JP4877330B2 - Optical fiber manufacturing method - Google Patents

Description

  In the present invention, a resin composition containing a solvent is applied around the drawn glass fiber, and further heated through a volatilization heating furnace to volatilize the solvent, and then heated through a curing heating furnace to form a resin composition. The present invention relates to a method of manufacturing a coated optical fiber by curing a product to form a resin coating layer.

  As a resin coating layer of an optical fiber, it is generally known to use an ultraviolet curable resin or a thermosetting resin. For example, when a resin coating layer is formed of a thermosetting resin, a drawn glass fiber A resin composition containing a solvent is applied to the surroundings and heated through a heating furnace to volatilize the solvent and cure the resin composition.

  Moreover, a polyimide resin is known as a thermosetting resin excellent in heat resistance, and a method of coating a traveling linear body with a polyimide resin is also known (see, for example, Patent Document 1).

  In the polyimide resin coating method described in Patent Document 1, as shown in FIG. 4, a supply device 101 that supplies polyimide resin and a coating device that coats the linear body 100 with the polyimide resin delivered from the supply device 101. 102, a curing furnace 103 that cures the coated polyimide resin, a gas supply device 104 that sends an inert gas into the curing furnace 103, and a device that includes a winder (not shown) and the like. Is set to 500 ° C. or higher, and the inside of the curing furnace 103 is set to an inert gas atmosphere so that the linear body 100 is coated with a polyimide resin.

Japanese Patent Laid-Open No. 63-1489

  By the way, in an optical fiber coated with a polyimide resin, the glass resin is coated with the polyimide resin by a solvent removal and imidization curing reaction from a polyimide resin (polyimide resin composition) having excellent heat resistance. However, since the polyimide resin contains a large amount of solvent at the time of this coating, sufficient heating is required to heat and remove the solvent and cure. That is, the quality of the resulting polyimide coating is affected by the degree of cure and the amount of residual solvent. For this reason, in order to obtain a good covering state, it is necessary to cure under optimum temperature conditions.

  Further, in order to improve the quality of the optical fiber, it is required to uniformly coat the glass fiber with the polyimide resin in the circumferential direction. In order to achieve a uniform coating thickness, it is also important to adjust the die for applying resin to the glass fiber. However, since the applied polyimide resin composition shrinks when the solvent volatilizes, it can be cured only by adjusting the die. It was difficult to adjust the shape of the subsequent polyimide resin, and the coating thickness was likely to be uneven in the circumferential direction.

  If the coating thickness is not uniform in the circumferential direction, the strength on the side where the coating thickness is thin is lowered, and the breaking strength during screening is significantly reduced. For example, in oil well applications, etc., a long optical fiber is required for a series length, but when the breaking strength is reduced, it becomes difficult to obtain a long optical fiber.

  Therefore, an object of the present invention is to sufficiently volatilize the solvent and cure the resin with respect to the resin composition applied around the glass fiber, and to form a coating layer with a uniform thickness in the circumferential direction. An object of the present invention is to provide a method for manufacturing an optical fiber.

The method for producing an optical fiber according to the present invention that can solve the above-mentioned problem is that a resin composition containing a solvent is applied around the drawn glass fiber, and further heated through a volatilization heating furnace to remove the solvent. It is a method for producing an optical fiber that is volatilized and then heated through a curing furnace to cure the resin composition to form a resin coating layer,
As the heating temperature distribution in the axial direction of the fiber with resin in the heating furnace for volatilization,
It is characterized by satisfying the relationship of “T _AVE1 > T ₀ > T _AVE2 ”.
However,
T _AVE1 : Average temperature in the longitudinal direction in the section of 0 ≦ L ≦ L ₀ (L = 0 is set as the volatilization furnace inlet)
T _AVE2 : Average temperature in the longitudinal direction in the section of L ₀ ≦ L ≦ L ₁ (the total length of the volatile heating furnace is L ₁ )
T ₀ : Solvent boiling point L ₀ = k × Vf (Vf: drawing speed, k: constant).

  In the optical fiber manufacturing method according to the present invention, the outer diameter of the resin-coated fiber is monitored on the downstream side of the volatilization heating furnace and on the upstream side of the curing heating furnace, It is preferable to adjust the heating temperature of the volatilization heating furnace in accordance with a deviation from a preset outer diameter target value.

