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    • 专利摘要:
    A drawing process is included of drawing while heating, in a heating furnace (20), a lower end portion of an optical fiber preform (1P) that is to be an optical fiber (1) having a core (10) consisting of silica glass containing a rare earth element compound, in which a temperature profile in the heating furnace (20) is a profile in which temperature is increased from an upstream side toward a downstream side to a maximum temperature and then decreased and that has a changing point at which a temperature decrease becomes steep on the downstream side from a place where the maximum temperature is reached, and the maximum temperature is a temperature at which temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase.
    公开号:DK202170065A1
    申请号:DKP202170065
    申请日:2021-02-12
    公开日:2021-02-17
    发明作者:Hosokawa Tsukasa
    申请人:Fujikura Ltd；
    IPC主号:
    专利说明:

    [0001] [0001] The present invention relates to a manufacturing method for an optical fiber and a manufacturing apparatus for an optical fiber.
    [0002] [0002] A fiber laser device is used in various fields such as a laser processing field and a medical field because it is excellent in light condensing property, has a high power density, and can obtain a light beam having a small beam spot. In such a fiber laser device, a rare earth-added optical fiber is used having a core to which a rare earth element is added.
    [0003] [0003] By the way, the optical fiber is obtained by heating an optical fiber preform in a heating furnace and drawing the optical fiber preform. A method for manufacturing an optical fiber in this way is described in Patent Literature 1 below. In the manufacturing method for an optical fiber of Patent Literature 1 below, to prevent the surface of the drawn 1
    [0004] [0004] However, when 1t is required to reduce optical transmission loss over a long distance as in an optical fiber used for optical communication, it is preferable to reduce the optical transmission loss by slowly cooling the drawn optical fiber to reduce a Rayleigh scattering coefficient. For example, in Patent Literature 2 below, a manufacturing method for an optical fiber is described capable of rapidly cooling only the surface of the optical fiber and slowly cooling the inside of the optical fiber.
    [0005] [0005] [Patent Literature 1] JP S53-125857 A [Patent Literature 2] JP 2017-36197 A Summary of Invention
    [0006] [0006] The core of the optical fiber described in Patent Literature 1 and Patent Literature 2 does not contain a rare earth element. The core consisting of silica glass that does not contain rare earth elements is unlikely to undergo crystallization during the manufacturing process of the optical fiber. On the other hand, in the case of a rare 2
    [0007] [0007] Since the manufacturing method for an optical fiber of Patent Literature 1 and Patent Literature 2 is premised on manufacture of an optical fiber containing no rare earth elements in the core, the crystallization and phase separation in the core as described above have not been studied. Thus, when an optical fiber having a core containing a rare earth element compound is manufactured by the manufacturing method for an optical fiber described in Patent Literature 1 and Patent Literature 2, there is a concern that the loss of the light propagating through the core cannot be sufficiently suppressed.
    [0008] [0008] An object of the present invention is therefore to provide a manufacturing method for an optical fiber and a 3
    [0009] [0009] A manufacturing method for an optical fiber of the present invention for solving the above problems, includes a drawing process of drawing while heating, in a heating furnace, a lower end portion of an optical fiber preform that is to be an optical fiber having a core consisting of silica glass containing a rare earth element compound, in which a temperature profile in the heating furnace is a profile in which temperature is increased from an upstream side toward a downstream side to a maximum temperature and then decreased and that has a changing point at which a temperature decrease becomes steep on the downstream side from a place where the maximum temperature is reached, and the maximum temperature is a temperature at which temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase.
    [0010] [0010] In the silica glass containing the rare earth element compound, the crystallization and phase separation of the rare earth element compound occur at a temperature lower than a temperature at which the silica glass containing the rare earth element compound is in a single phase at higher 4
    [0011] [0011] Furthermore, it is preferable that the temperature profile in the heating furnace is set to cause the cooling rate to be maximized at a temperature at which separation occurs into a plurality of liquid phases respectively having different composition ratios between the rare earth element compound and a pure silica glass in an equilibrium state.
    [0012] [0012] The cooling rate is maximized in a temperature range in which the phase separation occurs in the silica glass containing the rare earth element compound, whereby the phase separation of the silica glass containing the rare earth element compound can be further suppressed.
    [0013] [0013] Furthermore, it is preferable that the temperature profile on the upstream side from the changing point in the
    [0014] [0014] The larger the ratio 0:/0,, the steeper the temperature 6
    [0015] [0015] Furthermore, it is more preferable that the temperature of the heating furnace is set to cause the ratio o./0p to be greater than or equal to 3.
    [0016] [0016] The present inventor has found that the ratio oi./op is set to be greater than or equal to 3, whereby the cooling rate of the glass wire drawn from the optical fiber preform can be made larger on the downstream side of the place where the maximum temperature is reached in the heating furnace.
    [0017] [0017] Moreover, it is more preferable that the temperature of the heating furnace is set to cause the ratio o:./op, to be less than or equal to 8.
    [0018] [0018] As described above, the ratio 0+/0, is set to be greater than or equal to 2, whereby the cooling rate of the glass wire drawn from the optical fiber preform can be made sufficiently large on the downstream side from the place where the maximum temperature is reached in the heating 7
    [0019] [0019] Furthermore, it is preferable that the dispersion 0: is set to be greater than or equal to 100 mm and less than or equal to 300 mm.
