, wherein a stay time of the preform in a temperature range in which a difference from a peak temperature in a drawing furnace is within 30 ° C. is 15 minutes or less. An optical fiber manufacturing method for drawing an optical fiber by feeding a preform having a crystallization temperature Tx of 1000 ° C. or lower into a drawing furnace and softening the preform.
Place the tip of the preform below the point where the temperature in the drawing furnace reaches the peak temperature,
Soften the part located at the point of the preform at the peak temperature,
Draw down the lower end part of the preform below the softened part,
The optical fiber is drawn by winding up a filament formed between the lower end portion of the suspended preform and the upper portion of the preform that is located above the peak temperature and is not softened. An optical fiber manufacturing method.

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