  In the method for producing an optical fiber according to the present invention, the outer diameter of the glass fiber and the outer diameter before and after passing the resin-coated fiber through the heating furnace for volatilization are measured, and the resin composition applied by them is measured. It is preferable to calculate the volume change rate and set the outer diameter target value so that the volume change rate is equal to or higher than the content ratio of the solvent in the resin composition.

  In the optical fiber manufacturing method according to the present invention, the heating temperature in the axial direction of the resin-attached fiber in the heating furnace for volatilization can be adjusted in a plurality of regions, respectively, and the deviation between the outer diameter measurement value and the outer diameter target value Accordingly, it is preferable to adjust the heating temperature in the most outlet side region in the volatile heating furnace.

In the optical fiber manufacturing method according to the present invention, it is preferable that the resin-coated fiber is uniformly heated in the circumferential direction in at least a section of 0 ≦ L ≦ L ₀ of the volatilization heating furnace.

  In the optical fiber manufacturing method according to the present invention, it is preferable that the resin-coated fiber and the heating member in the volatilization heating furnace are relatively rotated with a central axis of the resin-coated fiber as a rotation axis.

  In the method of manufacturing an optical fiber according to the present invention, when the heating member includes a core tube and a heating member that raises the temperature of the core tube, the resin-coated fiber is the center of the resin-coated fiber. It is preferable to rotate the shaft relative to the core tube or the heat generating member with the shaft as a rotation shaft.

  According to the present invention, after applying a resin composition containing a solvent around the drawn glass fiber, the solvent is first volatilized by heating through a heating furnace for volatilization. Then, after that, the resin composition is cured by heating through a curing furnace to form a resin coating layer. Thus, since the solvent volatilization and the resin curing are performed on the applied resin composition using the dedicated heating furnace, the solvent volatilization can be sufficiently performed, and the subsequent curing is also sufficiently performed. be able to. Furthermore, the heating furnace for volatilization makes the heating temperature from the inlet that varies depending on the drawing speed to a predetermined location higher than the boiling temperature of the solvent, and the heating temperature to the outlet after that is less than the boiling temperature of the solvent. It is possible to easily volatilize the solvent in the resin composition on the inlet side and prevent foaming due to overheating of the resin composition on the outlet side. As an effect, the solvent is sufficiently evaporated and the resin is sufficiently cured to be uniform. The coating thickness can be increased to improve the breaking strength.

It is a schematic block diagram which shows an example of the coating | coated apparatus which enforces the manufacturing method of the optical fiber which concerns on this invention. (A) is the block diagram which expanded and showed the heating furnace for volatilization shown in FIG. 1, (b) is an example of the heating temperature distribution. It is a top view of an example of the guide roller shown in FIG. It is explanatory drawing which shows the coating part and hardening part of the manufacturing apparatus of the conventional polyimide coating fiber.

Hereinafter, an example of an embodiment of an optical fiber manufacturing method according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic view showing a manufacturing apparatus for carrying out the optical fiber manufacturing method of the present embodiment.
The manufacturing apparatus 10 is provided on a pass line in which a glass fiber 1 formed by heating and drawing an optical fiber glass base material (not shown) is running vertically downward, and is used for resin coating. A die 11, a volatilization heating furnace 12, and a curing heating furnace 13 are provided. Further, the upstream side of the die 11 in the pass line, the downstream side of the die 11 and upstream of the volatile heating furnace 12, the downstream side of the volatile heating furnace 12 and the upstream side of the curing heating furnace 13, At respective positions on the downstream side of the heating furnace 13, outer diameter measuring devices 14, 15, 16, and 19 that are a combination of a light emitter and a light receiver are provided. And the coating | coated apparatus 10 is provided with the control part 18 for adjusting the heating temperature of the volatilization heating furnace 12 according to the measured value of the outer diameter measuring device 14,15,16,19. The outer diameter measuring device 15 may be divided into two locations, the downstream proximity position of the die 11 and the upstream proximity position of the volatilization heating furnace 12, and the outer diameter measurement device 16 may be a heating for volatilization. Although it may be divided into two locations, the downstream proximity position of the furnace 12 and the upstream proximity position of the curing heating furnace 13, one location is provided in this embodiment. The outer diameter measuring devices 14 and 15 only need to monitor the outer diameter only at the start of drawing, so it is not necessary to always monitor after starting the drawing and can be omitted.