    [0020] [0020] As described above, the larger the ratio 0+/0p, the steeper the temperature decrease after the changing point of the temperature profile in the heating furnace. Thus, as the dispersion or is smaller, the ratio 0+:/0, 1s smaller, and the temperature decrease is gentle after the changing point of the temperature profile in the heating furnace. That is, as the dispersion 0. is smaller, it is easier for the cooling rate of the glass wire drawn from the optical fiber preform to asymptotically approach a constant value. The present inventor has found that the cooling rate of the glass wire can be made sufficiently high when the dispersion dr is greater than or equal to 100 mm. On the other hand, the larger the dispersion 0+, the slower the cooling rate of the 8
    [0021] [0021] Furthermore, it is preferable that a ratio T./Tmax Of a temperature T. of the changing point to a maximum temperature Thax 1S set to be greater than or equal to 0.5.
    [0022] [0022] When the ratio Tc/Tmax is greater than or equal to 0.5, it becomes easier to rapidly cool the glass wire drawn from the optical fiber preform after heating the glass wire to the maximum temperature. Thus, the crystallization and phase separation are more likely to be suppressed of the rare earth element compound in the silica glass constituting the core.
    [0023] [0023] Furthermore, it is preferable that the ratio Te¢/Tmax is set to be greater than or equal to 0.7.
    [0024] [0024] When the ratio Tc/Tmax is greater than or equal to 0.7, it becomes easier to rapidly cool the glass wire drawn from the optical fiber preform after heating the glass wire to the maximum temperature. Thus, the crystallization and phase separation are further likely to be suppressed of the rare earth element compound in the silica glass constituting the core.
    [0025] [0025] Furthermore, a rare earth element contained in the rare 9
    [0026] [0026] Since Yb is a rare earth element, the greater the concentration of Yb added to the core, the more likely it is that the crystallization and phase separation occur in the core. For example, when the concentration of Yb in the core is greater than or equal to 2.0 wt and less than or equal to 3.1 wt%, the crystallization and phase separation are likely to occur in the core. However, as described above, in the manufacturing method for an optical fiber, the temperature in the heating furnace is steeply decreased on the downstream side from a position where the temperature in the heating furnace is maximized, so that even when Yb of greater than or equal to 2.0 wt% and less than or equal to
    [0027] [0027] When the concentration of Yb added to the core is greater than or equal to 2.0 wt% and less than or equal to
    [0028] [0028] When Al and P are co-added with Yb, the crystallization and phase separation can be suppressed in the core to which Yb is added. In addition to this, in the manufacturing method for an optical fiber, as described above, the temperature in the heating furnace can be steeply decreased on the downstream side from the position where the temperature in the heating furnace is maximized. The crystallization and phase separation in the core can therefore be further suppressed.
    [0029] [0029] Furthermore, a manufacturing apparatus for an optical fiber of the present invention for solving the above problems, includes a heating furnace that heats, with a heating element, an optical fiber preform that is to be optical fiber having a core consisting of silica glass containing a rare earth element compound, in which a temperature profile in the heating furnace is a profile in which temperature dis increased from an upstream side toward a downstream side to a maximum temperature and then decreased and that has a changing point at which a temperature decrease becomes steep on the downstream side from a place where the maximum temperature is reached, and the maximum temperature is a temperature at which temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase.
    [0030] [0030] 11
    [0031] [0031] Furthermore, it is preferable that a cooling member that cools the glass wire drawn from the optical fiber preform is provided below the heating element.
    [0032] [0032] The cooling member that cools the glass wire drawn from the optical fiber preform is provided below the heating element, whereby it becomes easier to decrease the temperature in the heating furnace, in the lower side of the heating furnace. It is therefore possible to easily form the temperature profile having the changing point at which the temperature decrease becomes steep on the downstream side of the place where the maximum temperature is reached, in the heating furnace.
    [0033] [0033] Furthermore, it is preferable that the cooling member 12
    [0034] [0034] The blow of the cooling gas is applied as described above, whereby the temperature decrease can be made steeper on the downstream side of the place where the maximum temperature is reached, in the heating furnace. Furthermore, the blow of the cooling gas is applied from the bottom toward the top, whereby the cooling gas flows along the glass wire. In this case, shaking of the glass wire can be suppressed as compared with a case where the cooling gas is applied perpendicularly to the side surface of the glass wire as in the methods described in Patent Literature 1 and Patent Literature 2. Thus, the optical fiber can be manufactured with high accuracy as compared with the methods described in Patent Literature 1 and Patent Literature 2.
    [0035] [0035] Furthermore, it is preferable that a heat radiating material that transfers heat inside the heating furnace to the outside of the heating furnace is provided below the heating element.
    [0036] [0036] Such a heat radiating material is provided, whereby it becomes easier to radiate heat to the outside below the heating element in the heating furnace. It is therefore 13
    [0037] [0037] As described above, according to the present invention, the manufacturing method for an optical fiber and the manufacturing apparatus for an optical fiber are provided capable of suppressing the loss of the light propagating through the core containing the rare earth element compound. Brief Description of Drawings
    [0038] [0038] FIG. 1 is a diagram illustrating a cross section perpendicular to the longitudinal direction of an optical fiber according to an embodiment of the present invention.
    [0039] [0039] Hereinafter, preferred embodiments of a manufacturing method for an optical fiber and a manufacturing apparatus for an optical fiber according to the present invention will be described in detail with reference to the drawings. The embodiments exemplified below are for facilitating understanding of the present invention, and are not for 17
    [0040] [0040] FIG. 1 1s a diagram illustrating a cross section perpendicular to the longitudinal direction of an optical fiber according to an embodiment of the present invention. An optical fiber 1 of the present embodiment 1s an amplification optical fiber. As illustrated in FIG. 1, the optical fiber 1 of the present embodiment includes a core 10, an inner clad 11 that is a clad surrounding the outer peripheral surface of the core 10 without a gap, an outer clad 12 that coats the outer peripheral surface of the inner clad 11, and a protective layer 13 that coats the outer peripheral surface of the outer clad 12, as main components. As described above, the optical fiber 1 has a so-called double clad structure. A refractive index of the inner clad 11 is lower than a refractive index of the core 10, and a refractive index of the outer clad 12 is lower than the refractive index of the inner clad 11. Furthermore, the core 10 is disposed at the center of the inner clad 11.
    [0041] [0041] Fxamples of a material constituting the core 10 include silica glass to which a rare earth element such as ytterbium (Yb) is added. Examples of such a rare earth element include thulium (Tm), cerium (Ce), neodymium (Nd), europium (Eu), erbium (Er), and the like, in addition to Yb described above.
    [0042] [0042] Fxamples of a material constituting the inner clad 11 include pure silica glass to which no dopant is added. Note that, an element such as fluorine (F) that decreases the refractive index may be added to the material constituting the inner clad 11.
    [0043] [0043] The outer clad 12 includes, for example, a resin, and examples of the resin include an ultraviolet curable resin and a thermosetting resin.
    [0044] [0044] Examples of a material constituting the protective layer 13 include an ultraviolet curable resin and a thermosetting resin. When the outer clad 12 includes a resin, the material constituting the protective layer 13 is a resin different from the resin constituting the outer clad 12.
    [0045] [0045] Next, a description will be given of the manufacturing apparatus for an optical fiber according to the embodiment of the present invention.
    [0046] [0046] FIG. 2 is a diagram schematically illustrating the manufacturing apparatus for an optical fiber according to the present embodiment. A manufacturing apparatus 100 for the optical fiber 1 illustrated in FIG. 2 includes a preform feeding device 21, a heating furnace 20, a coating device 50, a turn pulley 60, a drawing device 61, and a winding device 62, as main components. The optical fiber 1 is manufactured by the manufacturing apparatus 100 for an optical fiber.
    [0047] [0047] The preform feeding device 21 is a device attached to the upper end portion of an optical fiber preform 1P that is to be the optical fiber 1, and including a motor that feeds the optical fiber preform 1P from the lower end side into the heating furnace 20 at a predetermined speed.
    [0048] [0048] The heating furnace 20 of the present embodiment includes a housing 23, a core tube 22, a heating element 30, a heat insulating material 25, and a cooling member 40, as main components.
    [0049] [0049] A refrigerant flow path 24 through which a refrigerant
    [0050] [0050] The heating element 30 of the present embodiment generates heat due to electric resistance when energized. The heating element 30 may be a part of the core tube 22. To effectively use the heat generated by the heating element 30, the heating element 30 and the core tube 22 are surrounded by the heat insulating material 25 in the hollow portion 20H. The number of the heat insulating materials 25 is not particularly limited, and the heat insulating material may be divided into a plurality of parts.
    [0051] [0051] The maximum temperature in the heating furnace 20 may 21
    [0052] [0052] The cooling member 40 is a member that cools a glass wire drawn from the optical fiber preform 1P, and is provided below the heating element 30 on the inner peripheral surface side of the core tube 22 in the heating furnace 20. Furthermore, the cooling member 40 of the present embodiment surrounds the glass wire drawn from the optical fiber preform 1P. Such a cooling member 40 is preferably configured such that cooling water flows inside, for example. The temperature of the cooling water is preferably a temperature at which boiling does not occur while the cooling water flows inside the cooling member 40, and a temperature at which excessive dew condensation does not occur on the cooling 22
    [0053] [0053] Furthermore, it is preferable that a blow of the cooling gas 1s applied from the bottom toward the top on the inner peripheral surface side of the cooling member 40 of the present embodiment. The blow of the cooling gas is applied from the bottom toward the top between the inner peripheral surface of the cooling member 40 and the surface of the glass wire drawn from the optical fiber preform 1P. The blow of the cooling gas is applied in this way, whereby the cooling gas easily flows along the surface of the glass wire drawn from the optical fiber preform 1P. Shaking of the glass wire can therefore be suppressed as compared with a case where the blow of the cooling gas is applied perpendicularly to the surface of the glass wire. The type of the cooling gas is not particularly limited, but the cooling gas is preferably He or Ar from viewpoints of thermal conductivity and the like.
    [0054] [0054] The coating device 50 of the present embodiment includes a first coating device 51 and a second coating device 52. The first coating device 51 is a device that forms the outer clad 12 that coats the outer peripheral surface of the bare optical fiber 1F by causing the bare optical fiber 1E including the core 10 and the inner clad 11 drawn in the heating furnace 20 to pass through. The second coating device 52 is a device that forms the protective layer 13 that coats the outer peripheral surface of the outer clad
    [0055] [0055] The drawing device 61 is a device that draws the optical fiber 1 whose direction is changed by the turn pulley 60 at a predetermined drawing speed, and the winding device 62 is a device that winds the optical fiber 1 around a bobbin.