  The die 11 is for applying a resin composition containing a solvent around the drawn glass fiber 1. Examples of the resin composition used here include a polyimide resin composition and an ester imide resin composition, and examples of the solvent contained therein include N-methyl-2-pyrodrine. The center of the hole for resin coating formed in the die 11 is arranged so as to coincide with the central axis of the traveling glass fiber 1, and the periphery of the glass fiber 1 that has passed through the die 11 is arranged in the circumferential direction. The resin composition is applied substantially uniformly.

The volatilization heating furnace 12 is provided in a vertically downward direction of the die 11, and inserts and heats a fiber (fiber with resin) 1 a coated with a resin composition around the glass fiber 1. The solvent is volatilized from the resin composition. As shown in FIG. 2 (a), the volatilization heating furnace 12 has a plurality of (three in the present embodiment) heaters (heating members) 20a, 20b, and 20c that are short cylindrical heating members in the vertical direction. It has a common cylindrical core tube 21 (heating member) inside thereof. In the heating furnace 12 for volatilization, the heaters 20a, 20b, 20c and the furnace core tube 21 are each cylindrical, and are heated by inserting the fiber 1a through the center thereof.
Further, since the heater has a multi-stage structure, the heating temperature in the axial direction of the fiber 1a in the volatile heating furnace 12 can be adjusted in a plurality of regions.
The core tube 21 is preferably made of a material having a high heat transfer coefficient and a high heat conductivity and is not corroded by the volatile components of the solvent. For example, aluminum may be used, and other materials include carbon, quartz, copper. Etc.

An exhaust unit 22 is connected to the outlet (lower end) side of the volatilization heating furnace 12, and the gas in the furnace core tube 21 is exhausted at a predetermined exhaust amount. Further, the exhaust unit 22 can measure the solvent concentration in the gas exhausted from the volatilization heating furnace 12 and adjust the exhaust amount based on the measured value. A processing unit (not shown) that can appropriately process the volatile components of the solvent contained in the exhausted gas is connected to the downstream side of the exhaust unit 22.
In addition, air is naturally introduced into the space in the core tube 21 of the volatilization heating furnace 12 from the inlet side (the upper end opening of the core tube 21) through which the fiber 1 a is sent along with the exhaust by the exhaust unit 22. . That is, the volatile component of the solvent volatilized by heating the resin composition in the volatilization heating furnace 12 is exhausted by the exhaust unit 22 and new air is introduced from the inlet side, whereby the gas in the volatilization heating furnace 12 is obtained. Is prevented from being saturated with volatile components.
In addition, the structure which introduce | transduces air from the exit side by providing the exhaust part 22 in the entrance side may be sufficient.

The heating temperature (core tube temperature) distribution in the longitudinal direction (fiber axis direction) of the volatile heating furnace 12 is such that the average heating temperature in the furnace is the solvent at the inlet side of the fiber 1a as shown in FIG. A region having a boiling point temperature T ₀ (for example, 202 ° C.) or higher is formed, and in other regions, it is lower than the boiling point temperature of the solvent. The longitudinal position of the volatile heating furnace 12 is L, the furnace inlet is L = 0, the furnace outlet is L = L ₁ , the constant k determined by the drawing speed Vf, the furnace heating structure, the atmosphere gas in the furnace, and the like. longitudinal in the product if the position obtained by the (k × Vf) was set to _{L 0, 0} ≦ _L ≦ _L longitudinal average temperature _{T AVE1} and _{L 0} ≦ _L ≦ _{L 1} interval at ₀ section of the Average temperature T _AVE2 satisfies the relationship of “T _AVE1 > T ₀ > T _AVE2 ”. T _AVE1 and T _AVE2 are defined by the following expressions (1) and (2).

  Since outside air is introduced at the inlet side of the volatilization heating furnace 12, it is difficult to quickly raise the temperature of the fiber 1a. For this reason, it becomes easy to volatilize the solvent in a resin composition by making the heating temperature of an entrance side more than the boiling point temperature of a solvent. Moreover, the foaming by the overheating of a resin composition can be prevented by making heating temperature into the area | regions other than an entrance side below the boiling point temperature of a solvent.

  Further, since the temperature of the resin composition in the die 11 needs to be about 50 ° C., the temperature of the fiber 1a when entering the volatile heating furnace 12 is relatively low, and the heating temperature at the inlet side of the volatile heating furnace 12 Even if is the boiling point temperature of the solvent, the resin composition does not foam. And the volatilization efficiency of a solvent improves by forming the area | region of the heating temperature more than the boiling point temperature of a solvent on the entrance side as mentioned above.