    [0056] [0056] Next, a description will be given of the manufacturing method for an optical fiber according to the embodiment of the present invention.
    [0057] [0057] FIG. 3 is a flowchart illustrating the manufacturing method for an optical fiber according to the embodiment of the present invention. According to the manufacturing method for an optical fiber of the present embodiment, the optical fiber 1 is manufactured by using the manufacturing apparatus 100 for an optical fiber. As illustrated in FIG.
    [0058] [0058] <Preparation process Pl> In this process, first, the optical fiber preform 1P is prepared including a core glass body that is to be the core of the optical fiber 1 and a clad glass body that is to be the inner clad 11. FIG. 4 is a diagram illustrating a cross section perpendicular to the longitudinal direction of the optical fiber preform 1P prepared in the preparation process Pl. As illustrated in FIG. 4, the optical fiber preform 1P includes a core glass body 10P that is to be the core 10 of the optical fiber 1 and a clad glass body 11P that is to be the inner clad 11. The method for producing the optical fiber preform 1P is not particularly limited, and for example, the optical fiber preform 1P can be produced by a modified chemical vapor deposition method (MCVD method).
    [0059] [0059] Next, the optical fiber preform 1P is set in the heating furnace 20. As illustrated in FIG. 2, the upper end portion of the optical fiber preform 1P is fixed to the preform feeding device 21, and the optical fiber preform 1P is inserted into the core tube 22 of the heating furnace 20 from the lower end portion.
    [0060] [0060] <Drawing process P2>
    [0061] [0061] After the optical fiber preform 1P is set in the heating furnace 20 in the preparation process Pl as described above, the heating element 30 of the heating furnace 20 is caused to generate heat to heat the lower end portion of the optical fiber preform 1P. The lower end portion of the optical fiber preform 1P is melted by being heated in the heating furnace 20, and a tapered neck-down ND is formed and the diameter is reduced. In this way, the lower end portion of the optical fiber preform 1P is reduced in diameter, the core glass body 10P becomes the core 10, the clad glass body 11P becomes the inner clad 11, and the bare optical fiber 1E is obtained including the core 10 and the inner clad 11.
    [0062] [0062] The outer diameter of the bare optical fiber 1E, that is, the outer diameter of the inner clad 11 is adjusted by adjustment of a speed at which the optical fiber preform 1P is fed to the downstream side of the heating furnace 20 by the preform feeding device 21 and a speed at which the optical fiber 1 1s drawn by the drawing device 61. Furthermore, when the bare optical fiber 1E is drawn as described above, downward pulling force, that is, drawing tension is applied to the neck-down ND. The drawing tension applied to the neck-down ND is adjusted by adjustment of the 26
    [0063] [0063] FIG. 5 is a diagram illustrating a temperature profile in the heating furnace 20. As illustrated by the solid line in FIG. 5, the temperature profile in the heating furnace 20 is a profile in which the temperature is increased from the upstream side toward the downstream side of the heating furnace 20 to the maximum temperature Tnx and then decreased and that has a changing point at which a temperature decrease becomes steep on the downstream side from a place where the maximum temperature Tmax is reached. A temperature of the changing point is set as Tv, and a position of the changing point is set as x.. Note that, the position in the heating furnace 20 is defined with the place where the maximum temperature Tmax is reached as a reference point (0), the downstream side from the reference point as the positive direction, and the upstream side as the negative direction.
    [0064] [0064] In the heating furnace 20 of the present embodiment, the cooling member 40 is disposed below the heating element 30 of the core tube 22, whereby the temperature of the lower part of the heating furnace 20 is lower than the temperature of the upper part. The temperature in the heating furnace therefore has a profile having the changing point as described above.
    [0065] [0065] The temperature profile illustrated by the broken line 27
    [0066] [0066] The maximum temperature Tmax in the heating furnace 20 is a temperature at which temperature of the silica glass constituting the core 10 is higher than or equal to the glass transition temperature and the silica glass is in a single phase. The maximum temperature Tmax in the heating furnace will be described with reference to a binary equilibrium diagram of YbzOs and SiO.
    [0067] [0067] FIG. 6 is the binary equilibrium diagram of YbzOs and S103.
    [0068] [0068] Silica glass (Si0,) containing a few percent of Yb>Os is in two liquid phases having composition ratios between Yb,0; and S10, are different from each other, in a predetermined 28
    [0069] [0069] FIG. 7 is a diagram for explaining the temperature profile in the heating furnace 20 illustrated in FIG. 5 in 29
    [0070] [0070] Here, 0: is a dispersion of the normal distribution when the temperature profile on the upstream side from the changing point is approximated to the part of the normal distribution represented by the equation (1), and op, is a dispersion of the normal distribution when the temperature profile on the downstream side from the changing point is approximated to the part of the normal distribution represented by the equation (2). Thus, or > 0. Furthermore, in the equations (1) and (2), T is a temperature at an
    [0071] [0071] In this case, a half width of the normal distribution illustrated in the equation (1) is 2V(21ln2)o., and a half width of the normal distribution illustrated in the equation (2) is 2V(21n2)oy.
    [0072] [0072] The ratio 0+/0, of the dispersion or of the equation (IL) to the dispersion oo, of the equation (2) is preferably greater than or equal to 2, more preferably greater than or equal to 3, and further preferably less than or equal to §, as described in the following calculation examples. Furthermore, the ratio 0:/0, may be less than or equal to 6.
    [0073] [0073] In the calculation examples described below, the temperature profile of the glass constituting the optical fiber 1 near the neck-down ND and the outer diameter of the neck-down ND are estimated from the outer diameter of the 31
    [0074] [0074] From the equilibrium of forces in the formation of the neck-down ND, the relational expression of the following equation (3) is derived.
    [0075] [0075] 32
    [0076] [0076] From the heat balance, a relational expression of the following equation (6) is derived. Note that, g(Ta) in the following equation (6) is obtained by the following equation (7), and p(Ta) is obtained by the following equation (8).
    [0077] [0077] (Calculation example 1) FIG. 8 illustrates estimation results of the temperature profile in the heating furnace 20, the 33
    [0078] [0078] Furthermore, FIG. 9 illustrates a relationship between the temperature of the glass obtained from the estimation results illustrated in FIG. 8 and a cooling rate of the glass at that time.
    [0079] [0079] (Calculation example 2) Estimation was performed of the temperature profile in the heating furnace 20, the temperature profile of the glass near the neck-down ND, and the outer diameter of the neck- down ND by changing the dispersion or within a range from 50 mm to 300 mm and the dispersion op within a range from 20 mm to 300 mm when the outer diameter of the optical fiber preform 1P is 30 mm, the outer diameter of the inner clad 11 is 0.25 mm, the drawing speed is 50 m/min, the drawing tension is 50 gf, the constant B of the equations (1) and 34
    [0080] [0080] Furthermore, FIG. 13 illustrates a relationship between the cooling rate of the glass at each position in the heating furnace 20, estimated from the temperature profile of the glass and the outer diameter of the neck-down ND when the dispersion or is 150 mm, and the temperature of the glass at that time.
    [0081] [0081] FIG. 14 illustrates a relationship between the ratio 0+:/0, and a maximum value of the cooling rate obtained from FIG. 13, and FIG. 15 illustrates a relationship between a value obtained by normalizing the maximum value of the cooling rate with the maximum value of the cooling rate when 0: = Op, and the ratio 0:/0,. Note that, FIGS. 14 and 15 also illustrate together the result of the same calculation for each case where the dispersion or is 50 mm, 100 mm, 150 mm, 200 mm, 300 mm, or 400 mm. From FIGS. 14 and 15, it can be seen that the larger the value of the ratio 0:/0p, the larger the cooling rate. From FIG. 15, when the ratio 0+/0, is less than 2, an increase in the maximum value of the cooling rate
    [0082] [0082] On the other hand, it can be seen that the maximum value of the cooling rate is a small value when the dispersion o: is larger than 300 mm. Thus, the dispersion &. is preferably less than or equal to 300 mm.
    [0083] [0083] (Calculation example 3) Fstimation was performed of the temperature profile in 36
    [0084] [0084] Furthermore, FIG. 19 illustrates a relationship between the cooling rate of the glass at each position in the heating furnace 20, estimated from the temperature profile of the glass and the outer diameter of the neck-down ND when the ratio 0+/09 = 3.0, and the temperature of the glass at that time.
    [0085] [0085] FIG. 20 illustrates a relationship between a value obtained by normalizing the maximum value of the cooling rate obtained from FIG. 19 with the maximum value of the cooling rate when x. = 0, and the ratio Tec/Tmax. From FIG. 20, it can be seen that if the ratio Tc/Tmax is greater than or equal to 0.5 regardless of the value of the ratio o./oy, 37
    [0086] [0086] In the heating furnace 20 whose temperature is set as described above, the lower end of the optical fiber preform 1P is heated and is in a molten state. Then, the glass wire melted is drawn from the optical fiber preform 1P. Upon coming out of the heating furnace 20, the drawn glass wire in the molten state solidifies immediately, and the core glass body 10P becomes the core 10, and the clad glass body 11P becomes the inner clad 11, whereby the bare optical fiber 1E is obtained including the core 10 and the inner clad 11.
    [0087] [0087] 38
    [0088] [0088] Then, a direction of the optical fiber 1 is changed by the turn pulley 60, and the optical fiber 1 is wound by the winding device 62.
    [0089] [0089] As described above, the manufacturing method for the optical fiber 1 of the present embodiment includes the drawing process P2 that performs drawing while heating, in the heating furnace 20, the lower end portion of the optical fiber preform 1P that is to be the optical fiber 1 including the core 10 consisting of silica glass containing the rare earth element compound. Furthermore, the temperature 39
    [0090] [0090] In the silica glass containing the rare earth element compound, the crystallization and phase separation of the rare earth element compound occur at a temperature lower than a temperature at which the silica glass containing the rare earth element compound is in a single phase at higher than or equal to the glass transition temperature. Thus, heating is performed once to the temperature at which temperature of the silica glass containing the rare earth element compound is higher than or equal to the glass transition temperature and the silica glass is in a single phase, and then cooling is performed to a predetermined temperature at an increased cooling rate, whereby a time spent in the area indicated by Two liquids illustrated in FIG. 6 is shortened, so that the crystallization and phase separation of the rare earth element compound can be suppressed. The manufacturing method for the optical fiber 40
    [0091] [0091] Furthermore, in the manufacturing method for the optical fiber 1 of the present embodiment, the temperature profile in the heating furnace 20 is set so that the cooling rate is maximized at a temperature at which separation occurs into a plurality of liquid phases respectively having different composition ratios between the rare earth element compound and the pure silica glass in the equilibrium state. The cooling rate is maximized in a temperature range in which the phase separation occurs in the silica glass containing the rare earth element compound, whereby the phase separation of the silica glass containing the rare earth element compound can be further suppressed.