  The curing heating furnace 13 is provided vertically below the volatilization heating furnace 12 and has a configuration including a heater and a core tube similar to the volatilization heating furnace 12. The curing heating furnace 13 cures the resin composition by heating the fiber 1b in which the solvent is sufficiently volatilized by the volatilization heating furnace 12 at a temperature higher than that of the volatilization heating furnace 12. In addition, hardening here is that a polyimide resin composition and an ester imide resin composition imidize. Thereby, the optical fiber 1c in which the coating layer of resin (polyimide resin, ester imide resin or the like) is formed around the glass fiber 1 is manufactured.

After that, the optical fiber 1c that has passed through the curing heating furnace 13 is changed in the traveling direction by a guide roller 17 provided vertically below the curing heating furnace 13, and is guided toward the winding side.
In the case of forming a plurality of resin coating layers such as two layers or three layers, the optical fiber 1c that has passed through the curing heating furnace 13 is again introduced into the die 11 (or another die).

Next, the manufacturing method of the optical fiber of this embodiment is demonstrated. In addition, the case where the coating | coated apparatus 10 shown in FIG. 1 is used is demonstrated as an example.
First, with the start of drawing, the glass fiber 1 is passed through the pass line of the coating apparatus 10 in FIG. 1, and the resin composition is supplied to the die 11 to apply the resin composition around the glass fiber 1.

The fiber 1a coated with the resin composition is heated in the volatilization heating furnace 12, and the solvent in the resin composition is volatilized. At that time, the heating temperature distribution of the volatile heating furnace 12 is set as shown in FIG. At the start of coating, the heating temperature is adjusted to obtain a predetermined coating outer diameter.
The outer diameter of the optical fiber 1c finally obtained is that the volume of the resin composition is reduced by volatilization of the solvent with respect to the outer diameter of the resin composition immediately after being applied to the glass fiber 1 by the die 11. The shrinkage is reduced by the curing reaction. Therefore, the outer diameter D ₀ of the glass fiber 1 prior to passing the die _11, the outer diameter D ₁ of the previous fiber 1a which resin composition is applied through a volatile heating furnace _12, after passing through the volatilization heating furnace 12 The fiber 1b is adjusted so that the volume change rate Δ calculated by the following equation (3) based on the outer diameter D ₂ of the fiber 1b is equal to or higher than the solvent content (for example, 75% by volume) in the resin composition. setting the outer diameter target value of the outer diameter D ₂ of the.
Volume change rate Δ (%) = 1 − {(D ₂ ² −D ₀ ² ) / (D ₁ ² −D ₀ ² )} × 100 (3)

At the start of coating, the outer diameter D ₀ of the glass fiber 1 before passing through the die 11 is measured by the outer diameter measuring device 14, and the outer diameter D of the fiber 1 a before applying the resin composition and passing through the heating furnace 12 for volatilization. ₁ was measured by the outer diameter measuring device 15, the outer diameter D ₂ of the fiber 1b after passing through the volatilization heating furnace 12 is measured by the outer diameter measuring device 16, the volume change rate calculated by the equation (3) Δ is such that the above content of the solvent in the resin composition, yet the outer diameter D ₂ of the fiber 1b is, so that the outer diameter target value set, to adjust the heating temperature of the volatile heating furnace 12 . For example, when the outer diameter measurement value is larger than the outer diameter target value, it can be determined that the shrinkage of the resin composition accompanying the volatilization of the solvent is small, so the heating temperature of the volatilization heating furnace 12 is increased.

  In addition, although adjustment of heating temperature may be performed by temperature adjustment of all the heaters 20a, 20b, and 20c, since the outer diameter change amount with respect to temperature change tends to increase on the outlet side of the volatile heating furnace 12, Even temperature adjustment on the outlet side of the volatilization heating furnace 12 (that is, temperature adjustment of the heater 20c) is effective.

  After adjusting the heating temperature at the start of coating, the outer diameter of the fiber 1b that has passed through the volatilization heating furnace 12 is monitored by the outer diameter measuring device 16, and the monitored outer diameter measurement value and the preset outer diameter target are monitored. The heating temperature of the volatilization heating furnace 12 is adjusted according to the deviation from the value. Thereby, the optical fiber 1c in which the solvent in the resin composition is sufficiently volatilized can be stably manufactured. Further, the outer diameter of the optical fiber 1c that has passed through the curing furnace 13 is monitored by the outer diameter measuring device 19, and the outer diameter of the obtained optical fiber 1c is checked.