    [0092] [0092] Furthermore, the manufacturing apparatus 100 for the optical fiber 1 of the present embodiment includes the heating furnace 20 that heats the optical fiber preform 1P that is to be the optical fiber 1 having the core 10 including the silica glass containing the rare earth element compound. The temperature profile in the heating furnace 20 is set as described above. As described above, the silica glass containing the rare earth element compound is once heated to the temperature that is higher than or equal to the glass transition temperature and at which the silica glass is in 41
    [0093] [0093] Furthermore, in the manufacturing apparatus 100 for the optical fiber 1 of the present embodiment, the cooling member 40 that cools the glass wire drawn from the optical fiber preform 1P is provided below the heating element 30 that heats the heating furnace 20. The cooling member 40 that cools the glass wire drawn from the optical fiber preform 1P is provided below the heating element 30 that heats the heating furnace 20, whereby it becomes easier to decrease the temperature in the heating furnace 20, in the lower side of the heating furnace 20. It is therefore possible to easily form the temperature profile having the changing point at which the temperature decrease becomes steep on the downstream side of the place where the maximum temperature Tmax 1S reached, in the heating furnace 20.
    [0094] [0094] Furthermore, in the manufacturing apparatus 100 for the optical fiber 1 of the present embodiment, it is preferable that the cooling member 40 surrounds the glass wire drawn 42
    [0095] [0095] Although the present invention has been described above by exemplifying embodiments, the present invention is not limited thereto.
    [0096] [0096] For example, a means that makes the temperature decrease steep on the downstream side from the place where the maximum temperature Tmax 1s reached in the heating furnace is not limited to the cooling member 40 exemplified in the embodiment described above. For example, a heat 43
    [0097] [0097] FIGS. 21 to 23 are diagrams illustrating a cross section of the heating furnace 20 according to such a modification.
    [0098] [0098] The heating furnace 20 illustrated in FIG. 21 includes a hollow tube 26 as a heat radiating material below the heat insulating material 25 in the hollow portion 20H of the housing 23. The hollow tube 26 includes, for example, carbon or the like. From a viewpoint of facilitating the transfer of the heat inside the heating furnace 20 to the outside of the heating furnace 20, the hollow tube 26 is preferably in contact with the outer peripheral surface of the core tube 22 and the inner peripheral surface of the housing 23.
    [0099] [0099] 44
    [0100] [0100] The heating furnace 20 illustrated in FIG. 23 includes metal powder 28 dispersed at the lower end portion of the heat insulating material 25. The metal powder 28 is a heat radiating material, and the metal constituting the metal powder 28 is the same as that of the metal rod 27.
    [0101] [0101] The examples illustrated in FIGS. 21 to 23 are only a part of cases where the heat radiating material is provided, and the method of providing the heat radiating material at the lower end portion of the heating furnace 20 is not 45
    [0102] [0102] Furthermore, in the embodiment described above, an example has been described in which the outer periphery of the inner clad 11 is «circular in the cross section perpendicular to the longitudinal direction of the optical fiber 1. However, the outer peripheral shape of the inner clad 11 is not limited to a circular shape, and may be a polygon such as a hexagon, a heptagon, or an octagon, or a non-circular shape such as a shape in which the corners of the polygon are rounded.
    [0103] [0103] Hereinafter, the content of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.
    [0104] [0104] (Example 1) FIG. 24 is a diagram illustrating a cross section of a heating furnace used in Example 1. In FIG. 24, components having the same configurations as those in FIG. 2 are designated by the same reference numerals. A heating furnace 20a used in Example is different from the heating furnace 20 exemplified in the embodiment in that the heat insulating material 25 is divided into three and the position of the heating element 30 is different.
    [0105] [0105] In normal operation, the temperature in the heating furnace 20a is about 2000°C, so it is difficult to actually measure the temperature in the heating furnace 20a. The temperature in the heating furnace 20a was therefore set lower than the temperature during actual operation, and the temperature in the heating furnace 20a was actually measured with an Ir/Ir-40% RH thermocouple.
    [0106] [0106] The length of the heating element 30 in the height direction was 40 mm, and the heat insulating material 25 having a height of 130 mm was disposed under the heating element 30. Furthermore, on the outside of the heating element 30, the heat insulating material 25 was disposed having a height of 300 mm from the lower end of the heating element 30. The core tube 22 extended downward to a position of 160 mm from the lower end of the heat insulating material
    [0107] [0107] FIG. 25 illustrates measurement results of the temperature profile in the heating furnace 20a in Example 1. In FIG. 25, the thick line indicates the measured temperature in the heating furnace 20a, and the thin lines indicate normal distributions that approximate the temperature profiles in the heating furnace 20a. Note that, in FIG. 25, the temperature profile is approximated to the normal distributions that are different between the upstream side and the downstream side from the changing point, and the lines that interpolate the respective normal distributions are indicated by broken lines.