  Further, the solvent concentration in the gas in the volatile heating furnace 12 or the solvent concentration in the gas in the exhaust unit 22 is measured, and the exhaust amount from the volatile heating furnace 12 is adjusted based on the measured value. Good. Thereby, it is possible to prevent the gas in the volatilization heating furnace 12 from being saturated with volatile components, and to maintain the volatilization efficiency in a good state.

The volatiles heating furnace 12, the average heating temperature of the inlet of the fiber 1a which varies with drawing speed to a predetermined position and the boiling point of the solvent temperature T ₀ or more, the boiling temperature of the solvent heating temperature up later exit Less than. Further, the longitudinal average temperature T _AVE1 (refer to the above formula (1)) in the section of the longitudinal position 0 ≦ L ≦ L ₀ of the volatilization heating furnace 12 and the length in the section of L ₀ ≦ L ≦ L _1. The direction average temperature T _AVE2 (see the above formula (2)) satisfies the relationship of “T _AVE1 > T ₀ > T _AVE2 ”. This facilitates volatilization of the solvent in the resin composition on the inlet side, and prevents the foaming due to overheating of the resin composition on the outlet side, and sufficiently evaporates the solvent and cures the resin to make it uniform in the circumferential direction. The coating thickness can be as follows.

In the volatile heating furnace 12, the heaters 20 a, 20 b, 20 c and the furnace tube 21, which are heating members, are each cylindrical and heated by inserting the fiber 1 a into the center thereof. By heating uniformly in the circumferential direction, the volatilization amount of the solvent can be made uniform in the circumferential direction. The fiber 1b in which the solvent is sufficiently volatilized in the volatilization heating furnace 12 and uniformly in the circumferential direction, the resin composition is sufficiently cured by the curing heating furnace 13, and the glass fiber 1 has a uniform and desired thickness. The resin coating layer is formed. Thus, the thickness of the resin coating layer in the optical fiber 1c can be made uniform in the circumferential direction. Incidentally, if it is possible to uniformly heat the circumferential direction at least ₀ ≦ L ≦ L 0 of the section, it is possible to form a resin coating layer of uniform thickness.

  Furthermore, in order to make the thickness of the resin coating layer uniform in the circumferential direction, it is preferable to rotate the fiber 1a relative to the furnace tube 21 or the heater 20a with the central axis of the fiber 1a as the rotation axis. The fiber 1a in the furnace 12 and the volatilization heating furnace 12 may be rotated relatively with the central axis of the fiber 1a as the rotation axis. For example, as shown in FIG. 3, the cross section of the guide surface 17a of the guide roller 17 is arcuate, and the guide roller 17 is swung as shown by the arrow in FIG. The fiber 1a in the volatilization heating furnace 12 can be rotated with the central axis as a rotation axis. Further, without rotating the fiber 1a, at least one of the core tube 21 or the heater 20a may be rotated relative to the fiber 1a with the central axis of the fiber 1a as the rotation axis.

An example and a comparative example in which the heating temperature (core tube temperature) distribution in the longitudinal direction (fiber axis direction) of the volatilization heating furnace 12 is made constant and the drawing speed is changed will be shown. The quality is judged based on the rupture frequency (average length per rupture, described as average rupture length in Table 2) at the time of screening (= 1% strain load).
The temperature distribution in the furnace is shown in Table 1, and the results of changing the linear velocity Vf are shown in Table 2. The length L _{1 of the} furnace is ₁ m, and the position L in Table 1 is a distance from the furnace inlet (L = 0). The constant k = 0.1.

The boiling temperature _{T 0} of the solvent is 202 ℃, 0 ≦ _L ≦ L longitudinal average temperature _{T AVE1} and _{L 0} ≦ L ≦ _L longitudinal average temperature _{T AVE2} in the interval ₁ in the interval of _0, The relationship “T _AVE1 > T ₀ > T _AVE2 ” is satisfied when the linear velocity Vf = 4 to 6 (m / min), and the average breaking length is 3.5 km or more. On the other hand, in the case of the linear velocity Vf = 3, 8 (m / min) that does not satisfy the relationship of “T _AVE1 > T ₀ > T _AVE2 ”, the average breaking length is 0.9 km or less, There is a clear difference between the results when the relationship is met and when it is not.