    [0108] [0108] (Comparative Example 1) The temperature profile in the heating furnace 20a was measured in the same manner as in Example 1 except that the cooling member 40 was not inserted into the heating furnace 20a, and He at 6 L/min was caused to flow from the upper side of the core tube 22, and He at 10 L/min and Ar at 3 L/min were caused to flow from the lower side of the core tube 22. The results are illustrated in FIG. 26.
    [0109] [0109] 48
    [0110] [0110] On the other hand, the temperature profile in the heating furnace 20a of Fxample 1 illustrated in FIG. 25 is approximated to normal distributions represented by the equations (1) and (2) with the dispersion or = 140 mm, the dispersion op, = 35 mm, A = 1715 K, and B = 300 K. Note that, Xe = 160mm and Te = 1204 K. Furthermore, the ratio o./0p =
    [0111] [0111] (Example 2) Using the same heating furnace 20a as in Example 1, the optical fiber 1 was manufactured in which 2.3 wt% Yb, 3.3 wt Al, and 3.8 wt3 P were added to the core 10. At the end of the drawing process P2, the feeding of the optical fiber 49
    [0112] [0112] (Comparative Example 2) A sample of the neck-down ND was collected in the same manner as in Example 2 except that the cooling member 40 was not inserted into the heating furnace 20a and the drawing speed of the optical fiber 1 was set to 80m/min. FIG. 27 illustrates results of measuring the outer diameter of the neck-down ND, and FIG. 28 illustrates temperatures of the glass estimated from the outer diameter of the neck-down ND.
    [0113] [0113] 50
    [0114] [0114] (Comparative Example 3) The optical fiber was manufactured in the same manner as in Example 2 except that the 2.3 wt% Yb, 3.1 wt®% Al, and
    [0115] [0115] (Examples 3-1 to 3-17) The optical fiber 1 was manufactured in the same manner as in Example 2 except that the length of the heating element in the heating furnace 20a, the distance in the height direction from the upper end of the cooling member 40 to the center of the heating element 30, the content of the dopant added to the core 10, and the drawing speed of the bare optical fiber 1E were as illustrated in Table 1 below.
    [0116] [0116] (Comparative Examples 4-1 to 4-11) The optical fiber 1 was manufactured in the same manner as in Example 2 except that the cooling member 40 was not inserted into the heating furnace 20a, and the length of the heating element 30 in the heating furnace 20a, the content 51
    [0117] [0117] The loss of the light having a wavelength of 1180 nm was measured for each of the optical fibers of Examples 2 and 3-1 to 3-17, and each of the optical fibers of Comparative Examples 3 and 4-1 to 4-11. The results are indicated in Table 1, Table 2, and FIG. 29. Note that, FIG. 29 illustrates a relationship between the concentration of Yb added to the core in Examples 2, Examples 3-1 to 3-17, Comparative Example 3, and Comparative Examples 4-1 to 4-11, and the loss of the light.
    [0118] [0118] 52
    [0119] [0119] 53
    [0120] [0120] Comparing the optical fiber in Example with the optical fiber in Comparative Example having the same Yb concentration in Tables 1 and 2, it has been found that the loss of the light is suppressed in Example 2 and Examples 3-1 to 3-17 in which the temperature in the heating furnace 20a is steeply 54
    [0121] [0121] Furthermore, as illustrated in FIG. 29, when the concentration of Yb is greater than or equal to 2.0 wt% and less than or equal to 3.1 wt%, it has been found that the loss of the light is reduced in Example 2 and Examples 3-1 to 3-17 in which the temperature in the heating furnace 20a is steeply decreased on the downstream side from the position where the temperature in the heating furnace 20a is maximized 55
    [0122] [0122] As described above, according to the present invention, the manufacturing method for an optical fiber and the manufacturing apparatus for an optical fiber are provided capable of suppressing the loss of the light propagating through the core containing the rare earth element compound, and are expected to be used in fields of a processing machine, a medical laser device, and the like.
    [0123] [0123]
    1...optical fiber 1P.. optical fiber preform
    10... core 10P ... core glass body
    11...inner clad 11P...clad glass body
    12... outer clad 13 ...protective layer 20, 20a...heating furnace 21 ...preform feeding device 22 ...core tube
    23... housing 56
    DK 2021 70065 A1 24 … refrigerant flow path … heat insulating material 30 ...heating element
    40... cooling member 100 ...manufacturing apparatus for an optical fiber 57
    权利要求:
    Claims (14)
    [1] 1. A manufacturing method for an optical fiber, comprising: a drawing process of drawing while heating, in a heating furnace, a lower end portion of an optical fiber preform that is to be an optical fiber having a core consisting of silica glass containing a rare earth element compound, wherein a temperature profile in the heating furnace is a profile in which temperature is increased from an upstream side toward a downstream side to a maximum temperature and then decreased and that has a changing point at which a temperature decrease becomes steep on the downstream side from a place where the maximum temperature is reached, and the maximum temperature is a temperature at which temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase.
    [2] 2. The manufacturing method for an optical fiber according to claim 1, wherein the temperature profile in the heating furnace is set to cause a cooling rate to be maximized at a temperature at which separation occurs into a plurality of liquid phases respectively having different composition ratios between the rare earth element compound and a pure silica glass in an equilibrium state.