Examples and comparative examples in which the drawing speed is constant and the heating temperature distribution in the longitudinal direction of the volatilization heating furnace 12 is changed are shown. The determination of pass / fail is the same as in the first embodiment.
Table 3 shows the four types of furnace temperature distributions, and Table 4 shows the results of changing the furnace temperature distributions. The length L _{1 of the} furnace is ₁ m, and the position L in Table 3 is a distance from the furnace inlet (L = 0). The constant k = 0.1. The linear velocity Vf is 5 (m / min).

The boiling temperature _{T 0} of the solvent is 202 ℃, 0 ≦ _L ≦ L longitudinal average temperature _{T AVE1} and _{L 0} ≦ L ≦ _L longitudinal average temperature _{T AVE2} in the interval ₁ in the interval of _0, The relationship of “T _AVE1 > T ₀ > T _AVE2 ” is satisfied in the case of the temperature distributions 1 and 4, and the average break length is 3.9 km or more. On the other hand, in the case of temperature distributions 2 and 3 that do not satisfy the relationship of “T _AVE1 > T ₀ > T _AVE2 ”, the average fracture length is 0.8 km, and the case where the relationship is satisfied is satisfied. If not, there is a clear difference in results.

Thus, as shown in Examples 1 and 2, it can be seen that satisfying the relationship of “T _AVE1 > T ₀ > T _AVE2 ” can greatly improve the frequency of screening disconnection compared to the conventional example that does not satisfy the relationship. It can be said that a satisfactory resin coating layer can be formed by sufficiently evaporating the solvent.

DESCRIPTION OF SYMBOLS 1 Glass fiber 1c Optical fiber 10 Coating | coated apparatus 11 Dies 12 Heating furnace for volatilization 13 Heating furnace for hardening 14, 15, 16, 19 Outer diameter measuring device 17 Guide roller 18 Control part 22 Exhaust part

Claims (7)

A resin composition containing a solvent is applied around the drawn glass fiber, and further heated through a volatilization heating furnace to volatilize the solvent, and then heated through a curing heating furnace to obtain the resin composition. A method of manufacturing an optical fiber that is cured to form a resin coating layer,
As the heating temperature distribution in the axial direction of the fiber with resin in the heating furnace for volatilization,
An optical fiber manufacturing method satisfying a relationship of “T _AVE1 > T ₀ > T _AVE2 ”.
However,
T _AVE1 : Average temperature in the longitudinal direction in the section of 0 ≦ L ≦ L ₀ (L = 0 is set as the volatilization furnace inlet)
T _AVE2 : Average temperature in the longitudinal direction in the section of L ₀ ≦ L ≦ L ₁ (the total length of the volatile heating furnace is L ₁ )
T ₀ : Solvent boiling point L ₀ = k × Vf (Vf: drawing speed, k: constant). Monitor the outer diameter of the resin-attached fiber on the downstream side of the volatile heating furnace and on the upstream side of the curing furnace,
2. The method of manufacturing an optical fiber according to claim 1, wherein the heating temperature of the volatilization heating furnace is adjusted according to a deviation between the monitored outer diameter measurement value and a preset outer diameter target value. Measure the outer diameter of the glass fiber and the outer diameter before and after passing the resin-attached fiber through the volatilization heating furnace, and calculate the volume change rate of the resin composition applied by them,
The optical fiber manufacturing method according to claim 2, wherein the outer diameter target value is set so that the volume change rate is equal to or greater than the content ratio of the solvent in the resin composition. The heating temperature in the axial direction of the resin-attached fiber in the heating furnace for volatilization can be adjusted respectively in a plurality of regions,
4. The optical fiber according to claim 2, wherein a heating temperature of a region at the most outlet side in the volatile heating furnace is adjusted according to a deviation between the outer diameter measurement value and the outer diameter target value. Production method. 5. The optical fiber according to claim 1, wherein the resin-coated fiber is uniformly heated in a circumferential direction in at least a section of 0 ≦ L ≦ L ₀ of the volatilization heating furnace. Production method.   6. The optical fiber manufacturing method according to claim 5, wherein the resin-attached fiber and the heating member in the volatilization heating furnace are relatively rotated with a central axis of the resin-attached fiber as a rotation axis. The heating member includes a core tube, and a heating member that raises the temperature of the core tube,
6. The method of manufacturing an optical fiber according to claim 5, wherein the fiber with resin is rotated relative to the core tube or the heat generating member with a central axis of the fiber with resin as a rotation axis.

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