    58
    DK 2021 70065 A1
    [3] 3. The manufacturing method for an optical fiber according to claim 1 or 2, wherein the temperature profile on the upstream side from the changing point in the temperature profile in the heating furnace is approximated to a part of a normal distribution represented by a following equation (1), and the temperature profile on the downstream side from the changing point is approximated to a part of a normal distribution represented by a following equation (2), and a temperature of the heating furnace is set to cause a ratio o./0p, of a dispersion 0. of the normal distribution represented by the equation (1) to a dispersion op of the normal distribution represented by the equation (2) to be greater than or equal to 2, x2 T= Aexpi- ——} +B (xX <x) (D | 20; | r= 40) CL (xx) — Ø) 20, wherein, in the above equations (1) and (2), T is a temperature at an arbitrary point in the heating furnace, A and B are constants, x is a distance to the arbitrary point from a reference point when the reference point is a position where the maximum temperature is reached and a direction from the reference point to the downstream side is a positive direction, x. is a distance from the reference point to a position where the changing point is reached, and x, is a 59
    DK 2021 70065 A1 distance from the reference point to a position where T calculated by the equation (2) 1s a calculated maximum temperature.
    [4] 4. The manufacturing method for an optical fiber according to claim 3, wherein the temperature of the heating furnace is set to cause the ratio 0:/0, to be greater than or equal to 3.
    [5] 5. The manufacturing method for an optical fiber according to claim 4, wherein the temperature of the heating furnace is set to cause the ratio 0:/0, to be less than or equal to 8.
    [6] 6. The manufacturing method for an optical fiber according to any one of claims 3 to 5, wherein the dispersion 0. is set to be greater than or equal to 100 mm and less than or equal to 300 mm.
    [7] 7. The manufacturing method for an optical fiber according to any one of claims 1 to 5, wherein a ratio Tc/Tmax Of a temperature T. of the changing point to a maximum temperature Tmax 1s set to be greater than or equal to 0.5.
    [8] 8. The manufacturing method for an optical fiber according to claim 7, wherein 60
    DK 2021 70065 A1 the ratio T./Tmax 18 set to be greater than or equal to
    0.7.
    [9] 9. The manufacturing method for an optical fiber according to any one of claims 1 to 8, wherein a rare earth element contained in the rare earth element compound 1s ytterbium (Yb), and a concentration of the rare earth element in the core is greater than or equal to 2.0 wt and less than or equal to 3.1 wt3.
    [10] 10. The manufacturing method for an optical fiber according to claim 9, wherein the core further contains aluminum (Al) of greater than or equal to 3.0 %wt and less than or equal to 5.3 wt$%, and phosphorus (P) of greater than or equal to 1.7 wt and less than or equal to 5.6 wt3.
    [11] 11. A manufacturing apparatus for an optical fiber, comprising: a heating furnace that heats, with a heating element, an optical fiber preform that is to be an optical fiber having a core consisting of silica glass containing a rare earth element compound, wherein a temperature profile in the heating furnace is a profile in which temperature is increased from an upstream side toward a downstream side to a maximum temperature and 61
    DK 2021 70065 A1 then decreased and that has a changing point at which a temperature decrease becomes steep on the downstream side from a place where the maximum temperature is reached, and the maximum temperature is a temperature at which temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase.
    [12] 12. The manufacturing apparatus for an optical fiber according to claim 11, wherein a cooling member that cools a glass wire drawn from the optical fiber preform is provided below the heating element.
    [13] 13. The manufacturing apparatus for an optical fiber according to claim 12, wherein the cooling member surrounds the glass wire, and a blow of a cooling gas is applied from a bottom toward a top between an inner peripheral surface of the cooling member and a surface of the glass wire.
    [14] 14. The manufacturing apparatus for an optical fiber according to any one of claims 11 to 13, wherein a heat radiating material that transfers heat inside the heating furnace to an outside of the heating furnace is provided below the heating element.
    62
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    同族专利:
    公开号 | 公开日
    JP2020045272A|2020-03-26|
    WO2020059683A1|2020-03-26|
    CN112424133A|2021-02-26|
    US20210292223A1|2021-09-23|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    JPH0332502Y2|1986-05-15|1991-07-10|
    JPH0435399Y2|1986-09-10|1992-08-21|
    JP3108545B2|1992-09-22|2000-11-13|古河電気工業株式会社|Optical fiber drawing furnace|
    JP4302367B2|2002-03-15|2009-07-22|古河電気工業株式会社|Optical fiber drawing method and drawing apparatus|
    WO2010055696A1|2008-11-14|2010-05-20|株式会社フジクラ|Ytterbium-doped optical fiber, fiber laser, and fiber amplifier|
    法律状态:
    2021-02-17| PAT| Application published|Effective date: 20210212 |
    优先权:
    申请号 | 申请日 | 专利标题
    JP2018174127|2018-09-18|
    JP2019142865A|JP2020045272A|2018-09-18|2019-08-02|Manufacturing method of optical fiber and manufacturing apparatus of optical fiber|
    PCT/JP2019/036303|WO2020059683A1|2018-09-18|2019-09-17|Manufacturing method for optical fiber and manufacturing apparatus for optical fiber|
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